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.
@article{arxiv.1305.0959,
title = {Signatures of a Pressure-Induced Topological Quantum Phase Transition in BiTeI},
author = {Xiaoxiang Xi and Chunli Ma and Zhenxian Liu and Zhiqiang Chen and Wei Ku and H. Berger and C. Martin and D. B. Tanner and G. L. Carr},
journal= {arXiv preprint arXiv:1305.0959},
year = {2013}
}