%% Papers Published @article{fds245070, Author = {Levi, M and Armstrong, T and Baranger, H and Bregman, M and Mael, D and Strait, J and Sulak, L and Bowen, T and Pifer, B and Polakos, P and Bradner, H and Parvulescu, A and Jones, H and Learned, J}, Title = {EXPERIMENTAL STUDIES OF THE ACOUSTIC SIGNATURE OF PROTON BEAMS TRAVERSING FLUID MEDIA.}, Journal = {IEEE Transactions on Nuclear Science}, Volume = {NS 25}, Number = {1}, Pages = {325-332}, Year = {1977}, url = {http://dx.doi.org/10.1109/TNS.1978.4329325}, Abstract = {This work establishes that a detectable sonic signal is produced by protons while traversing through or stopping in a fluid medium. Experiments exploring the global characteristics of both the acoustic generation mechanism and the radiation pattern performed at three different accelerators. The results are consistent with a simple thermal model for the transformation of the energy of moving charged particles into acoustic energy. This phenomenon could be exploited in several applications: (1) as a charged particle monitor in accelerator beams, (2) as a heavy ion detector sensitive to nuclear charge, e. g. , in measuring the cosmic ray isotope as an inexpensive shower detector in massive neutrino detectors at the next generation of high energy accelerators, e. g, the Fermilab energy doubler and (4) as the shower calorimeter (and perhaps the muon detector) in massive deep underwater detectors of cosmic neutrino and muon interactions.}, Doi = {10.1109/TNS.1978.4329325}, Key = {fds245070} } @article{fds245069, Author = {Sulak, L and Armstrong, T and Baranger, H and Bregman, M and Levi, M and Mael, D and Strait, J and Bowen, T and Pifer, AE and Polakos, PA and Bradner, H and Parvulescu, A and Jones, WV and Learned, J}, Title = {Experimental studies of the acoustic signature of proton beams traversing fluid media}, Journal = {Nuclear Instruments and Methods}, Volume = {161}, Number = {2}, Pages = {203-217}, Year = {1979}, ISSN = {0029-554X}, url = {http://dx.doi.org/10.1016/0029-554X(79)90386-0}, Abstract = {Recent experiments at Brookhaven National Laboratory and Harvard University demonstrate that a detectable sonic signal is produced by energetic proton beams while traversing a fluid medium. The observed acoustic wave agrees with the predictions of a thermal expansion model. Results are inconsistent with any significant contribution from either microbubble implosion or molecular dissociation, two other suggested means of sonic production. Frequency and amplitude distributions, radiation patterns, temperature, pressure, and medium dependencies are explored. This phenomenon may have immediate applications in beam monitoring and in detecting energetic heavy ions. Signal thresholds may be enough to permit detection of particle showers induced by single particles at the next generation of high energy accelerators or from high energy cosmic rays. The inexpensive transducers and long sonic transmission lengths obtainable in liquids suggest that high energy particle detectors may be feasible with masses many orders of magnitude greater than those currently in use. © 1979.}, Doi = {10.1016/0029-554X(79)90386-0}, Key = {fds245069} } @article{baranger:7349, Author = {Baranger, HU and Wilkins, JW}, Title = {Ballistic electrons in an inhomogeneous submicron structure: Thermal and contact effects}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {30}, Number = {12}, Pages = {7349-7351}, Publisher = {APS}, Year = {1984}, ISSN = {0163-1829}, url = {http://link.aps.org/abstract/PRB/v30/p7349}, Keywords = {SEMICONDUCTOR MATERIALS; TRANSPORT THEORY; ELECTRON SPECTRA; MICROSTRUCTURE; DIFFUSION; ELECTRIC CONTACTS; DEBYE LENGTH; BOLTZMANN EQUATION; TEMPERATURE EFFECTS}, Abstract = {For a simple submicron semiconductor structure we have calculated exactly the electron distribution f(v,x) within a relaxation-to-local-equilibrium assumption for the collision term of the Boltzmann equation. This is the first calculation of the electron distribution in an inhomogeneous semiconductor. Large applied voltages produce a substantial ballistic peak in f(v,x). But at all voltages contact inhomogeneities and local heating (and cooling) produce an I-V characteristic only weakly dependent on the scattering rate. © 1984 The American Physical Society.}, Doi = {10.1103/PhysRevB.30.7349}, Key = {baranger:7349} } @booklet{Baranger85, Author = {Baranger, HU and Wilkins, JW}, Title = {Ballistic electrons in a submicron structure: The distribution function and two valley effects}, Journal = {Physica B: Physics of Condensed Matter & C: Atomic, Molecular and Plasma Physics, Optics}, Volume = {134}, Number = {1-3}, Pages = {470-474}, Year = {1985}, ISSN = {0378-4363}, Abstract = {We have solved the Boltzman equation for a submicron N+-N--N+ GaAs structure within a two-valley model using energy-dependent relaxation times. Ballistic electrons produce a large peak in the velocity-distribution function throughout much of the N- region. Transfer of electrons from the lower to upper valley in the N- layer causes an accumulation of charge near the collecting N+ region. Transfer of electrons back from the upper to the lower valley in the collecting N+ region creates two new peaks in the distribution function which we call ballistic electron echoes. © 1985.}, Key = {Baranger85} } @booklet{Baranger85a, Author = {Baranger, HU and MacDonald, AH and Leavens, CR}, Title = {Heterocontact effects in point-contact electron-phonon spectroscopy of the alkali metals.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {31}, Number = {10}, Pages = {6197-6206}, Year = {1985}, Month = {May}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9935491}, Key = {Baranger85a} } @booklet{Stanton86, Author = {Stanton, CJ and Baranger, HU and Wilkins, JW}, Title = {Analytic Boltzmann equation approach for negative differential mobility in two-valley semiconductors}, Journal = {Applied Physics Letters}, Volume = {49}, Number = {3}, Pages = {176-178}, Year = {1986}, ISSN = {0003-6951}, url = {http://dx.doi.org/10.1063/1.97216}, Abstract = {We present results for the negative differential mobility and the distribution function in GaAs and InP for electric fields less than 40 kV/cm based on the analytic solution of the Boltzmann equation for a model with two valleys and three relaxation times. Using the measured low field mobility, lower valley mass, and valley separation energy Δ while adjusting three upper valley parameters, we obtain good agreement with the experimental velocity-field curves. The distribution function in the lower valley shows structure at energies ≊Δ due to the intervalley scattering.}, Doi = {10.1063/1.97216}, Key = {Stanton86} } @article{baranger:1708, Author = {Baranger, HU and Pelouard, J-L and Pône, J-F and Castagné, R}, Title = {Ballistic peaks in the distribution function from intervalley transfer in a submicron structure}, Journal = {Applied Physics Letters}, Volume = {51}, Number = {21}, Pages = {1708-1710}, Publisher = {AIP}, Year = {1987}, ISSN = {0003-6951}, url = {http://link.aip.org/link/?APL/51/1708/1}, Keywords = {GALLIUM ARSENIDES; MONTE CARLO METHOD; SIMULATION; SEMICONDUCTOR DEVICES; CHARGED–PARTICLE TRANSPORT; DISTRIBUTION FUNCTIONS}, Abstract = {Using Monte Carlo simulation, we show that ballistic electrons coupled with intervalley scattering produce peaks in the distribution function of electrons in submicron structures. The distribution functions f(v,x) and f(ε,x) for a submicron N+-N--N+ GaAs structure indicate that ballistic electrons cause both the dominant peak in f(v,x) throughout the N- region and additional peaks in f(ε,x) following transfer from the L valley to the Γ valley. For low densities and low temperatures (T=77), both ballistic peaks in f(ε,x) split into several sharp peaks separated in energy by the optic-phonon energy.}, Doi = {10.1063/1.98551}, Key = {baranger:1708} } @article{baranger:1487, Author = {Baranger, HU and Wilkins, JW}, Title = {Ballistic structure in the electron distribution function of small semiconducting structures: General features and specific trends.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {36}, Number = {3}, Pages = {1487-1502}, Publisher = {APS}, Year = {1987}, Month = {July}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9942980}, Keywords = {GALLIUM ARSENIDES; HETEROJUNCTIONS; ELECTRONS; DISTRIBUTION FUNCTIONS; TRANSPORT PROCESSES; HOT ELECTRONS; POISSON EQUATION; BOLTZMANN EQUATION; RELAXATION TIME; IV CHARACTERISTIC; MOBILITY}, Key = {baranger:1487} } @article{chang:2745, Author = {Chang, AM and Timp, G and Cunningham, JE and Mankiewich, PM and Behringer, RE and Howard, RE and Baranger, HU}, Title = {Real-space and magnetic-field correlation of quantum-resistance fluctuations in the ballistic regime in narrow GaAs-AlxGa}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {37}, Number = {5}, Pages = {2745-2748}, Publisher = {APS}, Year = {1988}, Month = {February}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9944842}, Keywords = {GALLIUM ARSENIDES; ALUMINIUM ARSENIDES; ONE – DIMENSIONAL SYSTEMS; WIRES; TRANSPORT PROCESSES; QUANTUM MECHANICS; HETEROSTRUCTURES; ELECTRIC CONDUCTIVITY; FLUCTUATIONS; CORRELATIONS; MAGNETIC FIELDS}, Key = {chang:2745} } @booklet{Baranger88, Author = {Baranger, HU and Stone, AD and DiVincenzo, DP}, Title = {Resistance fluctuations in multiprobe microstructures: Length dependence and nonlocality.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {37}, Number = {11}, Pages = {6521-6524}, Year = {1988}, Month = {April}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9943907}, Key = {Baranger88} } @article{timp:2081, Author = {Timp, G and Baranger, HU and deVegvar, P and Cunningham, JE and Howard, RE and Behringer, R and Mankiewich, PM}, Title = {Propagation around a bend in a multichannel electron waveguide.}, Journal = {Physical Review Letters}, Volume = {60}, Number = {20}, Pages = {2081-2084}, Publisher = {APS}, Year = {1988}, Month = {May}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10038252}, Keywords = {MAGNETORESISTANCE; WIRES; FABRICATION; GALLIUM ARSENIDES; ALUMINIUM ARSENIDES; HETEROSTRUCTURES; SIMULATION; NUMERICAL ANALYSIS; ONE – DIMENSIONAL SYSTEMS}, Doi = {10.1103/PhysRevLett.60.2081}, Key = {timp:2081} } @booklet{Behringer89, Author = {BEHRINGER, RE and MANKIEWICH, PM and TIMP, G and HOWARD, RE and BARANGER, HU and CUNNINGHAM, J and SAMPERE, S}, Title = {ONE-DIMENSIONAL BALLISTIC TRANSPORT IN ALGAAS/GAAS ELECTRON WAVEGUIDES}, Journal = {Journal of vacuum science & technology. B, Microelectronics and nanometer structures : processing, measurement, and phenomena : an official journal of the American Vacuum Society}, Volume = {7}, Number = {6}, Pages = {2039-2043}, Publisher = {AVS}, Year = {1989}, ISSN = {1071-1023}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:A1989CG91400147&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Doi = {10.1116/1.584644}, Key = {Behringer89} } @article{chang:2695, Author = {Chang, AM and Chang, TY and Baranger, HU}, Title = {Erratum: Quenching of the Hall resistance in a novel geometry [Phys. Rev. Lett. [bold 63], 996 (1989)]}, Journal = {Phys. Rev. Lett.}, Volume = {63}, Number = {24}, Pages = {2695-2695}, Publisher = {APS}, Year = {1989}, ISSN = {0031-9007}, url = {http://link.aps.org/abstract/PRL/v63/p2695/s4}, Doi = {10.1103/PhysRevLett.63.2695.4}, Key = {chang:2695} } @article{fds304505, Author = {Chang, AM and Chang, TY and Baranger, HU}, Title = {Erratum: Quenching of the Hall resistance in a novel geometry (Physical Review Letters (1989) 63, 996 (2695))}, Journal = {Physical Review Letters}, Volume = {63}, Number = {24}, Pages = {2695-}, Year = {1989}, ISSN = {0031-9007}, url = {http://dx.doi.org/10.1103/PhysRevLett.63.2695.4}, Doi = {10.1103/PhysRevLett.63.2695.4}, Key = {fds304505} } @booklet{Timp89, Author = {Timp, G and Mankiewich, PM and deVegvar, P and Behringer, R and Cunningham, JE and Howard, RE and Baranger, HU and Jain, JK}, Title = {Suppression of the Aharonov-Bohm effect in the quantized Hall regime.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {39}, Number = {9}, Pages = {6227-6230}, Publisher = {APS}, Year = {1989}, Month = {March}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9949054}, Keywords = {GALLIUM ARSENIDES; ALUMINIUM ARSENIDES; HETEROSTRUCTURES; RINGS; QUANTUM HALL EFFECT; MAGNETORESISTANCE}, Key = {Timp89} } @article{baranger:414, Author = {Baranger, HU and Stone, AD}, Title = {Quenching of the Hall resistance in ballistic microstructures: A collimation effect.}, Journal = {Physical Review Letters}, Volume = {63}, Number = {4}, Pages = {414-417}, Publisher = {APS}, Year = {1989}, Month = {July}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10041067}, Keywords = {HALL EFFECT; INHIBITION; MICROSTRUCTURE; MAGNETIC FIELDS; ONE – DIMENSIONAL SYSTEMS; WIRES; WIDTH; ELECTRIC PROBES}, Doi = {10.1103/PhysRevLett.63.414}, Key = {baranger:414} } @booklet{Chang89, Author = {Chang, AM and Chang, TY and Baranger, HU}, Title = {Quenching of the Hall resistance in a novel geometry.}, Journal = {Physical Review Letters}, Volume = {63}, Number = {9}, Pages = {996-999}, Publisher = {APS}, Year = {1989}, Month = {August}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10041242}, Keywords = {HALL EFFECT; INHIBITION; GEOMETRY; GALLIUM ARSENIDES; ALUMINIUM ARSENIDES; HETEROSTRUCTURES; QUANTUM MECHANICS; ELECTRON DENSITY; ULTRALOW TEMPERATURE; MAGNETIC FIELDS}, Doi = {10.1103/PhysRevLett.63.996}, Key = {Chang89} } @booklet{Baranger89, Author = {H. U. Baranger and A. D. Stone}, Title = {Electrical linear-response theory in an arbitrary magnetic-field - a new fermi-surface formation}, Journal = {Physical Review B}, Volume = {40}, Number = {12}, Pages = {8169 -- 8193}, Year = {1989}, Month = {October}, Key = {Baranger89} } @article{baranger:8169, Author = {Baranger, HU and Stone, AD}, Title = {Electrical linear-response theory in an arbitrary magnetic field: A new Fermi-surface formation.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {40}, Number = {12}, Pages = {8169-8193}, Publisher = {APS}, Year = {1989}, Month = {October}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9991272}, Keywords = {MAGNETIC FIELDS; QUANTUM HALL EFFECT; ELECTRIC CONDUCTORS; ELECTRON MOBILITY; ELECTRIC CURRENTS; RESPONSE FUNCTIONS; SEMICONDUCTOR MATERIALS; TRANSPORT PROCESSES}, Key = {baranger:8169} } @article{fds245049, Author = {Woodward, TK and Chemla, DS and Bar-Joseph, I and Baranger, HU and Sivco, DL and Cho, AY}, Title = {Sequential vs. coherent tunneling in double barrier diodes investigated by differential absorption spectroscopy}, Journal = {Technical Digest - International Electron Devices Meeting}, Pages = {959-962}, Year = {1990}, Abstract = {The charge distributions in the quantum wells of several double barrier diodes were measured. It is found that the ratio of the stored charge to the current is not equal to the coherent state lifetime and is basically insensitive to the amount of scattering. It was experimentally demonstrated that phase breaking collisions take place in the present structures by observing the energy distribution of the stored charge in both single and double resonance structures.}, Key = {fds245049} } @booklet{Baranger90a, Author = {Baranger, HU and Stone, AD}, Title = {Geometrical effects on the Hall resistance in ballistic microstructures}, Journal = {Surface Science}, Volume = {229}, Number = {1-3}, Pages = {212-215}, Year = {1990}, ISSN = {0039-6028}, Abstract = {We calculate the Hall resistance of four-probe junctions with unusual geometries similar to those used in recent experiments. We find a variety of behavior, including quenching at low magnetic fields and a negative Hall resistance at low fields. Our results are in excellent agreement with the experiments and are explained naturally through the concept of collimation of the electrons in the leads. In particular, we find that a gradually changing width is necessary on all four leads in order to produce good quenching, and that a negative Hall resistance in a widened cross structure requires both a region of gradual widening to provide collimation and a region of rapid widening to reflect the collimated beam. © 1990.}, Key = {Baranger90a} } @article{jalabert:2442, Author = {Jalabert, RA and Baranger, HU and Stone, AD}, Title = {Conductance fluctuations in the ballistic regime: A probe of quantum chaos?}, Journal = {Physical Review Letters}, Volume = {65}, Number = {19}, Pages = {2442-2445}, Publisher = {APS}, Year = {1990}, Month = {November}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10042549}, Keywords = {FLUCTUATIONS; SCATTERING; MAGNETIC FIELDS; CORRELATION FUNCTIONS; ENERGY; SEMICLASSICAL APPROXIMATION; NUMERICAL SOLUTION; CLASSICAL MECHANICS; CHAOTIC SYSTEMS; HALL EFFECT; JUNCTIONS; QUANTUM MECHANICS; TRAJECTORIES; CORRELATION LENGTH; DISKS}, Doi = {10.1103/PhysRevLett.65.2442}, Key = {jalabert:2442} } @article{baranger:11479, Author = {Baranger, HU}, Title = {Multiprobe electron waveguides: Filtering and bend resistances.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {42}, Number = {18}, Pages = {11479-11495}, Publisher = {APS}, Year = {1990}, Month = {December}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9995452}, Keywords = {WAVEGUIDES; QUANTUM ELECTRONICS; SUPERCONDUCTING WIRES; ELECTRIC CONDUCTIVITY; LOW TEMPERATURE; HETEROJUNCTIONS; CHARGED – PARTICLE TRANSPORT; ELECTRONS}, Key = {baranger:11479} } @booklet{Nixon91a, Author = {Nixon, JA and Davies, JH and Baranger, HU}, Title = {Conductance of quantum point contacts calculated using realistic potentials}, Journal = {Superlattices and Microstructures}, Volume = {9}, Number = {2}, Pages = {187-190}, Year = {1991}, ISSN = {0749-6036}, url = {http://dx.doi.org/10.1016/0749-6036(91)90280-5}, Abstract = {The quantized conductance of ballistic electrons in narrow constrictions requires the low scattering rates of a high mobility 2-dimensional electron gas(2DEG). Despite the spectacular mobilities of 2DEGs, quantization breaks down for constrictions longer than about 500 nm, whereas the mean free path in the ungated 2DEG may exceed 10 μm. We show that potential fluctuations from a random distribution of ionised donors modify the guiding potential from the gate in an unpredictable way. The fluctuations are responsible for the variability among nominally identical devices. For a short constriction (200 nm) the conductance can be well quantized. The accuracy of quantization in a longer constriction (600 nm) is reduced by scattering from the random potential of the donors. This occurs when the length scale of the constriction is greater than that of the fluctuations. The conductance characteristics depend strongly on the exact configuration of impurities. In some cases the random potential causes a resonance in the channel. © 1991.}, Doi = {10.1016/0749-6036(91)90280-5}, Key = {Nixon91a} } @article{behringer:930, Author = {Behringer, R and Timp, G and Baranger, HU and Cunningham, JE}, Title = {Quantum-mechanical features in the resistance of a submircon junction.}, Journal = {Physical Review Letters}, Volume = {66}, Number = {7}, Pages = {930-933}, Publisher = {APS}, Year = {1991}, Month = {February}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10043943}, Keywords = {WIRES; TEMPERATURE DEPENDENCE; ELECTRON – IMPURITY INTERACTIONS; MAGNETORESISTANCE; FLUCTUATIONS; DISORDERED SYSTEMS; HALL EFFECT; FERMI LEVEL; ELECTRON GAS; QUANTUM MECHANICS; NUMERICAL DATA; HETEROSTRUCTURES}, Doi = {10.1103/PhysRevLett.66.930}, Key = {behringer:930} } @booklet{Nixon91, Author = {Nixon, JA and Davies, JH and Baranger, HU}, Title = {Breakdown of quantized conductance in point contacts calculated using realistic potentials.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {43}, Number = {15}, Pages = {12638-12641}, Publisher = {APS}, Year = {1991}, Month = {May}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9997071}, Keywords = {QUANTUM WELL STRUCTURES; TRANSPORT THEORY; POINT CONTACTS; DONORS; IMPURITIES; ELECTRIC CONDUCTIVITY; HETEROSTRUCTURES}, Key = {Nixon91} } @article{woodward:1353, Author = {Woodward, TK and Chemla, DS and Bar-Joseph, I and Baranger, HU and Sivco, DL and Cho, AY}, Title = {Sequential versus coherent tunneling in double-barrier diodes investigated by differential absorption spectroscopy.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {44}, Number = {3}, Pages = {1353-1356}, Publisher = {APS}, Year = {1991}, Month = {July}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9999652}, Keywords = {HETEROSTRUCTURES; ABSORPTION SPECTRA; CHARGE DISTRIBUTION; ELECTRIC CURRENTS; QUANTUM WELL STRUCTURES; TUNNEL EFFECT}, Key = {woodward:1353} } @article{baranger:10637, Author = {Baranger, HU and DiVincenzo, DP and Jalabert, RA and Stone, AD}, Title = {Classical and quantum ballistic-transport anomalies in microjunctions.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {44}, Number = {19}, Pages = {10637-10675}, Publisher = {APS}, Year = {1991}, Month = {November}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9999090}, Keywords = {JUNCTIONS; TWO – DIMENSIONAL SYSTEMS; MAGNETIC FIELDS; TRANSPORT PROCESSES; CLASSICAL MECHANICS; ANOMALOUS PROPERTIES; BALLISTICS; HALL EFFECT; SCATTERING; INJECTION; MAGNETORESISTANCE}, Key = {baranger:10637} } @booklet{Goni92, Author = {Goñi, AR and Pfeiffer, LN and West, KW and Pinczuk, A and Baranger, HU and Stormer, HL}, Title = {Observation of quantum wire formation at intersecting quantum wells}, Journal = {Applied Physics Letters}, Volume = {61}, Number = {16}, Pages = {1956-1958}, Year = {1992}, ISSN = {0003-6951}, url = {http://dx.doi.org/10.1063/1.108375}, Abstract = {We report the first observation of a quantum bound state formed at the junction of two intersecting quantum wells in the shape of a T. The atomically precise T junctions are fabricated by a novel cleaved edge overgrowth process in the AlGaAs/GaAs system. The identification of bound states with energies in excess of 20 meV is made by optical emission and absorption spectroscopy. Such quantum wire states are caused by the unique confinement of the lowest state wave function to the region of the T junction.}, Doi = {10.1063/1.108375}, Key = {Goni92} } @booklet{Band92, Author = {Band, YB and Baranger, HU and Avishai, Y}, Title = {Relationship between resistance, localization length, and inelastic-scattering length.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {45}, Number = {3}, Pages = {1488-1491}, Publisher = {APS}, Year = {1992}, Month = {January}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10001639}, Keywords = {ELECTRIC CONDUCTIVITY; LOCALIZED STATES; INELASTIC SCATTERING; WIRES; DISTRIBUTION FUNCTIONS; ANALYTICAL SOLUTION; TEMPERATURE DEPENDENCE; ELASTIC SCATTERING; TRANSMISSION; REFLECTION; SCATTERING AMPLITUDES; INTEGRAL EQUATIONS; RANDOM WALK; MEAN FREE PATH}, Key = {Band92} } @booklet{Baranger93, Author = {Baranger, HU and Jalabert, RA and Stone, AD}, Title = {Weak localization and integrability in ballistic cavities.}, Journal = {Physical Review Letters}, Volume = {70}, Number = {25}, Pages = {3876-3879}, Year = {1993}, Month = {June}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10053988}, Doi = {10.1103/PhysRevLett.70.3876}, Key = {Baranger93} } @article{baranger:665, Author = {Baranger, HU and Jalabert, RA and Stone, AD}, Title = {Quantum-chaotic scattering effects in semiconductor microstructures.}, Journal = {Chaos}, Volume = {3}, Number = {4}, Pages = {665-682}, Publisher = {AIP}, Year = {1993}, Month = {October}, url = {http://www.ncbi.nlm.nih.gov/pubmed/12780071}, Keywords = {MICROSTRUCTURE; SEMICONDUCTOR MATERIALS; SCATTERING THEORY; CHAOTIC SYSTEMS; ELECTRIC CONDUCTIVITY; FLUCTUATIONS; SEMICLASSICAL APPROXIMATION; POWER SPECTRA; TRANSPORT PROCESSES; SCALING LAWS; POTENTIAL SCATTERING}, Abstract = {We show that classical chaotic scattering has experimentally measurable consequences for the quantum conductance of semiconductor microstructures. These include the existence of conductance fluctuations-a sensitivity of the conductance to either Fermi energy or magnetic field-and weak-localization-a change in the average conductance upon applying a magnetic field. We develop a semiclassical theory and present numerical results for these two effects in which we model the microstructures by billiards attached to leads. We find that the difference between chaotic and regular classical scattering produces a qualitative difference in the fluctuation spectrum and weak-localization lineshape of chaotic and nonchaotic structures. While the semiclassical theory within the diagonal approximation accounts well for the weak-localization lineshape and for the spectrum of the fluctuations, we uncover a surprising failure of the semiclassical diagonal-approximation theory in describing the magnitude of these quantum transport effects.}, Doi = {10.1063/1.165928}, Key = {baranger:665} } @booklet{Nockel93, Author = {J. U. Nockel and A. D. Stone and H. U. Baranger}, Title = {Adiabatic turn-on and the asymptotic limit in linear-response theory for open systems}, Journal = {Physical Review B}, Volume = {48}, Number = {23}, Pages = {17569 -- 17572}, Year = {1993}, Month = {December}, Key = {Nockel93} } @article{nockel:17569, Author = {Nöckel, JU and Stone, AD and Baranger, HU}, Title = {Adiabatic turn-on and the asymptotic limit in linear-response theory for open systems.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {48}, Number = {23}, Pages = {17569-17572}, Publisher = {APS}, Year = {1993}, Month = {December}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10008374}, Keywords = {TRANSPORT THEORY; KUBO FORMULA; ADIABATIC PROCESSES; MATHEMATICAL MODELS; ELECTRIC CONDUCTIVITY; SCATTERING}, Key = {nockel:17569} } @article{baranger:142, Author = {Baranger, HU and Mello, PA}, Title = {Mesoscopic transport through chaotic cavities: A random S-matrix theory approach.}, Journal = {Physical Review Letters}, Volume = {73}, Number = {1}, Pages = {142-145}, Publisher = {APS}, Year = {1994}, Month = {July}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10056740}, Keywords = {S MATRIX; TRANSPORT THEORY; MICROSTRUCTURE; NANOSTRUCTURES; CHAOTIC SYSTEMS; SCATTERING THEORY; INTERFERENCE; FLUCTUATIONS; MAGNETIC FIELD EFFECTS}, Doi = {10.1103/PhysRevLett.73.142}, Key = {baranger:142} } @article{hastings:8230, Author = {Hastings, MB and Stone, AD and Baranger, HU}, Title = {Inequivalence of weak localization and coherent backscattering.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {50}, Number = {12}, Pages = {8230-8244}, Publisher = {APS}, Year = {1994}, Month = {September}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9974840}, Keywords = {COHERENT SCATTERING; BACKSCATTERING; DISORDERED SYSTEMS; ELECTRIC CONDUCTIVITY; LOCALIZED STATES; CHAOTIC SYSTEMS; REFLECTION; BALLISTICS; SYMMETRY; ELECTRIC CONDUCTORS}, Key = {hastings:8230} } @booklet{Chang94, Author = {A. M. Chang and H. U. Baranger and L. N. Pfeiffer and K. W. West}, Title = {Weak-localization in chaotic versus nonchaotic cavities - a striking difference in the line-shape}, Journal = {Physical Review Letters}, Volume = {73}, Number = {15}, Pages = {2111 -- 2114}, Year = {1994}, Month = {October}, Key = {Chang94} } @article{chang:2111, Author = {Chang, AM and Baranger, HU and Pfeiffer, LN and West, KW}, Title = {Weak localization in chaotic versus nonchaotic cavities: A striking difference in the line shape.}, Journal = {Physical Review Letters}, Volume = {73}, Number = {15}, Pages = {2111-2114}, Publisher = {APS}, Year = {1994}, Month = {October}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10056974}, Keywords = {TRANSPORT PROCESSES; CHAOTIC SYSTEMS; SCATTERING; CAVITY RESONATORS; MAGNETORESISTANCE; AHARONOV – BOHM EFFECT; QUANTUM WELLS; COHERENCE LENGTH}, Doi = {10.1103/PhysRevLett.73.2111}, Key = {chang:2111} } @booklet{Mello95, Author = {Mello, PA and Baranger, HU}, Title = {Electronic transport through ballistic chaotic cavities: an information theoretic approach}, Journal = {Physica A: Statistical Mechanics and its Applications}, Volume = {220}, Number = {1-2}, Pages = {15-23}, Year = {1995}, ISSN = {0378-4371}, url = {http://dx.doi.org/10.1016/0378-4371(95)00121-M}, Abstract = {The statistical properties of the electronic conductance through a ballistic quantum dot are studied by means of an information-theoretic statistical model for the scattering matrix. The model, introduced in the past in the context of nuclear physics, describes the problem in terms of a prompt and an equilibrated component: it incorporates the average value of the scattering matrix to describe the prompt processes and satisfies the requirements of flux conservation, causality and ergodicity. The model describes well the results arising from the numerical solution of the Schrödinger equation for two-dimensional quantum cavities. © 1995.}, Doi = {10.1016/0378-4371(95)00121-M}, Key = {Mello95} } @booklet{Baranger95, Author = {Baranger, HU}, Title = {Quantum transport and chaos in semiconductor microstructures}, Journal = {Physica D: Nonlinear Phenomena}, Volume = {83}, Number = {1-3}, Pages = {30-45}, Year = {1995}, ISSN = {0167-2789}, Abstract = {It is shown that classical chaotic scattering has experimentally measurable consequences for the quantum conductance of semiconductor microstructures. These include the existence of conductance fluctuations -a sensitivity of the conductance to either Fermi energy or magnetic field- and weak-localization -a change in the average conductance upon applying a magnetic field. We use semiclassical theory, random S-matrix theory, and numerical results to describe these interference effects for microstructures modeled by billiards attached to leads. The semiclassical theory predicts that the difference between chaotic and regular classical scattering produces a qualitative difference in the fluctuation spectrum and weak-localization lineshape of chaotic versus non-chaotic structures. The random S-matrix theory yields results for the magnitude of these interference effects. The conductance fluctuation and weak-localization magnitudes are universal if the number of incoming modes, N, is large: they are independent of the size and shape of the cavity. Of more relevance experimentally, in the limit of small N the full distribution of the conductance shows a striking dependence on N and magnetic field. © 1995.}, Key = {Baranger95} } @booklet{Sumetskii95, Author = {Sumetskii, MI and Baranger, HU}, Title = {Change in sign of the photocurrent in a coherent asymmetric superlattice}, Journal = {Applied Physics Letters}, Volume = {67}, Number = {24}, Pages = {3560-3562}, Publisher = {AIP}, Year = {1995}, url = {http://link.aip.org/link/?APL/67/3560/1}, Keywords = {FREQUENCY DEPENDENCE; INTERFERENCE; OSCILLATIONS; PHOTOCONDUCTIVITY; PHOTOCURRENTS; QUANTUM WELLS; SUPERLATTICES}, Abstract = {This study shows that the oscillations of the photocurrent sign may be observed for the simplest double quantum well structure and for the superlattice with a double quantum well unit. Two series of the current reversal points have been found. Further study of the photocurrent induced in such structures may lead to a new kind of infrared detector based on this photocurrent reversal effect.}, Doi = {10.1063/1.114921}, Key = {Sumetskii95} } @article{sumetskii:1352, Author = {Sumetskii, MI and Baranger, HU}, Title = {Studying the insulator-conductor interface with a scanning tunneling microscope}, Journal = {Applied Physics Letters}, Volume = {66}, Pages = {1352-}, Publisher = {AIP}, Year = {1995}, ISSN = {0003-6951}, url = {http://link.aip.org/link/?APL/66/1352/1}, Keywords = {SILICON; SILICON OXIDES; INTERFACE STRUCTURE; STM; MORPHOLOGY; SPATIAL RESOLUTION; ROUGHNESS}, Abstract = {We suggest that a scanning tunneling microscope (STM) may be used for investigating the insulator-conductor interface, in particular SiO2/Si, at nanometer scale. For an insulating film transparent to tunneling, we estimate, using a simple model, the roughness of the interface from the STM image. It is found that the interface roughness is less than the roughness of the image surface times the ratio of effective decay lengths in the film and in vacuum. For relatively wide films, of order 10 nm, STM measurement in the field emission regime can give the interface image with 1 nm precision.© 1995 American Institute of Physics.}, Key = {sumetskii:1352} } @booklet{Baranger95a, Author = {Baranger, HU and Mello, PA}, Title = {Effect of phase breaking on quantum transport through chaotic cavities.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {51}, Number = {7}, Pages = {4703-4706}, Publisher = {APS}, Year = {1995}, Month = {February}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9979331}, Keywords = {CHAOTIC SYSTEMS; CAVITIES; QUANTUM DOTS; TRANSPORT PROCESSES; INTERFERENCE; PHASE SHIFT; S MATRIX; ANALYTICAL SOLUTION}, Key = {Baranger95a} } @booklet{Aleiner95, Author = {Aleiner, IL and Baranger, HU and Glazman, LI}, Title = {Tunneling into a Two-Dimensional Electron Liquid in a Weak Magnetic Field.}, Journal = {Physical Review Letters}, Volume = {74}, Number = {17}, Pages = {3435-3438}, Year = {1995}, Month = {April}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10058200}, Doi = {10.1103/PhysRevLett.74.3435}, Key = {Aleiner95} } @booklet{Gopar96, Author = {Gopar, VA and Martínez, M and Mello, PA and Baranger, HU}, Title = {The invariant measure for scattering matrices with block symmetries}, Journal = {Journal of Physics A: Mathematical and General}, Volume = {29}, Number = {4}, Pages = {881-888}, Year = {1996}, ISSN = {0305-4470}, url = {http://dx.doi.org/10.1088/0305-4470/29/4/014}, Abstract = {We find the invariant measure for two new types of S matrices relevant for chaotic scattering from a cavity in a waveguide. The S matrices considered can be written as a 2 × 2 matrix of blocks, each of rank N, in which the two diagonal blocks are identical and the two off-diagonal blocks are identical. The S matrices are unitary; in addition, they may be symmetric because of time-reversal symmetry. The invariant measure, with and without the condition of symmetry, is given explicitly in terms of the invariant measures for the well known circular unitary and orthogonal ensembles. Some implications are drawn for the resulting statistical distribution of the transmission coefficient through a chaotic cavity. © 1996 IOP Publishing Ltd.}, Doi = {10.1088/0305-4470/29/4/014}, Key = {Gopar96} } @booklet{Matveev96a, Author = {Matveev, KA and Glazman, LI and Baranger, HU}, Title = {Theory of Coulomb blockade of tunneling through a double quantum dot}, Journal = {Surface Science}, Volume = {361-362}, Number = {1-3}, Pages = {623-626}, Year = {1996}, url = {http://dx.doi.org/10.1016/0039-6028(96)00484-0}, Abstract = {We present a theory of Coulomb blockade oscillations in tunneling through a pair of quantum dots connected by a tunable tunneling junction. The positions and amplitudes of peaks in the linear conductance are directly related, respectively, to the ground state energy and to the dynamics of charge fluctuations. Our theory allows for a quantitative comparison with the experimentally observed peak positions. In the strong tunneling limit, we predict a striking powder-law temperature-dependence of the peak amplitudes.}, Doi = {10.1016/0039-6028(96)00484-0}, Key = {Matveev96a} } @booklet{Baranger96a, Author = {Baranger, HU and Mello, PA}, Title = {Short paths and information theory in quantum chaotic scattering: Transport through quantum dots}, Journal = {EPL (Europhysics Letters)}, Volume = {33}, Number = {6}, Pages = {465-470}, Year = {1996}, ISSN = {0295-5075}, url = {http://dx.doi.org/10.1209/epl/i1996-00364-5}, Abstract = {We propose an information-theoretic model to describe the common features of typical chaotic scattering processes by including two time scales, a prompt and an equilibrated component. The model, introduced in nuclear physics, uses the average value of the scattering matrix to describe the prompt processes, and satisfies flux conservation, causality, and ergodicity. We show that the model successfully describes electronic transport through a much larger class of chaotic quantum dots than previously considered. The predicted distribution of the conductance may differ dramatically from that of previous models.}, Doi = {10.1209/epl/i1996-00364-5}, Key = {Baranger96a} } @article{matveev:1034, Author = {Matveev, KA and Glazman, LI and Baranger, HU}, Title = {Tunneling spectroscopy of quantum charge fluctuations in the Coulomb blockade.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {53}, Number = {3}, Pages = {1034-1037}, Publisher = {APS}, Year = {1996}, Month = {January}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9983548}, Keywords = {COULOMB EXCITATION; ELECTRIC CONDUCTIVITY; ELECTRONIC STRUCTURE; FLUCTUATIONS; GROUND STATES; TEMPERATURE DEPENDENCE; TUNNEL EFFECT; ELECTRON CHARGE; QUANTUM DOTS}, Key = {matveev:1034} } @booklet{Chang96, Author = {A. M. Chang and H. U. Baranger and L. N. Pfeiffer and K. W. West and T. Y. Chang}, Title = {Non-Gaussian distribution of Coulomb blockade peak heights in quantum dots}, Journal = {Phys. Rev. Lett.}, Volume = {76}, Number = {10}, Pages = {1695 -- 1698}, Year = {1996}, Month = {March}, Key = {Chang96} } @article{chang:1695, Author = {Chang, AM and Baranger, HU and Pfeiffer, LN and West, KW and Chang, TY}, Title = {Non-Gaussian distribution of Coulomb blockade peak heights in quantum dots.}, Journal = {Physical Review Letters}, Volume = {76}, Number = {10}, Pages = {1695-1698}, Publisher = {APS}, Year = {1996}, Month = {March}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10060494}, Keywords = {QUANTUM DOTS; TUNNELING; IV CHARACTERISTIC; COULOMB FIELD; GALLIUM ARSENIDES; ALUMINIUM ARSENIDES}, Doi = {10.1103/PhysRevLett.76.1695}, Key = {chang:1695} } @booklet{Matveev96, Author = {K. A. Matveev and L. I. Glazman and H. U. Baranger}, Title = {Coulomb blockade of tunneling through a double quantum dot}, Journal = {Physical Review B}, Volume = {54}, Number = {8}, Pages = {5637 -- 5646}, Year = {1996}, Month = {August}, Key = {Matveev96} } @article{matveev:5637, Author = {Matveev, KA and Glazman, LI and Baranger, HU}, Title = {Coulomb blockade of tunneling through a double quantum dot.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {54}, Number = {8}, Pages = {5637-5646}, Publisher = {APS}, Year = {1996}, Month = {August}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9986527}, Keywords = {TUNNEL EFFECT; COULOMB FIELD; ELECTRIC CONDUCTIVITY; TEMPERATURE DEPENDENCE; FLUCTUATIONS; PEAKS; QUANTUM DOTS}, Key = {matveev:5637} } @booklet{Baranger96, Author = {Baranger, HU and Mello, PA}, Title = {Reflection symmetric ballistic microstructures: Quantum transport properties.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {54}, Number = {20}, Pages = {R14297-R14300}, Publisher = {APS}, Year = {1996}, Month = {November}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9985511}, Keywords = {NANOSTRUCTURES; CHAOTIC SYSTEMS; HETEROSTRUCTURES; TRANSPORT PROCESSES; ELECTRIC CONDUCTIVITY; TRANSMISSION; S MATRIX; REFLECTION; P INVARIANCE}, Key = {Baranger96} } @booklet{Hasen97, Author = {Hasen, J and Pfeiffer, LN and Pinczuk, A and Baranger, HU and West, KW and Dennis, BS}, Title = {Large excitonic confinement in asymmetric quantum T wires}, Journal = {Superlattices and Microstructures}, Volume = {22}, Number = {3}, Pages = {X-364}, Year = {1997}, url = {http://dx.doi.org/10.1006/spmi.1996.0283}, Abstract = {An asymmetric quantum T wire (QTWR) may be formed whenever two quantum wells (QW) of differing widths intersect. We measured the photoluminescence and photoluminescence excitation from such QTWRs using microscope optics with high spatial resolution. The introduction of an asymmetry in the design of the QWs allows us to compensate for the different effective masses of the heavy holes in the (100) and (110) directions. We find that the confinement energy for excitons in the asymmetric QTWR is 40 meV, which is greater than previously published reports on symmetric QTWRs. Consequently, the confinement energy exceeds kT at room temperature, which appeals to device applications. Furthermore, the confinement energy is greater than the LO phonon energy, a feature which may improve the capture rate of the QTWR and decrease the escape rate at higher temperatures. Finally, using the results from calculations, we estimate the binding energy of the exciton to be about 20 meV, which is substantially larger than the binding energy in QWs. This result agrees with theoretical predictions of an increase in exciton binding energy in ID confinement. © 1997 Academic Press Limited.}, Doi = {10.1006/spmi.1996.0283}, Key = {Hasen97} } @booklet{Ullmo97, Author = {D. Ullmo and K. Richter and H. U. Baranger and F. von Oppen and R. A. Jalabert}, Title = {Semiclassical approach to orbital magnetism of interacting diffusive quantum systems}, Journal = {Physica E}, Volume = {1}, Number = {1-4}, Pages = {268 -- 273}, Year = {1997}, Month = {December}, Key = {Ullmo97} } @booklet{Ullmo98, Author = {Ullmo, D and Baranger, HU and Richter, K and Oppen, FV and Jalabert, RA}, Title = {Chaos and interacting electrons in ballistic quantum dots}, Journal = {Physical Review Letters}, Volume = {80}, Number = {5}, Pages = {895-899}, Year = {1998}, Abstract = {We show that the classical dynamics of independent particles can determine the quantum properties of interacting electrons in the ballistic regime. This connection is established using diagrammatic perturbation theory and semiclassical finite-temperature Green functions. Specifically, the orbital magnetism is greatly enhanced by the combined effects of interactions and finite size. The presence of families of periodic orbits in regular systems makes their susceptibility parametrically larger than that of chaotic systems, a difference which emerges from correlation terms.}, Key = {Ullmo98} } @article{fds245170, Author = {Ullmo, D and Richter, K and Baranger, HU and Oppen, FV and Jalabert, RA}, Title = {Semiclassical approach to orbital magnetism of interacting diffusive quantum systems}, Journal = {Physica E: Low-Dimensional Systems and Nanostructures}, Volume = {1}, Number = {1-4}, Pages = {268-273}, Year = {1998}, Abstract = {We study interaction effects on the orbital magnetism of diffusive mesoscopic quantum systems. By combining many-body perturbation theory with semiclassical techniques, we show that the interaction contribution to the ensemble-averaged quantum thermodynamic potential can be reduced to an essentially classical operator. We compute the magnetic response of disordered rings and dots for diffusive classical dynamics. Our semiclassical approach reproduces the results of previous diagrammatic quantum calculations. © 1997 Elsevier Science B.V. All rights reserved.}, Key = {fds245170} } @article{fds245051, Author = {Narimanov, EE and Cerruti, NR and Baranger, HU and Tomsovic, S}, Title = {Anomalous low temperature behavior of superconducting Nd_{1.85}Ce_{0.15}CuO_{4-y}}, Journal = {Physical Review Letters}, Volume = {83}, Number = {13}, Pages = {2644-2647}, Year = {1999}, ISSN = {0031-9007}, Abstract = {Bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4-y are used to measure the temperature dependence of the in-plane London penetration depth λab(T) and the maximum Josephson current Ic(T). Results showed that λab(T) and Ic(T) anomalously increases and decreases, respectively, with decreasing temperature below 4 K due to the presence of the Nd3+ paramagnetic moments.}, Key = {fds245051} } @booklet{Ullmo99, Author = {Ullmo, D and Baranger, HU}, Title = {Wireless propagation in buildings: a statistical scattering approach}, Journal = {IEEE Transactions on Vehicular Technology}, Volume = {48}, Number = {3}, Pages = {947-955}, Year = {1999}, ISSN = {0018-9545}, url = {http://dx.doi.org/10.1109/25.765025}, Abstract = {A new approach to the modeling of wireless propagation in buildings is introduced. We treat the scattering by walls and local clutter probabilistically through either a relaxation-time approximation in a Boltzmann equation or by using a diffusion equation. The result is a range of models in which one can vary the tradeoff between the complexity of the building description and the accuracy of the prediction. The two limits of this range are ray tracing at the most accurate end and a simple decay law at the most simple. By comparing results for two of these new models with measurements, we conclude that a reasonably accurate description of propagation can be obtained with a relatively simple model. The most effective way to use the models is by combining them with a few measurements through a sampling technique.}, Doi = {10.1109/25.765025}, Key = {Ullmo99} } @article{fds245192, Author = {Narimanov, EE and Cerruti, NR and Baranger, HU and Tomsovic, S}, Title = {Chaos in quantum dots: dynamical modulation of coulomb blockade peak heights}, Journal = {Physical Review Letters}, Volume = {83}, Number = {13}, Pages = {2640-2643}, Year = {1999}, ISSN = {0031-9007}, Abstract = {We develop a semiclassical theory of Coulomb blockade peak heights in quantum dots and show that the dynamics in the dot leads to a large modulation of the peak height. The corrections to the standard statistical theory of peak height distributions, power spectra, and correlation functions are nonuniversal and can be expressed in terms of the classical periodic orbits of the dot that are well coupled to the leads. The resulting correlation function oscillates as a function of the peak number in a way defined by such orbits. In addition, the correlation of adjacent conductance peaks is enhanced. Both of these effects are in agreement with recent experiments. © 1999 The American Physical Society.}, Key = {fds245192} } @booklet{Mello99, Author = {Mello, PA and Baranger, HU}, Title = {Interference Phenomena in Electronic Transport Through Chaotic Cavities: An Information-Theoretic Approach}, Volume = {464}, Number = {2}, Pages = {281-333}, Year = {1999}, url = {http://arxiv.org/abs/cond-mat/9812225v1}, Abstract = {We develop a statistical theory describing quantum-mechanical scattering of a particle by a cavity when the geometry is such that the classical dynamics is chaotic. This picture is relevant to a variety of systems, ranging from atomic nuclei to microwave cavities; the main application here is to electronic transport through ballistic microstructures. The theory describes the regime in which there are two distinct time scales, associated with a prompt and an equilibrated response, and is cast in terms of the matrix of scattering amplitudes S. The prompt response is related to the energy average of S which, through ergodicity, is expressed as the average over an ensemble of systems. We use an information-theoretic approach: the ensemble of S-matrices is determined by (1) general physical features-- symmetry, causality, and ergodicity, (2) the specific energy average of S, and (3) the notion of minimum information in the ensemble. This ensemble, known as Poisson's kernel, is meant to describe those situations in which any other information is irrelevant. Thus, one constructs the one-energy statistical distribution of S using only information expressible in terms of S itself without ever invoking the underlying Hamiltonian. This formulation has a remarkable predictive power: from the distribution of S we derive properties of the quantum conductance of cavities, including its average, its fluctuations, and its full distribution in certain cases, both in the absence and presence prompt response. We obtain good agreement with the results of the numerical solution of the Schrodinger equation for cavities in which either prompt response is absent or there are two widely separated time scales. Good agreement with experimental data is obtained once temperature smearing and dephasing effects are taken into account.}, Doi = {10.1088/0959-7174/9/2/304}, Key = {Mello99} } @article{fds4755, Author = {H. U. Baranger and R. M. Westervelt}, Title = {Chaos in Ballistic Nanostructures}, Pages = {537-628}, Booktitle = {Nanotechnology}, Publisher = {Springer-Verlag}, Editor = {G. Timp}, Year = {1999}, Key = {fds4755} } @booklet{Narimanov99, Author = {E. E. Narimanov and N. R. Cerruti and H. U. Baranger and S. Tomsovic}, Title = {Chaos in quantum dots: Dynamical modulation of Coulomb blockade peak heights}, Journal = {Physical Review Letters}, Volume = {83}, Number = {13}, Pages = {2640 -- 2643}, Year = {1999}, Month = {September}, Key = {Narimanov99} } @booklet{Baranger00, Author = {Baranger, HU and Ullmo, D and Glazman, LI}, Title = {Interactions and interference in quantum dots: Kinks in Coulomb-blockade peak positions}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {61}, Number = {4}, Pages = {R2425-R2428}, Year = {2000}, ISSN = {0163-1829}, Abstract = {We investigate the spin of the ground state of a geometrically confined many-electron system. For atoms, shell structure simplifies this problem - the spin is prescribed by the well-known Hund's rule. In contrast, quantum dots provide a controllable setting for studying the interplay of quantum interference and electron-electron interactions in general cases. In a generic confining potential, the shell-structure argument suggests a singlet ground state for an even number of electrons. The interaction among the electrons produces, however, accidental occurrences of spin-triplet ground states, even for weak interaction, a limit which we analyze explicitly. Variation of an external parameter causes sudden switching between these states and hence a kink in the conductance. Experimental study of these kinks would yield the exchange energy for the "chaotic electron gas." ©2000 The American Physical Society.}, Key = {Baranger00} } @booklet{Oppen00, Author = {Oppen, FV and Ullmo, D and Baranger, HU}, Title = {Interaction-induced magnetization of a two-dimensional electron gas}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {62}, Number = {3}, Pages = {1935-1942}, Year = {2000}, ISSN = {0163-1829}, Abstract = {We consider the contribution of electron-electron interactions to the orbital magnetization of a two-dimensional electron gas, focusing on the ballistic limit in the regime of negligible Landau-level spacing. This regime can be described by combining diagrammatic perturbation theory with semiclassical techniques. At sufficiently low temperatures, the interaction-induced magnetization overwhelms the Landau and Pauli contributions. Curiously, the interaction-induced magnetization is third-order in the (renormalized) Coulomb interaction. We give a simple interpretation of this effect in terms of classical paths using a renormalization argument: a polygon must have at least three sides in order to enclose an area. To leading order in the renormalized interaction, the renormalization argument gives exactly the same result as the full treatment. ©2000 The American Physical Society.}, Key = {Oppen00} } @booklet{Moustakas00, Author = {A. L. Moustakas and H. U. Baranger and L. Balents and A. M. Sengupta and S. H. Simon}, Title = {Communication through a diffusive medium: Coherence and capacity}, Journal = {Science}, Volume = {287}, Number = {5451}, Pages = {287 -- 290}, Year = {2000}, Month = {January}, Key = {Moustakas00} } @article{fds245191, Author = {Moustakas, AL and Baranger, HU and Balents, L and Sengupta, AM and Simon, SH}, Title = {Communication through a diffusive medium: coherence and capacity}, Journal = {Science}, Volume = {287}, Number = {5451}, Pages = {287-290}, Year = {2000}, Month = {January}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10634779}, Abstract = {Coherent wave propagation in disordered media gives rise to many fascinating phenomena as diverse as universal conductance fluctuations in mesoscopic metals and speckle patterns in light scattering. Here, the theory of electromagnetic wave propagation in diffusive media is combined with information theory to show how interference affects the information transmission rate between antenna arrays. Nontrivial dependencies of the information capacity on the nature of the antenna arrays are found, such as the dimensionality of the arrays and their direction with respect to the local scattering medium. This approach provides a physical picture for understanding the importance of scattering in the transfer of information through wireless communications.}, Key = {fds245191} } @booklet{Mello00, Author = {Mello, PA and Baranger, HU}, Title = {Interference phenomena in electronic transport through chaotic cavities: an information-theoretic approach (vol 9, pg 105, 1999)}, Journal = {Waves Random Media}, Volume = {10}, Number = {2}, Pages = {337-337}, Year = {2000}, Month = {April}, ISSN = {0959-7174}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000086939200008&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Doi = {10.1088/0959-7174/10/2/501}, Key = {Mello00} } @article{fds303611, Author = {Ullmo, D and Nagano, T and Tomsovic, S and Baranger, HU}, Title = {Semiclassical Density Functional Theory: Strutinsky Energy Corrections in Quantum Dots}, Volume = {63}, Pages = {125339}, Year = {2000}, Month = {July}, url = {http://arxiv.org/abs/cond-mat/0007330v1}, Abstract = {We develop a semiclassical density functional theory in the context of quantum dots. Coulomb blockade conductance oscillations have been measured in several experiments using nanostructured quantum dots. The statistical properties of these oscillations remain puzzling, however, particularly the statistics of spacings between conductance peaks. To explore the role that residual interactions may play in the spacing statistics, we consider many-body systems which include electron-electron interactions through an explicit density functional. First, we develop an approximate series expansion for obtaining the ground state using the idea of the Strutinsky shell correction method. Next, we relate the second-order semiclassical corrections to the screened Coulomb potential. Finally, we investigate the validity of the approximation method by numerical calculation of a one-dimensional model system, and show the relative magnitudes of the successive terms as a function of particle number.}, Doi = {10.1103/PhysRevB.63.125339}, Key = {fds303611} } @article{fds303609, Author = {Mathur, H and Baranger, HU}, Title = {Random Berry Phase Magnetoresistance as a Probe of Interface Roughness in Si MOSFETs}, Volume = {64}, Pages = {235325}, Year = {2000}, Month = {August}, url = {http://arxiv.org/abs/cond-mat/0008375v1}, Abstract = {The effect of silicon-oxide interface roughness on the weak-localization magnetoconductance of a silicon MOSFET in a magnetic field, tilted with respect to the interface, is studied. It is shown that an electron picks up a random Berry's phase as it traverses a closed orbit. Effectively, due to roughness, the electron sees an uniform field parallel to the interface as a random perpendicular field. At zero parallel field the dependence of the conductance on the perpendicular field has a well known form, the weak-localization lineshape. Here the effect of applying a fixed parallel field on the lineshape is analyzed. Many types of behavior are found including homogeneous broadening, inhomogeneous broadening and a remarkable regime in which the change in lineshape depends only on the magnetic field, the two length scales that characterize the interface roughness and fundamental constants. Good agreement is obtained with experiments that are in the homogeneous broadening limit. The implications for using weak-localization magnetoconductance as a probe of interface roughness, as proposed by Wheeler and coworkers, are discussed.}, Doi = {10.1103/PhysRevB.64.235325}, Key = {fds303609} } @booklet{Usaj01a, Author = {Usaj, G and Baranger, HU}, Title = {Mesoscopic tunneling magnetoresistance}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {63}, Number = {18}, Pages = {1844181-1844185}, Year = {2001}, ISSN = {0163-1829}, url = {http://arxiv.org/abs/cond-mat/0006429v3}, Abstract = {We study spin-dependent transport through ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic Coulomb-blockade regime. We calculate the conductance in the absence or presence of spin-orbit interaction and for arbitrary orientation of the lead magnetizations. The tunneling magnetoresistance (TMR), defined at the Coulomb-blockade conductance peaks, is calculated and its probability distribution presented. We show that mesoscopic fluctuations can lead to the optimal value of the TMR and that the conductance in noncollinear configurations gives information about how the spin rotates inside the grain.}, Doi = {10.1103/PhysRevB.63.184418}, Key = {Usaj01a} } @booklet{Ullmo01a, Author = {Ullmo, D and Nagano, T and Tomsovic, S and Baranger, HU}, Title = {Semiclassical density functional theory: Strutinsky energy corrections in quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {63}, Number = {12}, Pages = {1253391-12533913}, Year = {2001}, ISSN = {0163-1829}, Abstract = {We develop a semiclassical density functional theory in the context of quantum dots. Coulomb blockade conductance oscillations have been measured in several experiments using nanostructured quantum dots. The statistical properties of these oscillations remain puzzling, however, particularly the statistics of spacings between conductance peaks. To explore the role that residual interactions may play in the spacing statistics, we consider many-body systems that include electron-electron interactions through an explicit density functional. First, we develop an approximate series expansion for obtaining the ground state using the idea of the Strutinsky shell correction method. Next, we relate the second-order semiclassical corrections to the screened Coulomb potential. Finally, we investigate the validity of the approximation method by numerical calculation of a one-dimensional model system, and show the relative magnitudes of the successive terms as a function of particle number.}, Key = {Ullmo01a} } @booklet{Narimanov01, Author = {Narimanov, EE and Baranger, HU and Cerruti, NR and Tomsovic, S}, Title = {Semiclassical theory of Coulomb blockade peak heights in chaotic quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {64}, Number = {23}, Pages = {2353291-23532913}, Year = {2001}, ISSN = {0163-1829}, Abstract = {We develop a semiclassical theory of Coulomb blockade peak heights in chaotic quantum dots. Using Berry's conjecture, we calculate peak height distributions and correlation functions. We demonstrate that corrections to the corresponding results of the standard statistical theory are nonuniversal, and can be expressed in terms of the classical periodic orbits of the dot that are well coupled to the leads. The main effect is an oscillatory dependence of the peak heights on any parameter which is varied; it is substantial for both symmetric and asymmetric lead placement. Surprisingly, these dynamical effects do not influence the full distribution of peak heights, but are clearly seen in the correlation function or power spectrum. For nonzero temperature, the correlation function obtained theoretically is consistent with that measured experimentally.}, Key = {Narimanov01} } @booklet{Ullmo01, Author = {Ullmo, D and Baranger, HU}, Title = {Interactions in chaotic nanoparticles: Fluctuations in Coulomb blockade peak spacings}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {64}, Number = {24}, Pages = {2453241-24532413}, Year = {2001}, ISSN = {0163-1829}, url = {http://arxiv.org/abs/cond-mat/0103098v1}, Abstract = {We use random matrix models and a Fermi-liquid approach to investigate the ground state energy of electrons confined to a nanoparticle. Our expression for the energy includes the charging effect, the single-particle energies, and the residual screened interactions treated in Hartree-Fock. This model is applicable to chaotic quantum dots or nanoparticles - in these systems the single-particle statistics follows random matrix theory at energy scales less than the Thouless energy. We find the distribution of Coulomb blockade peak spacings first for a large dot in which the residual interactions can be taken constant: the spacing fluctuations are of order the mean level separation Δ. Corrections to this limit are studied using the small parameter 1/kFL: both the residual interactions and the effect of the changing confinement on the single-particle levels produce fluctuations of order Δ/√kFL. The distributions we find are qualitatively similar to the experimental results. Thus, models beyond Fermi-liquid theory are not needed to describe this quantity.}, Doi = {10.1103/PhysRevB.64.245324}, Key = {Ullmo01} } @booklet{Mathur01, Author = {Mathur, H and Baranger, HU}, Title = {Random berry phase magnetoresistance as a probe of interface roughness in Si MOSFET'S}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {64}, Number = {23}, Pages = {2353251-23532520}, Year = {2001}, ISSN = {0163-1829}, Abstract = {The effect of silicon-oxide interface roughness on the weak-localization magnetoconductance of a silicon metal-oxide-semiconductor field-effect transistor in a magnetic field, tilted with respect to the interface, is studied. It is shown that an electron picks up a random Berry's phase as it traverses a closed orbit. Effectively, due to roughness, the electron sees a uniform field parallel to the interface as a random perpendicular field. At zero parallel field the dependence of the conductance on the perpendicular field has a well-known form, the weak-localization line shape. Here the effect of applying a fixed parallel field on the line shape is analyzed. Many types of behavior are found including homogeneous broadening, inhomogeneous broadening, and a remarkable regime in which the change in line shape depends only on the magnetic field, the two length scales that characterize the interface roughness, and fundamental constants. Good agreement is obtained with experiments that are in the homogeneous broadening limit. The implications for using weak-localization magneto-conductance as a probe of interface roughness, as proposed by Wheeler and co-workers, are discussed.}, Key = {Mathur01} } @booklet{Rubio01, Author = {Rubio, J and Pfeiffer, L and Szymanska, MH and Pinczuk, A and He, S and Baranger, HU and Littlewood, PB and West, KW and Dennis, BS}, Title = {Coexistence of excitonic lasing with electron-hole plasma spontaneous emission in one-dimensional semiconductor structures}, Journal = {Solid State Communications}, Volume = {120}, Number = {11}, Pages = {423-427}, Year = {2001}, ISSN = {0038-1098}, url = {http://dx.doi.org/10.1016/S0038-1098(01)00418-5}, Abstract = {We report that excitonic lasing gain coexists with spontaneous optical emission characteristic of an electron-hole plasma in highly photoexcited one-dimensional semiconductors. The experiments probe quantum T-wire laser structures optimized for high photoexcitation. Evidence of dense electron-hole plasma is clearly seen in the spontaneous recombination measured when lasing emission displays distinct excitonic character. These findings differ strikingly from those in higher dimentional semiconductors, and offer insights on optical processes considered by recent theories of dense electron-hole plasmas. © 2001 Published by Elsevier Science Ltd.}, Doi = {10.1016/S0038-1098(01)00418-5}, Key = {Rubio01} } @article{fds303610, Author = {Usaj, G and Baranger, HU}, Title = {Coulomb Blockade Peak Spacing Distribution: The Interplay of Temperature and Spin}, Journal = {Phys. Rev. B}, Volume = {64}, Number = {20}, Pages = {201319}, Year = {2001}, ISSN = {0163-1829}, url = {http://arxiv.org/abs/cond-mat/0108027v1}, Abstract = {We calculate the Coulomb Blockade peak spacing distribution at finite temperature using the recently introduced ``universal Hamiltonian'' to describe the e-e interactions. We show that the temperature effect is important even at kT~0.1\Delta (\Delta is the single-particle mean level spacing). This sensitivity arises because: (1) exchange reduces the minimum energy of excitation from the ground state and (2) the entropic contribution depends on the change of the spin of the quantum dot. Including the leading corrections to the universal Hamiltonian yields results in quantitative agreement with the experiments. Surprisingly, temperature appears to be the most important effect.}, Doi = {10.1103/PhysRevB.64.201319}, Key = {fds303610} } @article{fds303608, Author = {Narimanov, EE and Baranger, HU and Cerruti, NR and Tomsovic, S}, Title = {Semiclassical Theory of Coulomb Blockade Peak Heights in Chaotic Quantum Dots}, Volume = {64}, Number = {23}, Pages = {2353291-23532913}, Year = {2001}, Month = {January}, url = {http://arxiv.org/abs/cond-mat/0101034v1}, Abstract = {We develop a semiclassical theory of Coulomb blockade peak heights in chaotic quantum dots. Using Berry's conjecture, we calculate the peak height distributions and the correlation functions. We demonstrate that the corrections to the corresponding results of the standard statistical theory are non-universal and can be expressed in terms of the classical periodic orbits of the dot that are well coupled to the leads. The main effect is an oscillatory dependence of the peak heights on any parameter which is varied; it is substantial for both symmetric and asymmetric lead placement. Surprisingly, these dynamical effects do not influence the full distribution of peak heights, but are clearly seen in the correlation function or power spectrum. For non-zero temperature, the correlation function obtained theoretically is in good agreement with that measured experimentally.}, Doi = {10.1103/PhysRevB.64.235329}, Key = {fds303608} } @booklet{Usaj01, Author = {Usaj, G and Baranger, HU}, Title = {Coulomb-blockade peak-spacing distribution: Interplay of temperature and spin}, Journal = {Physical Review B}, Volume = {6420}, Number = {20}, Pages = {art. no.-201319}, Year = {2001}, Month = {November}, ISSN = {0163-1829}, Abstract = {We calculate the Coulomb-blockade peak-spacing distribution at finite temperature using the recently introduced "universal Hamiltonian" to describe the e-e interactions. We show that the temperature effect is important even at kBT∼Δ (Δ is the single-particle mean level spacing). This sensitivity arises because: 1) exchange reduces the minimum energy of excitation from the ground state, and 2) the entropic contribution depends on the change of the spin of the quantum dot. Including the leading corrections to the universal Hamiltonian yields results in quantitative agreement with the experiments. Surprisingly, temperature appears to be the most important effect.}, Key = {Usaj01} } @booklet{Usaj02, Author = {Usaj, G and Baranger, HU}, Title = {Spin and e-e interactions in quantum dots: Leading order corrections to universality and temperature effects}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {66}, Number = {15}, Pages = {1553331-15533315}, Year = {2002}, ISSN = {0163-1829}, url = {http://arxiv.org/abs/cond-mat/0203074v1}, Abstract = {We study the statistics of the spacing between Coulomb blockade conductance peaks in quantum dots with large dimensionless conductance g. Our starting point is the "universal Hamiltonian" - valid in the g → ∞ limit - which includes the charging energy, the single-electron energies (described by random matrix theory), and the average exchange interaction. We then calculate the magnitude of the most relevant finite g corrections, namely, the effect of surface charge, the "gate" effect, and the fluctuation of the residual e-e interaction. The resulting zero-temperature peak spacing distribution has corrections of order Δ/√g. For typical values of the e-e interaction (rs∼1) and simple geometries, theory predicts an asymmetric distribution with a significant even/odd effect. The width of the distribution is of order 0.3Δ, and its dominant feature is a large peak for the odd case, reminiscent of the δ function in the g→∞ limit. We consider finite temperature effects next. Only after their inclusion is good agreement with the experimental results obtained. Even relatively low temperature causes large modifications in the peak spacing distribution: (i) its peak is dominated by the even distribution at kBT∼0.3Δ (at lower T a double peak appears), (ii) the even/odd effect is considerably weaker, (iii) the δ function is completely washed out, and (v) fluctuation of the coupling to the leads becomes relevant. Experiments aimed at observing the T=0 peak spacing distribution should therefore be done at kBT<0.1Δ for typical values of the e-e interaction.}, Doi = {10.1103/PhysRevB.66.155333}, Key = {Usaj02} } @booklet{Mello02, Author = {Mello, PA and Baranger, HU}, Title = {Statistical wave scattering: From the atomic nucleus to mesoscopic systems to microwave cavities}, Journal = {Physica A: Statistical Mechanics and its Applications}, Volume = {306}, Number = {1-4}, Pages = {323-333}, Year = {2002}, ISSN = {0378-4371}, url = {http://dx.doi.org/10.1016/S0378-4371(02)00509-5}, Abstract = {Universal statistical aspects of wave scattering by a variety of physical systems ranging from atomic nuclei to mesoscopic systems and microwave cavities are described. A statistical model for the scattering matrix, introduced in the past in the context of nuclear physics, is employed to address the problem of quantum chaotic scattering. The main application of the model is the analysis of electronic transport through ballistic mesoscopic cavities: it describes well the results from the numerical solutions of the Schrödinger equation for two-dimensional systems. © 2002 Published by Elsevier Science B.V.}, Doi = {10.1016/S0378-4371(02)00509-5}, Key = {Mello02} } @booklet{Jiang03, Author = {Jiang, H and Baranger, HU and Yang, W}, Title = {Density-functional theory simulation of large quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {68}, Number = {16}, Pages = {1653371-1653379}, Year = {2003}, ISSN = {0163-1829}, url = {http://dx.doi.org/10.1103/PhysRevB.68.165337}, Abstract = {Kohn-Sham spin-density functional theory provides an efficient and accurate model to study electron-electron interaction effects in quantum dots, but its application to large systems is a challenge. Here an efficient method for the simulation of quantum dots using density-function theory is developed; it includes the particle-in-the-box representation of the Kohn-Sham orbitals, an efficient conjugate-gradient method to directly minimize the total energy, a Fourier convolution approach for the calculation of the Hartree potential, and a simplified multigrid technique to accelerate the convergence. We test the methodology in a two-dimensional model system and show that numerical studies of large quantum dots with several hundred electrons become computationally affordable. In the noninteracting limit, the classical dynamics of the system we study can be continuously varied from integrable to fully chaotic. The qualitative difference in the noninteracting classical dynamics has an effect on the quantum properties of the interacting system: integrable classical dynamics leads to higher-spin states and a broader distribution of spacing between Coulomb blockade peaks.}, Doi = {10.1103/PhysRevB.68.165337}, Key = {Jiang03} } @booklet{Kaul03, Author = {Kaul, RK and Ullmo, D and Baranger, HU}, Title = {Mesoscopic fluctuations in quantum dots in the Kondo regime}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {68}, Number = {16}, Pages = {1613051-1613054}, Year = {2003}, ISSN = {0163-1829}, Abstract = {Properties of the Kondo effect in quantum dots depend sensitively on the coupling parameters and so on the realization of the quantum dot-the Kondo temperature itself becomes a mesoscopic quantity. Assuming chaotic dynamics in the dot, we use random matrix theory to calculate the distribution of both the Kondo temperature and the conductance in the Coulomb blockade regime. We study two experimentally relevant cases: leads with single channels and leads with many channels. In the single-channel case, the distribution of the conductance is very wide as TK fluctuates on a logarithmic scale. As the number of channels increases, there is a slow crossover to a self-averaging regime.}, Key = {Kaul03} } @booklet{Usaj03, Author = {Usaj, G and Baranger, HU}, Title = {Exchange and the Coulomb blockade: Peak height statistics in quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {67}, Number = {12}, Pages = {1213081-1213084}, Year = {2003}, ISSN = {0163-1829}, url = {http://www.phy.duke.edu/research/cm/bg/paper/usajb03_exch.pdf}, Abstract = {We study the effect of the exchange interaction on the Coulomb blockade peak height statistics in chaotic quantum dots. Since exchange reduces the level repulsion in the many-body spectrum, it strongly affects the fluctuations of the peak conductance at finite temperature. We find that including exchange substantially improves the description of the experimental data. Moreover, it provides further evidence of the presence of high-spin states (S ≥ 1) in such systems.}, Key = {Usaj03} } @article{fds245186, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Addition Energies of Fullerenes and Carbon Nanotubes as Quantum Dots}, Journal = {Phys. Rev. Lett.}, Volume = {91}, Pages = {116803}, Year = {2003}, url = {http://www.phy.duke.edu/research/cm/bg/paper/keby03_nanotubes.pdf}, Key = {fds245186} } @booklet{Jiang03a, Author = {H. Jiang and H. U. Baranger and W. Yang}, Title = {Spin and conductance-peak-spacing distributions in large quantum dots: A density-functional theory study}, Journal = {Physical Review Letters}, Volume = {90}, Number = {2}, Year = {2003}, Month = {January}, Key = {Jiang03a} } @article{fds245187, Author = {Jiang, H and Baranger, HU and Yang, W}, Title = {Spin and conductance-peak-spacing distributions in large quantum dots: a density-functional theory study.}, Journal = {Physical Review Letters}, Volume = {90}, Number = {2}, Pages = {026806}, Year = {2003}, Month = {January}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/12570571}, Abstract = {We use spin-density-functional theory to study the spacing between conductance peaks and the ground-state spin of 2D model quantum dots with up to 200 electrons. Distributions for different ranges of electron number are obtained in both symmetric and asymmetric potentials. The even/odd effect is pronounced for small symmetric dots but vanishes for large asymmetric ones, suggesting substantially stronger interaction effects than expected. The fraction of high-spin ground states is remarkably large.}, Doi = {10.1103/PhysRevLett.90.026806}, Key = {fds245187} } @article{fds303607, Author = {Kaul, RK and Ullmo, D and Baranger, HU}, Title = {Mesoscopic Fluctuations in Quantum Dots in the Kondo Regime}, Journal = {Phys. Rev. B}, Volume = {68}, Number = {16}, Pages = {161305}, Year = {2003}, Month = {June}, url = {http://arxiv.org/abs/cond-mat/0306074v2}, Abstract = {Properties of the Kondo effect in quantum dots depend sensitively on the coupling parameters and so on the realization of the quantum dot -- the Kondo temperature itself becomes a mesoscopic quantity. Assuming chaotic dynamics in the dot, we use random matrix theory to calculate the distribution of both the Kondo temperature and the conductance in the Coulomb blockade regime. We study two experimentally relevant cases: leads with single channels and leads with many channels. In the single-channel case, the distribution of the conductance is very wide as $T_K$ fluctuates on a logarithmic scale. As the number of channels increases, there is a slow crossover to a self-averaging regime.}, Doi = {10.1103/PhysRevB.68.161305}, Key = {fds303607} } @booklet{Ke03, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Addition energies of fullerenes and carbon nanotubes as quantum dots: the role of symmetry.}, Journal = {Physical Review Letters}, Volume = {91}, Number = {11}, Pages = {116803}, Year = {2003}, Month = {September}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/14525451}, Abstract = {Using density-functional theory calculations, we investigate the addition energy (AE) of quantum dots formed of fullerenes or closed single-wall carbon nanotubes. We focus on the connection between symmetry and oscillations in the AE spectrum. In the highly symmetric fullerenes the oscillation period is large because of the large level degeneracy and Hund's rule. For long nanotubes, the AE oscillation is fourfold. Adding defects destroys the spatial symmetry of the tubes, leaving only spin degeneracy; correspondingly, the fourfold behavior is destroyed, leaving an even/odd behavior which is quite robust. We use our symmetry results to explain recent experiments.}, Doi = {10.1103/PhysRevLett.91.116803}, Key = {Ke03} } @article{fds245188, Author = {Jiang, H and Baranger, HU and Yang, WT}, Title = {Density-functional theory simulation of large quantum dots}, Journal = {Physical Review B}, Volume = {68}, Number = {16}, Pages = {1653371-1653379}, Year = {2003}, Month = {October}, ISSN = {1098-0121}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000186571800068&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {Kohn-Sham spin-density functional theory provides an efficient and accurate model to study electron-electron interaction effects in quantum dots, but its application to large systems is a challenge. Here an efficient method for the simulation of quantum dots using density-function theory is developed; it includes the particle-in-the-box representation of the Kohn-Sham orbitals, an efficient conjugate-gradient method to directly minimize the total energy, a Fourier convolution approach for the calculation of the Hartree potential, and a simplified multigrid technique to accelerate the convergence. We test the methodology in a two-dimensional model system and show that numerical studies of large quantum dots with several hundred electrons become computationally affordable. In the noninteracting limit, the classical dynamics of the system we study can be continuously varied from integrable to fully chaotic. The qualitative difference in the noninteracting classical dynamics has an effect on the quantum properties of the interacting system: integrable classical dynamics leads to higher-spin states and a broader distribution of spacing between Coulomb blockade peaks.}, Doi = {10.1103/PhysRevB.68.165337}, Key = {fds245188} } @article{fds245061, Author = {Kaul, RK and Ullmo, D and Baranger, HU}, Title = {Erratum: Mesoscopic fluctuations in quantum dots in the Kondo regime (Physical Review B - Condensed Matter and Materials Physics (October 14, 2003) 68 (161305) (DOI: 10.1103/PhysRevB.69.089902))}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {69}, Number = {8}, Pages = {899021-}, Year = {2004}, ISSN = {0163-1829}, Key = {fds245061} } @article{Vorojtsov04_multielecqubits, Author = {Vorojtsov, S and Mucciolo, ER and Baranger, HU}, Title = {Spin qubits in multielectron quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {69}, Number = {11}, Pages = {1153291-1153296}, Year = {2004}, ISSN = {0163-1829}, url = {http://arxiv.org/abs/cond-mat/0308118v3}, Keywords = {quantum dots; mesoscopic systems; exchange interactions (electron); electron spin; quantum computing}, Abstract = {We study the effect of mesoscopic fluctuations on the magnitude of errors that can occur in exchange operations on quantum dot spin qubits. Midsize double quantum dots, with an odd number of electrons in the range of a few tens in each dot, are investigated through the constant interaction model using realistic parameters. It is found that the constraint of having short pulses and small errors implies keeping accurate control, at the few percent level, of several electrode voltages. In practice, the number of independent parameters per dot that one should tune depends on the configuration and ranges from one to four.}, Doi = {10.1103/PhysRevB.69.115329}, Key = {Vorojtsov04_multielecqubits} } @article{Ke04_molectrans1, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Electron transport through molecules: Self-consistent and non-self-consistent approaches}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {70}, Number = {8}, Pages = {085410-1-085410-12}, Year = {2004}, url = {http://www.phy.duke.edu/research/cm/bg/paper/jianguyb04_dftreal1.pdf}, Keywords = {density functional theory; Green's function methods; transport processes; molecular electronics; carbon; aluminium; contact potential}, Abstract = {A self-consistent method for calculating electron transport through a molecular device is developed. It is based on density functional theory electronic structure calculations under periodic boundary conditions and implemented in the framework of the nonequilibrium Green function approach. To avoid the substantial computational cost in finding the I-V characteristic of large systems, we also develop an approximate but much more efficient non-self-consistent method. Here the change in effective potential in the device region caused by a bias is approximated by the main features of the voltage drop. As applications, the I-V curves of a carbon chain and an aluminum chain sandwiched between two aluminum electrodes are calculated-two systems in which the voltage drops very differently. By comparing to the self-consistent results, we show that this non-self-consistent approach works well and can give quantitatively good results.}, Doi = {10.1103/PhysRevB.70.085410}, Key = {Ke04_molectrans1} } @article{Ullmo04_sdftstrutinsky, Author = {Ullmo, D and Jiang, H and Yang, W and Baranger, HU}, Title = {Landau Fermi-liquid picture of spin density functional theory: Strutinsky approach to quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {70}, Number = {20}, Pages = {205309-1-205309-15}, Year = {2004}, ISSN = {0163-1829}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ullmojyb04_dftstr.pdf}, Abstract = {We analyze the ground-state energy and spin of quantum dots obtained from spin density functional theory (SDFT) calculations. First, we introduce a Strutinsky-type approximation, in which quantum interference is treated as a correction to a smooth Thomas-Fermi description. For large irregular dots, we find that the second-order Strutinsky expressions have an accuracy of about 5% of a mean level spacing compared to the full SDFT and capture all the qualitative features. Second, we perform a random matrix-theory/random-plane wave analysis of the Strutinsky SDFT expressions. The results are statistically similar to the SDFT quantum dot statistics. Finally, we note that the second-order Strutinsky approximation provides, in essence, a Landau Fermi-liquid picture of spin density functional theory. For instance, the leading term in the spin channel is simply the familiar exchange constant. A direct comparison between SDFT and the perturbation theory derived "universal Hamiltonian" is thus made possible.}, Doi = {10.1103/PhysRevB.70.205309}, Key = {Ullmo04_sdftstrutinsky} } @article{Jiang04_statistics, Author = {Jiang, H and Ullmo, D and Yang, W and Baranger, HU}, Title = {Electron-electron interactions in isolated and realistic quantum dots: A density functional theory study}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {69}, Number = {23}, Pages = {235326-1-235326-10}, Year = {2004}, ISSN = {0163-1829}, url = {http://www.phy.duke.edu/research/cm/bg/paper/jianguyb04_dftreal1.pdf}, Keywords = {quantum dots; electron-electron interactions; density functional theory; spin dynamics}, Abstract = {We use Kohn-Sham spin-density-functional theory to study the statistics of ground-state spin and the spacing between conductance peaks in the Coulomb blockade regime for both two-dimensional isolated and realistic quantum dots. We make a systematic investigation of the effects of electron-electron interaction strength and electron number on both the peak spacing and spin distributions. A direct comparison between the distributions from isolated and realistic dots shows that, despite the difference in the boundary conditions and confining potential, the statistical properties are qualitatively the same. Strong even/odd pairing in the peak spacing distribution is observed only in the weak e-e interaction regime and vanishes for moderate interactions. The probability of high spin ground states increases for stronger e-e interaction and seems to saturate around rs ∼4. The saturated value is larger than previous theoretical predictions. Both spin and conductance peak spacing distributions show substantial variation as the electron number increases, not saturating until N ∼150. To interpret our numerical results, we analyze the spin distribution in the even N case using a simple two-level model.}, Doi = {10.1103/PhysRevB.69.235326}, Key = {Jiang04_statistics} } @article{fds318400, Author = {Kaul, RK and Ullmo, D and Baranger, HU}, Title = {Mesoscopic fluctuations in quantum dots in the Kondo regime (vol 68, art no 161305, 2003)}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {69}, Number = {8}, Year = {2004}, Month = {February}, url = {http://dx.doi.org/10.1103/PhysRevB.69.089902}, Doi = {10.1103/PhysRevB.69.089902}, Key = {fds318400} } @article{Jiang04_scrambling, Author = {Jiang, H and Ullmo, D and Yang, W and Baranger, HU}, Title = {Scrambling and Gate Effects in Realistic Quantum Dots}, Volume = {71}, Pages = {085313}, Publisher = {(cond-mat/0405262)}, Year = {2004}, Month = {May}, url = {http://arxiv.org/abs/cond-mat/0405262v2}, Abstract = {We evaluate the magnitude of two important mesoscopic effects using a realistic model of typical quantum dots. ``Scrambling'' and ``gate effect'' are defined as the change in the single-particle spectrum due to added electrons or gate-induced shape deformation, respectively. These two effects are investigated systematically in both the self-consistent Kohn-Sham (KS) theory and a Fermi liquid-like Strutinsky approach. We find that the genuine scrambling effect is small because the potential here is smooth. In the KS theory, a key point is the implicit inclusion of residual interactions in the spectrum; these dominate and make scrambling appear larger. Finally, the gate effect is comparable in the two cases and, while small, is able to cause gate-induced spin transitions.}, Doi = {10.1103/PhysRevB.71.085313}, Key = {Jiang04_scrambling} } @article{fds245167, Author = {Hentschel, M and Ullmo, D and Baranger, HU}, Title = {Fermi-edge singularities in the mesoscopic x-ray edge problem.}, Journal = {Physical Review Letters}, Volume = {93}, Number = {17}, Pages = {176807}, Publisher = {cond-mat/0402207}, Year = {2004}, Month = {October}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15525108}, Abstract = {We study the x-ray edge problem for a chaotic quantum dot or nanoparticle displaying mesoscopic fluctuations. In the bulk, x-ray physics is known to produce Fermi-edge singularities-deviations from the naively expected photoabsorption cross section in the form of a peaked or rounded edge. For a coherent system with chaotic dynamics, we find substantial changes; in particular, a photoabsorption cross section showing a rounded edge in the bulk will change to a slightly peaked edge on average as the system size is reduced to a mesoscopic (coherent) scale.}, Doi = {10.1103/PhysRevLett.93.176807}, Key = {fds245167} } @article{Ke04_molectrans2, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Molecular conductance: chemical trends of anchoring groups.}, Journal = {Journal of the American Chemical Society}, Volume = {126}, Number = {48}, Pages = {15897-15904}, Year = {2004}, Month = {December}, ISSN = {0002-7863}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15571415}, Abstract = {Combining density functional theory calculations for molecular electronic structure with a Green function method for electron transport, we calculate from first principles the molecular conductance of benzene connected to two Au leads through different anchoring atoms-S, Se, and Te. The relaxed atomic structure of the contact, different lead orientations, and different adsorption sites are fully considered. We find that the molecule-lead coupling, electron transfer, and conductance all depend strongly on the adsorption site, lead orientation, and local contact atomic configuration. For flat contacts the conductance decreases as the atomic number of the anchoring atom increases, regardless of the adsorption site, lead orientation, or bias. For small bias this chemical trend is, however, dependent on the contact atomic configuration: an additional Au atom at the contact with the (111) lead changes the best anchoring atom from S to Se, although for large bias the original chemical trend is recovered.}, Doi = {10.1021/ja047367e}, Key = {Ke04_molectrans2} } @article{fds245063, Author = {Mucciolo, ER and Vorojtsov, S and Baranger, HU}, Title = {Phonon decoherence in quantum dot qubits}, Journal = {Proceedings of SPIE - The International Society for Optical Engineering}, Volume = {5815}, Pages = {53-61}, Year = {2005}, ISSN = {0277-786X}, url = {http://dx.doi.org/10.1117/12.603649}, Abstract = {The spin of an electron confined into a lateral semiconductor quantum dot has been proposed as a possible physical realization of a qubit. While the spin has the advantage of large decoherence times, operations with more than one qubit will necessarily involve orbital degrees of freedom, namely, charge, which is much more prone to decoherence. There are also alternative quantum dot qubit proposals that are entirely based on charge. We have used a realistic model to quantify the limitations imposed by acoustic phonons on the operation of quantum dot-based qubits. Our treatment includes essential aspects of the setup geometry, wave function profile and materials characteristics. The time dependence of the qubit density matrix is the presence of a phonon bath solved within the Born-Markov approximation. We find that the inclusion of geometric form factors makes the phonon-induced decoherence rates in double dot charge qubits nearly one order of magnitude lower than estimates previously in the literature. Moreover, our theoretical prediction for the quality factor of coherent charge oscillations based on phonon decoherence are higher than the values recently observed experimentally. This allows us to conclude that phonons are not the primary source of decoherence in double quantum dot qubits.}, Doi = {10.1117/12.603649}, Key = {fds245063} } @article{fds245064, Author = {Usaj, G and Baranger, HU}, Title = {Erratum: Mesoscopic tunneling magnetoresistance (Physical Review B- Condensed Matter and Materials Physics (2001) 63 (184418))}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {17}, Year = {2005}, url = {http://dx.doi.org/10.1103/PhysRevB.71.179903}, Doi = {10.1103/PhysRevB.71.179903}, Key = {fds245064} } @article{fds245065, Author = {Jiang, H and Ullmo, D and Yang, W and Baranger, HU}, Title = {Scrambling and gate-induced fluctuations in realistic quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {8}, Year = {2005}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.71.085313}, Abstract = {We evaluate the magnitude of two important mesoscopic effects using a realistic model of typical quantum dots. "Scrambling" and "gate effect" are defined as the change in the single-particle spectrum due to added electrons or gate-induced shape deformation, respectively. These two effects are investigated systematically in both the 'self-consistent Kohn-Sham (KS) theory and a Fermi liquidlike Strutinsky approach. We find that the genuine scrambling effect is small because the potential here is smooth. In the KS theory, a key point is the implicit inclusion of residual interactions in the spectrum; these dominate and make scrambling appear larger. Finally, the gate effect is comparable in the two cases and, while small, is able to cause gate-induced spin transitions. ©2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.085313}, Key = {fds245065} } @article{fds245066, Author = {Ghosal, A and Umrigar, CJ and Jiang, H and Ullmo, D and Baranger, HU}, Title = {Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {24}, Year = {2005}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.71.241306}, Abstract = {We address the issue of accurately treating interaction effects in the mesoscopic regime by investigating the ground-state properties of isolated irregular quantum dots. Quantum Monte Carlo techniques are used to calculate the distributions of ground-state spin and addition energy. We find a reduced probability of high spin and a somewhat larger even/odd alternation in the addition energy from quantum Monte Carlo than in local spin-density-functional theory. In both approaches, the even/odd effect gets smaller with increasing number of electrons, contrary to the theoretical understanding of large dots. We argue that the local spin-density approximation overpredicts the effects of interactions in quantum dots. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.241306}, Key = {fds245066} } @article{fds245108, Author = {Ullmo, D and Jiang, H and Yang, W and Baranger, HU}, Title = {Interactions and broken time-reversal symmetry in chaotic quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {20}, Pages = {201310(R)}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ullmojyb04_finiteb.pdf}, Abstract = {When treating interactions in quantum dots within a random-phase- approximation (RPA)-like approach, time-reversal symmetry plays an important role as higher-order terms-the Cooper series-need to be included when this symmetry is present. Here we consider model quantum dots in a magnetic field weak enough to leave the dynamics of the dot chaotic, but strong enough to break time-reversal symmetry. The ground-state spin and addition energy for dots containing 120-200 electrons are found using local spin-density-functional theory, and we compare the corresponding distributions with those derived from an RPA-like treatment of the interactions. The agreement between the two approaches is very good, significantly better than for analogous calculations in the presence of time-reversal-symmetry. This demonstrates that the discrepancies between the two approaches in the time-reversal symmetric case indeed originate from the Cooper channel, indicating that these higher-order terms might not be properly taken into account in the spin-density-functional calculations. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.201310}, Key = {fds245108} } @article{fds245111, Author = {Vorojtsov, S and Baranger, HU}, Title = {Coulomb blockade peak spacings: Interplay of spin and dot-lead coupling}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {72}, Number = {16}, Pages = {024525}, Publisher = {cond-mat/0505569}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/VorojtsovB05_dotleadcoup.pdf}, Abstract = {For Coulomb blockade peaks in the linear conductance of a quantum dot, we study the correction to the spacing between the peaks due to dot-lead coupling. This coupling can affect measurements in which Coulomb blockade phenomena are used as a tool to probe the energy level structure of quantum dots. The electron-electron interactions in the quantum dot are described by the constant exchange and interaction (CEI) model while the single-particle properties are described by random matrix theory. We find analytic expressions for both the average and rms mesoscopic fluctuation of the correction. For a realistic value of the exchange interaction constant Js, the ensemble average correction to the peak spacing is two to three times smaller than that at Js=0. As a function of Js, the average correction to the peak spacing for an even valley decreases monotonically, nonetheless staying positive. The rms fluctuation is of the same order as the average and weakly depends on Js. For a small fraction of quantum dots in the ensemble, therefore, the correction to the peak spacing for the even valley is negative. The correction to the spacing in the odd valleys is opposite in sign to that in the even valleys and equal in magnitude. These results are robust with respect to the choice of the random matrix ensemble or change in parameters such as charging energy, mean level spacing, or temperature. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.72.165349}, Key = {fds245111} } @article{fds245112, Author = {Yoo, J and Chandrasekharan, S and Kaul, RK and Ullmo, D and Baranger, HU}, Title = {On the sign problem in the Hirsch-Fye algorithm for impurity problems}, Journal = {Journal of Physics A: Mathematical and General}, Volume = {38}, Number = {48}, Pages = {10307-10310}, Publisher = {cond-mat/0412771}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/YooCKUB05_noHFsign.pdf}, Abstract = {We show that there is no fermion sign problem in the Hirsch and Fye algorithm for the single-impurity Anderson model. Beyond the particle-hole symmetric case for which a simple proof exists, this has been known only empirically. Here we prove the nonexistence of a sign problem for the general case by showing that each spin trace for a given Ising configuration is separately positive. We further use this insight to analyse under what conditions orbitally degenerate Anderson models or the two-impurity Anderson model develop a sign. © 2005 IOP Publishing Ltd.}, Doi = {10.1088/0305-4470/38/48/004}, Key = {fds245112} } @article{fds245114, Author = {Usaj, G and Baranger, HU}, Title = {Anisotropy in ferromagnetic nanoparticles: Level-to-level fluctuations of a collective effect}, Journal = {Europhysics Letters}, Volume = {72}, Number = {1}, Pages = {110-116}, Publisher = {cond-mat/0407771}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/usajb04_ferronanopart.pdf}, Abstract = {We calculate the mesoscopic fluctuations of the magnetic anisotropy of ferromagnetic nanoparticles; that is, the effect of single-particle interference on the direction of the collective magnetic moment. A microscopic spin-orbit Hamiltonian considered as a perturbation of the much stronger exchange interaction first yields an explicit expression for the anisotropy tensor. Then, assuming a simple random matrix model for the spin-orbit coupling allows us to describe the fluctuation of such a tensor analytically. In the case of uniaxial anisotropy, we calculate the distribution of the anisotropy constant for a given number of electrons, and its variation upon increasing this number by one. The magnitude of the latter scales inversely with the number of atoms in the particle and is sufficient to account for the experimental data. © EDP Sciences.}, Doi = {10.1209/epl/i2005-10210-4}, Key = {fds245114} } @article{fds245115, Author = {Kaul, RK and Ullmo, D and Chandrasekharan, S and Baranger, HU}, Title = {Mesoscopic Kondo problem}, Journal = {Europhysics Letters}, Volume = {71}, Number = {6}, Pages = {973-979}, Publisher = {cond-mat/0409211}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/kaulucb04_mesokondo.pdf}, Abstract = {We study the effect of mesoscopic fluctuations on a magnetic impurity coupled to a spatially confined electron gas with a temperature in the mesoscopic range (i.e. between the mean level spacing Δ and the Thouless energy ETh). Comparing "poor-man's scaling" with exact Quantum Monte Carlo, we find that for temperatures larger than the Kondo temperature, many aspects of the fluctuations can be captured by the perturbative technique. Using this technique in conjunction with semi-classical approximations, we are able to calculate the mesoscopic fluctuations for a wide variety of systems. For temperatures smaller than the Kondo temperature, we find large fluctuations and deviations from the universal behavior. © EDP Sciences.}, Doi = {10.1209/epl/i2005-10184-1}, Key = {fds245115} } @article{fds245116, Author = {Lee, J-W and Chandrasekharan, S and Baranger, HU}, Title = {Quantum Monte Carlo study of disordered fermions}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {72}, Number = {2}, Pages = {024525}, Publisher = {cond-mat/0411306}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/leecb04_disordfermion.pdf}, Abstract = {We study a strongly correlated fermionic model with attractive interactions in the presence of disorder in two spatial dimensions. Our model has been designed so that it can be solved using the recently discovered meron-cluster approach. Although the model is unconventional it has the same symmetries as the Hubbard model. Since the naive algorithm is inefficient, we develop an algorithm by combining the meron-cluster technique with the directed-loop update. This combination allows us to compute the pair susceptibility and the winding number susceptibility accurately. We find that the s -wave superconductivity, present in the clean model, does not disappear until the disorder reaches a temperature dependent critical strength. The critical behavior as a function of disorder close to the phase transition belongs to the Berezinky-Kosterlitz-Thouless universality class as expected. The fermionic degrees of freedom, although present, do not appear to play an important role near the phase transition. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.72.024525}, Key = {fds245116} } @article{fds245117, Author = {Miller, M and Ullmo, D and Baranger, HU}, Title = {Statistics of wave functions in disordered systems with applications to Coulomb blockade peak spacing}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {72}, Number = {4}, Pages = {045305}, Publisher = {cond-mat/0406493}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/millerub04_psistats.pdf}, Abstract = {Despite considerable work on the energy-level and wave function statistics of disordered quantum systems, numerical studies of those statistics relevant for electron-electron interactions in mesoscopic systems have been lacking. We plug this gap by using a tight-binding model to study a wide variety of statistics for the two-dimensional, disordered quantum system in the diffusive regime. Our results are in good agreement with random matrix theory (or its extensions) for simple statistics such as the probability distribution of energy levels or spatial correlation of a wave function. However, we see substantial disagreement in several statistics which involve both integrating over space and different energy levels, indicating that disordered systems are more complex than previously thought. These are exactly the quantities relevant to electron-electron interaction effects in quantum dots; in fact, we apply these results to the Coulomb blockade, where we find altered spacings between conductance peaks and wider spin distributions than traditionally expected. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.72.045305}, Key = {fds245117} } @article{fds245118, Author = {Ghosal, A and Umrigar, CJ and Jiang, H and Ullmo, D and Baranger, HU}, Title = {Interaction Effects in Irregular Quantum Dots: A Quantum Monte Carlo Study}, Journal = {Phys. Rev. B}, Volume = {71}, Pages = {241306(R)}, Publisher = {cond-mat/0411242}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ghosalujub04_qmcqdot.pdf}, Key = {fds245118} } @article{fds245119, Author = {Getty, SA and Engtrakul, C and Wang, L and Liu, R and Ke, S-H and Baranger, HU and Yang, W and Fuhrer, MS and Sita, LR}, Title = {Near-perfect conduction through a ferrocene-based molecular wire}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {24}, Pages = {241401(R)}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/GettyEWLKBYMS05_ferrocene.pdf}, Abstract = {Here we describe the design, single-molecule transport measurements, and theoretical modeling of a ferrocene-based organometallic molecular wire, whose bias-dependent conductance shows a clear Lorentzian form with magnitude exceeding 70% of the conductance quantum G0. We attribute this unprecedented level of single-molecule conductance to a manifestation of the low-lying molecular resonance and extended orbital network long predicted for a conjugated organic system. A similar-in-length, all-organic conjugated phenylethynyl oligomer molecular framework shows much lower conductance. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.241401}, Key = {fds245119} } @article{fds245120, Author = {Vorojtsov, S and Mucciolo, ER and Baranger, HU}, Title = {Phonon decoherence of a double quantum dot charge qubit}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {20}, Pages = {205322}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/vorojtsovmb04_ddot.pdf}, Abstract = {We study decoherence of a quantum dot charge qubit due to coupling to piezoelectric acoustic phonons in the Born-Markov approximation. After including appropriate form factors, we find that phonon decoherence rates are one to two orders of magnitude weaker than was previously predicted. We calculate the dependence of the Q factor on lattice temperature, quantum dot size, and interdot coupling. Our results suggest that mechanisms other than phonon decoherence play a more significant role in current experimental setups. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.205322}, Key = {fds245120} } @article{fds245122, Author = {Hentschel, M and Ullmo, D and Baranger, HU}, Title = {Fermi edge singularities in the mesoscopic regime: Anderson orthogonality catastrophe}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {72}, Number = {3}, Pages = {035310}, Publisher = {cond-mat/0503330}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/HentschelUB05_aoc.pdf}, Abstract = {For generic mesoscopic systems, such as quantum dots or nanoparticles, we study the Anderson orthogonality catastrophe (AOC) and Fermi-edge singularities in photoabsorption spectra in a series of two papers. In the present paper we focus on AOC for a finite number of particles in discrete energy levels where, in contrast to the bulk situation, AOC is not complete. Moreover, fluctuations characteristic for mesoscopic systems lead to a broad distribution of AOC ground-state overlaps. The fluctuations originate dominantly in the levels around the Fermi energy, and we derive an analytic expression for the probability distribution of AOC overlaps in the limit of strong perturbations. We address the formation of a bound state and its importance for symmetries between the overlap distributions for attractive and repulsive potentials. Our results are based on a random matrix model for the chaotic conduction electrons that are subject to a rank-one perturbation corresponding, for example, to the localized core hole generated in the photoabsorption process. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.72.035310}, Key = {fds245122} } @article{Yoo04_spinchain, Author = {Yoo, J and Chandrasekharan, S and Kaul, RK and Ullmo, D and Baranger, HU}, Title = {Cluster algorithms for quantum impurity models and mesoscopic Kondo physics}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {20}, Pages = {201309(R)}, Publisher = {cond-mat/0411313}, Year = {2005}, url = {http://www.phy.duke.edu/research/cm/bg/paper/yoockub04_clusterqimp.pdf}, Abstract = {Nanoscale physics and dynamical mean-field theory have both generated increased interest in complex quantum impurity problems and so have focused attention on the need for flexible quantum impurity solvers. Here we demonstrate that the mapping of single-quantum impurity problems onto spin chains can be exploited to yield a powerful and extremely flexible impurity solver. We implement this cluster algorithm explicitly for the Anderson and Kondo Hamiltonians, and illustrate its use in the "mesoscopic Kondo problem." To study universal Kondo physics, a large ratio between the effective bandwidth Deff and the temperature T is required; our cluster algorithm treats the mesoscopic fluctuations exactly while being able to approach the large Deff T limit with ease. We emphasize that the flexibility of our method allows it to tackle a wide variety of quantum impurity problems; thus, it may also be relevant to the dynamical mean-field theory of lattice problems. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.201309}, Key = {Yoo04_spinchain} } @article{Ke04_molecgate, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Electron transport through molecules: Gate-induced polarization and potential shift}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {71}, Number = {11}, Pages = {113401}, Publisher = {cond-mat/046640}, Year = {2005}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/keby04_gatepolar.pdf}, Abstract = {We analyze the effect of a gate on the conductance of molecules by separately evaluating the gate-induced polarization and the potential shift of the molecule relative to the leads. The calculations use ab initio density functional theory combined with a Green function method for electron transport. For a general view, we study several systems: (1) atomic chains of C or Al sandwiched between Al electrodes, (2) a benzene molecule between Au leads, and (3) (9,0) and (5,5) carbon nanotubes. We find that the polarization effect is small because of screening, while the effect of the potential shift is significant, providing a mechanism for single-molecule transistors. ©2005 The American Physical Society.}, Doi = {10.1103/PhysRevB.71.113401}, Key = {Ke04_molecgate} } @article{Liu04_molecinter, Author = {Liu, R and Ke, S-H and Baranger, HU and Yang, W}, Title = {Intermolecular effect in molecular electronics.}, Journal = {Journal of Chemical Physics}, Volume = {122}, Number = {4}, Pages = {44703}, Year = {2005}, Month = {January}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15740279}, Abstract = {We investigate the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The method we use combines a Green function approach to quantum transport with density functional theory for the electronic properties. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. A striking resonance is produced only 0.3 eV above the Fermi energy.}, Doi = {10.1063/1.1825377}, Key = {Liu04_molecinter} } @article{Ke04_molectrans3, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Contact atomic structure and electron transport through molecules.}, Journal = {Journal of Chemical Physics}, Volume = {122}, Number = {7}, Pages = {074704}, Publisher = {cond-mat/0405047}, Year = {2005}, Month = {February}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15743262}, Abstract = {Using benzene sandwiched between two Au leads as a model system, we investigate from first principles the change in molecular conductance caused by different atomic structures around the metal-molecule contact. Our motivation is the variable situations that may arise in break junction experiments; our approach is a combined density functional theory and Green function technique. We focus on effects caused by (1) the presence of an additional Au atom at the contact and (2) possible changes in the molecule-lead separation. The effects of contact atomic relaxation and two different lead orientations are fully considered. We find that the presence of an additional Au atom at each of the two contacts will increase the equilibrium conductance by up to two orders of magnitude regardless of either the lead orientation or different group-VI anchoring atoms. This is due to a resonance peak near the Fermi energy from the lowest energy unoccupied molecular orbital. In the nonequilibrium properties, the resonance peak manifests itself in a negative differential conductance. We find that the dependence of the equilibrium conductance on the molecule-lead separation can be quite subtle: either very weak or very strong depending on the separation regime.}, Doi = {10.1063/1.1851496}, Key = {Ke04_molectrans3} } @article{Yoo04_multilev, Author = {Yoo, J and Chandrasekharan, S and Baranger, HU}, Title = {Multilevel algorithm for quantum-impurity models.}, Journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, Volume = {71}, Number = {3 Pt 2B}, Pages = {036708}, Publisher = {cond-mat/0408123}, Year = {2005}, Month = {March}, ISSN = {1539-3755}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15903634}, Abstract = {A continuous-time path integral quantum Monte Carlo method using the directed-loop algorithm is developed to simulate the Anderson single-impurity model in the occupation number basis. Although the method suffers from a sign problem at low temperatures, the new algorithm has many advantages over conventional algorithms. For example, the model can be easily simulated in the Kondo limit without time discretization errors. Furthermore, many observables including the impurity susceptibility and a variety of fermionic observables can be calculated efficiently. Finally the new approach allows us to explore a general technique, called the multilevel algorithm, to solve the sign problem. We find that the multilevel algorithm is able to generate an exponentially large number of configurations with an effort that grows as a polynomial in inverse temperature such that configurations with a positive sign dominate over those with negative signs. Our algorithm can be easily generalized to other multi-impurity problems.}, Doi = {10.1103/PhysRevE.71.036708}, Key = {Yoo04_multilev} } @article{fds245113, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Models of electrodes and contacts in molecular electronics.}, Journal = {Journal of Chemical Physics}, Volume = {123}, Number = {11}, Pages = {114701}, Publisher = {cond-mat/0504089}, Year = {2005}, Month = {September}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16392577}, Abstract = {Bridging the difference in atomic structure between experiments and theoretical calculations and exploring quantum confinement effects in thin electrodes (leads) are both important issues in molecular electronics. To address these issues, we report here, by using Au-benzenedithiol-Au as a model system, systematic investigations of different models for the leads and the lead-molecule contacts: leads with different cross sections, leads consisting of infinite surfaces, and surface leads with a local nanowire or atomic chain of different lengths. The method adopted is a nonequilibrium Green's-function approach combined with density-functional theory calculations for the electronic structure and transport, in which the leads and molecule are treated on the same footing. It is shown that leads with a small cross section will lead to large oscillations in the transmission function T(E), which depend significantly on the lead structure (orientation) because of quantum waveguide effects. This oscillation slowly decays as the lead width increases, with the average approaching the limit given by infinite surface leads. Local nanowire structures around the contacts induce moderate fluctuations in T(E), while a Au atomic chain (including a single Au apex atom) at each contact leads to a significant conductance resonance.}, Key = {fds245113} } @article{fds245121, Author = {Liu, R and Ke, S-H and Baranger, HU and Yang, W}, Title = {Organometallic spintronics: dicobaltocene switch.}, Journal = {Nano Letters}, Volume = {5}, Number = {10}, Pages = {1959-1962}, Year = {2005}, Month = {October}, ISSN = {1530-6984}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16218717}, Abstract = {A single-molecule spintronic switch and spin valve using two cobaltocene moieties is proposed. Spin-dependent transport through a lead-molecule-lead junction has been calculated using first-principles density functional and nonequilibrium Green function methods. We find that the antiparallel (singlet) configuration of the cobaltocene spins blocks electron transport near the Fermi energy, while the spin parallel (triplet) configuration enables much higher current. The energy difierence between the antiparallel and parallel states depends on the insulating spacer separating the two cobaltocenes, allowing switching through the application of a moderate magnetic field.}, Doi = {10.1021/nl0513380}, Key = {fds245121} } @article{fds245067, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Development of ab initio calculation for electron transport and the effects of lead and contact structures in molecular electronics}, Journal = {Journal of computational and theoretical nanoscience}, Volume = {3}, Number = {5}, Pages = {819-823}, Year = {2006}, ISSN = {1546-1955}, url = {http://dx.doi.org/10.1166/jctn.2006.022}, Abstract = {A fully self-consistent method combining density functional theory (DFT) and nonequilibrium Green function approach for calculating electron transport through molecular devices is reviewed. It uses periodic boundary conditions for DFT and treats the leads and molecule of a device system on the same footing. Also reviewed is its application for the molecular conductance of Au-benzenedithiol-Au systems. Two important issues in molecular electronics are discussed: (1) quantum confinement effects in thin electrodes (leads) and (2) effects of local atomic configuration around the contacts. Quantum-confinement- induced waveguide effect causes large oscillations in the transmission function. Single or double apex Au atoms at each contact lead to a significant conductance resonance, which is quite similar to increasing the molecule-lead separation. Copyright © 2006 American Scientific Publishers All rights reserved.}, Doi = {10.1166/jctn.2006.022}, Key = {fds245067} } @article{Ghosal05_circdot1, Author = {Ghosal, A and Güçlü, AD and Umrigar, CJ and Ullmo, D and Baranger, HU}, Title = {Correlation-induced inhomogeneity in circular quantum dots}, Journal = {Nature Physics}, Volume = {2}, Number = {5}, Pages = {336-340}, Year = {2006}, ISSN = {1745-2473}, url = {http://www.phy.duke.edu/research/cm/bg/paper/GhosalGUUB06_circdots1.pdf}, Doi = {10.1038/nphys293}, Key = {Ghosal05_circdot1} } @article{Liu05_CoRectifier, Author = {Liu, R and Ke, S-H and Yang, W and Baranger, HU}, Title = {Organometallic molecular rectification.}, Journal = {Journal of Chemical Physics}, Volume = {124}, Number = {2}, Pages = {024718}, Year = {2006}, Month = {January}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16422637}, Abstract = {We study the rectification of current through a single molecule with an intrinsic spatial asymmetry. The molecule contains a cobaltocene moiety in order to take advantage of its relatively localized and high-energy d states. A rectifier with large voltage range, high current, and low threshold can be realized. The evolution of molecular orbitals under both forward and reverse biases is captured in a self-consistent nonequilibrium Green function plus density functional theory description. Our calculations demonstrate the plausibility of making excellent molecular diodes by using metallocenes, pointing to a fruitful class of molecules.}, Doi = {10.1063/1.2141955}, Key = {Liu05_CoRectifier} } @article{Kaul06_Kspect, Author = {Kaul, RK and Zaránd, G and Chandrasekharan, S and Ullmo, D and Baranger, HU}, Title = {Spectroscopy of the Kondo problem in a box.}, Journal = {Physical Review Letters}, Volume = {96}, Number = {17}, Pages = {176802}, Year = {2006}, Month = {May}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16712322}, Abstract = {Motivated by experiments on double quantum dots, we study the problem of a single magnetic impurity confined in a finite metallic host. We prove an exact theorem for the ground state spin, and use analytic and numerical arguments to map out the spin structure of the excitation spectrum of the many-body Kondo-correlated state, throughout the weak to strong coupling crossover. These excitations can be probed in a simple tunneling-spectroscopy transport experiment; for that situation we solve rate equations for the conductance.}, Doi = {10.1103/PhysRevLett.96.176802}, Key = {Kaul06_Kspect} } @article{Ke05_nanotubemetal, Author = {Ke, S-H and Yang, W and Baranger, HU}, Title = {Nanotube-metal junctions: 2- and 3-terminal electrical transport.}, Journal = {Journal of Chemical Physics}, Volume = {124}, Number = {18}, Pages = {181102}, Year = {2006}, Month = {May}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16709090}, Abstract = {We address the quality of electrical contact between carbon nanotubes and metallic electrodes by performing first-principles calculations for the electron transmission through ideal 2- and 3-terminal junctions, thus revealing the physical limit of tube-metal conduction. The structural model constructed involves surrounding the tube by the metal atoms of the electrode as in most experiments; we consider metallic (5,5) and n-doped semiconducting (10,0) tubes surrounded by Au or Pd. In the case of metallic tubes, the contact conductance is shown to approach the ideal 4e2/h in the limit of large contact area. For three-terminals, the division of flux among the different transmission channels depends strongly on the metal material. A Pd electrode has nearly perfect tube-electrode transmission and therefore turns off the straight transport along the tube. Our results are in good agreement with some recent experimental reports and clarify a fundamental discrepancy between theory and experiment.}, Doi = {10.1063/1.2200356}, Key = {Ke05_nanotubemetal} } @article{Liu05_CoNDR, Author = {Liu, R and Ke, S-H and Baranger, HU and Yang, W}, Title = {Negative differential resistance and hysteresis through an organometallic molecule from molecular-level crossing.}, Journal = {Journal of the American Chemical Society}, Volume = {128}, Number = {19}, Pages = {6274-6275}, Year = {2006}, Month = {May}, ISSN = {0002-7863}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16683765}, Abstract = {Analogous to a quantum double-dot system, diblock structured molecules could also show negative differential resistance (NDR). Using combined density functional theory and nonequilibrium Green function technique, we show that molecular-level crossing in a molecular double-dot system containing cobaltocene and ferrocene leads to NDR and hysteresis.}, Doi = {10.1021/ja057054z}, Key = {Liu05_CoNDR} } @article{Novais05_qec1, Author = {Novais, E and Baranger, HU}, Title = {Decoherence by correlated noise and quantum error correction.}, Journal = {Physical Review Letters}, Volume = {97}, Number = {4}, Pages = {040501}, Year = {2006}, Month = {July}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16907555}, Abstract = {We study the decoherence of a quantum computer in an environment which is inherently correlated in time and space. We first derive the nonunitary time evolution of the computer and environment in the presence of a stabilizer error correction code, providing a general way to quantify decoherence for a quantum computer. The general theory is then applied to the spin-boson model. Our results demonstrate that effects of long-range correlations can be systematically reduced by small changes in the error correction codes.}, Doi = {10.1103/PhysRevLett.97.040501}, Key = {Novais05_qec1} } @article{Priyadarshee06_hcbosons1, Author = {Priyadarshee, A and Chandrasekharan, S and Lee, J-W and Baranger, HU}, Title = {Quantum phase transitions of hard-core bosons in background potentials.}, Journal = {Physical Review Letters}, Volume = {97}, Number = {11}, Pages = {115703}, Year = {2006}, Month = {September}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17025902}, Abstract = {We study the zero temperature phase diagram of hard-core bosons in two dimensions subjected to three types of background potentials: staggered, uniform, and random. In all three cases there is a quantum phase transition from a superfluid (at small potential) to a normal phase (at large potential), but with different universality classes. As expected, the staggered case belongs to the XY universality, while the uniform potential induces a mean field transition. The disorder driven transition is clearly different from both; in particular, we find z approximately 1.4, nu approximately 1, and beta approximately 0.6.}, Doi = {10.1103/PhysRevLett.97.115703}, Key = {Priyadarshee06_hcbosons1} } @article{fds245093, Author = {Hentschel, M and Ullmo, D and Baranger, HU}, Title = {Fermi edge singularities in the mesoscopic regime: Photoabsorption spectra}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {76}, Number = {24}, Pages = {245419}, Year = {2007}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/HentschelUB07_mesfes2.pdf}, Abstract = {We study Fermi edge singularities in photoabsorption spectra of generic mesoscopic systems such as quantum dots or nanoparticles. We predict deviations from macroscopic-metallic behavior and propose experimental setups for the observation of these effects. The theory is based on the model of a localized, or rank one, perturbation caused by the (core) hole left behind after the photoexcitation of an electron into the conduction band. The photoabsorption spectra result from the competition between two many-body responses, Anderson's orthogonality catastrophe and the Mahan-Nozières-DeDominicis contribution. Both mechanisms depend on the system size through the number of particles and, more importantly, fluctuations produced by the coherence characteristic of mesoscopic samples. The latter lead to a modification of the dipole matrix element and trigger one of our key results: a rounded K -edge typically found in metals will turn into a (slightly) peaked edge on average in the mesoscopic regime. We consider in detail the effect of the "bound state" produced by the core hole. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevB.76.245419}, Key = {fds245093} } @article{fds245094, Author = {Hentschel, M and Valente, DCB and Mucciolo, ER and Baranger, HU}, Title = {Improving intrinsic decoherence in multiple-quantum-dot charge qubits}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {76}, Number = {23}, Pages = {235309}, Year = {2007}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/HentschelVMB07_3dotqubit.pdf}, Abstract = {We discuss decoherence in charge qubits formed by multiple lateral quantum dots in the framework of the spin-boson model and the Born-Markov approximation. We consider the intrinsic decoherence caused by the coupling to bulk phonon modes. Two distinct quantum dot configurations are studied: (i) Three quantum dots in a ring geometry with one excess electron in total and (ii) arrays of quantum dots where the computational basis states form multipole charge configurations. For the three-dot qubit, we demonstrate the possibility of performing one- and two-qubit operations by solely tuning gate voltages. Compared to a previous proposal involving a linear three-dot spin qubit, the three-dot charge qubit allows for less overhead on two-qubit operations. For small interdot tunnel amplitudes, the three-dot qubits have Q factors much higher than those obtained for double-dot systems. The high-multipole dot configurations also show a substantial decrease in decoherence at low operation frequencies when compared to the double-dot qubit. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevB.76.235309}, Key = {fds245094} } @article{fds245098, Author = {Herman, D and Ong, TT and Usaj, G and Mathur, H and Baranger, HU}, Title = {Level spacings in random matrix theory and Coulomb blockade peaks in quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {76}, Number = {19}, Pages = {195448}, Year = {2007}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/HermanOUMB07_rmtCB.pdf}, Abstract = {We obtain analytic formulas for the spacing between conductance peaks in the Coulomb blockade regime based on the universal Hamiltonian model of quantum dots. Random matrix theory results are developed in order to treat correlations between two and three consecutive spacings in the energy level spectrum. These are generalizations of the Wigner surmise for the probability distribution of single level spacing. The analytic formulas are shown to be in good agreement with numerical evaluation. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevB.76.195448}, Key = {fds245098} } @article{fds245102, Author = {Ghosal, A and Güçlü, AD and Umrigar, CJ and Ullmo, D and Baranger, HU}, Title = {Incipient Wigner localization in circular quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {76}, Number = {8}, Pages = {085341}, Year = {2007}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/GhosalGUUB06_circdots2.pdf}, Abstract = {We study the development of electron-electron correlations in circular quantum dots as the density is decreased. We consider a wide range of both electron number, N≤20, and electron gas parameter, rs 18, using the diffusion quantum Monte Carlo technique. Features associated with correlation appear to develop very differently in quantum dots than in bulk. The main reason is that translational symmetry is necessarily broken in a dot, leading to density modulation and inhomogeneity. Electron-electron interactions act to enhance this modulation ultimately leading to localization. This process appears to be completely smooth and occurs over a wide range of density. Thus there is a broad regime of "incipient" Wigner crystallization in these quantum dots. Our specific conclusions are (i) the density develops sharp rings while the pair density shows both radial and angular inhomogeneity; (ii) the spin of the ground state is consistent with Hund's (first) rule throughout our entire range of rs for all 4≤N≤20; (iii) the addition energy curve first becomes smoother as interactions strengthen-the mesoscopic fluctuations are damped by correlation-and then starts to show features characteristic of the classical addition energy; (iv) localization effects are stronger for a smaller number of electrons; (v) finally, the gap to certain spin excitations becomes small at the strong interaction (large rs) side of our regime. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevB.76.085341}, Key = {fds245102} } @article{fds318399, Author = {Novais, E and Mucciolo, ER and Baranger, HU}, Title = {Hamiltonian Formulation of Quantum Error Correction and Correlated Noise}, Journal = {CoRR}, Volume = {abs/0710.1624}, Year = {2007}, Key = {fds318399} } @article{Novais06_qec2, Author = {Novais, E and Mucciolo, ER and Baranger, HU}, Title = {Resilient quantum computation in correlated environments: a quantum phase transition perspective.}, Journal = {Physical Review Letters}, Volume = {98}, Number = {4}, Pages = {040501}, Year = {2007}, Month = {January}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17358749}, Abstract = {We analyze the problem of a quantum computer in a correlated environment protected from decoherence by quantum error correction using a perturbative renormalization group approach. The scaling equation obtained reflects the competition between the dimension of the computer and the scaling dimension of the correlations. For an irrelevant flow, the error probability is reduced to a stochastic form for a long time and/or a large number of qubits; thus, the traditional derivation of the threshold theorem holds for these error models. In this way, the "threshold theorem" of quantum computing is rephrased as a dimensional criterion.}, Doi = {10.1103/PhysRevLett.98.040501}, Key = {Novais06_qec2} } @article{Ke06_oep, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Role of the exchange-correlation potential in ab initio electron transport calculations.}, Journal = {Journal of Chemical Physics}, Volume = {126}, Number = {20}, Pages = {201102}, Year = {2007}, Month = {May}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17552745}, Abstract = {The effect of the exchange-correlation potential in ab initio electron transport calculations is investigated by constructing optimized effective potentials using different energy functionals or the electron density from second-order perturbation theory. The authors calculate electron transmission through two atomic chain systems, one with charge transfer and one without. Dramatic effects are caused by two factors: changes in the energy gap and the self-interaction error. The error in conductance caused by the former is about one order of magnitude while that caused by the latter ranges from several times to two orders of magnitude, depending on the coupling strength and charge transfer. The implications for accurate quantum transport calculations are discussed.}, Doi = {10.1063/1.2743004}, Key = {Ke06_oep} } @article{fds245101, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Contact transparency of nanotube-molecule-nanotube junctions.}, Journal = {Physical Review Letters}, Volume = {99}, Number = {14}, Pages = {146802}, Year = {2007}, Month = {October}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17930697}, Abstract = {The transparency of contacts between conjugated molecules and metallic single-walled carbon nanotubes is investigated using a single-particle Green's function method which combines a Landauer approach with ab initio density functional theory. We find that the overall conjugation required for good contact transparency is broken by connecting through a six-member ring on the tube. Full conjugation achieved by an all-carbon contact through a five-member ring leads to near perfect contact transparency for different conjugated molecular bridges.}, Doi = {10.1103/PhysRevLett.99.146802}, Key = {fds245101} } @article{fds245099, Author = {Ke, S-H and Baranger, HU and Yang, W}, Title = {Electron transport through single conjugated organic molecules: basis set effects in ab initio calculations.}, Journal = {Journal of Chemical Physics}, Volume = {127}, Number = {14}, Pages = {144107}, Year = {2007}, Month = {October}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17935386}, Abstract = {We investigate electron transport through single conjugated molecules--including benzenedithiol, oligophenylene ethynylenes of different lengths, and a ferrocene-containing molecule sandwiched between two gold electrodes with different contact structures--by using a single-particle Green function method combined with density functional theory calculation. We focus on the effect of the basis set in the ab initio calculation. It is shown that the position of the Fermi energy in the transport gap is sensitive to the molecule-lead charge transfer which is affected by the size of basis set. This can dramatically change, by orders of magnitude, the conductance for long molecules, though the effect is only minor for short ones. A resonance around the Fermi energy tends to pin the position of the Fermi energy and suppress this effect. The result is discussed in comparison with experimental data.}, Doi = {10.1063/1.2770718}, Key = {fds245099} } @article{fds245100, Author = {Liu, R and Ke, S-H and Yang, W and Baranger, HU}, Title = {Cobaltocene as a spin filter.}, Journal = {Journal of Chemical Physics}, Volume = {127}, Number = {14}, Pages = {141104}, Year = {2007}, Month = {October}, ISSN = {0021-9606}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17935378}, Abstract = {In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin dependence because the conduction channels of only one spin component align with the chemical potential of the leads, resulting in a spin polarized electric current. The possibility to create such a spin polarized current is investigated here with the organometallic moiety cobaltocene. According to our calculations, cobaltocene contacted with gold electrodes acts as a robust spin filter: Applying a voltage less than 0.2 V causes the current of one spin component crossing the molecular bridge to be two orders of magnitude larger than the other. We address the key issue of sensitivity to molecule-lead geometry by showing that a weak barrier generated by CH(2) groups between the cobaltocene and the leads is crucial in reducing the sensitivity to the contact geometry while only reducing the current modestly. These results suggest cobaltocene as a robust basic building block for molecular spintronics.}, Doi = {10.1063/1.2796151}, Key = {fds245100} } @article{fds245091, Author = {Novais, E and Mucciolo, ER and Baranger, HU}, Title = {Hamiltonian formulation of quantum error correction and correlated noise: Effects of syndrome extraction in the long-time limit}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {78}, Number = {1}, Pages = {012314 (18 pages)}, Year = {2008}, ISSN = {1050-2947}, url = {http://www.phy.duke.edu/research/cm/bg/paper/NovaisBM07_qec3.pdf}, Abstract = {We analyze the long-time behavior of a quantum computer running a quantum error correction (QEC) code in the presence of a correlated environment. Starting from a Hamiltonian formulation of realistic noise models, and assuming that QEC is indeed possible, we find formal expressions for the probability of a given syndrome history and the associated residual decoherence encoded in the reduced density matrix. Systems with nonzero gate times ("long gates") are included in our analysis by using an upper bound on the noise. In order to introduce the local error probability for a qubit, we assume that propagation of signals through the environment is slower than the QEC period (hypercube assumption). This allows an explicit calculation in the case of a generalized spin-boson model and a quantum frustration model. The key result is a dimensional criterion: If the correlations decay sufficiently fast, the system evolves toward a stochastic error model for which the threshold theorem of fault-tolerant quantum computation has been proven. On the other hand, if the correlations decay slowly, the traditional proof of this threshold theorem does not hold. This dimensional criterion bears many similarities to criteria that occur in the theory of quantum phase transitions. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevA.78.012314}, Key = {fds245091} } @article{fds245092, Author = {Güçlü, AD and Ghosal, A and Umrigar, CJ and Baranger, HU}, Title = {Interaction-induced strong localization in quantum dots}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {77}, Number = {4}, Pages = {041301(R)}, Year = {2008}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/GucluGUB07_stronglocdots.pdf}, Abstract = {We argue that Coulomb blockade phenomena are a useful probe of the crossover to strong correlation in quantum dots. Through calculations at low density using variational and diffusion quantum Monte Carlo (up to rs ∼55), we find that the addition energy shows a clear progression from features associated with shell structure to those caused by commensurability of a Wigner crystal. This crossover (which occurs near rs ∼20 for spin-polarized electrons) is, then, a signature of interaction-driven localization. As the addition energy is directly measurable in Coulomb blockade conductance experiments, this provides a direct probe of localization in the low density electron gas. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevB.77.041301}, Key = {fds245092} } @article{Ke08_qint, Author = {Ke, S-H and Yang, W and Baranger, HU}, Title = {Quantum-interference-controlled molecular electronics.}, Journal = {Nano Letters}, Volume = {8}, Number = {10}, Pages = {3257-3261}, Year = {2008}, Month = {October}, ISSN = {1530-6984}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18803424}, Abstract = {Quantum interference in coherent transport through single molecular rings may provide a mechanism to control the current in molecular electronics. We investigate its applicability, using a single-particle Green function method combined with ab initio electronic structure calculations. We find that the quantum interference effect (QIE) is strongly dependent on the interaction between molecular pi-states and contact sigma-states. It is masked by sigma tunneling in small molecular rings with Au leads, such as benzene, due to strong pi-sigma hybridization, while it is preserved in large rings, such as [18]annulene, which then could be used to realize quantum interference effect (QIE) transistors.}, Doi = {10.1021/nl8016175}, Key = {Ke08_qint} } @article{Guclu08_inhomowire, Author = {Güçlü, AD and Umrigar, CJ and Jiang, H and Baranger, HU}, Title = {Localization in an inhomogeneous quantum wire}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {80}, Number = {20}, Pages = {201302(R)}, Year = {2009}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/GucluUJB08_inhomoqwire.pdf}, Abstract = {We study interaction-induced localization of electrons in an inhomogeneous quasi-one-dimensional system-a wire with two regions, one at low density and the other high. Quantum Monte Carlo techniques are used to treat the strong Coulomb interactions in the low-density region, where localization of electrons occurs. The nature of the transition from high to low density depends on the density gradient-if it is steep, a barrier develops between the two regions, causing Coulomb blockade effects. Ferromagnetic spin polarization does not appear for any parameters studied. The picture emerging is in good agreement with measurements of tunneling between wires. © 2009 The American Physical Society.}, Doi = {10.1103/PhysRevB.80.201302}, Key = {Guclu08_inhomowire} } @article{fds245086, Author = {Wurm, J and Wimmer, M and Adagideli, I and Richter, K and Baranger, HU}, Title = {Interfaces within graphene nanoribbons}, Journal = {New Journal of Physics}, Volume = {11}, Pages = {095022}, Year = {2009}, ISSN = {1367-2630}, url = {http://www.phy.duke.edu/research/cm/bg/paper/WurmWARB09_graphenenanoribbons.pdf}, Abstract = {We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure-such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Although we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.}, Doi = {10.1088/1367-2630/11/9/095022}, Key = {fds245086} } @article{fds245089, Author = {Kaul, RK and Ullmo, D and Zaránd, G and Chandrasekharan, S and Baranger, HU}, Title = {Ground state and excitations of quantum dots with magnetic impurities}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {80}, Number = {3}, Year = {2009}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.80.035318}, Abstract = {We consider an "impurity" with a spin degree of freedom coupled to a finite reservoir of noninteracting electrons, a system which may be realized by either a true impurity in a metallic nanoparticle or a small quantum dot coupled to a large one. We show how the physics of such a spin impurity is revealed in the many-body spectrum of the entire finite-size system; in particular, the evolution of the spectrum with the strength of the impurity-reservoir coupling reflects the fundamental many-body correlations present. Explicit calculation in the strong- and the weak-coupling limits shows that the spectrum and its evolution are sensitive to the nature of the impurity and the parity of electrons in the reservoir. The effect of the finite-size spectrum on two experimental observables is considered. First, we propose an experimental setup in which the spectrum may be conveniently measured using tunneling spectroscopy. A rate equation calculation of the differential conductance suggests how the many-body spectral features may be observed. Second, the finite-temperature magnetic susceptibility is presented, both the impurity and the local susceptibilities. Extensive quantum Monte Carlo calculations show that the local susceptibility deviates from its bulk scaling form. Nevertheless, for special assumptions about the reservoir-the "clean Kondo box" model-we demonstrate that finite-size scaling is recovered. Explicit numerical evaluations of these scaling functions are given, both for even and odd parities and for the canonical and the grand-canonical ensembles. © 2009 The American Physical Society.}, Doi = {10.1103/PhysRevB.80.035318}, Key = {fds245089} } @article{Ke08_thermopower, Author = {Ke, S-H and Yang, W and Curtarolo, S and Baranger, HU}, Title = {Thermopower of Molecular Junctions}, Journal = {Nano Lett.}, Volume = {9}, Number = {3}, Pages = {1011-1014}, Year = {2009}, Month = {January}, ISSN = {1530-6984}, url = {http://www.phy.duke.edu/research/cm/bg/paper/KeYCB09_thermopower1.pdf}, Abstract = {Molecular nanojunctions may support efficient thermoelectric conversion through enhanced thermopower. Recently, this quantity has been measured for several conjugated molecular nanojunctions with gold electrodes. Considering the wide variety of possible metal/molecule systems-almost none of which have been studied-it seems highly desirable to be able to calculate the thermopower of junctions with reasonable accuracy and high efficiency. To address this task, we demonstrate an effective approach based on the single particle green function (SPGF) method combined with density functional theory (DFT) using B3LYP and PBE0 energy functionals. Systematic good agreement between theory and experiment is obtained; indeed, much better agreement is found here than for comparable calculations of the conductance.}, Doi = {10.1021/nl8031229}, Key = {Ke08_thermopower} } @article{Wurm08_graphene, Author = {Wurm, J and Rycerz, A and Adagideli, I and Wimmer, M and Richter, K and Baranger, HU}, Title = {Symmetry classes in graphene quantum dots: universal spectral statistics, weak localization, and conductance fluctuations.}, Journal = {Physical Review Letters}, Volume = {102}, Number = {5}, Pages = {056806}, Year = {2009}, Month = {February}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19257538}, Abstract = {We study the symmetry classes of graphene quantum dots, both open and closed, through the conductance and energy level statistics. For abrupt termination of the lattice, these properties are well described by the standard orthogonal and unitary ensembles. However, for smooth mass confinement, special time-reversal symmetries associated with the sublattice and valley degrees of freedom are critical: they lead to block diagonal Hamiltonians and scattering matrices with blocks belonging to the unitary symmetry class even at zero magnetic field. While the effect of this structure is clearly seen in the conductance of open dots, it is suppressed in the spectral statistics of closed dots, because the intervalley scattering time is shorter than the time required to resolve a level spacing in the closed systems but longer than the escape time of the open systems.}, Doi = {10.1103/PhysRevLett.102.056806}, Key = {Wurm08_graphene} } @article{fds304506, Author = {Ke, S-H and Yang, W and Curtarolo, S and Baranger, HU}, Title = {Thermopower of molecular junctions: an ab initio study.}, Journal = {Nano Letters}, Volume = {9}, Number = {3}, Pages = {1011-1014}, Year = {2009}, Month = {March}, ISSN = {1530-6984}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19203208}, Abstract = {Molecular nanojunctions may support efficient thermoelectric conversion through enhanced thermopower. Recently, this quantity has been measured for several conjugated molecular nanojunctions with gold electrodes. Considering the wide variety of possible metal/molecule systems-almost none of which have been studied-it seems highly desirable to be able to calculate the thermopower of junctions with reasonable accuracy and high efficiency. To address this task, we demonstrate an effective approach based on the single particle green function (SPGF) method combined with density functional theory (DFT) using B3LYP and PBE0 energy functionals. Systematic good agreement between theory and experiment is obtained; indeed, much better agreement is found here than for comparable calculations of the conductance.}, Doi = {10.1021/nl8031229}, Key = {fds304506} } @article{Kaul08_Kspect2, Author = {R. K. Kaul and D. Ullmo and G. Zarand and S. Chandrasekharan and H. U. Baranger}, Title = {Ground State Excitations of Quantum Dots with ``Magnetic Impurities''}, Journal = {Phys. Rev. B}, Volume = {80}, Pages = {035318}, Year = {2009}, Month = {July}, url = {http://www.phy.duke.edu/research/cm/bg/paper/KaulUZCB09_longkondo.pdf}, Key = {Kaul08_Kspect2} } @article{Huaixiu10_1TLS, Author = {Zheng, H and Gauthier, DJ and Baranger, HU}, Title = {Waveguide QED: Many-body bound-state effects in coherent and Fock-state scattering from a two-level system}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {82}, Number = {6}, Pages = {063816}, Year = {2010}, ISSN = {1050-2947}, url = {http://hdl.handle.net/10161/8974 Duke open access}, Abstract = {Strong coupling between a two-level system (TLS) and bosonic modes produces dramatic quantum optics effects. We consider a one-dimensional continuum of bosons coupled to a single localized TLS, a system which may be realized in a variety of plasmonic, photonic, or electronic contexts. We present the exact many-body scattering eigenstate obtained by imposing open boundary conditions. Multiphoton bound states appear in the scattering of two or more photons due to the coupling between the photons and the TLS. Such bound states are shown to have a large effect on scattering of both Fock- and coherent-state wave packets, especially in the intermediate coupling-strength regime. We compare the statistics of the transmitted light with a coherent state having the same mean photon number: as the interaction strength increases, the one-photon probability is suppressed rapidly, and the two- and three-photon probabilities are greatly enhanced due to the many-body bound states. This results in non-Poissonian light. © 2010 The American Physical Society.}, Doi = {10.1103/PhysRevA.82.063816}, Key = {Huaixiu10_1TLS} } @article{Dong10_conductance, Author = {Liu, DE and Chandrasekharan, S and Baranger, HU}, Title = {Conductance of quantum impurity models from quantum monte carlo}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {82}, Number = {16}, Pages = {165447}, Year = {2010}, ISSN = {1098-0121}, url = {http://hdl.handle.net/10161/4258 Duke open access}, Abstract = {The conductance of two Anderson impurity models, one with twofold and another with fourfold degeneracy, representing two types of quantum dots, is calculated using a world-line quantum Monte Carlo (QMC) method. Extrapolation of the imaginary time QMC data to zero frequency yields the linear conductance, which is then compared to numerical renormalization-group results in order to assess its accuracy. We find that the method gives excellent results at low temperature (T TK) throughout the mixed-valence and Kondo regimes but it is unreliable for higher temperature. © 2010 The American Physical Society.}, Doi = {10.1103/PhysRevB.82.165447}, Key = {Dong10_conductance} } @article{Gleb10_kondobox, Author = {Bomze, Y and Borzenets, I and Mebrahtu, H and Makarovski, A and Baranger, HU and Finkelstein, G}, Title = {Two-stage Kondo effect and Kondo-box level spectroscopy in a carbon nanotube}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {82}, Number = {16}, Pages = {161411(R)}, Year = {2010}, ISSN = {1098-0121}, url = {http://hdl.handle.net/10161/4257 Duke open access}, Abstract = {The concept of the "Kondo box" describes a single spin, antiferromagnetically coupled to a quantum dot with a finite level spacing. Here, a Kondo box is formed in a carbon nanotube interacting with a localized electron. We investigate the spins of its first few eigenstates and compare them to a recent theory. In an "open" Kondo-box, strongly coupled to the leads, we observe a nonmonotonic temperature dependence of the nanotube conductance, which results from a competition between the Kondo-box singlet and the "conventional" Kondo state that couples the nanotube to the leads. © 2010 The American Physical Society.}, Doi = {10.1103/PhysRevB.82.161411}, Key = {Gleb10_kondobox} } @article{Novais10_howlong, Author = {Novais, E and Mucciolo, ER and Baranger, HU}, Title = {Bound on quantum computation time: Quantum error correction in a critical environment}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {82}, Number = {2}, Pages = {020303(R)}, Year = {2010}, ISSN = {1050-2947}, url = {http://hdl.handle.net/10161/3348 Duke open access}, Abstract = {We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user. © 2010 The American Physical Society.}, Doi = {10.1103/PhysRevA.82.020303}, Key = {Novais10_howlong} } @article{fds245084, Author = {Wurm, J and Wimmer, M and Baranger, HU and Richter, K}, Title = {Graphene rings in magnetic fields: Aharonov-Bohm effect and valley splitting}, Journal = {Semiconductor Science and Technology}, Volume = {25}, Number = {3}, Pages = {034003}, Year = {2010}, ISSN = {0268-1242}, url = {http://www.phy.duke.edu/research/cm/bg/paper/WurmWBR09_graphenerings.pdf}, Abstract = {We study the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field by means of numerical calculations based on a tight-binding model. First, we consider the magnetoconductance of such rings and observe the Aharonov-Bohm effect. We investigate different regimes of the magnetic flux up to the quantum Hall regime, where the Aharonov-Bohm oscillations are suppressed. Results for both clean (ballistic) and disordered (diffusive) rings are presented. Second, we study rings with smooth mass boundary that are weakly coupled to leads. We show that the valley degeneracy of the eigenstates in closed graphene rings can be lifted by a small magnetic flux, and that this lifting can be observed in the transport properties of the system. © 2010 IOP Publishing Ltd.}, Doi = {10.1088/0268-1242/25/3/034003}, Key = {fds245084} } @article{Ke10_timedep, Author = {Ke, S-H and Liu, R and Yang, W and Baranger, HU}, Title = {Time-dependent transport through molecular junctions.}, Journal = {Journal of Chemical Physics}, Volume = {132}, Number = {23}, Pages = {234105}, Year = {2010}, Month = {June}, url = {http://www.ncbi.nlm.nih.gov/pubmed/20572687}, Abstract = {We investigate transport properties of molecular junctions under two types of bias--a short time pulse or an ac bias--by combining a solution for Green's functions in the time domain with electronic structure information coming from ab initio density functional calculations. We find that the short time response depends on lead structure, bias voltage, and barrier heights both at the molecule-lead contacts and within molecules. Under a low frequency ac bias, the electron flow either tracks or leads the bias signal (resistive or capacitive response) depending on whether the junction is perfectly conducting or not. For high frequency, the current lags the bias signal due to the kinetic inductance. The transition frequency is an intrinsic property of the junctions.}, Doi = {10.1063/1.3435351}, Key = {Ke10_timedep} } @article{Dong10_4dotsqpt, Author = {Liu, DE and Chandrasekharan, S and Baranger, HU}, Title = {Quantum phase transition and emergent symmetry in a quadruple quantum dot system.}, Journal = {Physical Review Letters}, Volume = {105}, Number = {25}, Pages = {256801}, Year = {2010}, Month = {December}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21231607}, Abstract = {We propose a system of four quantum dots designed to study the competition between three types of interactions: Heisenberg, Kondo, and Ising. We find a rich phase diagram containing two sharp features: a quantum phase transition (QPT) between charge-ordered and charge-liquid phases and a dramatic resonance in the charge liquid visible in the conductance. The QPT is of the Kosterlitz-Thouless type with a discontinuous jump in the conductance at the transition. We connect the resonance phenomenon with the degeneracy of three levels in the isolated quadruple dot and argue that this leads to a Kondo-like emergent symmetry from left-right Z2 to U(1).}, Doi = {10.1103/PhysRevLett.105.256801}, Key = {Dong10_4dotsqpt} } @article{fds245074, Author = {Ullmo, D and Burdin, S and Liu, DE and Baranger, HU}, Title = {Kondo effect and mesoscopic fluctuations}, Journal = {Pramana}, Volume = {77}, Number = {5}, Pages = {769-779}, Year = {2011}, ISSN = {0304-4289}, url = {http://dx.doi.org/10.1007/s12043-011-0191-3}, Abstract = {Two important themes in nanoscale physics in the last two decades are correlations between electrons and mesoscopic fluctuations. Here we review our recent work on the intersection of these two themes. The setting is the Kondo effect, a paradigmatic example of correlated electron physics, in a nanoscale system with mesoscopic fluctuations; in particular, we consider a small quantum dot coupled to a finite reservoir (which itself may be a large quantum dot). We discuss three aspects of this problem. First, in the high-temperature regime, we argue that a Kondo temperature TK which takes into account the mesoscopic fluctuations is a relevant concept: for instance, physical properties are universal functions of T/TK. Secondly, when the temperature is much less than the mean level spacing due to confinement, we characterize a natural cross-over from weak to strong coupling. This strong coupling regime is itself characterized by well-defined single-particle levels, as one can see from a Nozières Fermi-liquid theory argument. Finally, using a mean-field technique, we connect the mesoscopic fluctuations of the quasiparticles in the weak coupling regime to those at strong coupling. © Indian Academy of Sciences.}, Doi = {10.1007/s12043-011-0191-3}, Key = {fds245074} } @article{Dong11_majoranadetect, Author = {Liu, DE and Baranger, HU}, Title = {Detecting a Majorana-fermion zero mode using a quantum dot}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {84}, Number = {20}, Pages = {201308(R)}, Year = {2011}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/LiuB11_majoranadetect.pdf}, Abstract = {We propose an experimental setup for detecting a Majorana zero mode consisting of a spinless quantum dot coupled to the end of a p-wave superconducting nanowire. The Majorana bound state at the end of the wire strongly influences the conductance through the quantum dot: Driving the wire through the topological phase transition causes a sharp jump in the conductance by a factor of 1/2. In the topological phase, the zero-temperature peak value of the dot conductance (i.e., when the dot is on resonance and symmetrically coupled to the leads) is e2/2h. In contrast, if the wire is in its trivial phase, the conductance peak value is e2/h, or if a regular fermionic zero mode occurs on the end of the wire, the conductance is 0. The system can also be used to tune Flensberg's qubit system to the required degeneracy point. © 2011 American Physical Society.}, Doi = {10.1103/PhysRevB.84.201308}, Key = {Dong11_majoranadetect} } @article{Huaixiu11_4LS, Author = {Zheng, H and Gauthier, DJ and Baranger, HU}, Title = {Cavity-free photon blockade induced by many-body bound states.}, Journal = {Physical Review Letters}, Volume = {107}, Number = {22}, Pages = {223601}, Year = {2011}, Month = {November}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22182028}, Abstract = {The manipulation of individual, mobile quanta is a key goal of quantum communication; to achieve this, nonlinear phenomena in open systems can play a critical role. We show theoretically that a variety of strong quantum nonlinear phenomena occur in a completely open one-dimensional waveguide coupled to an N-type four-level system. We focus on photon blockade and the creation of single-photon states in the absence of a cavity. Many-body bound states appear due to the strong photon-photon correlation mediated by the four-level system. These bound states cause photon blockade, which can generate a sub-Poissonian single-photon source.}, Doi = {10.1103/PhysRevLett.107.223601}, Key = {Huaixiu11_4LS} } @article{fds245071, Author = {Liu, DE and Burdin, S and Baranger, HU and Ullmo, D}, Title = {Mesoscopic Anderson box: Connecting weak to strong coupling}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {85}, Number = {15}, Pages = {155455}, Year = {2012}, ISSN = {1098-0121}, url = {http://www.phy.duke.edu/research/cm/bg/paper/LiuBBU12_mesoAndbox.pdf}, Abstract = {We study the Anderson impurity problem in a mesoscopic setting, namely the "Anderson box," in which the impurity is coupled to finite reservoir having a discrete spectrum and large sample-to-sample mesoscopic fluctuations. Note that both the weakly coupled and strong coupling Anderson impurity problems are characterized by a Fermi-liquid theory with weakly interacting quasiparticles. We study how the statistical fluctuations in these two problems are connected, using random matrix theory and the slave boson mean-field approximation (SBMFA). First, for a resonant level model such as results from the SBMFA, we find the joint distribution of energy levels with and without the resonant level present. Second, if only energy levels within the Kondo resonance are considered, the distributions of perturbed levels collapse to universal forms for both orthogonal and unitary ensembles for all values of the coupling. These universal curves are described well by a simple Wigner-surmise-type toy model. Third, we study the fluctuations of the mean-field parameters in the SBMFA, finding that they are small. Finally, the change in the intensity of an eigenfunction at an arbitrary point is studied, such as is relevant in conductance measurements. We find that the introduction of the strongly coupled impurity considerably changes the wave function but that a substantial correlation remains. © 2012 American Physical Society.}, Doi = {10.1103/PhysRevB.85.155455}, Key = {fds245071} } @article{fds245072, Author = {Zheng, H and Gauthier, DJ and Baranger, HU}, Title = {Strongly correlated photons generated by coupling a three- or four-level system to a waveguide}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {85}, Number = {4}, Pages = {043832}, Year = {2012}, ISSN = {1050-2947}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ZhengGB12_strongcor3LS4LS.pdf}, Abstract = {We study the generation of strongly correlated photons by coupling an atom to photonic quantum fields in a one-dimensional waveguide. Specifically, we consider a three-level or four-level system for the atom. Photon-photon bound states emerge as a manifestation of the strong photon-photon correlation mediated by the atom. Effective repulsive or attractive interaction between photons can be produced, causing either suppressed multiphoton transmission (photon blockade) or enhanced multiphoton transmission (photon-induced tunneling). As a result, nonclassical light sources can be generated on demand by sending coherent states into the proposed system. We calculate the second-order correlation function of the transmitted field and observe bunching and antibunching caused by the bound states. Furthermore, we demonstrate that the proposed system can produce photon pairs with a high degree of spectral entanglement, which have a large capacity for carrying information and are important for large-alphabet quantum communication. © 2012 American Physical Society.}, Doi = {10.1103/PhysRevA.85.043832}, Key = {fds245072} } @article{fds245075, Author = {Liu, DE and Burdin, S and Baranger, HU and Ullmo, D}, Title = {From weak- to strong-coupling mesoscopic Fermi liquids}, Journal = {EPL (Europhysics Letters)}, Volume = {97}, Number = {1}, Pages = {17006}, Year = {2012}, ISSN = {0295-5075}, url = {http://www.phy.duke.edu/research/cm/bg/paper/LiuBBU11_weaktostrong.pdf}, Abstract = {We study mesoscopic fluctuations in a system in which there is a continuous connection between two distinct Fermi liquids, asking whether the mesoscopic variation in the two limits is correlated. The particular system studied is an Anderson impurity coupled to a finite mesoscopic reservoir described by the random matrix theory, a structure which can be realized using quantum dots. We use the slave boson mean-field approach to connect the levels of the uncoupled system to those of the strong-coupling Nozières' Fermi liquid. We find strong but not complete correlation between the mesoscopic properties in the two limits and several universal features. © 2012 Europhysics Letters Association.}, Doi = {10.1209/0295-5075/97/17006}, Key = {fds245075} } @article{fds303604, Author = {Zheng, H and Baranger, HU}, Title = {Persistent Quantum Beats and Long-Distance Entanglement from Waveguide-Mediated Interactions}, Journal = {Phys. Rev. Lett.}, Volume = {110}, Pages = {113601}, Year = {2012}, Month = {June}, url = {http://arxiv.org/abs/1206.4442v2}, Abstract = {We study photon-photon correlations and entanglement generation in a one-dimensional waveguide coupled to two qubits with an arbitrary spatial separation. We develop a novel Green function method to study vacuum-mediated qubit-qubit interactions, including both spontaneous and coherent couplings. As a result of these interactions, quantum beats appear in the second-order correlation function. We go beyond the Markovian regime and observe that such quantum beats persist much longer than the qubit life time. Using these non-Markovian processes, a high degree of long-distance entanglement can be generated, making waveguide-QED systems promising candidates for scalable quantum networking.}, Doi = {10.1103/PhysRevLett.110.113601}, Key = {fds303604} } @article{Henok11_RLdissip1, Author = {Mebrahtu, HT and Borzenets, IV and Liu, DE and Zheng, H and Bomze, YV and Smirnov, AI and Baranger, HU and Finkelstein, G}, Title = {Quantum phase transition in a resonant level coupled to interacting leads.}, Journal = {Nature}, Volume = {488}, Number = {7409}, Pages = {61-64}, Year = {2012}, Month = {August}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22859201}, Abstract = {A Luttinger liquid is an interacting one-dimensional electronic system, quite distinct from the 'conventional' Fermi liquids formed by interacting electrons in two and three dimensions. Some of the most striking properties of Luttinger liquids are revealed in the process of electron tunnelling. For example, as a function of the applied bias voltage or temperature, the tunnelling current exhibits a non-trivial power-law suppression. (There is no such suppression in a conventional Fermi liquid.) Here, using a carbon nanotube connected to resistive leads, we create a system that emulates tunnelling in a Luttinger liquid, by controlling the interaction of the tunnelling electron with its environment. We further replace a single tunnelling barrier with a double-barrier, resonant-level structure and investigate resonant tunnelling between Luttinger liquids. At low temperatures, we observe perfect transparency of the resonant level embedded in the interacting environment, and the width of the resonance tends to zero. We argue that this behaviour results from many-body physics of interacting electrons, and signals the presence of a quantum phase transition. Given that many parameters, including the interaction strength, can be precisely controlled in our samples, this is an attractive model system for studying quantum critical phenomena in general, with wide-reaching implications for understanding quantum phase transitions in more complex systems, such as cold atoms and strongly correlated bulk materials.}, Doi = {10.1038/nature11265}, Key = {Henok11_RLdissip1} } @article{fds245047, Author = {Zheng, H and Gauthier, DJ and Baranger, HU}, Title = {Decoy-state quantum key distribution with nonclassical light generated in a one-dimensional waveguide.}, Journal = {Optics Letters}, Volume = {38}, Number = {5}, Pages = {622-624}, Year = {2013}, Month = {March}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23455244}, Abstract = {We investigate a decoy-state quantum key distribution (QKD) scheme with a sub-Poissonian single-photon source, which is generated on demand by scattering a coherent state off a two-level system in a one-dimensional waveguide. We show that, compared to coherent state decoy-state QKD, there is a two-fold increase of the key generation rate. Furthermore, the performance is shown to be robust against both parameter variations and loss effects of the system.}, Doi = {10.1364/OL.38.000622}, Key = {fds245047} } @article{fds221117, Author = {H. Zheng and H. U. Baranger}, Title = {Persistent Quantum Beats and Long-Distance Entanglement from Non-Markovian Processes}, Journal = {Phys. Rev. Lett.}, Volume = {110}, Pages = {113601}, Year = {2013}, Month = {March}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ZhengB12_twoimp.pdf}, Doi = {10.1103/PhysRevLett.110.113601}, Key = {fds221117} } @article{fds303601, Author = {Mehta, AC and Umrigar, CJ and Meyer, JS and Baranger, HU}, Title = {Zigzag Phase Transition in Quantum Wires}, Journal = {Physical Review Letters}, Volume = {110}, Number = {24}, Pages = {246802}, Year = {2013}, Month = {June}, url = {http://arxiv.org/abs/1302.5429v2}, Abstract = {We study the quantum phase transition of interacting electrons in quantum wires from a one-dimensional (1D) linear configuration to a quasi-1D zigzag arrangement using quantum Monte Carlo methods. As the density increases from its lowest values, first, the electrons form a linear Wigner crystal; then, the symmetry about the axis of the wire is broken as the electrons order in a quasi-1D zigzag phase; and, finally, the electrons form a disordered liquid-like phase. We show that the linear to zigzag phase transition is not destroyed by the strong quantum fluctuations present in narrow wires; it has characteristics which are qualitatively different from the classical transition.}, Doi = {10.1103/PhysRevLett.110.246802}, Key = {fds303601} } @article{fds245046, Author = {Liu, DE and Levchenko, A and Baranger, HU}, Title = {Floquet Majorana Fermions for Topological Qubits in Superconducting Devices and Cold-Atom Systems}, Journal = {Physical Review Letters}, Volume = {111}, Number = {4}, Pages = {047002}, Year = {2013}, Month = {July}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23931396}, Abstract = {We develop an approach to realizing a topological phase transition and non-Abelian braiding statistics with dynamically induced Floquet Majorana fermions (FMFs). When the periodic driving potential does not break fermion parity conservation, FMFs can encode quantum information. Quasienergy analysis shows that a stable FMF zero mode and two other satellite modes exist in a wide parameter space with large quasienergy gaps, which prevents transitions to other Floquet states under adiabatic driving. We also show that in the asymptotic limit FMFs preserve non-Abelian braiding statistics and, thus, behave like their equilibrium counterparts.}, Doi = {10.1103/PhysRevLett.111.047002}, Key = {fds245046} } @article{fds221156, Author = {E. Novais and E. R. Mucciolo and H. U. Baranger}, Title = {Hamiltonian Methods in Quantum Error Correction and Fault Tolerance}, Pages = {585-611}, Booktitle = {Quantum Error Correction}, Publisher = {Cambridge University Press}, Editor = {D. Lidar and P. Zanardi}, Year = {2013}, Month = {August}, url = {http://www.phy.duke.edu/research/cm/bg/paper/NovaisMB09_qecbook.pdf}, Key = {fds221156} } @article{fds245045, Author = {Ullmo, D and Liu, DE and Burdin, S and Baranger, HU}, Title = {Mesoscopic fluctuations in the Fermi-liquid regime of the Kondo problem}, Journal = {The European Physical Journal B - Condensed Matter and Complex Systems}, Volume = {86}, Number = {8}, Year = {2013}, Month = {August}, ISSN = {1434-6028}, url = {http://dx.doi.org/10.1140/epjb/e2013-40418-3}, Abstract = {We consider the low temperature regime of the mesoscopic Kondo problem, and in particular the relevance of a Fermi-liquid description of this regime. Mesoscopic fluctuations of both the quasiparticle energy levels and the corresponding wavefunctions are large in this case. These mesoscopic fluctuations make the traditional approach to Fermi-liquids impracticable, as it assumes the existence of a limited number of relevant parameters. We show here how this difficulty can be overcome and discuss the relationship between the resulting Fermi-liquid description "à la Nozières" and the mean field slave fermion approximation. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.}, Doi = {10.1140/epjb/e2013-40418-3}, Key = {fds245045} } @article{fds303603, Author = {Zheng, H and Gauthier, DJ and Baranger, HU}, Title = {Waveguide-QED-Based Photonic Quantum Computation}, Journal = {Physical Review Letters}, Volume = {111}, Number = {9}, Pages = {090502}, Year = {2013}, Month = {August}, url = {http://arxiv.org/abs/1211.1711v3}, Abstract = {We propose a new scheme for quantum computation using flying qubits--propagating photons in a one-dimensional waveguide--interacting with matter qubits. Photon-photon interactions are mediated by the coupling to a three- or four-level system, based on which photon-photon \pi-phase gates (Controlled-NOT) can be implemented for universal quantum computation. We show that high gate fidelity is possible given recent dramatic experimental progress in superconducting circuits and photonic-crystal waveguides. The proposed system can be an important building block for future on-chip quantum networks.}, Doi = {10.1103/PhysRevLett.111.090502}, Key = {fds303603} } @article{fds221118, Author = {H. Zheng and D. J. Gauthier and H. U. Baranger}, Title = {Waveguide-QED-Based Photonic Quantum Computation}, Journal = {Phys. Rev. Lett.}, Volume = {111}, Pages = {090502}, Year = {2013}, Month = {August}, url = {http://www.phy.duke.edu/research/cm/bg/paper/ZhengGB12_photongate.pdf}, Doi = {10.1103/PhysRevLett.111.090502}, Key = {fds221118} } @article{fds221154, Author = {D. Ullmo and D. E. Liu and S. Burdin and H. U. Baranger}, Title = {Fermi-liquid regime of the mesoscopic Kondo problem}, Journal = {Eur. Phys. J. B}, Volume = {86}, Pages = {353}, Year = {2013}, Month = {August}, url = {http://www.phy.duke.edu/research/cm/bg/paper/UllmoLBB_fermiliqmesoKondo.pdf}, Doi = {10.1140/epjb/e2013-40418-3}, Key = {fds221154} } @article{fds245044, Author = {Mebrahtu, HT and Borzenets, IV and Zheng, H and Bomze, YV and Smirnov, AI and Florens, S and Baranger, HU and Finkelstein, G}, Title = {Observation of majorana quantum critical behaviour in a resonant level coupled to a dissipative environment}, Journal = {Nature Physics}, Volume = {9}, Number = {11}, Pages = {732-737}, Year = {2013}, Month = {November}, ISSN = {1745-2473}, url = {http://dx.doi.org/10.1038/nphys2735}, Abstract = {A quantum phase transition is an abrupt change between two distinct ground states of a many-body system, driven by an external parameter. In the vicinity of the quantum critical point (QCP) where the transition occurs, a new phase may emerge that is determined by quantum fluctuations and is very different from either phase. In particular, a conducting system may exhibit non-Fermi-liquid behaviour. Although this scenario is well established theoretically, controllable experimental realizations are rare. Here, we experimentally investigate the nature of the QCP in a simple nanoscale system - a spin-polarized resonant level coupled to dissipative contacts. We fine-tune the system to the QCP, realized exactly on-resonance and when the coupling between the level and the two contacts is symmetric. Several anomalous transport scaling laws are demonstrated, including a striking non-Fermi-liquid scattering rate at the QCP, indicating fractionalization of the resonant level into two Majorana quasiparticles. © 2013 Macmillan Publishers Limited.}, Doi = {10.1038/nphys2735}, Key = {fds245044} } @article{fds225583, Author = {Y.-L. L. Fang and H. Zheng and H. U. Baranger}, Title = {One-Dimensional Waveguide Coupled to Multiple Qubits: Photon-Photon Correlations}, Journal = {Eur. Phys. J. Quantum Technology}, Volume = {1}, Pages = {3}, Year = {2014}, Month = {January}, url = {http://arxiv.org/pdf/1308.6551v2.pdf}, Doi = {10.1140/epjqt3}, Key = {fds225583} } @article{fds303599, Author = {Liu, DE and Zheng, H and Finkelstein, G and Baranger, HU}, Title = {Tunable quantum phase transitions in a resonant level coupled to two dissipative baths}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {89}, Number = {8}, Pages = {085116}, Year = {2014}, Month = {February}, url = {http://arxiv.org/abs/1310.4773v2}, Abstract = {We study tunneling through a resonant level connected to two dissipative bosonic baths: one is the resistive environment of the source and drain leads, while the second comes from coupling to potential fluctuations on a resistive gate. We show that several quantum phase transitions (QPT) occur in such a model, transitions which emulate those found in interacting systems such as Luttinger liquids or Kondo systems. We first use bosonization to map this dissipative resonant level model to a resonant level in a Luttinger liquid, one with, curiously, two interaction parameters. Drawing on methods for analyzing Luttinger liquids at both weak and strong coupling, we obtain the phase diagram. For strong dissipation, a Berezinsky-Kosterlitz-Thouless QPT separates strong-coupling and weak-coupling (charge localized) phases. In the source-drain symmetric case, all relevant backscattering processes disappear at strong coupling, leading to perfect transmission at zero temperature. In fact, a QPT occurs as a function of the coupling asymmetry or energy of the resonant level: the two phases are (i) the system is cut into two disconnected pieces (zero transmission), or (ii) the system is a single connected piece with perfect transmission, except for a disconnected fractional degree of freedom. The latter arises from the competition between the two fermionic leads (source and drain), as in the two-channel Kondo effect.}, Doi = {10.1103/PhysRevB.89.085116}, Key = {fds303599} } @article{fds225584, Author = {D. E. Liu and H. Zheng and G. FInkelstein and H. U. Baranger}, Title = {Tunable Quantum Phase Transitions in a Resonant Level Coupled to Two Dissipative Baths}, Journal = {Phys. Rev. B}, Volume = {89}, Pages = {085116}, Year = {2014}, Month = {February}, url = {http://arxiv.org/pdf/1310.4773v2.pdf}, Doi = {10.1103/PhysRevB.89.085116}, Key = {fds225584} } @article{fds303600, Author = {Bera, S and Florens, S and Baranger, HU and Roch, N and Nazir, A and Chin, AW}, Title = {Stabilizing spin coherence through environmental entanglement in strongly dissipative quantum systems}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {89}, Number = {12}, Pages = {121108}, Year = {2014}, Month = {March}, url = {http://arxiv.org/abs/1307.5681v2}, Abstract = {The key feature of a quantum spin coupled to a harmonic bath---a model dissipative quantum system---is competition between oscillator potential energy and spin tunneling rate. We show that these opposing tendencies cause environmental entanglement through superpositions of adiabatic and antiadiabatic oscillator states, which then stabilizes the spin coherence against strong dissipation. This insight motivates a fast-converging variational coherent-state expansion for the many-body ground state of the spin-boson model, which we substantiate via numerical quantum tomography.}, Doi = {10.1103/PhysRevB.89.121108}, Key = {fds303600} } @article{fds225585, Author = {S. Bera and S. Florens and H. U. Baranger and N. Roch and A. Nazir and A. W. Chin}, Title = {Stabilizing Spin Coherence through Environmental Entanglement in Strongly Dissipative Quantum Systems}, Journal = {Phys. Rev. B}, Volume = {89}, Pages = {121108(R)}, Year = {2014}, Month = {March}, url = {http://arxiv.org/pdf/1307.5681v2.pdf}, Doi = {10.1103/PhysRevB.89.121108}, Key = {fds225585} } @article{fds245043, Author = {Zheng, H and Florens, S and Baranger, HU}, Title = {Transport signatures of Majorana quantum criticality realized by dissipative resonant tunneling}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {89}, Number = {23}, Pages = {235135}, Year = {2014}, Month = {June}, ISSN = {1098-0121}, url = {http://arxiv.org/pdf/1403.5175v1.pdf}, Doi = {10.1103/PhysRevB.89.235135}, Key = {fds245043} } @article{fds245042, Author = {Bera, S and Nazir, A and Chin, AW and Baranger, HU and Florens, S}, Title = {Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {90}, Number = {7}, Pages = {075110}, Year = {2014}, Month = {August}, ISSN = {1098-0121}, url = {http://arxiv.org/pdf/1406.4983v2.pdf}, Doi = {10.1103/PhysRevB.90.075110}, Key = {fds245042} } @article{fds330532, Author = {Fang, Y-LL and Zheng, H and Baranger, HU}, Title = {One-dimensional waveguide coupled to multiple qubits: photon-photon correlations}, Journal = {EPJ Quantum Technology}, Volume = {1}, Number = {1}, Year = {2014}, Month = {December}, url = {http://dx.doi.org/10.1140/epjqt3}, Doi = {10.1140/epjqt3}, Key = {fds330532} } @article{fds245041, Author = {Fang, Y-LL and Baranger, HU}, Title = {Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {91}, Number = {5}, Year = {2015}, Month = {May}, ISSN = {1050-2947}, url = {http://dx.doi.org/10.1103/PhysRevA.91.053845}, Doi = {10.1103/PhysRevA.91.053845}, Key = {fds245041} } @article{fds318398, Author = {Jin, L-J and Houzet, M and Meyer, JS and Baranger, HU and Hekking, FWJ}, Title = {Detecting photon-photon interactions in a superconducting circuit}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {92}, Number = {13}, Year = {2015}, Month = {October}, url = {http://dx.doi.org/10.1103/PhysRevB.92.134503}, Doi = {10.1103/PhysRevB.92.134503}, Key = {fds318398} } @article{fds318397, Author = {Bera, S and Baranger, HU and Florens, S}, Title = {Dynamics of a qubit in a high-impedance transmission line from a bath perspective}, Journal = {Physical Review A}, Volume = {93}, Number = {3}, Year = {2016}, Month = {March}, url = {http://dx.doi.org/10.1103/PhysRevA.93.033847}, Doi = {10.1103/PhysRevA.93.033847}, Key = {fds318397} } @article{fds318396, Author = {Fang, Y-LL and Baranger, HU}, Title = {Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems}, Journal = {Physica E: Low-dimensional Systems and Nanostructures}, Volume = {78}, Pages = {92-99}, Year = {2016}, Month = {April}, url = {http://dx.doi.org/10.1016/j.physe.2015.11.004}, Doi = {10.1016/j.physe.2015.11.004}, Key = {fds318396} } @article{fds318395, Author = {Fang, Y-LL and Baranger, HU}, Title = {Reprint of : Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems}, Journal = {Physica E: Low-dimensional Systems and Nanostructures}, Volume = {82}, Pages = {71-78}, Year = {2016}, Month = {August}, url = {http://dx.doi.org/10.1016/j.physe.2016.02.015}, Doi = {10.1016/j.physe.2016.02.015}, Key = {fds318395} } @article{fds330531, Author = {Zhang, G and Chung, C-H and Ke, CT and Lin, C-Y and Mebrahtu, H and Smirnov, AI and Finkelstein, G and Baranger, HU}, Title = {Universal Nonequilibrium I-V Curve at an Interacting Impurity Quantum Critical Point}, Journal = {arXiv}, Volume = {1609}, Year = {2016}, Month = {September}, Abstract = {The nonlinear I-V curve at an interacting quantum critical point (QCP) is typically out of reach theoretically. Here, however, we provide an analytical calculation of the I-V curve at a QCP under nonequilibrium conditions and, furthermore, present experimental results to which the theory is compared. The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an ohmic electromagnetic environment. A two channel Kondo like QCP occurs when the level is on resonance and symmetrically coupled to the leads. Though similar to a resonant level in a Luttinger liquid, a key difference enables us to obtain the current at finite temperature and bias: because there are modes that do not initially couple to the environment, an analysis in terms of weak backscattering of non-interacting fermions coupled to a modified environment is possible. Drawing on dynamical Coulomb blockade theory, we then obtain an analytical expression for the nonlinear I-V curve. The agreement between our theoretical and experimental results is remarkable.}, Key = {fds330531} } @article{fds323837, Author = {Zhang, G and Novais, E and Baranger, HU}, Title = {Rescuing a Quantum Phase Transition with Quantum Noise}, Journal = {Physical Review Letters}, Volume = {118}, Number = {5}, Pages = {050402}, Year = {2017}, Month = {February}, url = {http://dx.doi.org/10.1103/PhysRevLett.118.050402}, Abstract = {We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroy quantum effects, as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment, the source of quantum noise. While the charge transport inhibits a quantum phase transition, the quantum noise reduces charge transport and restores the transition. We find a non-Fermi-liquid intermediate fixed point for all strengths of the noise. For strong noise, it is similar to the intermediate fixed point of the two-impurity Kondo model.}, Doi = {10.1103/PhysRevLett.118.050402}, Key = {fds323837} } @article{fds328611, Author = {Fang, Y-LL and Baranger, HU}, Title = {Multiple emitters in a waveguide: Nonreciprocity and correlated photons at perfect elastic transmission}, Journal = {Physical Review A}, Volume = {96}, Number = {1}, Year = {2017}, Month = {July}, url = {http://dx.doi.org/10.1103/PhysRevA.96.013842}, Doi = {10.1103/PhysRevA.96.013842}, Key = {fds328611} } @article{fds330530, Author = {Fang, Y-LL and Ciccarello, F and Baranger, HU}, Title = {Non-Markovian Dynamics of a Qubit Due to Single-Photon Scattering in a Waveguide}, Journal = {arXiv}, Volume = {1707}, Publisher = {arXiv}, Year = {2017}, Month = {July}, Key = {fds330530} } @article{fds330529, Author = {Zhang, XHH and Baranger, HU}, Title = {Photon Statistics in a Waveguide: Beyond Bunching and Antibunching}, Journal = {arXiv}, Volume = {1710}, Publisher = {arXiv}, Year = {2017}, Month = {October}, Key = {fds330529} } @article{fds332752, Author = {Zhang, XHH and Baranger, HU}, Title = {Quantum interference and complex photon statistics in waveguide QED}, Journal = {Physical Review A}, Volume = {97}, Number = {2}, Year = {2018}, Month = {February}, url = {http://dx.doi.org/10.1103/PhysRevA.97.023813}, Abstract = {© 2018 American Physical Society. We obtain photon statistics by using a quantum jump approach tailored to a system in which one or two qubits are coupled to a one-dimensional waveguide. Photons confined in the waveguide have strong interference effects, which are shown to play a vital role in quantum jumps and photon statistics. For a single qubit, for instance, the bunching of transmitted photons is heralded by a jump that increases the qubit population. We show that the distribution and correlations of waiting times offer a clearer and more precise characterization of photon bunching and antibunching. Further, the waiting times can be used to characterize complex correlations of photons which are hidden in g(2)(τ), such as a mixture of bunching and antibunching.}, Doi = {10.1103/PhysRevA.97.023813}, Key = {fds332752} } %% Papers Submitted @article{Lee06_disordsuper, Author = {J.-W. Lee and S. Chandrasekharan and H. U. Baranger}, Title = {Disorder Induced Superconductivity of Hard-Core Bosons in Two Dimensions}, Journal = {submitted to Phys. Rev. B}, Year = {2007}, Key = {Lee06_disordsuper} }