Magnonic Weyl states in copper-oxo-selenite

The multiferroic compound Cu₂OSeO₃ is well known as a host of skyrmion-lattice phases, i.e. regular arrangements of topologically nontrivial spin vortices. Now, it turned out that its magnetic excitation spectrum also possesses topological properties. By a comparison of inelastic neutron scattering measurements with spin-dynamical calculations that take into account Dzyaloshinskii-Moriya interactions, the authors prove the existence of at least two pairs of magnonic Weyl points in the spin-wave spectrum. This opens the way to exploring the physics of intertwined complex direct-space and magnonic topologies. Calculations of the thermal Hall conductivity, based on these results, predict experimentally measurable signatures in the thermal transport properties of Cu₂OSeO₃ that could serve as an independent confirmation for the existence of the Weyl magnon modes. The paper also illustrates the close relationship between the position of the Weyl nodes in reciprocal space and the direction of the Dzyaloshinskii-Moriya vectors in direct space, offering a way to the accurate estimation of such interactions from the neutron-spectroscopy data.

L. Zhang, Y. A. Onykiienko, P. M. Buhl, Y. V. Tymoshenko, P. Čermák, A. Schneidewind, J. R. Stewart, A. Henschel, M. Schmidt, S. Blügel, D. S. Inosov, Y. Mokrousov, Magnonic Weyl states in Cu₂OSeO₃, Phys. Rev. Research 2, 013063 (2020) (arXiv)