Thermally Driven Ratchet Motion of Skyrmion Microcrystal and Topological Magnon Hall Effect

By means of the Lorentz TEM, we have found that micron-sized crystals of topologically nontrivial spin textures so called skyrmions in thin specimens of MnSi and Cu2OSeO3 show unidirectional rotations. Our numerical simulation based on a stochastic Landau-Lifshitz-Gilbert equation demonstrates that these rotations are driven sheerly by thermal fluctuations in the presence of temperature gradient. We show that hidden behind the skyrmion rotation is the rotational flow of magnons deflected by the effective magnetic field of skyrmions.