The Josephson Effect in Single Spin Superconductors

TL;DR

This paper develops a theoretical framework for the Josephson effect in single spin superconductors, proposing unique signatures that could help identify this unobserved state in half-metallic antiferromagnets.

Contribution

It introduces a detailed theory of Josephson effects specific to single spin superconductors, highlighting their unique tunneling properties and potential for experimental detection.

Findings

Josephson effect depends on the relative orientation of order parameters.

No current flows between SSS and s-wave BCS systems due to symmetry mismatch.

Tunneling can serve as a probe for triplet order parameters in materials.

Abstract

The Josephson Effect provides a primary signature of single spin superconductivity (SSS), the as yet unobserved superconducting state which was proposed recently as a low temperature phase of half-metallic antiferromagnets. These materials are insulating in the spin-down channel but are metallic in the spin-up channel. The SSS state is characterized by a unique form of p-wave pairing within a single spin channel. We develop the theory of a rich variety of Josephson effects that arise due to the form of the SSS order parameter. Tunneling is allowed at a SSS-SSS' junction but of course depends on the relative orientation of their order parameters. No current flows between an SSS and an s-wave BCS system due to their orthogonal symmetries, which potentially can be used to distinguish SSS from other superconducting states. Single spin superconductors also offer a means to probe other materials, where tunneling is a litmus test for any form of ``triplet'' order parameter.