Magnon Dispersion and Anisotropies in SrCu$_2$(BO$_3$)$_2$
  We study the dispersion of the magnons (triplet states) in SrCu$_2$(BO$_3$)$_2$ including all symmetry-allowed Dzyaloshinskii-Moriya interactions. We can reduce the complexity of the general Hamiltonian to a new simpler form by appropriate rotations of the spin operators. The resulting Hamiltonian is studied by both perturbation theory and exact numerical diagonalization on a 32-site cluster. We argue that the dispersion is dominated by Dzyaloshinskii-Moriya interactions. We point out which combinations of these anisotropies affect the dispersion to linear-order, and extract their magnitudes. 
Y. F. Cheng, O. Cepas, P. W. Leung, and T. Ziman