Itinerant magnetic multipole moments of rank five as the hidden order in URu(2)Si(2)

Phys Rev Lett. 2009 Sep 4;103(10):107202. doi: 10.1103/PhysRevLett.103.107202. Epub 2009 Sep 1.

Abstract

A broken symmetry ground state without any magnetic moments has been calculated by means of the local-density approximation to density functional theory plus a local exchange term, the so-called LDA+U approach, for URu(2)Si(2). The solution is analyzed in terms of a multipole tensor expansion of the itinerant density matrix and is found to be a nontrivial magnetic multipole. Analysis and further calculations show that this type of multipole enters naturally in time reversal breaking in the presence of large effective spin-orbit coupling and coexists with magnetic moments for most magnetic actinides.