Damped Dirac magnon in a metallic kagome antiferromagnet FeSn

TL;DR

This study investigates topological spin excitations in the metallic kagome magnet FeSn, revealing a damped Dirac magnon influenced by itinerant electrons, through inelastic neutron scattering and spin wave theory.

Contribution

It provides the first detailed experimental and theoretical analysis of Dirac magnons in a metallic kagome antiferromagnet, highlighting the impact of itinerant carriers on topological spin excitations.

Findings

Observation of well-defined spin waves up to 120 meV.

Identification of a damped Dirac magnon at the K-point.

Interaction of spin waves with the Stoner continuum.

Abstract

The kagome lattice is a fertile platform to explore topological excitations with both Fermi-Dirac and Bose-Einstein statistics. While relativistic Dirac Fermions and flat-bands have been discovered in the electronic structure of kagome metals, the spin excitations have received less attention. Here we report inelastic neutron scattering studies of the prototypical kagome magnetic metal FeSn. The spectra display well-defined spin waves extending up to 120 meV. Above this energy, the spin waves become progressively broadened, reflecting interactions with the Stoner continuum. Using linear spin wave theory, we determine an effective spin Hamiltonian that reproduces the measured dispersion. This analysis indicates that the Dirac magnon at the K-point remarkably occurs on the brink of a region where well-defined spin waves become unobservable. Our results emphasize the influential role of itinerant carriers on the topological spin excitations of metallic kagome magnets.