Tunable superconducting diode effect in a topological nano-SQUID

TL;DR

This paper demonstrates a large, tunable superconducting diode effect in a topological insulator nanowire-based Josephson junction, indicating the emergence of topological superconductivity, with potential for advanced quantum devices.

Contribution

It reports the first observation of a highly tunable superconducting diode effect in a topological insulator nanowire device, linking it to topological superconductivity.

Findings

Diode efficiency η reaches 0.3 under magnetic field.

The diode effect is tunable by magnetic field and back-gate voltage.

The effect indicates the emergence of topological superconductivity.

Abstract

A Josephson diode passes current with zero resistance in one direction but is resistive in the other direction. While such an effect has been observed in several platforms, a large and tunable Josephson diode effect has been rare. Here we report that a simple device consisting of a topological-insulator (TI) nanowire side-contacted by superconductors to form a lateral Josephson junction presents a large diode effect with the efficiency $\eta$ reaching 0.3 when a parallel magnetic field $B_{||}$ is applied. Interestingly, the sign and the magnitude of $\eta$ is tunable not only by $B_{||}$ but also by the back-gate voltage. This diode effect can be understood by modeling the system as a nano-SQUID, in which the top and bottom surfaces of the TI nanowire each form a line junction and $B_{||}$ creates a magnetic flux to thread the SQUID loop. This model further shows that the observed diode effect marks the emergence of topological superconductivity in TI-nanowire-based Josephson junction.