⁷⁵As NQR and NMR studies of superconductivity and electron correlations in iron arsenide LiₓFeAs

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We report the ⁷⁵As-NQR and NMR studies on the iron arsenide superconductor LiₓFeAs with T c 17 K. The spin lattice relaxation rate, 1/T₁, 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/T₁T 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 that in other families of iron arsenides, which may account for the lower T c in this material.