Electrical transport and defect structures in yttrium-barium-copper-oxide thin films

The electrical properties of superconducting {dollar}rm YBasb2Cusb3Osb x{dollar} thin films are extremely sensitive to the presence of structural disorder, perhaps much more so than the elemental and alloy superconductors that were their predecessors. This dissertation presents a careful study of the relationship between several electrical transport properties and defect structures observed in {dollar}rm YBasb2Cusb3Osb x{dollar} thin films. The motivation for this study is both the desire to identify important issues pertinent to technological application of these materials and to understand the physics of the superconductor. Technological development of these superconductors will require understanding and control of crystalline disorder in order to optimize the electrical properties pertinent to a given application. This work focuses on measurement and discussion of two important figures of merit in the application of superconductors, surface impedance and critical current density. Two general classes of defects have been found to have a large impact on these quantities, grain boundaries and atomic scale or point-like defects. Simple models of the effect of these defect structures clarify some important constraints for the development of a successful technology. The models also provide insight into the underlying physics. In general, the properties of {dollar}rm YBasb2Cusb3Osb x{dollar} are partly consistent and partly inconsistent with conventional theories of superconductivity. This dissertation identifies some important, unresolved issues in understanding the nature of the superconducting state.