Angle-Resolved Photoemission Spectroscopy Study Of Novel Quantum Materials

In condensed matter physics,every new discovery of novel quantum matters always at-tracts a lot of research interest,such as topological insulator,Dirac semimetal,Weyl semimetal,topological superconductor,Mn doped dilute magnetic semiconductor,giant linear Magneto-resistance.Most of basic properties are originated from their electronic structure.Thus,it is greatly important to study the electronic structures for understanding these novel proper-ties of materials.In this thesis,we study several kinds of quantum materials:large gap 2D topological insulators?single layer stanene and ZrTe₅single crystal?,3D topological insulators?PbTe/Bi₂Te₃?111?heterostructure film?,giant linear Magneto-resistance??-PtBi₂single crys-tal?,Mn based diluted magnetic semiconductor(Ba(Zn_0.875Mn_0.125)₂As₂single crystal).MBE was used to grow thin films;Low temperature STM was used to determine the topography and atomic structure;ARPES was used to measure the band structure.The main results are as fol-lows:1.Single stanene films were grew on Bi₂Te₃?111?successfully.We confirmed its A-Bstacking and honeycomb-like atomic structure by using the low temperature STM.Also,stanene's electronic structure were measured by ARPES.The experimental band disper-sion agrees well with the DFT results.We found that the band near K points in Brillouin zone is originate from the p_zorbit of Sn atoms,and the dangling bonds can be easily saturated.Our results showed that single layer stanene can be stable on the substrate,which opened a door for research of stanene.2.The electronic structure of ZrTe₅was studied and new edge states were observed directlyBy ARPES.ZrTe₅with layered structure is proposed to be weak topological insulator or strong topological insulator by theory depending on the lattice constant.The band structure measured in two cleavage surfaces?ac plane and ab plane?shows that ZrTe₅is weak topological insulator.Every single layer ZrTe₅is a 2D topological insulator.1D edge states of 2D topological insulators were directly observed by ARPES in the firsttime.3.Various thickness of PbTe?111?films were grew on Bi₂Te₃?111?by MBE method andtheir band structure were studied by ARPES.The growing process of high quality PbTe?111?films were monitored by RHEED.Diracshaped band dispersions were observed in 1 ML PbTe films without annealing and in2ML films with annealing process.The Dirac band is consistent with previous cal-culated electronic structure of PbBi₃Te₄,which indicate that inter-diffusion happenedbetween PbTe and Bi₂Te₃films.4.The electronic structure of?-PtBi₂were studied by high-resolved ARPES experiment.Non-centrosymmetric lattice structure was confirmed by STM and ARPES with the helpof LDA calculation.Different surface states were observed on two sides of?-PtBi₂bysystematically photon energy dependent ARPES experiments.STM's results supportedthat there are two kinds of cleavage surfaces.The electronic structure was calculatedby using the optimized non-centrosymmetric lattice model.The bulk band dispersionagreed well with the DFT calculated results.And the calculated results show that thereare some special quasi-2D fermi surfaces which may bring some explanation to theprevious reported exotic quantum oscillation in transport.5.Electronic structure of Ba?Zn0.875Mn0.125?2As2were studyed by ultraviolet?UV?ARPES.Except the localized states of Mn,We suggest that the hybridization between Mn and As orbitals strongly enhanced the density of states around-1.6 e V.No clear hybridization gap was detected between Mn 3d states and the valence bands,which means there were no strong correlation in this DMS system.The ARPES experiments of high quality Ba Zn2As2 single crystal is needed,so we can compare the bands between Mn-doped and undoped Ba Zn2As2 to check the theoretical model in the future.