Sign of the crossed conductances at a FSF double interface

TL;DR

This paper investigates how local Andreev reflections influence crossed conductance in FSF structures, explaining experimental signs through a detailed analysis of transmission and reflection channels.

Contribution

It provides a refined theoretical model that incorporates local Andreev reflections, improving understanding of crossed conductance sign in FSF structures.

Findings

Local Andreev reflections significantly modify crossed conductance.

The model explains experimental signs of crossed resistances.

Both multiterminal and planar interface models are analyzed.

Abstract

Crossed conductance in hybrid Ferromagnet / Superconductor / Ferromagnet (FSF) structures results from the competition between normal transmission and Andreev reflection channels. Crossed Andreev reflection (CAR) and elastic cotunneling (EC) between the ferromagnets are dressed by local Andreev reflections, which play an important role for transparent enough interfaces and intermediate spin polarizations. This modifies the simple result previously obtained at lowest order, and can explain the sign of the crossed resistances in a recent experiment [D. Beckmann {\sl et al.}, cond-mat/0404360]. This holds both in the multiterminal hybrid structure model (where phase averaging over the Fermi oscillations is introduced ``by hand'' within the approximation of a single non local process) and for infinite planar interfaces (where phase averaging naturally results in the microscopic solution with multiple non local processes).