  We performed X-ray diffraction and electrical resistivity measurement up to
pressures of 5 GPa and the first-principles calculations utilizing experimental
structural parameters to investigate the pressure-induced topological phase
transition in BiTeBr having a noncentrosymmetric layered structure (space group
P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of
lattice constants, c/a, has a minimum at pressures of 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, according to the Wilson loop analysis, the topological
nature of electronic states in noncentrosymmetric BiTeBr at 0 and 5 GPa are
explicitly revealed to be trivial and non-trivial, respectively. These results
strongly suggest that pressure-induced topological phase transition in BiTeBr
occurs at the pressures of 2.9 GPa.
