Superfluid-like spin transport in the dynamic states of easy-axis magnets

TL;DR

This paper demonstrates that superfluid-like spin transport can be achieved in easy-axis magnets through dynamic non-equilibrium states, expanding the range of materials capable of supporting such phenomena beyond easy-plane magnets.

Contribution

It introduces a method to realize superfluid-like spin transport in easy-axis magnets by inducing a non-equilibrium easy-cone state, broadening material options for spin transport applications.

Findings

Superfluid-like spin transport can occur in easy-axis magnets under non-equilibrium conditions.

Dynamic easy-cone states support spontaneous U(1) symmetry breaking.

Micromagnetic simulations confirm theoretical predictions.

Abstract

The existing proposals for superfluid-like spin transport have been based on easy-plane magnets where the U(1) spin-rotational symmetry is spontaneously broken in equilibrium, and this has been limiting material choices for realizing superfluid-like spin transport to restricted class of magnets. In this work, we lift this limitation by showing that superfluid-like spin transport can also be realized based on easy-axis magnets, where the U(1) spin-rotational symmetry is intact in equilibrium but can be broken in non-equilibrium. Specifically, we find the condition to engender a non-equilibrium easy-cone state by applying a spin torque to easy-axis magnets, which dynamically induces the spontaneous breaking of the U(1) spin-rotational symmetry and thereby can support superfluid-like spin transport. By exploiting this dynamic easy-cone state, we show theoretically that superfluid-like spin transport can be achieved in easy-axis magnets under suitable conditions and confirmed the prediction by micromagnetic simulations. We envision that our work broadens material library for realizing superfluid-like spin transport, showing the potential utility of dynamic states of magnets as venue to look for spin-transport phenomena that do not occur in static magnetic backgrounds.