$^{75}$As NQR and NMR studies of superconductivity and electron correlations in iron arsenide Li$_{x}$FeAs

TL;DR

This study investigates the superconducting properties and electron correlations in Li$_{x}$FeAs using $^{75}$As-NQR and NMR, revealing s$^{ m f extpm}$-wave gap symmetry and weaker spin correlations compared to other iron arsenides.

Contribution

First detailed NQR and NMR analysis of Li$_{x}$FeAs showing gap symmetry and spin correlation strength, highlighting differences from other iron arsenide superconductors.

Findings

Superconducting gap has s$^{ m f extpm}$-wave symmetry.

Spin correlations are weaker than in other iron arsenides.

Normal state shows constant $1/T_1T$ and Knight shift below 50 K.

Abstract

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.