Investigation of topological phase transition in BiTeBr under high pressure

The polar semiconductor BiTeBr has the P3m1 symmetry, similar to that of BiTeI, in which a pressure-induced topological phase transition from a trivial semiconductor to a topological insulator has been theoretically predicted. To investigate the topological phase transition in BiTeBr, we performed X-ray diffraction and electrical resistivity measurement under high pressure, and the band calculation using experimental structural parameters. The P3m1 structure is stable up to the pressure of ~7 GPa; the ratio of lattice constants (c/a) reaches a minimum at around 3 GPa. Furthermore, the following phenomena are observed at around this pressure; 1) the band-gap energy closes and reopens with pressure, 2) the temperature dependence of resistivity changes from metallic to semiconducting. From theoretical prediction in BiTeI, the topological phase transition is accompanied by the band gap closing/reopening. Therefore, the results obtained in BiTeBr suggest that the topological phase transition occurs at around 3 GPa.