Electronic Structure Of Black Phosphorus And Topological Materials

Recently,the two dimensional materials such as graphene,topological insulators,transition metal chalcogenide and so on have attracted tremendous attentions due to their exotic electronic,magnetic,optical properties and many potential applications.In this thesis,we have detailed and systematically study of the transport proper-ties,topological properties,and electronic band structure of Black Phosphorus single crystal,Sr-doped superconduting topological insulators?Sr_xBi₂Se₃?,and heterostruc-ture of ultrathin Bi?111?grown on topological insulators?Bi₂Se₃,Bi₂Te₃?,using high-resolution angular resolved photoemission electron spectroscopy?ARPES?,molecular beam epitaxy?MBE?,and scanning tunneling spectroscopy?STM?.The main results are as follows:1.Electronic structures of single crystalline black phosphorus were studied by state-of-art angle-resolved photoemission spectroscopy.Through high resolution pho-ton energy dependence measurements,the band dispersions along out-of-plane and in-plane directions are experimentally determined.The electrons were found to be more localized in the ab-plane than that is predicted in calculations.Beside the k_z-dispersive bulk bands,resonant surface state is also observed in the momentum space.2.Using high-resolution angle-resolved photoemission spectroscopy and scan-ning tunneling microscopy/spectroscopy,the atomic and low energy electronic struc-ture of the Sr-doped superconducting topological insulators?Sr_xBi₂Se₃?were studied.Scanning tunneling microscopy shows that most of the Sr atoms are not in the van der Waals gap.After the Sr doping,the Fermi level was found to move a little bit upwards compared with the parent compound Bi₂Se₃,which is consistent with the low carrier density in this system.The topological surface state was clearly observed and the posi-tion of the Dirac point was determined in all doped samples.The surface state is well separated from the bulk conduction bands in the momentum space.The persistence of separated topological surface state combining with small Fermi energy makes this new superconducting material a very promising candidate of the time reversal invariant topological superconductor.3.Electronic transport properties of topological insulators?TIs?Bi₂Se₃,Bi₂Te₃and ultra thin Bi?111?/TI were studied using in situ scanning-tunneling-microscope-based micro-four-probe technique.The measured conductivity were found to be dom-inated by two dimensional?2D?conducting channels.The 2D conductivity is in the order of 1×10^-3S,Temperature dependence measurements indicate that the electron-phonon scattering is much stronger in Bi₂Te₃than that in Bi₂Se₃.Our results suggest that the in situ micro-four-probe measurements can be used to detect the intrinsic elec-tronic transport properties of exotic 2D electron systems.