MICROSCOPIC BARRIER PROPERTIES IN ELECTRON-BEAM SCRIBED YBCO JOSEPHSON-JUNCTIONS

We present an analysis of the microscopic properties of the Josephson barrier in electron-beam junctions scribed at low temperatures in YBa2 Cu3O7. These junctions behave as high-quality, uniform super-normal-su perconductor (SNS) junctions which allows their characteristics to be compared in detail to well-established SNS theory. Combining this data with a Boltzmann transport model of the irradiated region, and treati ng the oxygen-sublattice defects as pair-breaking, allows quantificati on of the interlayer's microscopic properties such as normal coherence length, quasiparticle mean-free path, and resistivity. We find that t he barrier exhibits properties of a dirty metal near the metal-insulat or transition, with a Fermi surface area reduced an order of magnitude from that of the unirradiated film. In addition. we analyze the limit ing normal properties of irradiated YBCO, showing that the normal cohe rence length at the original transition temperature is constrained to less than twice the zero-temperature superconducting coherence length of the original film. This analysis applies in general to weak-link st ructures in which the barrier is created from the electrode material t hrough weakening by a pair-breaking mechanism. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.