Metal-Insulator Transitions in Ti₄O₇: Pressure-Induced Melting of the Electron Pairs

Abstract

We discovered a pressure-induced metal-insulator transition in Ti₄O₇ which is a bipolaronic insulator at ambient pressure. In the pressure-induced metallic phase, the resistivity shows T²-behavior att low temperatures. From the remarkably large magnitude of T²-resistivity and its pressure dependence, we suggest that electron correlations are very likely the primal origin of the bipolaronic insulator phase of Ti₄O₇. In spite of early expectations, superconductivity was not observed down to 3 K.