TY - JOUR TI - Thin film study of topological materials via atomic scale engineering DO - https://doi.org/doi:10.7282/t3-bgc2-j218 PY - 2019 AB - This dissertation seeks to deepen our understanding of the novel physical properties in a class of topological materials named topological insulators (TIs). In particular, electrical transport properties in Bi2Se3 TI thin films grown by the molecular beam epitaxy (MBE) technique are mainly investigated through an experimental standpoint. It first begins by reviewing the topological phases from the quantum Hall effect (QHE) to the TIs in a conceptual point of view, which will lead to what the TIs are. This is followed by a comprehensive introduction to the thin film growth using the MBE as atomically precise technique in consideration of atomic scale engineering for various defects. This is then follow by an approach to discern unknown physical properties via electrical transport measurements, which is the main experimental technique used in this work. Throughout the following chapters these techniques are applied to manipulate the topological properties of the TIs and explained in details. For the experimental results, we first discuss the hole doping problem in Bi2Se3 thin films and its solution. This study shows 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, we show the method of implementing the ferromagnetic (FM) anomalous Hall effect (AHE) to the Bi2Se3 thin films. While the Cr-doped Bi2Se3, among the three dimensional TI families, was predicted to be the most promising candidate to exhibit the quantum anomalous Hall effect (QAHE), the observation was quite the contrary. It has failed to exhibit even the FM AHE, which is an expected predecessor to the QAHE in comparison to the Cr- or V-doped (Sb,Bi)2Te3 showing the quantum anomalous Hall effect (QAHE) and V-doped Bi2Se3 exhibiting the AHE. In great succession via utilizing a surface state engineering scheme, we show the achievement of the FM AHE in Cr-doped Bi2Se3 thin films, and consequently emerging positive anomalous Hall conductivity. We explain the sign problem by analyzing the mass-gap susceptibility based on a tight binding model and first-principles study. KW - Physics and Astronomy KW - Topological insulators -- Electric properties LA - English ER -