The Study Of Magnetic Topological Insulator MnBi_2nTe_3n+1?n=3,4? By Angle-resolved Photoemission Spectroscopy

The interplay between topology and magnetism is essential for realizing novel topological states such as axion insulators,the magnetic Weyl semi-metals,Chern insulators.In 2018,M.M.Otrokov et al have confirmed that Mn Bi₂Te₄ was the first antiferromagnetic topological insulator material in the world[1].Subsequently,people found that the compounds of MnBi_2nTe_3n+1?n = 1,2,3,...?system are Magnetic topological insulators,these materials arouse great interest in condensed matter physics field.The antiferromagnetic structure of the MnBi_2nTe_3n+1 system is the key to open the band gap in its topological surface state.As long as the Fermi surface is adjusted into band gap by doping,the quantum anomalous Hall effect can be achieved.The so-called quantum anomaly Hall effect refers to a quantized Hall effect that does not require an external magnetic field and has chiral edge states.As MnBi_2nTe_3n+1 system's n become larger and larger,the antiferromagnetic coupling strength between the magnetic layer and the magnetic layer become weaker and weaker,which makes it easier to transfer antiferromagetic phase into ferromagnetic phase.Compared to Mn Bi₂Te₄,MnBi₆Te₁₀?n = 3?and MnBi₈Te₁₃?n = 4?are more promising candidates to realize Quantum Anomalous Hall effect.At present,there are few experiments focus on the physical properties of MnBi₆Te₁₀ and MnBi₈Te₁₃.A systematical study of the physical properties of these two phases will help us to understand the overall characteristics of the MnBi_2nTe_3n+1 system better and provide a reference for subsequent research on this system.In this thesis,high-quality MnBi₆Te₁₀ and MnBi₈Te₁₃ single crystals are successfully synthesis by the flux method,and the electrical and magnetical properties of the system are measured by Physical Property Measurement System?PPMS?and Magnetical Property Measurement System?MPMS?.We find that: with the increase of n,the phase transition temperature of the MnBi_2nTe_3n+1 system decreases,and the magnetic field required for spin flip also decreases;MnBi₆Te₁₀ is an intrinsic antiferromagnetic topological insulator,MnBi₈Te₁₃ is an intrinsic ferromagnetic topological insulator;The longitudinal resistance of MnBi₆Te₁₀ and MnBi₈Te₁₃ decrease as the temperature decrease,showing a metallic phase property.In addition,we also used Angle Resolved Photoemission Spectroscopy?ARPES?to measure the band structure of these two materials systematically.We found that the samples showed different band structures according to different stacking order of the structural units.Three different band structures of MnBi₆Te₁₀ and four different band structures of MnBi₈Te₁₃ are successfully observed in experiment.Moreover,the corresponding map information of different band structures is also very different.Our work provides the possibility to use natural heterostructure to rationally design and control magnetism and other broken symmetry states in layered vd W materials.