Spin relaxation in mesoscopic superconducting Al wires

TL;DR

This study investigates how polarized quasiparticle spins diffuse and relax in mesoscopic superconducting Al wires, revealing temperature-dependent spin relaxation behavior influenced by quasiparticle condensation.

Contribution

It provides experimental insights into spin relaxation mechanisms in superconducting Al wires, highlighting the temperature dependence and enhanced relaxation in the superconducting state.

Findings

Spin diffusion length is nearly temperature independent below the transition.

Spin relaxation is more effective in the superconducting state.

Spin diffusion length increases as the transition temperature is approached.

Abstract

We studied the diffusion and the relaxation of the polarized quasiparticle spins in superconductors. To that end, quasiparticles of polarized spins were injected through an interface of a mesoscopic superconducting Al wire in proximity contact with an overlaid ferromagnetic Co wire in the single-domain state. The superconductivity was observed to be suppressed near the spin-injecting interface, as evidenced by the occurrence of a finite voltage for a bias current below the onset of the superconducting transition. The spin diffusion length, estimated from finite voltages over a certain length of Al wire near the interface, was almost temperature independent in the temperature range sufficiently below the superconducting transition but grew as the transition temperature was approached. This temperature dependence suggests that the relaxation of the spin polarization in the superconducting state is governed by the condensation of quasiparticles to the paired state. The spin relaxation in the superconducting state turned out to be more effective than in the normal state.