Robustness of Topologically Protected Surface States in Layering of Bi₂Te₃ Thin Films

Bulk Bi2Te3 is known to be a topological insulator. We investigate surface states of Bi₂Te₃(111) thin films using density-functional theory including spin-orbit coupling. We construct a method to unambiguously identify surface states of thin film topological insulators. Applying this method for one to six quintuple layers of Bi₂Te₃, we find that the topological nature of the surface states remains robust with the film thickness and that the films of three or more quintuple layers have topologically non-trivial or protected surface states, in agreement with recent experiments.