Minigap suppression in S(N/F)S junctions

TL;DR

This paper analyzes how inhomogeneity-induced depairing in a diffusive S(N/F)S junction suppresses the minigap in the density of states, providing an effective 1D model and experimental suggestions.

Contribution

It introduces an effective 1D Usadel equation for S(N/F)S junctions that accounts for inhomogeneity-induced depairing, highlighting its impact on the minigap.

Findings

Depairing suppresses the minigap in the density of states.

The effective 1D theory matches numerical solutions.

Experimental methods to observe the effect are proposed.

Abstract

We consider a long diffusive Josephson junction where the weak link is a thin normal metal (N) - ferromagnetic (F) bilayer (N and F form parallel links between the superconductors (S)). We show that superconductivity in the weak link can be described by an effective one-dimensional Usadel equation containing a "diluted" exchange field as well as a weak depairing term that is caused by the inherent inhomogeneity of the bilayer. The depairing mechanism distinguishes the S(N/F)S system from an SFS junction and affects the density of states of the S(N/F)S junction. It results in the suppression of the minigap in the spin-resolved density of states. The depairing rate and the minigap are expressed in terms of geometrical parameters, the Thouless energy and the effective exchange field. The effective one-dimensional theory can be applied to various structures with thin inhomogenous links and shows good agreement with numerical solutions of the original two-dimensional equations. We also discuss ways to reveal the predicted effect experimentally.