75As NQR and NMR Studies of Superconductivity and Electron Correlations in Iron Arsenide LiFeAs

We report the 75 As-NQR and NMR studies on the iron arsenide superconductor LiFeAs with T c ∼17 K. The spin lattice relaxation rate, 1/ T 1 , decreases below T c without a coherence peak, and can be fitted by gaps with s ± -wave symmetry in the presence of impurity scattering. In the normal state, both 1/ T 1 T and the Knight shift decrease with decreasing temperature but become constant below T ≤50 K. Estimate of the Korringa ratio shows that the spin correlations are weaker than those in other families of iron arsenides, which may account for the lower T c in this material.