Inter-chain transport in the quasi-one-dimensional metal, Li$_{0.9}$Mo$_6$O$_{17}$

We report measurements of electrical resistivity ($\rho$) and thermoelectric power ($S$) transverse to the conducting chains (crystallographic \textit{c} axis) on single crystals of the quasi-one-dimensional metal, Li$_{0.9}$Mo$_6$O$_{17}$. While $\rho_c(T)$ exhibits metallic behavior at $T\leq T_{max}\sim 270$~K, it decreases with increasing $T$ above this temperature similar to the behavior of $\rho$ transverse to the conducting planes in a variety of two-dimensional metals.\footnote{See, e.g., D. B. Gutman and D. L. Maslov, Phys. Rev. Lett. {\bf 99}, 196602 (2007).} We discuss the corresponding thermopower, $S_c$, which is relatively $T$-independent and a modest 30 $\mu$V/K at low $T$, increases sharply with increasing $T$ near $T_{max}$, and exceeds 200 $\mu$V/K at $T>400$~K.