Conductance oscillations at the interface between a superconductor and the helical edge channel in a narrow HgTe quantum well

TL;DR

This study observes conductance oscillations at the superconductor-helical edge interface in a narrow HgTe quantum well, revealing interference effects in a topological edge channel influenced by magnetic fields.

Contribution

It provides experimental evidence of conductance oscillations caused by interference in a superconductor-helical edge channel interface in HgTe quantum wells.

Findings

Oscillations occur only within the superconducting gap at low temperatures.

Oscillations are suppressed by magnetic fields perpendicular to the 2D plane.

Oscillation period is weakly affected by high in-plane magnetic fields.

Abstract

We experimentally investigate electron transport through the interface between a superconductor and the edge of a two-dimensional electron system with band inversion. The interface is realized as a tunnel NbN side contact to a narrow 8~nm HgTe quantum well. It demonstrates a typical Andreev behavior with finite conductance within the superconducting gap. Surprisingly, the conductance is modulated by a number of equally-spaced oscillations. The oscillations are present only within the superconducting gap and at lowest, below 1~K, temperatures. The oscillations disappear completely in magnetic fields, normal to the two-dimensional electron system plane. In contrast, the oscillations' period is only weakly affected by the highest, up to 14~T, in-plane oriented magnetic fields. We interpret this behavior as the interference oscillations in a helical one-dimensional edge channel due to a proximity with a superconductor.