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**Field theory of a hexagonal antiferromagnet with 3 sublattices**

Sayak Dasgupta, John’s Hopkins University, Department of Physics

We present a classical field theory of magnetization dynamics in a generic 3-sublattice antiferromagnet in 2 spatial dimensions exemplified by the Heisenberg model on the triangular [1] and kagome [2] lattices. In a ground state, spins from the 3 sublattices are coplanar and at angles of 120° to one another such that ** S**_{1}+**S**_{2}+**S**_{3}=0. The six normal modes, shown in Fig. 1, either keep the spins in this plane (the a modes) or take them out of the plane (the b modes). The soft modes b* _{x}*, b

The 3 Goldstone modes can be grouped into the trivial singlet a_{0} and the irreducible doublet **b **= (b* _{x}*, b

[1] A. V. Chubukov, S. Sachdev, and T. Senthil, “Large-*S* expansion for quantum antiferromagnets on a triangular lattice,” J. Phys.: Condens. Matter **6**, 8891 (1999).

[2] A. B. Harris, C. Kallin, and A. J. Berlinsky, “Possible Néel orderings of the Kagomé antiferromagnet,” Phys. Rev. B **45**, 2899 (1992).

[3] S. Nakatsuji, N. Kiyohara, and T. Higo, “Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature,” Nature **527**, 212 (2015).

[4] Y. Chen, J. Gaudet, S. Dasgupta, G. Marcus, J. Lin, Y. Zhao, W. C. Chen, M.B. Stone, O. Tchernyshyov, S. Nakatsuji, C. Broholm, “Antichiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn3Ge”, arXiv: 2001.09495.

Host: Shulei Zhang