Pressure-induced topological phase transition in the polar semiconductor BiTeBr

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 nontrivial, respectively. These results strongly suggest that pressure-induced topological phase transition in BiTeBr occurs at the pressures of 2.9 GPa.

Figure 1

(a) Temperature dependence of electrical resistivity at pressures up to 5 GPa in a BiTeBr single crystal (sample 1). Resistivity data at 1 atm is measured using another sample with the size of $1.5\times 1.0\times 0.12{\mathrm{mm}}^3$. Inset: Crystal structure of BiTeBr at ambient conditions. (b) Variation of electrical resistivity as a function of pressure at ambient temperature (sample 2). Inset: Magnified view of pressure ranges of 1 to 3 GPa. Red and blue areas show positive and negative ranges of $d\rho /dT$, respectively, based on the results of (a). Arrow indicates a pressure range in which the $c/a$ of $P3m1$ structure reaches a minimum as shown in Fig. 2.

Figure 2

(a) X-ray diffraction image of the polycrystalline BiTeBr sample at 0.57 GPa. (b) Diffraction patterns on compression at ambient temperature. (c) Pressure variations of lattice constants (main panel) and their ratio $c/a$ (inset). (d) Compression curve of BiTeBr. Dashed line represents the Murnaghan EOS fit to the experimental data.

Figure 3

(a) Bulk electronic states of BiTeBr along the $L\text{−}A\text{−}H$ direction calculated using experimental lattice constants under various pressures. (b) Pressure variation of energy gap $\left(E_g\right)$ shown as red circles. Blue circles are symmetric points of red ones with respect to $E_g=0$ eV. Solid lines are guide for the eye.

Figure 4

Wilson loop analysis of topological electronic states in BiTeBr at pressures of (a) 0 GPa and (b) 5 GPa. A pair of the Wannier charge center evolution around $y_n=0$ is highlighted as blue and red curves.