We present new 29-Si NMR spectra in URu2Si2 for varying temperature T, and external field H. On lowering T, the systematics of the low-field lineshape and width reveal an extra component (lambda) to the linewidth below T_N ~ 17 K not observed previously. We find that lambda is magnetic-field independent and dominates the low-field lineshape for all orientations of H with respect to the tetragonal c axis. The behavior of lambda indicates a direct relationship between the 29-Si spin and the transition at T_N, but it is inconsistent with a coupling of the nuclei to static antiferromagnetic order/disorder of the U-spin magnetization. This leads us to conjecture that lambda is due to a coupling of 29-Si to the system's hidden-order parameter. A possible coupling mechanism involving charge degrees of freedom and indirect nuclear spin/spin interactions is proposed. We also propose further experiments to test for the existence of this coupling mechanism.
@article{arxiv.cond-mat/0106479,
title = {29-Si NMR and Hidden Order in URu2Si2},
author = {O. O. Bernal and C. Rodrigues and A. Martinez and H. G. Lukefahr and D. E. MacLaughlin and A. A. Menovsky and J. A. Mydosh},
journal= {arXiv preprint arXiv:cond-mat/0106479},
year = {2009}
}