YBCO-BASED RAMP-EDGE JOSEPHSON-JUNCTIONS AND DC SQUIDS WITH A CUBIC-YBCO BARRIER LAYER

Recently, the discovery of a nonsuperconducting metastable cubic phase of YBa2Cu3O7 (YBCO) has been reported. Because of the structural, chemical, and depositional compatibility of cubic-YBCO with superconducting YBCO, it is an excellent candidate for use in heteroepitaxial structures. Such structures involving superconducting YBCO/cubic YBCO/superconducting YBCO ramp-edge proximity-effect Josephson junctions were fabricated on MgO substrates. Junctions having critical current densities of approximately 8 X 10(4) A/cm2 and I(c)R(n) products as high as 0.8 mV at 15 K were produced. Shapiro steps were seen in the presence of RF radiation. DC SQUIDs were fabricated with these junctions and showed periodic critical current modulation with applied magnetic field to temperatures in excess of 77 K.