YBa₂Cu₃O₇ Bicrystal Josephson Junctions and dc SQUIDs

Bicrystal Josephson junctions and direct current superconducting quantum interference devices ( dc SQUIDs) were prepares on YBa₂Cu₃O₇( YBCO ) thin films deposited on yttrium stabilized ZrO₂ bicrystal substrates The critical current densities J_c ~ 2 X 10⁶ A/cm² for YBCO thin film and (1 - 3 ) X 10³ A/cm² at boundaries were obtained at 77K. For YBCO Josephson junction made on 28°misorientated boundary, the Shapiro steps were observed. The dc SQUID was made on the 32° misorientated boundary junctions, which consisted of 40 X 40μm of loop and 2000 X 2000μm planar superconductive flux focuser. The voltage modulation depth of this SQUID was 6μV, and the magnetic field sensitivity was estimated to be ~ 2pT /√Hz from the measured noise level.