Two pathways to break the insulating state in a correlated transition metal oxide

TL;DR

This study explores the microscopic origins of insulator-metal transitions in Ti3O5, revealing how temperature and pressure induce changes in titanium dimers and orbital populations, advancing understanding of correlated transition metal oxides.

Contribution

It uncovers the microscopic mechanisms behind temperature- and pressure-induced insulator-metal transitions in Ti3O5, emphasizing the roles of orbital physics and dimer interactions.

Findings

Insulating phase features titanium dimers forming orbital selective valence bonds.

Thermal transition involves breakup of one titanium dimer type, causing insulator-metal transition.

Pressure induces a distinct insulator-metal transition driven by competition between intra- and inter-dimer hopping.

Abstract

Correlated transition metal oxides present exciting prospects as switches or memory and storage devices owing to the possibility to control electronic properties using various external stimuli. While their complex behaviour is known to stem from interplay between electronic correlations, atomic structure and orbital physics, they remain poorly understood on the microscopic level. Here, we investigate such origins as a function of temperature and pressure in the transition metal oxide Ti3O5. We find that the insulating room-temperature phase is characterized by one-dimensional zig-zag chains composed by two types of titanium dimers forming orbital selective valence bonds. At the thermal phase transition, one type of titanium dimer breaks up, resulting in an insulator to metal transition with a large orbital repopulation between the two states. Moreover, optical spectroscopy reveals that an additional pressure-driven insulator to metal transition occurs in Ti3O5 at room temperature. The phenomenology of this novel pressure-induced metallic transition is completely different from the insofar studied transitions and results from a competition between intra- and inter-dimer hopping. Our combined results suggest that Ti3O5 is a prototypical correlated transition metal oxide, where both correlations as well as orbital interactions need to be considered to fully understand the evolution of the electronic states.