Phase transition between trivial and non-trivial states in BiTeBr under high pressure

We report the topological phase transition at ~3 GPa in BiTeBr. The transition from a trivial state to a non-trivial one in BiTeI was theoretically predicted at a few gigapascals under hydrostatic condition. Both the layered structure with a symmetry of P3m1 and the electronic state of BiTeBr are similar to those of BiTeI. This transition was therefore also expected to occur in BiTeBr. We investigated the transition in combination with experiments up to 5 GPa (XRD, resistivity) under hydrostatic condition and the first-principles calculations utilizing experimental structural parameters. The P3m1 structure remains stable up to pressures of 5 GPa with a minimum of the ratio of lattice constants at 2.5-3 GPa. In the same range, the temperature dependence of resistivity changes from metallic to semiconducting at 3 GPa and has a plateau region between 50 and 150 K in the semiconducting state. Meanwhile, the pressure variation of band structure shows that the bulk band-gap energy closes at 2.9 GPa and re-opens at higher pressures. Furthermore, Wilson loop analysis revealed that the topological nature of electronic states at 0 and 5 GPa are trivial and non-trivial, respectively. These results suggest that topological phase transition in BiTeBr occurs at 2.9 GPa.