Surface versus bulk state in topological insulator Bi2Se3 under   environmental disorder
  Topological insulators (TIs) are predicted to be composed of an insulating bulk state along with conducting channels on the boundary of the material. In Bi2Se3, however, the Fermi level naturally resides in the conduction band due to intrinsic doping by selenium vacancies, leading to metallic bulk states. In such non-ideal TIs it is not well understood how the surface and bulk states behave under environmental disorder. In this letter, based on transport measurements of Bi2Se3 thin films, we show that the bulk states are sensitive to environmental disorder but the surface states remain robust. 
Matthew Brahlek, Yong Seung Kim, Namrata Bansal, Eliav Edrey, and   Seongshik Oh
cond-mat.mtrl-sci