Collapse of Charge Order in a Quasi-One-Dimensional Organic Conductor with a Quarter-Filled Band

Abstract

A charge-ordered insulator, $(\mathrm{D}\mathrm{I}\mathrm{\text{\ensuremath{-}}}\mathrm{D}\mathrm{C}\mathrm{N}\mathrm{Q}\mathrm{I}{)}_{2}\mathrm{A}\mathrm{g}$, with a quasi-one-dimensional quarter-filled band is metallized by pressure. It was found that the charge order melts into a curious metallic state with cubic-temperature dependence of the resistivity, which implies the unprecedented mechanism of the electron-electron scattering. We constructed the pressure-temperature phase diagram, where the melting line has a tricritical point dividing the second-order line at low pressures and the first-order line at high pressures just before it vanishes.