CU-63 NMR-STUDY OF THE SUPERCONDUCTING THIOSPINEL CU15RH1.5S4

The Cu-63 NMR Knight shift K and spin-lattice relaxation rate 1/T-1 ha ve been measured to study the thiospinel superconductor Cu1.5Rh1.5S4 f rom a microscopic viewpoint. K is negative and has a weak dependence o n temperature, and the hyperfine coupling constant H-hf(d) is estimate d to be -52.4 kOe/mu(B). 1/T-1 is proportional to the temperature in t he normal state. In the superconducting state, 1/T-1 takes a coherence peak just below T-c, and decreases exponentially well below T-c, from whose temperature dependence the superconducting energy gap has been proved to be close to 2 Delta = 3.52k(B)T(c) given by the BCS theory.