Quantum spin Hall insulator under ion irradiation: assessing the robustness of topological insulating states against realistic structural defects

Abstract Two-dimensional topological insulator, or quantum spin Hall (QSH) insulator, holds topologically protected edge states with significant implications for diverse fields, yet the robustness against realistic structural defects remains elusive. Here, by combining first-principles calculations, ab initio molecular dynamics (AIMD) and Monte Carlo simulations, we consider Bi(111) bilayer–a large-gap QSH insulator–under ion irradiation, and explore the topological robustness with the generated defect structures. Systematic Ar-ion irradiation simulations allow the determination of defect types and concentrations over a broad range of incident ion energies and fluences, with single and double vacancies identified as the dominant defects. Analyses on the band structures of irradiated Bi(111) samples reveal that the spin–orbit coupling induced band inversion would be destroyed by the electronic defect states when the defect concentration reaches ∼3%. This is confirmed by direct visualization of the real-space topological edge states and defect states in 1D nanoribbons, exhibiting strong hybridization. Our work not only provides fundamental insights into the topological robustness of QSH insulators, but also sheds light on their practical implementation in quantum information processing and spintronic devices under extreme conditions.