Quantum anomalous Hall effect using interfacial Green's function method for an accurate mass gap

By using a Green’s function method with DFT-based tight-binding parameters, we investigate the quantum anomalous Hall (QAH) effect at the interface between topological insulators (SnTe, SnSe) and magnetic insulators (EuS, EuSe, EuTe). QAH or axionic states, a subject of recent broad interest, are achieved by introducing an effective Zeeman field to a topological insulator whose surface Dirac cone then acquires a mass gap, resulting in exotic electromagnetic responses within the mass gap. A number of studies have demonstrated the appearance of such states by using diverse interfacial, magnetic-element-doped, and magnetic-topological systems in agreement with predictions. Although achieving a large mass gap is critical for further investigations and room temperature devices, the microscopic mechanisms determining the size of the mass gap have not been clearly addressed. In this study, we enumerate several combinations of topological crystalline insulators and magnetic insulators in a search for an optimal electronic structure, where a large mass gap is isolated inside a bulk insulating gap. The underlying mechanisms and their dependence on factors such as an external field will be discussed.