The Josephson effect in single spin superconductors

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 anti ferro magnets. 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 as a result of 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.