Thin film study of Bi2Se3 topological insulator via atomic scale engineering
Bi2Se3 is one of the most widely studied 3D topological insulators (TIs) due to its large bulk band gap. However, it has been difficult to perform Fermi level tuning close to the Dirac point in Bi2Se3 thin films, not to mention that p-type Bi2Se3 thin films did not exist. In this talk, I will first discuss the hole doping problem in Bi2Se3 thin films and its solution. This study will show that the main culprit resides in the high density of interfacial defects on the substrates, and how a solution is achieved by a properly designed buffer layer engineering. Subsequently, I will go over the method of implementing the ferromagnetic (FM) anomalous Hall effect (AHE) to the Bi2Se3 thin films. While the Cr-doped Bi2Se3, among the 3D TI family, (Bi,Sb)2(Te,Se)3, was predicted to be the most promising candidate to exhibit the quantum anomalous Hall effect (QAHE), the observation was quite the contrary. I will show the achievement of the FM AHE in the Cr-doped Bi2Se3 thin films via surface engineering with combination of charge compensation doping. Furthermore, emerging positive anomalous Hall conductivity will be discussed by analyzing the mass-gap susceptibility based on a tight binding model and the first-principles study.