Spin-split conductance and subgap peak in ferromagnet/superconductor spin valve heterostructures

TL;DR

This paper investigates the spin-dependent conductance in ferromagnet/superconductor spin valve heterostructures, revealing a spin-split subgap conductance peak influenced by ferromagnetic layer thickness and interface scattering, with implications for superconducting spin valves.

Contribution

It introduces a detailed numerical and analytical study of spin-split conductance and subgap peaks in F/S heterostructures, highlighting the effects of layer thickness and interface scattering.

Findings

Spin-split conductance exhibits a prominent subgap peak.

The subgap peak depends periodically on ferromagnetic layer thickness.

A strong angular valve effect on subgap conductance is observed.

Abstract

We consider the separate spin channel contributions to the charge conductance in superconducting/ferromagnetic spin valve $F_1/N/F_2/S$ structures. We find that the up- and down-spin conductance contributions may have a very different behavior in the subgap bias region (i.e. there is a spin-split conductance). This leads to a subgap %EM2 added spin-split conductance peak in the total conductance. This peak behavior, which can be prominent also in $N/F/S$ systems, is strongly dependent, in a periodic way, on the thickness of the intermediate ferromagnetic layer. We study this phenomenon using a numerical self consistent method, with additional insights gained from an approximate analytic calculation for an infinite $N/F/S$ structure. We study also the angular dependence on the relative magnetization angle between $F_1$ and $F_2$ of both the spin-split and the total conductance. We do so for realistic material parameters and layer thicknesses relevant to experimental studies on these devices. We also find that the spin-split conductance is highly dependent on the interfacial scattering in these devices, and we carefully include these effects for realistic systems. A strong valve-effect is found for the angularly dependent subgap peak conductance that is largely independent on the scattering and may prove useful in actual realizations of a superconducting spin valve device.