Effects of spin-orbit interaction on superconductor-ferromagnet heterostructures: spontaneous electric and spin surface currents

TL;DR

This paper demonstrates that spin-orbit interaction in superconductor-ferromagnet heterostructures induces spontaneous surface electric and spin currents below the superconducting transition temperature, driven by Andreev surface states.

Contribution

It reveals the joint effect of spin-orbit interaction and exchange field in generating spontaneous surface currents in superconductor-ferromagnet heterostructures.

Findings

Spontaneous spin and electric surface currents occur below T_c.

Currents are carried by Andreev surface states.

Conditions for electric and spin currents differ significantly.

Abstract

We find proximity-induced spontaneous spin and electric surface currents, at all temperatures below the superconducting T_c, in an isotropic s-wave superconductor deposited with a thin ferromagnetic metal layer with spin-orbit interaction. The currents are carried by Andreev surface states and generated as a joint effect of the spin-orbit interaction and the exchange field. The background spin current arises in the thin layer due to different local spin polarizations of electrons and holes, which have almost opposite velocities in each of the surface states. The spontaneous surface electric current in the superconductor originates in asymmetry of Andreev states with respect to sign reversal of the momentum component parallel to the surface. Conditions for electric and spin currents to show up in the system, significantly differ from each other.