Spin-orbit entangled magnetic dipoles, often referred to as pseudospins, provide a new avenue to explore novel magnetism inconceivable in the weak spin-orbit coupling limit, but the nature of their low-energy interactions remains to be understood. We present a comprehensive study of the static magnetism and low-energy pseudospin dynamics in the archetypal spin-orbit Mott insulator Sr2IrO4. We find that in order to understand even basic magnetization measurements, a formerly overlooked in-plane anisotropy is fundamental. In addition to magnetometry, we use neutron diffraction, inelastic neutron scattering and resonant elastic and inelastic x-ray scattering to identify and quantify the interactions that determine the global symmetry of the system and govern the linear responses of pseudospins to external magnetic felds and their low-energy dynamics. We find that a pseudospin-only Hamiltonian is insufficient for an accurate description of the magnetism in Sr2IrO4 and that pseudospin-lattice coupling is essential. This finding should be generally applicable to other pseudospin systems with sizable orbital moments sensitive to anisotropic crystalline environments.
@article{arxiv.1808.06920,
title = {Pseudospin-lattice coupling in the spin-orbit Mott insulator Sr2IrO4},
author = {J. Porras and J. Bertinshaw and H. Liu and G. Khaliullin and N. H. Sung and J. -W. Kim and S. Francoual and P. Steffens and G. Deng and M. Moretti Sala and A. Effimenko and A. Said and D. Casa and X. Huang and T. Gog and J. Kim and B. Keimer and B. J. Kim},
journal= {arXiv preprint arXiv:1808.06920},
year = {2019}
}