Universal spin wave damping in magnetic Weyl semimetals

TL;DR

This paper demonstrates that spin wave decay in magnetic Weyl semimetals follows a universal pattern dependent on frequency, momentum, and Weyl spectrum parameters, with implications for probing electronic structures via neutron scattering.

Contribution

It introduces a universal decay law for spin waves in magnetic Weyl semimetals and shows how spin wave measurements can reveal details of the Weyl spectrum.

Findings

Spin wave decay rate depends universally on frequency and momentum.

Weyl electrons do not contribute to Gilbert damping.

Spin wave analysis can infer Weyl Fermi pocket characteristics.

Abstract

We analyze the decay of spin waves into Stoner excitations in magnetic Weyl semimetals. The lifetime of a mode is found to have a universal dependence on its frequency and momentum, and on a few parameters that characterize the relativistic Weyl spectrum. At the same time, Gilbert damping by Weyl electrons is absent. The decay rate of spin waves is calculated perturbatively using the s-d model of itinerant Weyl or Dirac electrons coupled to local moments. We show that many details of the Weyl spectrum, such as the momentum-space locations, dispersions and sizes of the Weyl Fermi pockets, can be deduced indirectly by probing the spin waves of local moments using inelastic neutron scattering.