NMR studies of anisotropy and metal-insulator crossover in quasi-one-dimensional metal Li$_{0.9}$Mo$_{6}$O$_{17}$

The quasi-1D metal Li$_{0.9}$Mo$_{6}$O$_{17}$ is thought to exhibit transport properties associated with a Luttinger liquid at high temperatures, and otherwise many of its properties have long been mysterious. Among these is an unusual increase in resistivity at low temperatures, for which a robust explanation remains elusive. We present the $^{7}$Li-NMR/$^{95}$Mo-NMR measurements over a wide range of temperature and angle of alignment of applied magnetic field (B0) from 6 T to 14.8 T on single crystal of Li$_{0.9}$Mo$_{6}$O$_{17}$. We find a Korringa relation at high temperatures which indicates electron correlations are unimportant for $T > T_{m}$ (resistivity minimum temperature), and apparent deviations from Korringa for $T$ $\leq$ 24 K. Further, in the single crystal studied, inequivalent magnetic environments are detected at the Li sites in the same low-temperature regime, but only for fields applied near to $B_{0}$ $\parallel$ $c$. Only one $^{95}$Mo site (out of 6 different crystallographic sites) was detected, and 1/($T_{1}T$) at this site is decreasing at low temperatures. We discuss these observations in relation to possible mechanisms for the low temperature resistivity increase.