Artificially layered YBa2Cu3O7-PrBa2Cu3O7 heterostructures; growth, properties, and device applications (Invited Paper)
We have investigated the influence of interface effects and CuO2 plane orientation on transport properties of high temperature superconducting (HTS) thin films in YBa2 Cu3O7-PrBa2Cu3O7 (YBCO-PrBCO) heterostructures grown by pulsed laser deposition. Two unit cell (≈ 24 angstroms) thick YBCO films, isolated in c-axis oriented PrBCO/YBCO/PrBCO trilayers, are found to superconduct at temperatures above 20 K, while films thicker than 6 unit cells display bulk superconducting properties. An epitaxial process has also been developed to grow YBCO films and YBCO/PrBCO heterostructures with the CuO2 planes oriented normal to the film surface. These a-axis oriented films display transport properties comparable to the best c-axis oriented films and, moreover, are better suited to the fabrication of sandwich-type Josephson junction devices by virtue of the longer superconductive coherence length normal to the direction of the YBCO-PrBCO barrier interface.