Universal spin superconducting diode effect from spin-orbit coupling

TL;DR

This paper introduces a universal spin superconducting diode effect caused by spin-orbit coupling, demonstrating that spin supercurrents in opposite directions are unequal, with theoretical analysis and numerical examples supporting its existence.

Contribution

The paper presents the first unified theoretical framework for spin and charge superconducting diode effects induced by spin-orbit coupling, supported by numerical simulations.

Findings

Spin SDE arises from opposite phase gradients of Cooper pairs due to SOC.

Both toy model and practical nanowire exhibit spin SDE.

Proposes experimental methods for detecting spin SDE.

Abstract

We propose a universal spin superconducting diode effect (SDE) induced by spin-orbit coupling (SOC), where the critical spin supercurrents in opposite directions are unequal. By analysis from both the Ginzburg-Landau theory and energy band analysis, we show that the spin-$\uparrow \uparrow$ and spin-$\downarrow \downarrow$ Cooper pairs possess opposite phase gradients and opposite momenta from the SOC, which leads to the spin SDE. Two superconductors with SOC, a $p$-wave superconductor as a toy model and a practical superconducting nanowire, are numerically studied and they both exhibit spin SDE. In addition, our theory also provides a unified picture for both spin and charge SDEs. Besides, we propose spin-polarized detection and nonlocal spin transport, as mature experimental technologies, to confirm the spin SDE in superconducting nanowires.