title: Infrared- and Raman-spectroscopy measurements of a transition in the crystal structure and a closing of the energy gap of BiTeI under pressure.
abstract: BiTeI is a giant Rashba spin splitting system, in which a noncentrosymmetric 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∼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.
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: M K
authors.initials: MK
authors.lastname: Tran
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Levallois
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Lerch
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Teyssier
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: A B
authors.initials: AB
authors.lastname: Kuzmenko
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Autès
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: O V
authors.initials: OV
authors.lastname: Yazyev
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Ubaldini
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Giannini
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: van der Marel
authors.affiliation: Département de la Matière Condensée, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Akrap