Topological insulator (TI) is a new quantum state of matter where the insulating bulk is enclosed by Dirac surface states protected by the topology of the bulk band structure[1-3]. This quantum state may host various exotic phenomena such as quantum anomalous Hall effect, Majoranan fermions, and giant spin-hall effect, often realized by chemical doping of TIs. In most TI’s, however, significant bulk conduction due to native atomic defects overwhelms that of surface states, which hampers potential applications of topological surface states. Despite many years’ studies, the nature of native defects in many TIs is still illusive. In this talk, I will present our recent studies of native defects in Bi2Se3 by combining high resolution scanning tunneling microscopy (STM) and first principle calculation [4]. We identified the major native defects, in particular the Se vacancies and Se interstitial defects that are responsible for the bulk conduction and nanoscale potential fluctuations in single crystals of archetypal topological insulator Bi2Se3. Identification and control of defects in topological insulators are crucial steps toward experimental explorations of topological quantum phenomena. Preliminary results of topological phase transition induced by In doping will also be presented.

[1] X.-L. Qi and S.-C. Zhang, Reviews of Modern Physics 83, 1057 (2011).
[2] M. Z. Hasan and J. E. Moore, Annual Review of Condensed Matter Physics 2, 55 (2011).
[3] M. Z. Hasan and C. L. Kane, Reviews of Modern Physics 82, 3045 (2010).
[4] J. Dai, D. West, X. Wang, Y. Wang, D. Kwok, S.-W. Cheong, S. B. Zhang, and W. Wu, Phys Rev Lett 117, 106401 (2016).