Interfacial spin-orbit coupling in superconducting hybrid systems

TL;DR

This paper develops a theoretical framework to analyze interfacial spin-orbit coupling effects in superconducting hybrid systems, revealing how ISOC influences critical temperature and enables a superconducting diode effect.

Contribution

It introduces a symmetry-based nonlinear sigma model to derive boundary conditions for superconducting interfaces with ISOC, enabling analysis without microscopic details.

Findings

Critical temperature cannot be enhanced by an external magnetic field in these systems.

ISOC combined with magnetic fields can induce a superconducting diode effect.

The diode efficiency depends on the balance between spin-galvanic and spin relaxation effects.

Abstract

We investigate the effects of interfacial spin-orbit coupling (ISOC) on superconductors, focusing on its impact on electronic transport and spin-charge conversion. Using a symmetry-based nonlinear sigma model, we derive effective boundary conditions for the Usadel and Maxwell equations that account for the spin-galvanic effect, spin relaxation, and spin precession. This approach allows for the analysis of various interfaces without relying on specific microscopic models. We apply these boundary conditions to derive ISOC-induced terms in the Ginzburg-Landau functional, which is then used to compute the critical temperature of superconducting films with ISOC subjected to an external magnetic field. Our findings show that, contrary to a recent prediction, the critical temperature of a film cannot be enhanced by an external magnetic field. Additionally, we demonstrate that the combination of ISOC and an external magnetic field leads to a superconducting diode effect. Its efficiency strongly depends on the interplay between the spin-galvanic and the spin relaxation terms. Our results provide a framework for understanding ISOC in superconducting systems and highlight the potential for optimizing diode efficiency through careful interface engineering.