Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

TL;DR

This paper investigates ballistic graphene Josephson junctions, revealing quantum oscillations in critical current, high-field proximity effects, and mesoscopic Andreev states, expanding understanding of superconductivity in graphene.

Contribution

It demonstrates the existence of high-field superconducting proximity effects and quantum oscillations in ballistic graphene junctions, highlighting new regimes controlled by quantum confinement.

Findings

Pronounced Fabry-Pérot oscillations in resistance and critical current.

Superconducting proximity persists above 1 T magnetic field.

Supercurrent capacity approaches the quantum limit.

Abstract

Graphene-based Josephson junctions provide a novel platform for studying the proximity effect due to graphene's unique electronic spectrum and the possibility to tune junction properties by gate voltage. Here we describe graphene junctions with a mean free path of several micrometres, low contact resistance and large supercurrents. Such devices exhibit pronounced Fabry-P\'erot oscillations not only in the normal-state resistance but also in the critical current. The proximity effect is mostly suppressed in magnetic fields below 10mT, showing the conventional Fraunhofer pattern. Unexpectedly, some proximity survives even in fields higher than 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each of them exhibits a supercurrent carrying capacity close to the universal quantum limit. We attribute the high-field Josephson effect to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.