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We discuss my recent joint work between theory and experiments on the equilateral triangular-lattice Heisenberg antiferromagnet (TLHAF) Ba3CoSb2O9 with effective S = 1/2 magnetic moments. The materials is an ideal realization of TLHAF with small exchange anisotropy, a fairly good two-dimensionality, and the high-symmetric crystal structure essentially precluding Dzyaloshinskii-Moriya interactions. We focus on the spin dynamics in the 1/3 magnetization plateau phase [1] and also in zero field [2]. We show that nonlinear spin wave theory reproduces the experiments in the plateau phase, thereby allowing us to determine model parameters. However, spin wave theory cannot explain intrinsic features in the spectrum in zero field, such as the magnon-line broadening throughout the Brillouin zone and the high-intensity continuum at high frequencies, even though the ground state is the conventional 120-degree structure. Finally, we also discuss our alternative theoretical approach, the 1/N expansion for the ordered phase, to study the zero-field spin dynamics under the strong influence of quantum fluctuations [3].
References:
[1] J. Ma et al., Phys. Rev. Lett. 116, 087201 (2016)
[2] Y. Kamiya et al., Nature Comm. 9, 2666 (2018)
[3] E. A. Ghioldi et al., Phys. Rev. B 98, 184403 (2018)
Yoshi Kamiya obtained his Ph.D. in ISSP, University of Tokyo, in 2011. From 2011 to 2014, he was in Los Alamos National Laboratory as a postdoc with Cristian Batista. He was back to Japan from 2014 to November in 2018 as a special postdoctoral researcher at RIKEN with Akira Furusaki. Very recently, he just jointed Shanghai Jiao Tong University as an assistant professor in December 2018. He is an expert in various numerical techniques especially in the quantum Monte Carlo simulation. He also uses analytical methods such as spin wave theory and 1/N expansion. His research interests include spin liquids, multiferroics, exotic spin textures (such as skyrmion and vortex crystals), and development of novel Monte Carlo techniques. He also has many collaborations with experimentalists working in the field of frustrated magnetism.