Seminar : Designing topological antiferro-magnons

[Title]

Designing topological antiferro-magnons

[Speaker]

Prof. Chisa Hotta - University of Tokyo

Ph. D (2002) in University of Tokyo. 
2.5 years of postdoc fellow in Riken, 
3.5 years of research associate in Aoyama Gakuin University, 
2007-2014, associate prof. in Kyoto Sango University, 
2014- present, associate Prof. in the University of Tokyo. 

[Abstract]

Antiferromagnetic insulators can be a very rich playground for designing topological transports. However, to see how and when such things happen is not really straightforward. For example, on a square lattice, the conventional U(1) gauges are wiped out by the lattice symmetry, and the thermal Hall effect was not expected until we find a SU(2) thermal Hall effect of topological antiferromagnons[1]. We introduce the pseudo-spin picture: two species of magnons belonging to different sublattices take care of the up/down degrees of freedom. This allows us to exactly reformulate the 4x4 Bololiubov-de-Gennes equation of antiferromagnons to the typical pseudo-spin-orbit coupling term[2]. This generalized treatment allows us to discover rich spin textures easily. We show some examples of rich moment-spin textures in a square lattice Rashba-Dressehaus model and Kane-Mele model with Dzyaloshinskii-Moriya interaction (an analogue of spin-orbit interaction), and also a quite unconventional one in a Kitaev-Heisenberg -Gamma model[2,3]. 

[1] M. Kawano, C. Hotta, Phys. Rev. B 99, 054422 (2019) 
[2] M. Kawano, C. Hotta, Phys. Rev. B 100, 174402 (2019)
[3]M. Kawano, Y. Onose, C. Hotta, Communications Physics 2, 27 (2019). 

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