Tunable pure spin supercurrents and the demonstration of a superconducting spin-wave device

TL;DR

This paper demonstrates a tunable pure spin supercurrent in a superconducting structure, showing control over spin transport via spin-orbit coupling and magnetization, and introduces a prototype superconducting spin-wave device.

Contribution

It reveals the role of spin-orbit coupling in generating and controlling pure spin supercurrents in superconducting structures, and demonstrates a prototype superconducting spin-wave device.

Findings

Pure spin supercurrent pumping efficiency is tunable by magnetization direction.

Rashba spin-orbit coupling is essential for transmitting pure spin supercurrents.

A prototype superconducting spin-wave device with gate-controlled spin propagation is demonstrated.

Abstract

Recent ferromagnetic resonance experiments and theory of Pt/Nb/Ni8Fe2 proximity-coupled structures strongly suggest that spin-orbit coupling (SOC) in Pt in conjunction with a magnetic exchange field in Ni8Fe2 are the essential ingredients to generate a pure spin supercurrent channel in Nb. Here, by substituting Pt for a perpendicularly magnetized Pt/Co/Pt spin-sink, we are able to demonstrate the role of SOC, and show that pure spin supercurrent pumping efficiency across Nb is tunable by controlling the magnetization direction of Co. By inserting a Cu spacer with weak SOC between Nb and Pt/(Co/Pt) spin-sink, we also prove that Rashba type SOC is key for forming and transmitting pure spin supercurrents across Nb. Finally, by engineering these properties within a single multilayer structure, we demonstrate a prototype superconducting spin-wave (SW) device in which lateral SW propagation is gateable via the opening or closing of a vertical pure spin supercurrent channel in Nb.