Nonlocal spin correlations mediated by a superconductor

TL;DR

This paper explores how pure spin currents can be nonlocally transmitted through a superconductor, highlighting the roles of crossed Andreev reflection and elastic cotunneling in mediating spin correlations.

Contribution

It investigates nonlocal spin correlations mediated by a superconductor, focusing on the distinct behavior of spin currents compared to charge currents and the combined effects of CAR and EC.

Findings

Spin currents from CAR and EC add due to superconductor's inability to sustain net spin current.

Nonlocal spin correlations can be mediated over distances comparable to the superconducting coherence length.

The study provides insights into spin transport mechanisms in superconductor-normal metal systems.

Abstract

Nonlocal charge correlations induced in two normal metals contacted separately to a supercon- ductor have been studied intensively in the past few years. Here we investigate nonlocal correlations induced by the transfer of pure spin currents through a superconductor on a scale comparable to the superconducting coherence length. As with charge currents, two processes contribute to the nonlocal spin signal: crossed Andreev reflection (CAR), where an electron with spin up injected from one normal metal into the superconductor results in a hole with spin down being injected into the second normal metal, and elastic cotunneling (EC), where the electron with spin up injected from the first normal metal results in an electron with spin up being injected into the second normal metal. Unlike charge currents, however, the spin currents associated with CAR and EC add due to the fact that the bulk superconductor cannot sustain a net spin current.