Abstract:
Carbon nanotubes present an ideal system to
investigate electronic transport phenomena at
the nanoscale. We study the evolution of the
nanotube conductance by controlling the
contact transparency within the same sample.
At sufficiently open contacts and low enough
temperatures, single-electron conductance
peaks corresponding to doubly degenerate
orbitals (“shells”) merge, as the Kondo
processes develop in the valleys. Contrary to
expectations, the low-temperature conductance
continues to grow even when the temperature
is reduced far below the Kondo temperature
and the original single-electron features are
completely overgrown. The resulting low-
temperature conductance demonstrates
pronounced modulations with a four-electron
periodicity. We show that this regime is
different from either the Coulomb blockade or
the single-particle interference and suggest
that electrons on a partially filled shell
form a novel many-body state, where the
different charge states are hybridized by
Kondo processes. Finally, we find that the
Kondo features at one-electron and three-
electron shell occupations behave distinctly
differently in magnetic field, in violation
of the electron-hole symmetry. 1