Spin injection from a normal metal into a mesoscopic superconductor

TL;DR

This study demonstrates spin injection into a superconductor from both ferromagnetic and normal-metal contacts, revealing a long spin relaxation length that increases with magnetic field, independent of temperature.

Contribution

It shows that normal-metal contacts can inject spin imbalance into superconductors, and uses combined detection methods to distinguish charge and spin effects.

Findings

Spin imbalance is created by normal-metal injectors.

Spin relaxation length is several micrometers and increases with magnetic field.

Charge and spin imbalances can be completely separated.

Abstract

We report on nonlocal transport in superconductor hybrid structures, with ferromagnetic as well as normal-metal tunnel junctions attached to the superconductor. In the presence of a strong Zeeman splitting of the density of states, both charge and spin imbalance is injected into the superconductor. While previous experiments demonstrated spin injection from ferromagnetic electrodes, we show that spin imbalance is also created for normal-metal injector contacts. Using the combination of ferromagnetic and normal-metal detectors allows us to directly discriminate between charge and spin injection, and demonstrate a complete separation of charge and spin imbalance. The relaxation length of the spin imbalance is of the order of several $\mu$m and is found to increase with a magnetic field, but is independent of temperature. We further discuss possible relaxation mechanisms for the explanation of the spin relaxation length.