Hidden order and disorder effects in URu2Si2

NMR experiments at ambient pressure in URu2Si2 demonstrate a linewidth enhancement effect below the hidden order transition temperature T-0. We present single-crystal Si-29 NMR parameters for various temperatures and for an applied magnetic field perpendicular to the crystal c-axis. By comparing oriented-powder and single-crystal data, we observe that the size of the linewidth enhancement below T-0 correlates with the size of the high-T broadening. We measure a Si-29 up-field line shift below T-0 which indicates the presence of an internal-field average for the entire crystal. This shift also correlates with the high-temperature width. The Ru-101 NQR frequency as a function of temperature was also measured. No strong effect on the NQR frequency is observed at T-0. Both NMR and NQR measurements suggest a connection between linewidth/disorder effects and the transition to hidden order. (c) 2006 Elsevier B.V. All rights reserved.