Electron tunneling studies of the cuprate superconductors yttrium barium cuprate and bismuth strontium calcium cuprate

Electron tunneling has long been regarded as one of the best techniques to study the energy gap, excitation spectrum, and ground state structure of superconductors. This thesis reports on the results of various efforts to fabricate single particle tunneling and Josephson proximity devices on the "high-T{dollar}sb{lcub}rm c{rcub}{dollar}" cuprate superconductors YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb7{dollar} and Bi{dollar}sb2{dollar}Sr{dollar}sb2{dollar}CaCu{dollar}sb2{dollar}O{dollar}sb8{dollar} for the purpose of measuring the microscopic superconducting properties of these materials.; It is well known that the cuprate superconductors have many undesirable chemical properties that can degrade the quality of the samples, particularly near the surface. For this reason, several methods of constructing tunnel junctions, each aimed at getting around some of the more obvious material problems, will be described, and the resulting data presented. Particular emphasis and attention will be paid to those major features of the data that are reproducible independent of the method of junction construction.; Much of the data presented do not much resemble the classical norms given by the standard Bardeen-Cooper-Schrieffer theory of superconductivity. These differences from classical behavior include an anomalously large ratio of the energy gap to the transition temperature 2{dollar}Delta{dollar}/kT{dollar}sb{lcub}rm c{rcub}approx{dollar} 6 to 7, a background tunneling conductance that is at least partially a linear function of voltage bias, the presence of a large normal electron contribution to the single-particle spectrum and the Josephson effect well below T{dollar}sb{lcub}rm c{rcub}{dollar}, and a prominent anisotropy in the Josephson coupling to a standard superconductor like Pb. In addition, there is evidence that the classical proximity effect model of the coupling between a cuprate superconductor and a good normal metal must undergo some alterations in order to describe the proximity effect between YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb7{dollar} and an inert metal overlayer such as Ag.