Quantum Anomalous Hall Effect In Topological Insulators By Nonmagnetic Doping And Magnetic Proximity Coupling

The two-dimensional electronic systems have many novel quantum phenomena and one prominent example is the Quantum Anomalous Hall Effect(QAHE).QAHE can manifest as a quantized transverse conductance in response to a longitudinally applied electric field in the absence of an external magnetic field.After tens-years effort,QAHE has been experimentally realized in magnetically doped topological insulators or intrinsic magnetic topological insulator MnBi₂Te₄ by applying an external magnetic field.However,the ultra-low temperature(usually below 300 m K)resulted by inhomogeneous magnetic doping,and the unexpected external magnetic field(tuning all MnBi ₂Te₄ layers to be ferromagnetic)become daunting challenges for potential applications of QAHE.Therefore,it is urgent to find a way to enhance the observed temperature of QAHE in the field.In this paper,we mainly propose two different methods that not only can solve the inhomogeneous and metallization-like of magnetic doping in the topological insulator Sb₂Te₃ system,but also can achieve the purpose of introducing ferromagnetism into the material,and finally to realize the high-temperature QAHE.Specifically,our studies include the following two aspects based on the first-principles calculations and the tight-binding model.1.A nonmagnetic-doping strategy is proposed to produce ferromagnetism and realize QAHE in topological insulators.We numerically demonstrated that magnetic moments can be induced by nitrogen or carbon substitution in Bi₂Se₃,Bi₂Te₃,and Sb₂Te₃,but only nitrogen-doped Sb₂Te₃ exhibits long-range ferromagnetism and preserve large bulk band gap.We further show that its corresponding thin-film can harbor QAHE at temperatures of 17-29 Kelvin,which is two orders of magnitude higher than the typical temperatures in similar systems.Our proposed nonmagnetic doping scheme may shed new light in experimental realization of high-temperature QAHE in topological insulators.2.We theoretically demonstrate that proper stacking of MnBi₂Te₄ and Sb₂Te₃ layers is able to produce intrinsically ferromagnetic van der Waals heterostructures to realize the high-temperature QAHE.We find that interlayer ferromagnetic transition can happen at T_C=42 K when a five-quintuple-layer Sb₂Te₃ topological insulator is inserted into two septuple-layer MnBi₂Te₄ with interlayer antiferromagnetic coupling.Band structure and topological property calculations show that MnBi₂Te₄/Sb₂Te₃/MnBi₂Te₄heterostructure exhibits a topologically nontrivial band gap around 26 me V,that hosts a QAHE with a Chern number of C=1.In addition,our proposed materials system should be considered as an ideal platform to explore high-temperature QAHE due to the fact of natural charge compensation,originating from the intrinsic n-type defects in MnBi₂Te₄and p-type defects in Sb₂Te₃.