| Several scanning tunneling microscope (STM) studies of the electronic structure of high Tc superconductors make up this thesis.; First high-resolution Fourier-transform scanning tunneling spectroscopy (FT-STS) is introduced as as a new technique for study quasiparticles in the high Tc superconductor Bi2Sr2CaCu2O 8+delta. Using it a characteristic 'octet' of quasiparticle states that determine the quasiparticle scattering processes was found. By analyzing the wavevectors of quantum interference patterns generated by the scattering, we determine the normal-state Fermi-surface and the momentum-dependence of the superconducting energy gap &vbm0;D&parl0;k&ar;&parr0;&vbm0; . These are in excellent agreement with angle resolved photoemission spectroscopy (ARPES). Another finding is the discovery of very strong quasiparticle scattering at the Brillouin zone-face.; Next, doping dependence of nanoscale electronic structure in superconducting Bi2Sr2CaCu2O8+delta is studied. At all dopings, the low energy density-of-states modulations are analyzed according to the same simple model of quasiparticle interference and found to be consistent with Fermi-arc superconductivity. The superconducting coherence-peaks, ubiquitous in near-optimal tunneling spectra, are destroyed with strong underdoping and a new spectral type appears. Exclusively in regions exhibiting this new spectrum, we find local 'checkerboard' charge-order with wavevector Q&ar; = (+/-2pi/4.5a0, O) and (O, +/-2pi/4.5 a0) +/- 15%. Surprisingly, this order coexists harmoniously with the low energy quasi-particle states.; Finally, the dopant oxygen atoms are located and related to the various manifestations of disorder in Bi2Sr2CaCu2O 8+delta. In previous work a '1 eV feature' was predicted by angle resolved ultraviolet photoemission (ARUPS) to be associated with local, non-hybridized, 2p orbitals of oxygen atoms. We detected this feature by spectroscopic mapping STM. It consists of a peak in the filled state tunneling conductance at about -0.960 eV and is localized to ≈8 A. The number of these '-0.96V features' are found to scale correctly with oxygen doping and they are therefore identified as the dopant oxygen atoms. This feature is imaged with atomic-resolution along with simultaneous low energy spectroscopic information on the cuprate electronic structure. Strong correlations between the oxygen map and the gapmap, Dr&ar; , the quasiparticle interference LDOS-modulations, and the low-bias topographic disorder is found. Thus, for the first time, we can begin to understand how the dopant atoms control the electronic structure of a cuprate high-T c superconductor. |
