Superconducting proximity effect through graphene from zero field to the Quantum Hall regime

TL;DR

This study explores the superconducting proximity effect in graphene across various magnetic fields, revealing unique behaviors near charge neutrality and potential Cooper pair injection into edge states in the Quantum Hall regime.

Contribution

It demonstrates the first observation of specular Andreev reflection specific to graphene's Dirac band structure and investigates proximity effects in the Quantum Hall regime using high critical field superconductors.

Findings

Suppression of critical current near charge neutrality point.

Observation of interference effects suggestive of Cooper pair injection into edge states.

Zero resistance state achieved at low temperature and high doping.

Abstract

We investigate the superconducting proximity effect through graphene in the long diffusive junction limit, at low and high magnetic field. The interface quality and sample phase coherence lead to a zero resistance state at low temperature, zero magnetic field, and high doping. We find a striking suppression of the critical current near graphene\rq{}s charge neutrality point, which we attribute to specular reflexion of Andreev pairs at the interface of charge puddles. This type of reflexion, specific to the Dirac band structure, had up to now remained elusive. At high magnetic field the use of superconducting electrodes with high critical field enables the investigation of the proximity effect in the Quantum Hall regime. Although the supercurrent is not directly detectable in our two wire configuration, interference effects are visible which may be attributed to the injection of Cooper pairs into edge states.