Infrared and Raman spectroscopy measurements of a transition in the crystal structure and a closing of the energy gap of BiTeI under pressure

TL;DR

This study uses infrared, Raman spectroscopy, and optical measurements to investigate pressure-induced structural and electronic changes in BiTeI, revealing a phase transition at 9 GPa that affects its topological properties.

Contribution

It provides new experimental evidence of a crystal structure transition in BiTeI at 9 GPa and its impact on the material's electronic and topological phases.

Findings

Optical gap vanishes above 9 GPa

Phase transition at 9 GPa involves crystal structure change

High-pressure topological phase likely inhibited

Abstract

BiTeI is a giant Rashba spin splitting system, in which a non-centro symmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, under pressures up to $15$ GPa. The gap feature in the optical conductivity vanishes above $p \sim 9$ GPa and does not reappear up to at least $15$ GPa. The plasma edge, associated with intrinsically doped charge carriers, is smeared out through a phase transition at $9$ GPa. Using high pressure Raman spectroscopy, we follow the vibrational modes of BiTeI, providing additional clear evidence that the transition at 9 GPa involves a change of crystal structure. This change of crystal structure possibly inhibits the high-pressure topological phase from occurring.