Andreev current and subgap conductance of spin-valve SFF structures

TL;DR

This paper investigates how the Andreev current and subgap conductance behave in superconductor/insulator/ferromagnet structures with complex magnetic configurations, revealing that features depend on an effective magnetic field in multi-domain ferromagnets.

Contribution

It extends previous work by analyzing the effects of arbitrary magnetization directions in ferromagnetic layers on Andreev current and conductance, introducing the concept of an effective magnetic field.

Findings

Features like current enhancement and conductance peaks occur at the effective field value.

The effective field is an average over the decay length in multi-domain ferromagnets.

The study briefly discusses heat transport and electron cooling in these structures.

Abstract

The Andreev current and the subgap conductance in a superconductor/ insulator/ ferromagnet (SIF) structure in the presence of a small spin-splitting field show novel interesting features (A. Ozaeta et al., Phys. Rev. B 86, 060509(R), 2012). For example, the Andreev current at zero temperature can be enhanced by a spin-splitting field h, smaller than the superconducting gap, as has been recently reported by the authors. Also at finite temperatures the Andreev current has a peak for values of the spin-splitting field close to the superconducting gap. Finally, the differential subgap conductance at low temperatures shows a peak at the bias voltage eV = h. In this paper we investigate the Andreev current and the subgap conductance in SFF structures with arbitrary direction of magnetization of the F layers. We show that all aforementioned features occur now at the value of the "effective field", which is the field acting on the Cooper pairs in the multi-domain ferromagnetic region, averaged over the decay length of the superconducting condensate into a ferromagnet. We also briefly discuss the heat transport and electron cooling in the considered structures.