Robust topological surface state against direct surface contamination

Angle resolved photoemission spectroscopy (ARPES) study were performed on the (111) surface of topological insulators Bi2Te3, Bi2Se3 and semimetals Bi and Sb. In all four materials, we observed clear surface states centered at the Γ point of the surface Brillouin zone. We further studied the evolution of these surface states under controlled surface contamination of CO and O2 gas molecules, and found that the surface states in Bi2Te3 and Bi2Se3 were both robust against the direct influence of these gas molecules, while the surface states of Bi and Sb could be easily destroyed under the same condition. Our finding provides direct experimental evidence confirming the unusual robustness of the topological surface state of topological insulators with the presence of the time reversal symmetry.