Induced superconductivity in the three-dimensional topological insulator HgTe

TL;DR

This study demonstrates proximity-induced superconductivity in the surface states of a three-dimensional topological insulator HgTe using Josephson junctions, revealing Josephson effect precursors in topological surface states.

Contribution

First experimental observation of proximity-induced superconductivity and Josephson effect signatures in HgTe topological insulator surface states.

Findings

Zero-bias anomaly indicating superconductivity in surface states

Fraunhofer-like oscillations confirming Josephson effect precursors

Low interface transparency still supports induced superconductivity

Abstract

A strained and undoped HgTe layer is a three-dimensional topological insulator, in which electronic transport occurs dominantly through its surface states. In this Letter, we present transport measurements on HgTe-based Josephson junctions with Nb as superconductor. Although the Nb-HgTe interfaces have a low transparency, we observe a strong zero-bias anomaly in the differential resistance measurements. This anomaly originates from proximity-induced superconductivity in the HgTe surface states. In the most transparent junction, we observe periodic oscillations of the differential resistance as function of an applied magnetic field, which correspond to a Fraunhofer-like pattern. This unambiguously shows that a precursor of the Josephson effect occurs in the topological surface states of HgTe.