29Si NMR and hidden order in URu2Si2 -: art. no. 196402

Below T-N similar to 17 K the Si-29 NMR line in URu2Si2 exhibits a previously unobserved field-independent nearly isotropic contribution to the Linewidth, which increases to similar to 12 G as T --> 0. We argue that this feature does not arise from static freezing of the U-spin magnetization, but is due to coupling between Si-29 spins and a hidden order parameter. We discuss time-reversal symmetry-breaking orbital antiferromagnetism and indirect nuclear spin-spin interactions as possible coupling mechanisms. Further NMR experiments and theoretical calculations are suggested.