Magnetotransport properties in purple bronze Li$_{0.9}$Mo$_6$O$_{17}$ Single Crystal

Abstract

We have measured resistivity along the a, b and c axes of Li$_{0.9}$Mo$_6$O$_{17}$ single crystal. The anisotropy $\rho$$_c$ / $\rho$$_a$ and $\rho$$_c$ / $\rho$$_b$ is given, confirming the quasi-one-dimensionality of the compound. The sharp decrease in the anisotropy below a certain temperature (T$_M$) indicates dimensional crossover. Superconductivity occurs at 1.8 K well below $T_M$. Negative MRs are observed with magnetic field (H) applied along b axis. This could be ascribed to suppression of energy gap associated with CDW state. While large positive MR is observed with H $\parallel$ c-axis. The MR data can be well fitted by a modified two-band model which has been used in CDW compounds such as quasi-two-dimensional purple bronzes A$_{0.9}$Mo$_6$O$_{17}$ (A = K, Na, Tl) and quasi-one-dimensional conductor NbSe$_3$. The behavior of MR provides a strong evidence for the existence of CDW instability in $Li_{0.9}Mo_6O_{17}$.