Nonequilibrium spin-dependent phenomena in mesoscopic superconductor-normal metal tunnel structures

TL;DR

This paper investigates spin-dependent nonequilibrium transport in superconductor-normal metal hybrid structures, revealing large magnetoresistance and spin-polarized currents controllable by bias voltages and exchange field orientations.

Contribution

It introduces a detailed analysis of spin-dependent quasiparticle distributions and transport properties in superconductor-normal metal systems with exchange fields, highlighting their potential for spintronic applications.

Findings

Electric current depends strongly on the relative angle between exchange fields.

The system exhibits wide-range spin polarization of current.

Effective temperature of distributions is spin-dependent and sensitive to inelastic collisions.

Abstract

We analyze the broad range of spin-dependent nonequilibrium transport properties of hybrid systems composed of a normal region tunnel coupled to two superconductors with exchange fields induced by the proximity to thin ferromagnetic layers and highlight its functionalities. By calculating the quasiparticle distribution functions in the normal region we find that they are spin-dependent and strongly sensitive to the relative angle between exchange fields in the two superconductors. The impact of inelastic collisions on their properties is addressed. As a result, the electric current flowing through the system is found to be strongly dependent on the relative angle between exchange fields, giving rise to a huge value of magnetoresistance. Moreover, the current presents a complete spin-polarization in a wide range of bias voltages, even in the quasiequilibrium case. In the nonequilibrium limit we parametrize the distributions with an ``effective`` temperature, which turns out to be strongly spin-dependent, though quite sensitive to inelastic collisions. By tunnel coupling the normal region to an additional superconducting electrode we show that it is possible to implement a spin-polarized current source of both spin species, depending on the bias voltages applied.