Topological Superconductivity in a Phase-Controlled Josephson Junction

TL;DR

This paper demonstrates a tunable two-dimensional topological superconductor using a HgTe quantum well Josephson junction, showing signatures of Majorana states through tunneling conductance measurements under magnetic fields.

Contribution

It introduces a novel experimental platform for topological superconductivity in 2D, controllable via phase difference and magnetic field, advancing scalable Majorana mode research.

Findings

Zero-bias conductance peaks emerge at higher magnetic fields.

Tunneling spectra evolve with magnetic field, indicating topological transition.

Numerical simulations support experimental observations.

Abstract

Topological superconductors can support localized Majorana states at their boundaries. These quasi-particle excitations have non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner. While signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scalable to large numbers of states. Here we present a novel experimental approach towards a two-dimensional architecture. Using a Josephson junction made of HgTe quantum well coupled to thin-film aluminum, we are able to tune between a trivial and a topological superconducting state by controlling the phase difference $\phi$ across the junction and applying an in-plane magnetic field. We determine the topological state of the induced superconductor by measuring the tunneling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunneling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunneling conductance develops a zero-bias peak which persists over a range of $\phi$ that expands systematically with increasing magnetic fields. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and will therefore open new avenues for probing topological superconducting phases in two-dimensional systems.