Perturbative Analysis of the Field-Free Josephson Diode Effect in a Multilayered Josephson Junction

TL;DR

This paper provides a theoretical analysis of the Josephson diode effect in multilayered junctions, revealing how spin-orbit interaction and exchange fields induce nonreciprocal supercurrents without external magnetic fields.

Contribution

It introduces analytical expressions for the Josephson current considering spin-triplet pairing and demonstrates the emergence of the diode effect in ferromagnetic-normal metal junctions with spin-orbit coupling.

Findings

JDE can occur without external magnetic fields.

Spin-triplet Cooper pairs dominate the supercurrent in the JDE regime.

JDE efficiency is tunable via normal metal thickness and RSOI strength.

Abstract

The Josephson diode effect (JDE) is a novel phenomenon in which a superconducting junction exhibits asymmetric Josephson currents with respect to the superconducting phase difference. In this study, we theoretically investigate how the interplay between a static exchange field and Rashba spin-orbit interaction (RSOI) influences the JDE. By employing the quasiclassical Green's function method and perturbative calculations, we derive analytical expressions for the Josephson current in a junction composed of a ferromagnetic layer and a normal metal with RSOI. Remarkably, the JDE is found to emerge even in the absence of any external magnetic field. In this regime, the Josephson current is exclusively carried by spin-triplet Cooper pairs, as spin-singlet components are strongly suppressed by the ferromagnet. Furthermore, our results show that the efficiency of the JDE can be enhanced by tuning the thickness of the normal metal and the strength of the RSOI. These findings offer valuable theoretical guidelines for the design of superconducting devices exhibiting nonreciprocal transport effects.