BiTeCl and BiTeBr: a comparative high-pressure optical study

TL;DR

This study investigates how high pressure affects the optical properties of BiTeCl and BiTeBr, revealing phase transitions and potential Weyl phase emergence in BiTeBr through infrared transmission measurements.

Contribution

It provides the first detailed high-pressure optical analysis of BiTeCl and BiTeBr, identifying phase transitions and electronic structure changes.

Findings

BiTeCl undergoes a phase transition at 6 GPa.

BiTeBr shows signs of a Weyl phase at 5-6 GPa.

Structural transition in BiTeBr occurs at 7 GPa.

Abstract

We here report a detailed high-pressure infrared transmission study of BiTeCl and BiTeBr. We follow the evolution of two band transitions: the optical excitation $\beta$ between two Rashba-split conduction bands, and the absorption $\gamma$ across the band gap. In the low pressure range, $p< 4$~GPa, for both compounds $\beta$ is approximately constant with pressure and $\gamma$ decreases, in agreement with band structure calculations. In BiTeCl, a clear pressure-induced phase transition at 6~GPa leads to a different ground state. For BiTeBr, the pressure evolution is more subtle, and we discuss the possibility of closing and reopening of the band gap. Our data is consistent with a Weyl phase in BiTeBr at 5$-$6~GPa, followed by the onset of a structural phase transition at 7~GPa.