6,139 research outputs found
Electronic Highways in Bilayer Graphene
Bilayer graphene with an interlayer potential difference has an energy gap
and, when the potential difference varies spatially, topologically protected
one-dimensional states localized along the difference's zero-lines. When
disorder is absent, electronic travel directions along zero-line trajectories
are fixed by valley Hall properties. Using the Landauer-B\"uttiker formula and
the non-equilibrium Green's function technique we demonstrate numerically that
collisions between electrons traveling in opposite directions, due to either
disorder or changes in path direction, are strongly suppressed. We find that
extremely long mean free paths of the order of hundreds of microns can be
expected in relatively clean samples. This finding suggests the possibility of
designing low power nanoscale electronic devices in which transport paths are
controlled by gates which alter the inter-layer potential landscape.Comment: 8 pages, 5 figure
Transport Through Andreev Bound States in a Graphene Quantum Dot
Andreev reflection-where an electron in a normal metal backscatters off a
superconductor into a hole-forms the basis of low energy transport through
superconducting junctions. Andreev reflection in confined regions gives rise to
discrete Andreev bound states (ABS), which can carry a supercurrent and have
recently been proposed as the basis of qubits [1-3]. Although signatures of
Andreev reflection and bound states in conductance have been widely reported
[4], it has been difficult to directly probe individual ABS. Here, we report
transport measurements of sharp, gate-tunable ABS formed in a
superconductor-quantum dot (QD)-normal system, which incorporates graphene. The
QD exists in the graphene under the superconducting contact, due to a
work-function mismatch [5, 6]. The ABS form when the discrete QD levels are
proximity coupled to the superconducting contact. Due to the low density of
states of graphene and the sensitivity of the QD levels to an applied gate
voltage, the ABS spectra are narrow, can be tuned to zero energy via gate
voltage, and show a striking pattern in transport measurements.Comment: 25 Pages, included SO
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