Spin diffusion equation in superconductors in the vicinity of Tc

TL;DR

This paper derives the spin diffusion equation near the superconducting transition temperature, revealing enhancements in spin relaxation time and diffusion length below Tc, which explains recent experimental observations.

Contribution

It provides a microscopic derivation of the spin diffusion equation in superconductors near Tc, showing how spin transport properties are renormalized in the superconducting state.

Findings

Spin relaxation time increases below Tc

Spin diffusion coefficient increases below Tc

Enhanced spin diffusion length observed in superconductors

Abstract

We microscopically derive the spin diffusion equation in an s-wave superconductor in the vicinity of the superconducting transition temperature Tc. Applying the general relation between the relaxation function and the response function to the present spin diffusion problem, we examine how the spin relaxation time and the spin diffusion coefficient are renormalized in the superconducting state. The analysis reveals that, below Tc, both the spin relaxation time and the spin diffusion coefficient are increased, resulting in an enhancement of the spin diffusion length. The present result may provide an explanation for the recent observation of an enhanced spin pumping signal below Tc in a Py/Nb/Pt system that is free from the coherence peak effect.