Odd-parity electronic multipolar ordering in URu_2Si_2: Conclusions from Si and Ru NMR measurements

摘要

We report ~(29)Si and ~(101)Ru NMR measurements on high-quality, single-crystal URu_2Si_2 samples with a residual resistivity ratio RRR ~ 70. Our results show that the Si and Ru sites exhibit fourfold electronic symmetry around the c axis in the hidden-order state. A previously observed twofold contribution of Si NMR linewidth is concluded to be due to extrinsic magnetic centers. Since the U and Si sites are aligned along the c axis, we conclude further that the electronic state shows fourfold symmetry around the U site below the hidden-order transition. From this observed local symmetry, possible space groups for the hidden-order state are P_4nc or I4/m. based on group theoretical considerations. Since the order vector is considered to be Q = (001). the hidden-order state is then found to be P4nc with rank 5 odd parity, i.e.. electric dotriacontapolar order.