Mechanisms of Andreev reflection in quantum Hall graphene

Abstract

We perform realistic simulations of a hybrid superconductor-graphene device in the quantum Hall regime to indentify the origin of downstream resistance oscillations in a recent experiment [Zhao et. al. Nature Physics 16, (2020)]. A comparison between the simulations and the experimental data suggests that disorderinduced intervalley scattering at the normal-superconductor (NS) interface can be the dominant cause of oscillations. We also show conductance oscillations due to additional edge states on clean interfaces with Fermi level mismatch. However, the regular pattern as a function of external parameters is not visible in the presence of disorder. Our work provides a way to qualitatively probe the quality of NS interfaces on multiterminal quantum Hall devices.

Disorder in Andreev reflection of a quantum Hall edge

“…Robust Andreev reflection, being enabled by disorder, is naturally sensitive to its realization in a sample. As a result, the charge transport varies stochastically with control parameters such as the magnetic field or the electron density, as is observed both in experiment [11] and in numerical simulation [14].…”

Effects of the geometry on the downstream conductance in quantum Hall-superconductor hybrid systems

“…This stimulated further theoretical research. A suppression of the measured signal may be explained by the absorption of quasiparticles in the superconductor, for example by subgap states in nearby vortices [14,[18][19][20], whereas the oscillations may be strongly affected by disorder [18,19].…”