Semimetal to semimetal charge density wave transition in 1T-TiSe$_2$

TL;DR

This study uses infrared spectroscopy to demonstrate that 1T-TiSe$_2$ is metallic across its phase transition, revealing changes in carrier dynamics that support an Overhauser-type charge density wave mechanism.

Contribution

It provides conclusive optical evidence that 1T-TiSe$_2$ is metallic in both phases and clarifies the nature of its CDW transition, which was previously unresolved.

Findings

1T-TiSe$_2$ is metallic in both normal and CDW phases.

Carrier scattering rate varies significantly between phases.

Carrier density changes with temperature, supporting an Overhauser-type CDW mechanism.

Abstract

We report an infrared study on 1$T$-TiSe$_2$, the parent compound of the newly discovered superconductor Cu$_x$TiSe$_2$. Previous studies of this compound have not conclusively resolved whether it is a semimetal or a semiconductor: information that is important in determining the origin of its unconventional CDW transition. Here we present optical spectroscopy results that clearly reveal that the compound is metallic in both the high-temperature normal phase and the low-temperature CDW phase. The carrier scattering rate is dramatically different in the normal and CDW phases and the carrier density is found to change with temperature. We conclude that the observed properties can be explained within the scenario of an Overhauser-type CDW mechanism.