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

References in corpus (11)

• Doping graphene with metal contacts
• Quantum interference and Klein tunneling in graphene heterojunctions
• Specular Andreev reflection in graphene
• Evidence of the role of contacts on the observed electron-hole asymmetry in graphene
• Quantum dots in graphene
• Klein Backscattering and Fabry-Perot Interference in Graphene Heterojunctions
• Josephson Current and Multiple Andreev Reflections in Graphene SNS Junctions
• Tunneling conductance of graphene NIS junctions
• Even-odd effect in Andreev Transport through a Carbon Nanotube Quantum Dot
• 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

Cited by in corpus (6)

• Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices
• Mutation of Andreev into Majorana bound states in long NS and SNS junctions
• Visualizing landscapes of the superconducting gap in heterogeneous superconductor thin films: geometric influences on proximity effects
• Transport Measurement of Andreev Bound States in a Kondo-Correlated Quantum Dot
• Zero-bias conductance peak and Josephson effect in graphene-NbTiN junctions
• Renormalization effects in interacting quantum dots coupled to superconducting leads