Spin-wave chirality and its manifestations in antiferromagnets

TL;DR

This paper demonstrates that magnetic spin systems can exhibit chirality effects similar to optical systems, with spin-wave chirality density linked to asymmetries in energy absorption, and proposes spin current injection as a symmetry-breaking mechanism.

Contribution

It introduces the concept of spin-wave chirality density in antiferromagnets and establishes a formal analogy with optical chirality, proposing a new way to control magnetic chirality.

Findings

Spin-wave chirality density is proportional to local energy absorption asymmetry.

Injection of spin current induces a nonequilibrium spin-wave chirality density.

Theoretical framework connects spin current effects with chiral symmetry breaking.

Abstract

As first demonstrated by Tang and Cohen in chiral optics, the asymmetry in the rate of electromagnetic energy absorption between left and right enantiomers is determined by an optical chirality density [1]. Here, we demonstrate that this effect can exist in magnetic spin systems. By constructing a formal analogy with electrodynamics, we show that in antiferromagnets with broken chiral symmetry the asymmetry in local spin-wave energy absorption is proportional to a spin-wave chirality density, which is a direct counterpart of optical zilch. We propose that injection of a pure spin current into an antiferromagnet may serve as a chiral symmetry breaking mechanism, since its effect in the spin-wave approximation can be expressed in terms of additional Lifshitz invariants. We use linear response theory to show that the spin current induces a nonequilibrium spin-wave chirality density.