Andreev reflection in the fractional quantum Hall state

TL;DR

This paper demonstrates high CAR probabilities in graphene-based fqH-superconductor devices, revealing filling-dependent behaviors and potential for topological superconducting phases.

Contribution

It reports the first observation of crossed Andreev reflection in fractional quantum Hall states with graphene and NbN, highlighting new spin-orbit effects and device capabilities.

Findings

Higher CAR in fractional fillings compared to integer fillings

CAR probability depends strongly on temperature and magnetic field

Filling-independent CAR in integer fillings due to spin-orbit coupling

Abstract

We construct high-quality graphene-based van der Waals devices with narrow superconducting niobium nitride (NbN) electrodes, in which superconductivity and robust fqH coexist. We find crossed Andreev reflection (CAR) across the superconductor separating two fqH edges. Our observed CAR probabilities in the particle-like fractional fillings are markedly higher than those in the integer and hole-conjugate fractional fillings and depend strongly on temperature and magnetic field unlike the other fillings. Further, we find a filling-independent CAR probability in integer fillings, which we attribute to spin-orbit coupling in NbN allowing for Andreev reflection between spin-polarized edges. These results provide a route to realize novel topological superconducting phases in fqH-superconductor hybrid devices based on graphene and NbN.