Transport Through Andreev Bound States in a Graphene Quantum Dot

Abstract

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.

25 Pages, included SOM

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• Specular Andreev reflection in graphene
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• Josephson Current and Multiple Andreev Reflections in Graphene SNS Junctions
• Self-consistent description of Andreev bound states in Josephson quantum dot devices
• Tunneling conductance of graphene NIS junctions
• Andreev Level Qubit
• Even-odd effect in Andreev Transport through a Carbon Nanotube Quantum Dot
• Quantum transport through a graphene nanoribbon-superconductor junction
• Tuning the proximity effect in a superconductor-graphene-superconductor junction
• Non-equilibrium Tunneling Spectroscopy in Carbon Nanotubes
• Dynamics and phonon-induced decoherence of Andreev level qubit
• Reentrance effect in a graphene n-p-n junction coupled to a superconductor
• Spectrum of Andreev Bound States in a Molecule Embedded Inside a Microwave-Excited Superconducting Junction
• Superconducting Tunneling Spectroscopy of a Carbon Nanotube Quantum Dot

Cited by in corpus (90)

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