Long-range spin imbalance in mesoscopic superconductors under a Zeeman splitting

TL;DR

This paper presents a new theory explaining long-range spin relaxation in Zeeman-split superconductors, accounting for high relaxation lengths and their magnetic field dependence through a novel spin relaxation mechanism.

Contribution

It introduces a specific spin relaxation mechanism unique to Zeeman-split superconductors, explaining experimental observations of long spin relaxation lengths.

Findings

High spin relaxation lengths explained by the new mechanism.

Spin signal formed by spin-independent quasiparticle distribution.

Relaxation length determined by energy relaxation at the superconducting gap.

Abstract

We develop a theory of spin relaxation in Zeeman-splitted superconducting films at low temperatures. A new mechanism of spin relaxation, specific only for Zeeman-splitted superconductors is proposed. It can explain the extremely high spin relaxation lengths, experimentally observed in Zeeman-splitted superconductors, and their strong growth with the magnetic field. In the framework of this mechanism the observed spin signal is formed by the spin-independent nonequilibrium quasiparticle distribution weighted by the spin-split DOS. We demonstrate that the relaxation length of such a spin signal is determined by the energy relaxation length at energies of the order of the superconducting gap.