Multipole order and global/site symmetry in the hidden-order phase of URu2 Si2

On the basis of group theory and first-principles calculations, we investigate high-rank multipole orderings in URu2Si2, which have been proposed as a genuine primary order parameter in the hidden-order phase below 17.5 K. We apply Shubnikov group theory to the multipole ordered states characterized by the wave vector Q0=(0,0,1) and specify the global/site symmetry and the secondary order parameters, such as induced dipole moments and change in charge distribution. We find that such antiferroic magnetic multipole orderings are particularly advantageous to conceal the primary order parameter due to preserving high symmetry in charge distribution. Experimental observations of the induced low-rank multipoles, which are explicitly classified in this paper, will be key pieces to understand the puzzling hidden-order phase.