Observation of Fermi-energy dependent unitary impurity resonances in a   strong topological insulator Bi2Se3 with scanning tunneling spectroscopy
  Scanning tunneling spectroscopic studies of Bi2Se3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level ({E_F}) and the Dirac point ({E_D}) and diverges as {E_F} approaches {E_D}. The Dirac-cone surface state of the host recovers within ~ 2{\AA} spatial distance from impurities, suggesting robust topological protection of the surface state of topological insulators against high-density impurities that preserve time reversal symmetry. 
M. L. Teague, H. Chu, F.-X. Xiu, L. He, K.-L. Wang, N.-C. Yeh
cond-mat.mes-hall cond-mat.str-el