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.