Duke Physics

I joined the Physics department at Duke in 2003 as a graduate assistant in the Low Temperature Transport group of Prof. Albert Chang. Prior to this, I worked for one year as a research assistant at the Institute of Physics, Academia Sinica, Taiwan. I concurrently took on a part-time teaching position, lecturing high school AP level physics at National Experimental High School (NEHS) in Taiwan. I received my BA in Physics from Columbia University in 2002.

My research at Duke focuses on several interesting questions, the first being, “How does charge flow at the nanoscale?” Modern lithography techniques allow the fabrication of test systems with dimensions on the order of a hundred nanometers, which becomes comparable in size to the Fermi wavelength, or the spread of the electron’s “waviness.” For systems this small, non-classical quantum effects could dominate the electronic transport behavior. This is clearly seen in the Coulomb blockade of semiconducting quantum dots and coherent electron focusing in quantum point contacts. Quantum point contacts are nano-constrictions that can be tuned to allow a single or multiple quantized conductance modes through. Quantum dots are nanosized charge islands that contain a fixed and isolated number of charge from the larger external charge reservoirs. When attempting to add an additional charge to the island, the Coulomb energy of the electrons already on the island resist a change in the total number of charge by “blockading” transport. This is very fascinating because we now are able to control quite precisely the flow of a single electron through the structure.

The second interesting question that builds on the first is “How does spin complicate matters?” By applying a magnetic field, one can induce Zeeman splitting of the quantum dot energy levels. This allows for the manipulation of the spin degree of freedom. Single and double quantum dots have been used to study the effect spin impurities can have on transport, or the Kondo effect. Controllable entangled spins on quantum dots is also a candidate for qubits.

Spin also shows up in interesting ways in quantum point contacts, for example, as the 0.7 anomaly at zero field, which is thought to be the effects of frozen-in spin polarization. Gating of point contacts can potentially also affect the structure inversion asymmetry or spin-orbit coupling. Understanding and controlling spin currents through point contacts are interesting for their potential application in spintronics.

In addition to the ongoing and fascinating research on low dimensional transport, I am participating in the study of the new Fe based superconductors. This work is in collaboration with the Superconductivity Lab under M.K. Wu at the Institute of Physics, Academia Sinica, Taiwan. The layered FeAs based superconductors have Tc as high as 55 K, making them the only non-cuprate high temperature superconductors known to date. Our collaboration discovered the superconducting β-FeSe compound. Although Tc is ~ 8 K, the crystal lattice structure of β-FeSe is by far the simplest of the Fe superconductors, as it consists of only Fe and Se arranged in a layered tetrahedral conformation. Se also has much less stringent safety requirements in the laboratory compared to the highly toxic As. A subsequent study found Te doping and high pressure can significantly enhance Tc. This strongly suggests that the structural conformation of the system plays an important role in the emergent superconductivity. Understanding the structural phase transition in β-FeSe may elucidate how superconductivity arises in the Fe-based materials, and give key insights in the search for new high Tc superconductors.