Quantum-geometric spin and charge Josephson diode effects

TL;DR

This paper introduces a quantum-geometric phase-based mechanism for achieving large charge and spin Josephson diode effects in spin-polarized superconductor-ferromagnet structures with noncoplanar spin textures, enabling high efficiency and controllable supercurrents.

Contribution

It presents a novel quantum-geometric framework for Josephson diode effects in noncoplanar spin textures, including necessary conditions, numerical results, and a practical SQUID device for spin current control.

Findings

Achieves up to 100% spin-diode efficiency.

Demonstrates controllable switching of supercurrents via flux reversal.

Provides numerical results for disordered materials relevant to applications.

Abstract

We present a general mechanism for large charge and spin Josephson diode effects in strongly spin-polarized superconductor-ferromagnet hybrid structures with a noncoplanar spin texture, formulated in terms of quantum-geometric phases. We present necessary conditions for this effect to occur, and show numerical results for disordered materials, relevant for applications. We calculate Josephson diode efficiencies for both charge- and spin-diodes and show that a spin-diode efficiency of 100% can be reached. Finally, we present a SQUID device that can switch between nearly pure spin-up and spin-down equal-spin supercurrents across the ferromagnet by reversing the flux. These findings establish functionalities that are absent for coplanar spin textures.