Identification of magnetic dopants on the surfaces of topological insulators: Experiment and theory for Fe on Bi2Te3(111)

Magnetic impurities are crucial for probing spin-polarized topological surface states. Scanning tunneling microscopy (STM) studies of Fe on the Bi2Te3(111) surface are preformed and unveil distinct impurity structures of unknown origin which exhibit temperature-dependent characteristics. Using density functional theory with spin-orbit coupling, we show that Fe prefers highly coordinated subsurface configurations. By comparing simulated STM images we can explain the experimental results of both low-temperature deposition, in which Fe exists in metastable states of which only the transition-metal Bi split interstitial is STM visible, and after room-temperature annealing, in which iron forms substitutional Fe-Bi.