Quasi-one-dimensional bismuth halides offer an exceptional platform for exploring diverse topological phases, yet the nature of the room-temperature topological phase transition in ${\mathrm{Bi}}_4{\mathrm{I}}_4$ remains unresolved. While theory predicts the high-temperature $\beta$ phase to be a strong topological insulator (TI), experiments observe a weak TI. Here we resolve this discrepancy by revealing the critical role of electron-phonon coupling. Using our ab initio scheme for phonon-induced band renormalization, we show that thermal phonons alone drive $\beta –{\mathrm{Bi}}_4{\mathrm{I}}_4$ from the strong TI predicted by static-lattice calculations to a weak TI at temperatures where $\beta –{\mathrm{Bi}}_4{\mathrm{I}}_4$ is stable, with calculated surface states in close agreement with experiments. We further reveal that high-energy states shape the low-energy topology in $\beta –{\mathrm{Bi}}_4{\mathrm{I}}_4$ via phonon-mediated processes. Our work establishes the critical role of electron-phonon coupling in driving the topological phase transition and provides a broadly applicable approach for predicting topological electronic structure at finite temperatures.

Close

PrevNext

View figure in article

• Electron-phonon coupling
• Topological insulators
• Topological phase transition
• Topological materials
• van der Waals systems
• Electronic structure
• First-principles calculations