Long-range spin-polarized quasiparticle transport in mesoscopic Al superconductors with a Zeeman splitting

TL;DR

This paper demonstrates long-range spin-polarized quasiparticle transport in mesoscopic aluminum superconductors under Zeeman splitting, revealing relaxation lengths exceeding typical scales and suggesting a quasiparticle recombination mechanism.

Contribution

It provides experimental evidence of extended spin transport distances in superconductors with Zeeman splitting and proposes a new understanding of the relaxation length mechanism.

Findings

Spin transport over several micrometers observed.

Relaxation length increases linearly with magnetic field.

Recombination length likely governs spin relaxation.

Abstract

We report on nonlocal transport in multiterminal superconductor-ferromagnet structures, which were fabricated by means of e-beam lithography and shadow evaporation techniques. In the presence of a significant Zeeman splitting of the quasiparticle states, we find signatures of spin transport over distances of several {\mu}m, exceeding other length scales such as the coherence length, the normal-state spin-diffusion length, and the charge-imbalance length. The relaxation length of the spin signal shows a nearly linear increase with magnetic field, hinting at a freeze-out of relaxation by the Zeeman splitting. We propose that the relaxation length is given by the recombination length of the quasiparticles rather than a renormalized spin-diffusion length.