Transport Properties Of Cerium-doped Topological Insulator Bi₂Te₃

Topological insulators(TIs)are a class of materials with special topological characteristics.They have attracted the attention of a large number of researchers in the past two decades because they have great research significance in the fields of theoretical physics,quantum computers,and spintronic devices.The importance of topological materials can be seen from the 2016 Nobel Prize in Physics awarded to topological phase transition theory.Due to the stable structure,simple energy band structure,large body energy gap and only one topological Dirac point,three-dimensional topological insulators(3D-TIs)have gradually entered people's field of vision with the deepening of research.Among them,the most representative materials are Bi2Se3,Bi2Te3 and Sb2Te3.The TRS of 3D-TIs could be broken by introducing magnetism,and some novel phenomena are predicted,such as quantum anomalous Hall effect(QAHE),topological magnetoelectric effect and mirror magnetic monopole,etc.Doping with magnetic elements is a widely used method of introducing magnetism into TIs.The use of transition element doping research has achieved many important research results,including the discovery of the quantum anomalous Hall effect in the experiment.However,the transition element doping needs to produce obvious magnetic interaction at very low temperature,which brings great challenges to the practical application of the corresponding system.The f-electron rare earth element(RE)is suitable for the study of magnetic element doping of topological insulators due to its very large magnetic moment.Cerium is the first element in the periodic table to be occupied by f electrons.Its f electron occupancy configuration is simpler than other f electron systems,and its trivalent ion can equivalently replace Bi/Sb ions without changing the carrier concentration in the system.Therefore,the cerium-doped topological insulator is a good prototype research system,which is of great significance for the in-depth understanding of the interaction between f electrons and topological insulators.In this thesis,the sample preparation and electron transport properties of the cerium-doped topological insulator Bi2Te3 film are studied,and the following research results have been obtained:(1)The preparation technology of cerium-doped topological insulator Bi2Te3 thin film samples was studied.Bi2Te3 films with different cerium doping concentrations were grown on 4H-Si C epitaxial graphene substrate and sapphire substrateby molecular beam epitaxy;RHEED and XRD characterization results show that Ce atoms are doped into Bi2Te3 lattice by replacing Bi atoms to form(Cex Bi1-x)2Te3 structure,which has little effect on the lattice parameters of the system.(2)The electron transport properties of(Cex Bi1-x)2Te3 film are studied.The cerium-doped Bi2Te3 film exhibits metallic behavior in the high-temperature region,and the resistivity gradually decreases with the decrease of temperature,and a minimum resistance value appears in the low-temperature region(5-25 K).The data fitting results show that the resistance behavior at low temperature is the result of the combined effect of the Kondo effect and the Fermi liquid behavior.(3)The weak delocalization effect in(Cex Bi1-x)2Te3 film is studied.The results show that the obvious weak anti-localization in topological insulators will gradually be suppressed as the concentration and temperature increase.The cerium-doped Bi2Te3 film exhibits negative conductivity.Through the fitting of the HLN model,the relationship of the phase coherence length of the system with the concentration and temperature is obtained.The results show that the phase coherence length gradually decreases with increasing concentration and temperature.It is always longer than the mean free path of the system,indicating that the system always remains in the quantum interference state.The number of conductance channels is changed from two to one for x ? 0.02,indicating that the two-dimensional transport channel is gradually suppressed with the increase of the cerium concentration,which indicates that there is a strong competition between magnetism and topological surface states for x = 0.01~0.02.