# Out-of-Equilibrium Spin Transport in Mesoscopic Superconductors

## TL;DR

This paper reviews how spin transport occurs in mesoscopic superconductors, highlighting experimental techniques, quasiparticle spin dynamics, and the impact of out-of-equilibrium conditions on superconducting properties.

## Contribution

It provides a comprehensive review of recent experiments on spin injection and out-of-equilibrium spin phenomena in mesoscopic superconductors, emphasizing the role of Zeeman splitting.

## Key findings

- Quasiparticle spin transport can be controlled via Zeeman splitting.
- Out-of-equilibrium spin imbalances affect the superconducting gap.
- Spin dynamics influence superconducting properties in mesoscopic systems.

## Abstract

The excitations in conventional superconductors, Bogoliubov quasiparticles, are spin-1/2 fermions but their charge is energy-dependent and, in fact, zero at the gap edge. Therefore, in superconductors (unlike normal metals) the spin and charge degrees of freedom may be separated. In this article, we review spin injection into conventional superconductors and focus on recent experiments on mesoscopic superconductors. We show how quasiparticle spin transport and out-of-equilibrium spin dependent superconductivity can be triggered using the Zeeman splitting of the quasiparticle density of states in thin-film superconductors with small spin-mixing scattering. Finally, we address the spin dynamics and the feedback of quasiparticle spin imbalances on the strength of the superconducting energy gap.