Andreev drag effect in ferromagnetic-normal-superconducting systems

TL;DR

This paper explores how Andreev reflection causes current drag and positive current correlations in a ferromagnetic-normal-superconducting system, influenced by lead polarization, conductance, and spin-flip scattering.

Contribution

It provides a detailed analysis of Andreev drag effects and current correlations in a multi-terminal ferromagnetic-superconductor setup, including conditions for positive correlations.

Findings

Current injection from one ferromagnet can induce current in another via Andreev reflection.

Positive current correlations can occur even with spin relaxation.

Conditions for Andreev drag depend on polarization, conductance, and spin-flip scattering.

Abstract

We investigate conductances and current correlations in a system consisting of a normal multichannel conductor connected to one superconducting and two ferromagnetic electrodes. For antiparallel orientation of the ferromagnet polarizations, current injection from one ferromagnet can, due to Andreev reflection, lead to a net drag of current from the second ferromagnet toward the superconductor. We present the conditions for the Andreev drag in terms of the degree of lead polarizations, contact conductances and spin-flip scattering. Remarkably, both equilibrium and nonequilibrium zero-frequency current correlations between the ferromagnets become positive even in the presence of spin relaxation.