Doping study of high temperature superconductors using angle-resolved photo-electron spectroscopy

The electronic structure of the high temperature superconductor, {dollar}rm Bisb2Srsb2CaCusb2Osb{lcub}8+delta{rcub}{dollar} is studied, especially, the evolution of its electronic structure with hole doping. Techniques were developed to prepare cleaved surfaces of thin film samples grown by molecular beam epitaxy (MBE) within the ultra-high-vacuum environment of the photoemission chamber. Angle-resolved photoemission was used to collect data from {dollar}rm Bisb2Srsb2Casb{lcub}1-x{rcub}Dysb{lcub}x{rcub}Cusb2Osb{lcub}8+delta{rcub}{dollar} and oxygen depleted {dollar}rm Bisb2Srsb2CaCusb2Osb{lcub}8+delta{rcub}{dollar} investigating the evolution of the electronic structure above T{dollar}rmsb{lcub}c{rcub}{dollar} in materials with hole doping levels ranging from insulating to optimally doped. The spectra of near-optimally doped {dollar}rm Bisb2Srsb2CaCusb2Osb{lcub}8+delta{rcub} (Tsb{lcub}c{rcub}sim85K){dollar} grown by MBE are virtually identical to those of similarly doped bulk crystals. The spectra of insulating {dollar}rm Bisb2Srsb2Casb{lcub}0.5{rcub}Dysb{lcub}0.5{rcub}Cusb2Osb{lcub}8+delta{rcub}{dollar} behave qualitatively like those of {dollar}rm Srsb2CuOsb2Clsb2,{dollar} a model antiferromagnetic insulator with one CuO{dollar}sb2{dollar} plane. Near optimal hole doping {dollar}rm(Tsb{lcub}c{rcub}sim85K),{dollar} the Fermi surface is large and consistent with band calculations. In underdoped material with {dollar}rm Tsb{lcub}c{rcub}{dollar} of 60-70K, portions of this Fermi surface are not seen. This change is related to the opening of an energy gap above {dollar}rm Tsb{lcub}c{rcub}{dollar} in the region of the Brillouin zone near {dollar}(pi,0).{dollar}...