Existence of line nodes in the superconducting energy gap of antiferromagnetic superconductor URu2Si2-Ru-101 NQR study

We have carried out Ru-101 NQR measurements of URu2Si2 in zero magnetic field in the temperature, T, range from 0.16 K to 26 K. From the NQR spectrum, the electric quadrupole interaction parameters were determined to be nu(Q) =5.72 MHz and eta =0. The nuclear spin-lattice relaxation rate, 1/T-1, decreases drastically below 17.5 K. This decrease is associated with antiferromagnetic ordering. In the superconducting state, 1/T-1 has no coherence peak just below T-c=1.2 K, and decreases in proportion to T-3 With no deviation down to 0.2 K, which indicates the existence of line nodes in the superconducting energy gap.