Andreev reflection at the edge of a two-dimentional semimetal

TL;DR

This study explores electron transport at the interface of a superconductor and a 2D semimetal, revealing unique Andreev reflection phenomena and resistance anomalies specific to the 2D semimetal edge.

Contribution

It reports novel zero-bias resistance anomalies and subgap oscillations in Andreev reflection at a 2D semimetal edge, highlighting effects independent of the superconductor used.

Findings

Observation of zero-bias resistance anomaly

Detection of shallow subgap resistance oscillations with 1/n periodicity

Effects are specific to 2D semimetal edges, not dependent on superconductor material

Abstract

We investigate electron transport through the interface between a niobium superconductor and the edge of a two-dimensional semimetal, realized in a 20~nm wide HgTe quantum well. Experimentally, we observe that typical behavior of a single Andreev contact is complicated by both a pronounced zero-bias resistance anomaly and shallow subgap resistance oscillations with $1/n$ periodicity. These results are demonstrated to be independent of the superconducting material and should be regarded as specific to a 2D semimetal in a proximity with a superconductor. We interpret these effects to originate from the Andreev-like correlated process at the edge of a two-dimensional semimetal.