Quasiparticle conductance in Spin Valve Josephson Structures

TL;DR

This paper investigates quasiparticle conductance in ferromagnetic Josephson structures, revealing resonance peaks and oscillations influenced by layer thickness and magnetic misalignment, with implications for spin Josephson device fabrication.

Contribution

It introduces a fully self-consistent numerical method combined with an analytic approach to analyze conductance features in ferromagnetic Josephson structures, highlighting resonance phenomena and oscillatory behavior.

Findings

Resonance peaks depend on intermediate layer thickness and misalignment angle.

Multiple subgap conductance peaks oscillate with bias, layer thickness, and angle.

Results inform the design of spin Josephson devices.

Abstract

We study the quasiparticle current in clean ferromagnetic Josephson structures of the form $S_1/F_1/N/F_2/S_2$, where $S$, $F$, and $N$ denote superconducting, ferromagnetic or normal layers respectively. Our focus is on the structure of the conductance $G$ as a function of bias $V$, emphasizing the subgap region. We use a fully self consistent numerical method, coupled to a transfer matrix procedure to extract $G(V)$. We choose material parameters appropriate to experimentally realized Co Cu Nb structures. We find a resonance peak structure as a function of the intermediate layer thickness and of the misalignement angle $\phi$ between $F$ layers. To understand this resonance structure, we develop an approximate analytic method. For experimentally relevant thicknesses, the conductance has multiple subgap peaks which oscillate in position between low and critical bias positions. These oscillations occur in both $\phi$ and the layer thicknesses. We compare our results with those obtained for the spin valve structures $(F_1/N/F_2/S_2)$ and discuss the implications of our results for the fabrication of spin Josephson devices.