Topological Weyl magnons and thermal Hall effect in layered honeycomb ferromagnets

We study the topological properties and magnon Hall effect of a 3D ferromagnet in the ABC stacked honeycomb lattice, relevant to the recent inelastic neutron scattering study of CrI3 [1]. We find that the magnon band structure and Chern numbers of the magnon branches are significantly affected by the interlayer coupling Jc, which moreover has a qualitatively different effect in the ABC stacking compared to the AA stacking case. Tuned by the ratio of the interlayer coupling Jc and the third-neighbour Heisenberg interaction J3, several gapless Weyl points appear, which separate the non-equivalent Chern insulating phases. We further show that the topological character of magnon bands results in non-zero thermal Hall conductivity, whose sign and magnitude depend on Jc and the intra-layer couplings. Since the interlayer coupling strength Jc can be easily tuned by applying pressure to the quasi-2D material such as CrI3, this provides a potential route to tuning the magnon thermal Hall effect in an experiment.

[1] L. Chen, J.-H. Chung, B. Gao, T. Chen, M. B. Stone,A. I. Kolesnikov, Q. Huang, and P. Dai, Phys. Rev. X8, 041028 (2018)