Nuclear quadrupole resonance study of heavy fermion superconductors

By using nuclear quadrupole resonance (NQR), nuclear spin-lattice relaxation rate 1/T-1 of the heavy fermion superconductors (URu2Si2, UPd2Al3, CeRu2) has been measured. The NQR measurement requires no external field, and is especially suitable for Pd-105 and Ru-101, which have very small nuclear gyromagnetic ratios and large electric quadrupole moments. In URu2Si2 and UPd2Al3, the absence of the Hebel-Slichter coherence peak just below the superconducting transition temperature T-C and the power law temperature dependence (T-3) in the superconducting state has shown appearance of anisotropic non-s-wave superconductivity. On the contrary, an exponential temperature dependence of 1/T-1 was observed in CeRu2, indicating the superconductivity to be conventional s-wave.