Phase Control in a Spin-Triplet SQUID

TL;DR

This paper experimentally verifies that a three-layer magnetic Josephson junction can exhibit a controllable phase shift, advancing understanding of spin-triplet supercurrents and enabling potential superconducting memory applications.

Contribution

It demonstrates the ground-state phase shift in a three-magnetic-layer Josephson junction with controllable magnetization orientations, confirming a key theoretical prediction.

Findings

Successful phase control via magnetic layer orientation

Verification of theoretical phase shift prediction

Potential for superconducting memory implementation

Abstract

It is now well established that a Josephson junction made from conventional spin-singlet superconductors containing ferromagnetic layers can carry spin-triplet supercurrent under certain conditions. The first experimental signature of that fact is the propagation of such supercurrent over long distances through strong ferromagnetic materials. Surprisingly, one of the most salient predictions of the theory has yet to be verified experimentally -- namely that a Josephson junction containing three magnetic layers with coplanar magnetizations should exhibit a ground-state phase shift of either zero or pi depending on the relative orientations of those magnetizations. Here we demonstrate this property using Josephson junctions containing three different types of magnetic layers, chosen so that the magnetization of one layer can be switched by 180 degrees without disturbing the other two. Phase-sensitive detection is accomplished using a superconducting quantum interference device, or SQUID. Such a phase-controllable junction could be used as the memory element in a fully-superconducting computer.