title: Signatures of a pressure-induced topological quantum phase transition in BiTeI.
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 p(z) 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.
authors.affiliation: Photon Sciences, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Xiaoxiang
authors.initials: X
authors.lastname: Xi
authors.forename: Chunli
authors.initials: C
authors.lastname: Ma
authors.forename: Zhenxian
authors.initials: Z
authors.lastname: Liu
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Ku
authors.forename: H
authors.initials: H
authors.lastname: Berger
authors.forename: C
authors.initials: C
authors.lastname: Martin
authors.forename: D B
authors.initials: DB
authors.lastname: Tanner
authors.forename: G L
authors.initials: GL
authors.lastname: Carr