Visualizing the native atomic defects in Bi$_2$Se$_3$ with scanning tunneling microscopy*

In topological insulators such as Bi$_2$Se$_3$ the existence of native atomic defects is one of the major bottlenecks for potential applications utilizing the topologically protected surface states. Native defects such as vacancies or antisites are believed to be responsible for the metallic transport observed in Bi$_2$Se$_3$. In this study, we examined a series of Bi$_2$Se$_3$ samples that were grown with different conditions using atomically resolving scanning tunneling microscopy. We have successfully identified several types of intrinsic defects, including Se vacancies and Bi-Se antisites. The individual defect images are corroborated by first principle calculations. The densities of these defects across different samples are correlated with their growth conditions. Preliminary results suggest the defect densities can account for the charge carrier density estimated from tunneling spectroscopy.