Distinct intermediate states in the isostructural R−3m phase of the topological insulator Bi2Se3 at high pressure

The electronic state of layered three-dimensional topological insulators at high pressure is a compelling but a puzzling hot topic. The open question is the structural origins for the pressure-induced novel physics of electronic topological transition (ETT), topological superconductivity, and Majorana fermions in the same isostructural $R\text{\ensuremath{-}}3m$ phase. Here, we report a combined investigation on the local structure and bulk electronic state of topological insulator $\mathrm{B}{\mathrm{i}}₂\mathrm{S}{\mathrm{e}}₃$ using x-ray diffraction, high quality x-ray absorption fine-structure spectroscopies both at the $\mathrm{Bi}\phantom{\rule{0.16em}{0ex}}{L}₃$ edge and at the Se K edge, and first-principles theoretical calculations. We have found three pressure-induced distinct intermediate states in the isostructural rhombohedral phase of $\mathrm{B}{\mathrm{i}}₂\mathrm{S}{\mathrm{e}}₃$. The bulk electronic structure of the $R\text{\ensuremath{-}}3m$ phase was calculated based on the experimental structure. The corresponding distinct electronic states provide the origins of ETT at \ensuremath{\sim}3 GPa and the metallization at 7--9.5 GPa in the $R\text{\ensuremath{-}}3m$ phase of $\mathrm{B}{\mathrm{i}}₂\mathrm{S}{\mathrm{e}}₃$. Our results demonstrate that the local structure plays a critical role in the electronic states of topological insulator $\mathrm{B}{\mathrm{i}}₂\mathrm{S}{\mathrm{e}}₃$.