Gaps in topological magnon spectra: Intrinsic versus extrinsic effects
Seung-Hwan Do, Joseph A. M. Paddison, Gabriele Sala, T. J. Williams, Koji Kaneko, Keitaro Kuwahara, Andrew F. May, Jiaqiang Yan, Michael A. McGuire, M. B. Stone, M. D. Lumsden, A. D. Christianson
Abstract
Using inelastic neutron scattering measurements of a high-quality single crystal of the prototype honeycomb-lattice ferromagnet CrCl${}_{3}$, the authors highlight critical issues in determining the sizes of topological gaps in magnon spectra. In particular, when the spin excitation spectrum contains a singularity such as a Dirac magnon crossing point, the measured spin-wave dispersion is extremely sensitive to experimental conditions such as sample mosaic, resolution, and data integration range. This work resolves an apparent dichotomy between measured and predicted gaps at Dirac crossing points, and provides guidelines for accurate measurement of magnon gap sizes in candidate materials for magnon spintronics applications.