Exceptional surface states and topological order in Bi2Se3

Topological insulators possess time reversal symmetry protected metallic surface states over the insulating bulk, where these surface states are expected to be immune to small disorder, chemical passivation of the surface or temperature change. However, significant discrepancy from such behavior has been found experimentally in various materials. Here, we review some of our recent results on the electronic structure of a typical topological insulator, Bi2Se3. Both, the band structure results and high-resolution angle resolved photoemission data reveal significantly different surface electronic structure for different surface terminations. Furthermore, oxygen impurity on Se terminated surface exhibits an electron doping scenario, while oxygen on Bi terminated surface corresponds to a hole-doping scenario. The intensity of the Dirac states reduces with aging indicating fragility of the topological order due to surface impurities.