Molecular Beam Epitaxy Growth and Magnetization Characterization of Fe-doped Bi2Se3*

Bi₂Se₃ is a prototypical 3D topological insulator (TI), which hosts gapless surface states protected by time-reversal-symmetry (TRS). When TRS is broken by doping with magnetic elements, this system can realize exotic electronic states, such as the quantum anomalous hall states (QAHS) (Rui Yu et al., Science 329 , 61 (2010)). We grow Fe-doped Bi₂Se₃ thin films on SrTiO₃(001) substrates by molecular beam epitaxy (MBE), and characterize them using a combination of low-temperature scanning tunneling microscopy/spectroscopy (STM/S) and magnetization measurements. We find a large difference between the Fe concentration in the topmost layer determined from STM topographs and that inferred from magnetization measurements. Moreover we find an intriguing magnetic anisotropy of the thin films, different from that observed in their bulk counterparts. Our findings provide a fresh insight into the idea of doping Fe into Bi₂Se₃ as a route towards achieving QAHS.