Giant Bipolar Nernst Effect in the Quasi-One-Dimensional Metal, Li$_{0.9}$Mo$_6$O$_{17}$

The Nernst coefficient for the quasi-one-dimensional metal, Li$_{0.9}$Mo$_6$O$_{17}$, is found to be among the largest known for metals ($\nu\simeq 500\ \mu$V/KT at $T\sim 20$~K), and is enhanced in a broad range of temperature by orders of magnitude over the value expected from Boltzmann theory for carrier diffusion. A comparatively small Seebeck coefficient implies that Li$_{0.9}$Mo$_6$O$_{17}$ is bipolar with large, partial Seebeck coefficients of opposite sign. A very large thermomagnetic figure of merit, $ZT\sim 0.5$, is found at high field in the range $T\approx 35-50$~K.