Gaps in Topological Magnon Spectra: Intrinsic vs. Extrinsic Effects

Abstract

For topological magnon spectra, determining and explaining the presence of a gap at a magnon crossing point is a key to characterize the topological properties of the system. An inelastic neutron scattering study of a single crystal is a powerful experimental technique that is widely employed to probe the magnetic excitation spectra of topological materials. Here, we show that when the scattering intensity rapidly disperses in the vicinity of a crossing point, such as a Dirac point, the apparent topological gap size is extremely sensitive to experimental conditions including sample mosaic, resolution, and momentum integration range. We demonstrate these effects using comprehensive neutron-scattering measurements of CrCl${}_3$. Our measurements confirm the gapless nature of the Dirac magnon in CrCl${}_3$, but also reveal an artificial, i.e. extrinsic, magnon gap unless the momentum integration range is carefully controlled. Our study provides an explanation of the apparent discrepancies between spectroscopic and first-principles estimates of Dirac magnon gap sizes, and provides guidelines for accurate spectroscopic measurement of topological magnon gaps.

6 pages and 4 figures

References in corpus (7)

• Mantid - Data Analysis and Visualization Package for Neutron Scattering and $\mu SR$ Experiments
• Dirac magnons in honeycomb ferromagnets
• Relativistic exchange interactions in CrX${}_3$ (X=Cl, Br, I) monolayers
• Magnetic field effect on topological spin excitations in CrI${}_3$
• Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr${}_3$
• Massless Dirac magnons in the two dimensional van der Waals honeycomb magnet CrCl3
• Neutron Scattering Signatures of Magnon Weyl Points

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• Determining Kitaev interaction in spin-$S$ honeycomb Mott insulators
• Self-selecting vapor growth of transition metal halide single crystals
• Thermal Hall effect in a van der Waals ferromagnet CrI3
• Sizable suppression of magnon Hall effect by magnon damping in Cr${}_2$Ge${}_2$Te${}_6$
• Phonons and phase symmetries in bulk $CrC{l}_3$ from scattering measurements and theory
• First-principles study of the gap in the spin excitation spectrum of the CrI${}_3$ honeycomb ferromagnet
• Kernel Polynomial Method for Linear Spin Wave Theory
• Long-lived Zone-boundary Magnons in an Antiferromagnet
• Topological Magnetic Phases and Magnon-Phonon Hybridization in the Presence of Strong Dzyaloshinskii-Moriya Interaction
• Angular-Dependent Thermal Hall Effect in a Honeycomb Magnet: Disentangling Kitaev and Dzyaloshinskii-Moriya Interactions
• Spin-orbit coupling controlled two-dimensional magnetism in chromium trihalides
• Sizable Ligand-Mediated Bond-Dependent Interactions in a Spin-1 Triangular Antiferromagnet NiI${}_2$