LARGE CRITICAL CURRENTS AND CURRENT STEPS IN SHUNTED BICRYSTAL JOSEPHSON-JUNCTIONS AT LIQUID-NITROGEN TEMPERATURES

The amplitudes of the critical current and constant-voltage steps in s hunted bicrystal Josephson junctions were explored as a function of th e grain boundary type (symmetrical or asymmetrical), misorientation an gle Theta and thickness of YB2Cu3O7-delta films. Two new results were demonstrated. First, we found that for the given angles Theta of 19 de grees to 38 degrees the junctions on symmetrical grain boundaries gene rated the highest critical current density j(c). Second, the increase of superconducting film thickness up to 1 mu m allowed us to measure t he first current step height of 1 mA and 2 mA in high-T-c junctions op erated at 80 K and 50 K respectively. Simulations with a wide-junction model have shown that the maximal current step amplitude in large cri tical current bicrystal junctions is controlled by a self-field effect .