Proximity effect gaps in S/N/FI structures

TL;DR

This paper investigates how ferromagnetic insulators influence the density of states in superconductor-normal-ferromagnetic insulator structures, revealing a suppression mechanism similar to magnetic impurities, using Usadel equations.

Contribution

It provides a detailed analysis of the proximity effect and gap suppression in S/N/FI structures, highlighting the dual role of ferromagnets.

Findings

Ferromagnets shift the density of states.

Ferromagnets suppress the superconducting gap.

Suppression mechanism resembles magnetic impurity effects.

Abstract

We study the proximity effect in hybrid structures consisting of superconductor and ferromagnetic insulator separated by a normal diffusive metal (S/N/FI structures). These stuctures were proposed to realize the absolute spin-valve effect. We pay special attention to the gaps in the density of states of the normal part. We show that the effect of the ferromagnet is twofold: It not only shifts the density of states but also provides suppression of the gap. The mechanism of this suppression is remarkably similar to that due to magnetic impurities. Our results are obtained from the solution of one-dimensional Usadel equation supplemented with boundary conditions for matrix current at both interfaces.