NMR studies of layered nitride superconductors

Layered nitride superconductor, Li-0.48(THF)(y)HfNCl with T-c=25.5 K, was investigated by means of nuclear magnetic resonance (NMR). Li-7-, Cl-35-NMR studies clarified that the partial electron density of states at Fermi level at Li and Cl sites are negligibly small. From the N-15 NMR Knight shift studies, the spin susceptibility decreases toward zero below T,, evidencing that the pairing symmetry is an even-parity spin-singlet. These results indicate that superconductivity is derived from the HfN layer. We also measured N-15-, Li-7-NMR spin-lattice relaxation rate in the temperature range of 4.2K - 100 K and observed the enhancement of the spin-lattice relaxation rate, 1/T-1, by field fluctuations generated by the vortex dynamics.