Spin-dependent Cooper Pair Phase and Pure Spin Supercurrents in Strongly Polarized Ferromagnets

TL;DR

This paper explores how spin-dependent phases in superconductor-ferromagnet heterostructures enable tunable pure spin supercurrents and reveal unique Josephson effects influenced by spin polarization.

Contribution

It demonstrates the emergence of a relative phase between superconducting amplitudes in spin bands and introduces a method to generate and control pure spin supercurrents in strongly polarized ferromagnets.

Findings

Pure spin supercurrents can be achieved in strongly polarized ferromagnets.

Josephson junctions are most effective at a spin polarization of around 0.3.

Critical currents differ for positive and negative bias due to phase effects.

Abstract

We study heterostructures of singlet superconductors (SC) and strongly spin-polarized ferromagnets (sFM) and show that a relative phase arises between the superconducting proximity amplitudes in the two ferromagnetic spin bands. We find a tunable pure spin supercurrent in a sFM contacted with only one SC electrode. We show that Josephson junctions are most effective for a spin polarization $P\sim 0.3$, and that critical currents for positive and negative bias differ for a high transmission Josephson junction, due to a relative phase between single and double pair transmission.