Theoretical prediction of rotating magnon wavepacket in ferromagnets

TL;DR

This paper theoretically predicts that magnon wavepackets in ferromagnets exhibit rotational motions caused by Berry phase effects, leading to corrections in the magnon Hall effect, with implications for classical spin waves.

Contribution

It introduces a theoretical framework showing rotational motions of magnons due to Berry curvature, distinct from electron cyclotron motion, and discusses their impact on magnon Hall effect.

Findings

Magnon wavepackets exhibit self-rotation and edge currents.

Rotational motions are caused by Berry phase, not Lorentz force.

Additional correction to magnon Hall effect is identified.

Abstract

We theoretically show that the magnon wavepacket has a rotational motion in two ways; a self-rotation and a motion along the boundary of the sample (edge current). They are similar to cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to Lorenz force. These rotational motions are caused by the Berry phase in momentum space from magnon band structure. Furthermore, these rotational motions of the magnon give an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.