$4\pi$-periodic supercurrent tuned by an axial magnetic flux in topological insulator nanowires

TL;DR

This paper investigates how an axial magnetic flux can tune topological superconductivity in topological insulator nanowires, revealing a transition from trivial to topological supercurrent behavior at certain magnetic fields.

Contribution

It demonstrates the magnetic flux dependence of the $4 extpi$-periodic supercurrent, indicating a transition to topological superconductivity in TI nanowire-based Josephson junctions.

Findings

$4 extpi$-periodic supercurrent appears at higher magnetic fields.

Supercurrent transition occurs around half a flux quantum.

Trivial supercurrent dominates at lower magnetic fields.

Abstract

Topological insulator (TI) nanowires in proximity with conventional superconductors have been proposed as a tunable platform to realize topological superconductivity and Majorana zero modes (MZM). The tuning is done using an axial magnetic flux $\Phi$ which allows transforming the system from trivial at $\Phi=0$ to topologically nontrivial when half a magnetic flux quantum $\Phi_0/2$ threads the wire's cross-section. Here we explore the expected topological transition in TI-wire-based Josephson junctions as a function of magnetic flux by probing the $4\pi$-periodic fraction of the supercurrent, which is considered as an indicator of topological superconductivity. Our data suggest that this $4\pi$-periodic supercurrent is at lower magnetic field largely of trivial origin, but that at magnetic fields above $\sim\Phi_{0}/4$ topological $4\pi$-periodic supercurrents take over.