Angle Resolved Photoemission Spectroscopy Study On AMnSb₂(A=Ca,Ba And Eu)

Topological materials,including topological insulators,topological semimetals,topological superconductors and etc.,have become the research frontier in condensed matter physics because of their unique electronic structure and physical properties.The AMnPn2(A=Ca,Sr,Ba,Eu and Yb;Pn=Bi and Sb)system provides an important plat-form to explore for new topological materials and study their topological properties.In this thesis,the electronic structure and topological properties of CaMnSb2,BaMnSb2 and EuMnSb2 have been investigated systematically by using angle resolved photoe-mission spectroscopy(ARPES).The thesis consists of the following parts:1.A brief introduction of the research about topological physics and some basic concepts.The main classification of topological materials is described.In particular,the AMnPn2 materials(A=Ca,Sr,Ba,Eu and Yb;Pn=Bi and Sb)is introduced and reviewed.2.The principle,experimental system and operation of ARPES are introduced.The ARPES systems in our laboratory are introduced,with an emphasis on the design,construction and test results of the large momentum extremely low temperature Laser-ARPES system.3.Developed a Molecular Beam epitaxy(MBE)system.The MBE technique is briefly introduced.The design,installation and test results of the MBE system are de-scribed.4.High quality Zr(Te,Se)5 single crystals are successfully grown by chemical va-por transport method.High quality Ca-Sr-Cu-0 single crystals,including SrCu02,Sr2CuO3,Ca0.24Sr0.56CuO2 and infinite-layer Ca0.86Sr0.14CuO2 single crystals,are grown by using travelling solvent floating zone method.These grown single crystals are char--acterized in the composition,crystal structure and physical properties and they lay a foundation for the further studies.5.The electronic structure and topological properties of CaMnSb2 has been stud-ied for the first time by high resolution ARPES measurements and band structure cal-culations.The observed Fermi surface mainly consists of one hole pocket around the? point and one tiny hole pocket at the Y point.A strong spectral weight accumulation along the ?-X direction on the hole-like Fermi surface around ? point is observed,indi-cating a strong anisotropy of the density of states along the Fermi surface.The tiny hole pocket at the Y point originates from an anisotropic Dirac-like band with the crossing point of the linear bands lying?10 meV above the Fermi level.These observations are in a good agreement with the band structure calculations.In addition,we also observe additional features along the ?-Y line that cannot be accounted for by the band structure calculations.These results indicate that the Dirac-like structure at the Y point may play an important role in dictating the physical properties of CaMnSb2.They provide im-portant information in understanding and exploration of novel properties in CaMnSb2 and related materials.6.The unusual electronic structure of BaMnSb2 has been revealed by high reso-lution ARPES measurements and band structure calculations.The measured electronic structure of BaMnSb2 is unusual in three aspects.First,all the measured bands are nearly linear that extend to a wide energy range.Second,the observed Fermi surface mainly consists of one hole pocket around ? and a strong spot at Y.The Fermi surface is formed from the crossing points of the linear bands.Third,the measured electronic structure deviates strongly from the band structure calculations.These results will stim-ulate further efforts to theoretically understand the electronic structure of BaMnSb2 and search for novel properties in this Dirac material.7.The electronic structure of EuMnSb2 has been investigated in detailed by high resolution ARPES measurements combined with band structure calculations.The ob-served electronic structure is not equivalent in the first and second Brillouin zones.These results indicate that there is an additional factor in EuMnSb2 to determine its unusual electronic structure.