We report the $^{ 75}$As-NQR and NMR studies on the iron arsenide superconductor Li$_{ x}$FeAs with $T_{ \rm c} \sim 17$ K. The spin lattice relaxation rate, $1/T_{ 1}$, decreases below $T_{ \rm c}$ without a coherence peak, and can be fitted by gaps with s$^{ \pm}$-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 $T \leq 50 K$. Estimate of the Korringa ratio shows that the spin correlations are weaker than that in other families of iron arsenides, which may account for the lower $T_{ \rm c}$ in this material.
Categories: cond-mat.supr-con