Signatures of a topological phase transition in a planar Josephson junction

TL;DR

This study demonstrates signatures of a topological phase transition in a planar Josephson junction using an improved epitaxial heterostructure, with observable gap closing and zero-bias conductance peaks indicating potential topological states.

Contribution

The paper presents an experimental investigation of topological phase transition signatures in a planar Josephson junction with an improved design and integrated quantum point contacts.

Findings

Observation of superconducting gap closing and reopening.

Detection of zero-bias conductance peaks at certain conditions.

Differences in ZBCP characteristics at the two ends of the junction.

Abstract

A growing body of work suggests that planar Josephson junctions fabricated using superconducting hybrid materials provide a highly controllable route toward one-dimensional topological superconductivity. Among the experimental controls are in-plane magnetic field, phase difference across the junction, and carrier density set by electrostatic gate voltages. Here, we investigate planar Josephson junctions with an improved design based on an epitaxial InAs/Al heterostructure, embedded in a superconducting loop, probed with integrated quantum point contacts (QPCs) at both ends of the junction. For particular ranges of in-plane field and gate voltages, a closing and reopening of the superconducting gap is observed, along with a zero-bias conductance peak (ZBCP) that appears upon reopening of the gap. Consistency with a simple theoretical model supports the interpretation of a topological phase transition. While gap closings and reopenings generally occurred together at the two ends of the junction, the height, shape, and even presence of ZBCPs typically differed between the ends, presumably due to disorder and variation of couplings to local probes.