Investigation of Local Symmetries in the Hidden-Order Phase of URu2Si2

The local symmetry at the Ru(\(4d\)) and Si(\(4e\)) sites in URu2Si2 was investigated above and below the hidden-order temperature \(T_{\text{O}}=17.5\) K by measuring 101Ru-nuclear quadrupole resonance (NQR) and 99Ru-nuclear magnetic resonance (NMR) in single-crystalline samples and 73Ge-NMR in a 10%-73Ge-substituted polycrystalline sample. For both sites, no evidence of symmetry change below \(T_{\text{O}}\) was observed. The asymmetry parameter η of the electric field gradient, which reflects the local rotation symmetry, was estimated to be zero with accuracies of 0.0010–0.0015 and 0.05 for the \(4d\) and \(4e\) sites, respectively. The results suggest that the symmetry change at \(T_{\text{O}}\) is extremely small or intrinsically invisible by the present method.