Повышение температуры ослабляет спин-орбитальное взаимодействие и разрушает топологическое состояние в полупроводниках

Spin-orbit coupling (SOC), an interaction between an electron's spin and its motion, plays a key role in creating topological insulators—unusual materials that are insulating in their interior but can conduct electricity along their surfaces. Now, a new study published in Newton finds that increasing temperature weakens SOC in the topological insulator Bi2Se3, driving a transition to a normal insulating state. The findings suggest that temperature could serve as a new "knob" for controlling the topological properties of materials. The research was led by Prof. SUN Yiyang from the Shanghai Institute of Ceramics (SIC) of the Chinese Academy of Sciences (CAS). The first author of the paper is LU Lingyan, a PhD candidate at SIC. SOC is a key interaction underlying many physical phenomena, including the formation of topological insulators. As a relativistic effect, SOC is generally perceived to be determined by the constituent atomic species of a material and not to be strongly correlated with temperature. To investigate its temperature dependence, the researchers combined first-principles calculations with ab initio molecular dynamics simulations to track the evolution of the electronic structure of Bi2Se3 across the range of 0–900 K (about -273°C to 627°C). The results showed that increasing temperature progressively reduced the SOC-induced band gap correction by up to 0.19 eV over this range, suppressing the band inversion required for topological order. By sampling molecular dynamics trajectories, the researchers observed that topologically trivial snapshot structures emerged above 500 K, with their population quickly rising at higher temperatures. Surface spectral function calculations confirmed the loss of gapless Dirac cones in these structures. After separating the effects of thermal lattice expansion from those of structural disorder, the researchers showed that lattice expansion alone could not account for the observed transition from a topological insulator to a normal insulator. Instead, the temperature-induced weakening of SOC was identified as the primary driving force behind the transition. This phenomenon was further validated in two other typical topological insulators, Bi2Te3 and Sb2Te3, where SOC was similarly found to weaken with increasing temperature. According to the researchers, this work breaks with the general perception that SOC is intrinsic to a material and mainly determined by its atomic species. Consequently, SOC strength could become a tuning knob for controlling materials' electronic properties, with potential applications in spintronics and quantum computing.