First Principles Study Of In-Plane Magnetization And Quantum Anomalous Hall Effect In Low Dimensional Materials

Since Edwin Herbert Hall discovered the Hall effect in 1879,the Hall effect has become a very significant research area in the field of condensed matter physics.In1988,Frederick Duncan Michael Haldane first proposed a quantum Hall effect model without external magnetic field in monolayer graphene system,which was later named quantum anomalous Hall effect.For more than 100 years,with the joint efforts of many scientists,the Hall effect has developed from the early classical Hall effect to today’s quantum anomalous Hall effect,and from the early Hall voltage to today’s lossless edge conductive state,which has laid a solid theoretical foundation for the preparation of high-speed electronic devices and high temperature quantum devices.In this thesis,the development of Hall effect family is systematically reviewed,and two theoretical works on quantum anomalous Hall effect during doctoral study are briefly introduced.The electronic properties of two-dimensional materials and hybrid two-dimensional materials are studied by using the first principles calculation method.The specific content of this thesis can be divided into the following aspects:firstly,the basic concepts,development process and theoretical analysis of six Hall effects in the Hall effect family are systematically summarized;secondly,the development history and theoretical concepts of the first principles calculation method based on density functional theory are described.In the first work,we theoretically predict the large band gap high temperature quantum anomalous Hall effect in the new two-dimensional electronic compound gadolinium halide Gd X（X=F,Cl,Br and I）.Two dimensional Gd X system is intrinsic quantum anomalous Hall effect insulator with in-plane magnetization.In addition,the quantum anomalous Hall effect with out-of-plane magnetization can be realized by using external weak magnetic field induction.In the two-dimensional gadolinium halide system considered,the two-dimensional Gd I material has the maximum band gap,which is about 84.3 me V.The theoretical Curie temperature of two-dimensional Gd X system is higher than room temperature,about 510-650 K.The two-dimensional electronic compound Gd X system provides an attractive and excellent candidate material for researchers to experimentally explore the high temperature quantum anomalous Hall effect with adjustable large band gap.In the second work,we theoretically study the electronic structure at the interface of superlattice system composed of perovskite bismuth ferrite（BiFeO₃）and graphene.Based on the first principles calculation results,it is found that in the superlattice composed of monolayer graphene embedded in[111]oriented perovskite BiFeO₃,the energy band structure at the interface opens the band gap near the Fermi level.The ground state magnetic configuration of BiFeO₃/graphene superlattice system is of in-plane antiferromagnetism.The size of the spin orbit coupling induced band gap of BiFeO₃/graphene superlattice depends not only on the in-plane magnetization direction of Fe atoms,but also on the distance between graphene and Fe atomic layers.In the experiment,the layer spacing of superlattice can be adjusted by applying external vertical stress.The theoretical calculation results provide a way to design hybrid two-dimensional materials with high performance.These unique physical properties are difficult to be found in a single material.Finally,the advantages of the first principles calculation method in the research of high temperature quantum anomalous Hall effect are discussed.The latest development of high temperature quantum anomalous Hall effect is prospected theoretically and experimentally.The new members of the Hall effect family,valley Hall effect,anomalous valley Hall effect and quantum valley Hall effect,are introduced,and the next research objectives and research plans are further described.