Supercurrent reversal in ferromagnetic hybrid nanowire Josephson junctions

TL;DR

This study demonstrates supercurrent reversal in ferromagnetic hybrid nanowire Josephson junctions, showing a switch between 0 and π phases driven by magnetic domain flipping, without external magnetic fields.

Contribution

It provides experimental evidence of supercurrent phase switching in ferromagnetic nanowire junctions and offers a qualitative theory linking exchange fields to supercurrent reversal.

Findings

Abrupt 0-π phase switch observed within the superconducting window.

Supercurrent reversal driven by EuS domain flipping.

Both phases achievable at zero external magnetic field.

Abstract

We report supercurrent transport measurements in hybrid Josephson junctions comprised of semiconducting InAs nanowires with epitaxial ferromagnetic insulator EuS and superconducting Al coatings. The wires display a hysteretic superconducting window close to the coercivity, away from zero external magnetic field. Using a multi-interferometer setup, we measure the current-phase relation of multiple magnetic junctions and find an abrupt switch between $\pi$ and 0 phases within the superconducting window. We attribute the 0-$\pi$ transition to the discrete flipping of the EuS domains and provide a qualitative theory showing that a sizable exchange field can polarize the junction and lead to the supercurrent reversal. Both $0$ and $\pi$ phases can be realized at zero external field by demagnetizing the wire.