Quantum Hall effect in graphene with superconducting electrodes

TL;DR

This paper demonstrates the coexistence of the integer quantum Hall effect with superconductivity in graphene devices with niobium electrodes, revealing enhanced conductance due to Andreev processes and edge states.

Contribution

It reports the first observation of quantum Hall effect coexisting with superconductivity in graphene with superconducting contacts, highlighting Andreev edge-states as a key mechanism.

Findings

Quantum Hall effect coexists with superconductivity below 4 Tesla.

Enhanced conductance on quantum Hall plateaus due to Andreev processes.

Dependence of enhancement on filling factor and Landau level.

Abstract

We have realized an integer quantum Hall system with superconducting contacts by connecting graphene to niobium electrodes. Below their upper critical field of 4 tesla, an integer quantum Hall effect coexists with superconductivity in the leads, but with a plateau conductance that is larger than in the normal state. We ascribe this enhanced quantum Hall plateau conductance to Andreev processes at the graphene-superconductor interface leading to the formation of so-called Andreev edge-states. The enhancement depends strongly on the filling-factor, and is less pronounced on the first plateau, due to the special nature of the zero energy Landau level in monolayer graphene.