On the Negative Magnetoresistance Observed in Li_0.9Mo₆O₁₇

Li_0.9Mo₆O₁₇ consists of zigzag chains of MoO₆ octahedra along the crystallographic b-axis, with weak interchain coupling. Positioned near the boundary between superconducting and Mott insulating states, it is highly sensitive to perturbations. Single crystals of Li_0.9Mo₆O₁₇ exhibit both insulating and superconducting behavior at zero magnetic field. Under applied magnetic fields, the b-axis magnetoresistance (MR_b) shows strong directional dependence—changing from large positive values for H || a to negative for H || b. Remarkably, the magnetic torque (τ) reverses sign at the same field orientation. The directional dependence of both MR_b and τ provides key insight into the interplay between superconductivity, dimensionality, and electronic correlations in Li_0.9Mo₆O₁₇.