Electrical resistivity of the Ti4O7 Magneli phase under high pressure

TL;DR

This study investigates how high pressure affects the electrical resistivity and conduction mechanisms of Ti4O7, revealing anisotropic behavior, suppression of bipolaron formation, and potential proximity to a quantum critical point.

Contribution

It provides new insights into pressure-induced changes in bipolaron dynamics and anisotropic conduction in Ti4O7, including the absence of superconductivity down to 1.2 K.

Findings

Pressures over 4 kbar reduce bipolaron localization.

At pressures above 40 kbar, bipolaron formation is suppressed.

Anisotropic conduction observed with metallic behavior along principal axis.

Abstract

We have measured resistivity as a function of temperature and pressure of Ti4O7 twinned crystals using different contact configurations. Pressures over 4kbar depress the localization of bipolarons and allow the study of the electrical conduction of the bipolaronic phase down to low temperatures. For pressures P > 40 kbar the bipolaron formation transition is suppressed and a nearly pressure independent behavior is obtained for the resistivity. We observed an anisotropic conduction. When current is injected parallel to the principal axis, a metallic conduction with interacting carrier effects is predominant. A superconducting state was not obtained down to 1.2 K, although evidences of the proximity of a quantum critical point were noticed. While when current is injected non-parallel to the crystal's principal axis, we obtained a logarithmic divergence of the resistivity at low temperatures. For this case, our results for the high pressure regime can be interpreted in the framework of interacting carriers (polarons or bipolarons) scattered by Two Level Systems.