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arXiv · 2204.11355

Thermal Evolution of Dirac Magnons in the Honeycomb Ferromagnet CrBr$_3$

S. E. Nikitin·B. Fåk·K. W. Krämer·T. Fennell·B. Normand·A. M. Läuchli·Ch. Rüegg
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Abstract

CrBr$_3$ is an excellent realization of the two-dimensional honeycomb ferromagnet, which offers a bosonic equivalent of graphene with Dirac magnons and topological character. We perform inelastic neutron scattering (INS) measurements using state-of-the-art instrumentation to update 50-year-old data, thereby enabling a definitive comparison both with recent experimental claims of a significant gap at the Dirac point and with theoretical predictions for thermal magnon renormalization. We demonstrate that CrBr$_3$ has next-neighbor $J_2$ and $J_3$ interactions approximately 5\% of $J_1$, an ideal Dirac magnon dispersion at the K point, and the associated signature of isospin winding. The magnon lifetime and the thermal band renormalization show the universal $T^2$ evolution expected from an interacting spin-wave treatment, but the measured dispersion lacks the predicted van Hove features, highlighting the need for a deeper theoretical analysis.

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S. E. Nikitin, B. Fåk, K. W. Krämer, T. Fennell, B. Normand, A. M. Läuchli, Ch. Rüegg. 2022-04-24. Thermal Evolution of Dirac Magnons in the Honeycomb Ferromagnet CrBr$_3$. https://doi.org/10.1103/physrevlett.129.127201

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