Tuning The Quantum Anomalous Hall Effect In Magnetic Topological Insulator

The quantum Anomalous Hall（QAH）effect has been realized in MBE-grown thin films of Cr or V doped（Bi,Sb）₂Te₃ topological insulators in the absence of external magnetic field.However,so far the QAH effect state can only be observed at very low temperatures in thin films with accurately controlled chemical compositions.In order to find better QAH effect materials and facilitate its applications in low energy consumption electronic and spintronic devices,it is crucial to understand the various parameters that affect the QAH effect.In this thesis we summarize recent progresses on tuning of QAH effect in magnetic topological insulators and understanding the quantum phase transitions in quantum anomalous Hall edge transport.In particular,we have carried out systematic experimental studies with several tuning parameters including temperature,external magnetic field,and electric current density.The effects of magnetic doping level,film thickness,and the structure of device have also been carried out.We show that the competition between surface and bulk transport,as well as that between magnetism and topology,are the crucial factors that determine the parameter space for the optimization of the QAH effect.These results reveal the intrinsic transport properties and shed new lights on searching for better QAH effect materials and novel spintronic device applications.