Robust Topological States in Bi₂Se₃ against Surface Oxidation

Nontrivial surface states in topological insulators originate from the bulk band topology and thus are protected against nonmagnetic surface perturbations. However, previous theoretical findings exhibit the fragility of surface electronic properties caused by surface oxidation in the topological insulator bismuth selenide (Bi₂Se₃) even though the oxidation reaction does not break the time-reversal symmetry. Motivated by this question, using first-principles calculations, we revisit to systematically investigate surface oxidation in Bi₂Se₃. The results reveal that the hybridized states derived from O atoms and substrate Se (or Bi) atoms keep far away from the Fermi level and thus topological surface states can remain intact in the band gap. We further study the oxidation of Bi₂Se₃ in O₂-rich and -poor conditions, and the topological surface states are always preserved at the interface between oxidized and non-oxidized layers. The robustness of topological surface states against surface oxidization matches with topological invariant features. This work provides the exotic insight into topological insulators coexisting with a time-reversal invariant chemical reaction.