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 YBa2Cu3O7. These junctions behave as high-quality, uniform super-normal-superconductor (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 treating the oxygen-sublattice defects as pair-breaking, allows quantification of the interlayer's microscopic properties such as normal coherence length, quasiparticle mean-free path, and resistivity. We find that the barrier exhibits properties of a dirty metal near the metal-insulator transition, with a Fermi surface area reduced an order of magnitude from that of the unirradiated film. In addition, we analyze the limiting normal properties of irradiated YBCO, showing that the normal coherence 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 structures in which the barrier is created from the electrode material through weakening by a pair-breaking mechanism.