Crossed conductance in FSF double junctions: role of out-of-equilibrium populations

TL;DR

This paper models FSF double junctions considering out-of-equilibrium quasiparticles, analyzing how geometry and residual states influence crossed conductance, revealing conditions where normal and superconducting phases exhibit similar behaviors.

Contribution

It introduces a model accounting for out-of-equilibrium quasiparticles and residual states, elucidating their effects on crossed conductance in FSF junctions with lateral contacts.

Findings

Crossed conductances are similar in normal and superconducting phases for small interface distances.

Sequential tunneling enables crossed current due to residual states within the superconducting gap.

Different signs of crossed current arise depending on magnetic alignment and tunneling processes.

Abstract

We discuss a model of Ferromagnet / Superconductor / Ferromagnet (FSF) double junction in which the quasiparticles are not in equilibrium with the condensate in a region of the superconductor containing the two FS contacts. The role of geometry is discussed, as well as the role of a small residual density of states within the superconducting gap, that allows a sequential tunneling crossed current. With elastic quasiparticle transport and the geometry with lateral contacts, the crossed conductances in the sequential tunneling channel are almost equal in the normal and superconducting phases, if the distance between the FS interfaces is sufficiently small. The sequential tunneling and spatially separated processes (the so-called crossed Andreev reflection and elastic cotunneling processes) lead to different signs of the crossed current in the antiparallel alignment for tunnel interfaces.