Pumping of spin supercurrent in unitary triplet superconductors

TL;DR

This paper introduces a novel mechanism for generating dissipationless spin supercurrents in triplet superconductors through magnetization dynamics, expanding the potential for spintronics applications beyond conventional methods.

Contribution

It proposes a general principle for spin supercurrent generation in triplet superconductors and suggests an efficient implementation involving magnetization dynamics.

Findings

Spin torque proportional to the triplet order parameter converts particle spin to Cooper pair spin.

Efficient spin supercurrent generation possible even without equilibrium spin polarization.

The method surpasses traditional electron spin pumping by leveraging particle-hole symmetry.

Abstract

One efficient mechanism for generating a charge supercurrent is Andreev reflection, in which the electric current injected from a normal metal into a conventional superconductor is converted into a supercurrent, thereby preserving charge conservation. We here propose a general principle for generating spin supercurrents in triplet superconductors by analogy with such charge transport, i.e., assuming spin conservation. We find a spin torque that is proportional to the triplet superconducting order parameter and, in the spin-conservation scenario, converts the particle spin to that of Cooper pairs. Based on this general principle, we propose an implementation to efficiently generate a spin supercurrent in unitary triplet superconductors, even though Cooper pairs carry no spin polarization at equilibrium, by the magnetization dynamics ${\bf M}(t)$ of a proximity magnetic nanostructure. The efficiency of this spin pumping is not solely limited to the $d{\bf M}/dt\times {\bf M}$ due to the emergent particle-hole symmetry, thereby going beyond the conventional spin pumping of electrons. This general principle provides an efficient approach to generating and manipulating dissipationless spin currents in many unconventional superconductors.