Pressure-induced structural transitions triggering dimensional crossover in lithium purple bronze Li0.9M6O17

TL;DR

This study investigates how applying pressure to lithium molybdenum purple bronze induces structural phase transitions that alter its electronic dimensionality, shifting from quasi-one-dimensional to more isotropic behavior.

Contribution

It provides the first detailed analysis of pressure-induced structural transitions and their impact on the electronic properties of Li0.9Mo6O17, revealing a pressure-driven dimensional crossover.

Findings

Pressure induces multiple phase transitions between 0 and 12 GPa.

High pressure causes metallization along the c-axis.

Pressure reduces conductivity along the b-axis, indicating a dimensional crossover.

Abstract

At ambient pressure, lithium molybdenum purple bronze (Li0.9Mo6O17) is a quasi-one dimensional solid in which the anisotropic crystal structure and the linear dispersion of the underlying bands produced by electronic correlations possibly bring about a rare experimental realization of Tomomaga-Luttinger liquid physics. It is also the sole member of the broader purple molybdenum bronzes family where a Peierls instability has not been identified at low temperatures. The present study reports a pressure-induced series of phase transitions between 0 and 12 GPa. These transitions are strongly reflected in infrared spectroscopy, Raman spectroscopy, and x-ray diffraction. The most dramatic effect seen in optical conductivity is the metallization of the c-axis, concomitant to the decrease of conductivity along the b-axis. This indicates that high pressure drives the material away from its quasi-one dimensional behavior at ambient pressure. While the first pressure-induced structure of the series is resolved, the identification of the underlying mechanisms driving the dimensional change in the physics remains a challenge.