Mechanisms of Andreev reflection in quantum Hall graphene

TL;DR

This paper uses simulations to analyze Andreev reflection mechanisms in quantum Hall graphene, revealing that disorder at interfaces causes resistance oscillations, with implications for superconductor integration.

Contribution

It introduces a comprehensive simulation approach considering disorder and interface effects, clarifying the origin of resistance oscillations in quantum Hall graphene devices.

Findings

Disorder-induced scattering causes resistance oscillations.

Counter-propagating states arise from interface density mismatch.

Lattice-matched superconductors are needed for ballistic effects.

Abstract

We simulate a hybrid superconductor-graphene device in the quantum Hall regime to identify the origin of downstream resistance oscillations in a recent experiment [Zhao et. al. Nature Physics 16, (2020)]. In addition to the previously studied Mach-Zehnder interference between the valley-polarized edge states, we consider disorder-induced scattering, and the previously overlooked appearance of the counter-propagating states generated by the interface density mismatch. Comparing our results with the experiment, we conclude that the observed oscillations are induced by the interfacial disorder, and that lattice-matched superconductors are necessary to observe the alternative ballistic effects.