Weakened spin-orbit coupling drives topological-to-normal-insulator transition at elevated temperatures

Spin-orbit coupling (SOC) is a key interaction underlining many physical phenomena, yet it is typically assumed to be only weakly temperature dependent. Here, we reveal that the SOC effect exhibits a pronounced temperature dependence that can determine the topological state of topological insulator materials, such as Bi 2 Se 3 . We employ a statistical approach based on sampling molecular dynamics (MD) trajectories to capture the phase transition. For the MD snapshots, we examine their band inversion, Z 2 invariant, and surface spectral function. As temperature increases, the SOC correction to the band gap is strongly reduced by 0.19 eV from 0 to 900 K, causing an increasing fraction of the MD snapshots to lose band inversion and become topologically trivial. We exclude alternative causes, such as thermal expansion, that could otherwise explain the transition. These results demonstrate that, while temperature-driven topological phase transitions have been discussed in the literature, the direct driving force here is the weakening of SOC strength with increasing temperature.