Signatures of a Pressure-Induced Topological Quantum Phase Transition in BiTeI

TL;DR

This study provides experimental evidence of a pressure-induced topological quantum phase transition in BiTeI, using x-ray diffraction and infrared spectroscopy to identify structural and electronic signatures.

Contribution

It reports the first observation of two key signatures of a topological phase transition in BiTeI under pressure, confirming theoretical predictions.

Findings

c/a ratio shows a minimum between 2.0-2.9 GPa

optical spectral weight peaks indicating band gap closing and reopening

structure remains unchanged up to 8 GPa

Abstract

We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through pz band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition, and are consistent with a recent theoretical proposal.