Pressure-induced topological crystalline insulating phase in TlBiSe₂: Experiments and theory

We report in situ high-pressure studies on three-dimensional topological insulator TlBiSe2 using Raman scattering and synchrotron x-ray-diffraction experiments corroborated with the first-principles theoretical calculations. The phonon modes of a rhombohedral phase of TlBiSe2 show a systematic increase in frequencies under hydrostatic pressure up to similar to 7.0 GPa. Interestingly, the linewidth of the A(1g), N, and E-g phonon modes show clear anomalies at similar to 2.5 GPa which is indicating the isostructural electronic transition. With the help of calculated electron-phonon coupling constant lambda, anomalies in the Raman linewidth of E-g mode are attributed to electron-phonon coupling changes. Moreover, our theoretical results reveal that the observed phonon anomalies are due to pressure-induced band inversion at the F points of the Brillouin zone which leads to the changes in electronic topology reflected in the mirror Chern number n(M) and Z(2) topological invariant. Therefore, the phonon anomalies and change in mirror Chern number n(M) confirm the pressure-induced topological crystalline insulator phase in TlBiSe2 at similar to 2.5 GPa. Further, a reversible structural phase transition has been observed above similar to 7.0 GPa from both synchrotron x-ray-diffraction and Raman-scattering measurements. Finally, our studies suggest the use of hydrostatic pressure as a potential pathway for exploring the topological crystalline insulating phase in strong spin-orbit coupling compounds, such as the thallium-based III-V-VI2 ternary chalcogenide TlBiX2 (X = S, Se, Te) family.