Controlling superconducting spin flow with spin-flip immunity using a single homogeneous ferromagnet

TL;DR

This paper demonstrates a novel method to generate non-decaying spin supercurrents using a single homogeneous ferromagnet, enabling dissipationless spin transport and independent control of spin and charge flows in superconducting spintronics.

Contribution

It introduces a new approach to produce spin supercurrents with no decay using only a homogeneous ferromagnet, bypassing the need for complex multilayers or magnetic disorder.

Findings

Spin supercurrent does not decay spatially in the proposed setup.

Superconductivity-mediated torque exists without magnetic inhomogeneities.

Different components of spin polarization respond differently to phase changes.

Abstract

Spin transport via electrons is typically plagued by Joule heating and short decay lengths due to spin-flip scattering. It is known that dissipationless spin currents can arise when using conventional superconducting contacts, yet this has only been experimentally demonstrated when using intricate magnetically inhomogeneous multilayers, or in extreme cases such as half-metals with interfacial magnetic disorder. Moreover, it is unknown how such spin supercurrents decay in the presence of spin-flip scattering. Here, we present a method for generating a spin supercurrent by using only a single homogeneous magnetic element. Remarkably, the spin supercurrent generated in this way does not decay spatially, in stark contrast to normal spin currents that remain polarized only up to the spin relaxation length. We also expose the existence of a superconductivity-mediated torque even without magnetic inhomogeneities, showing that the different components of the spin supercurrent polarization respond fundamentally differently to a change in the superconducting phase difference. This establishes a mechanism for tuning dissipationless spin and charge flow separately, and confirms the advantage that superconductors can offer in spintronics.