Josephson coupling in a-axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich-type junctions

We have studied Josephson coupling in a-axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich-type superconductor/normal/superconductor (SNS) junctions. Growth parameters for the films were optimized for smoothness of the barrier interfaces and the films were well characterized by scanning electron microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy. Transport of the barrier material was highly dependent upon the doping: for x=0, the resistivity followed a T−1/4 behavior and was ∼105 Ω cm at 4.2 K; for x=0.45, the resistivity was nearly metallic and was 10−1 Ω cm at 4.2 K. In the small junction regime W<λj, the critical current scaled with junction area, and was modulated by a magnetic field. We have compared our results to other SNS work and found that the coupling strength of the barrier increases with the conductivity of the barrier material. Possible sources of the coupling are discussed.