Dynamics of spin transport in voltage-biased Josephson junctions

TL;DR

This paper explores how spin transport behaves in voltage-biased Josephson junctions with ferromagnetic interfaces, revealing complex voltage-dependent effects and control mechanisms for spin currents.

Contribution

It provides a detailed analysis of the nonlinear voltage dependence of spin currents in spin-active Josephson junctions, highlighting the effects of spin mixing and multiple Andreev reflections.

Findings

Spin current exhibits sub-harmonic gap structure sensitive to spin mixing.

Pronounced even-odd effect in spin transport during multiple Andreev reflections.

Strong spin mixing allows voltage-controlled manipulation of spin current magnitude and direction.

Abstract

We investigate spin transport in voltage-biased spin-active Josephson junctions. The interplay of spin filtering, spin mixing, and multiple Andreev reflection leads to nonlinear voltage dependence of the dc and ac spin current. We compute the voltage characteristics of the spin current (I_S) for superconductor-ferromagnet-superconductor (SFS) Josephson junctions. The sub-harmonic gap structure of I_S(V) is shown to be sensitive to the degree of spin mixing generated by the ferromagnetic interface, and exhibits a pronounced even-odd effect associated with spin transport during multiple Andreev reflection processes. For strong spin mixing both the magnitude and the direction of the dc spin current can be sensitively controlled by the bias voltage.