TUNNELING THROUGH GRAIN-BOUNDARIES OF YBA2CU3O7 STEP-EDGE JUNCTIONS

Tunneling experiments were done on YBa2CU3O7 step-edge junctions. The temperature dependence of the superconducting gap parameter, Delta(T), was measured. From the peak-to-peak distance in the conductance curve , Delta was estimated to vary from 24 to 32 meV at 4.2 K. The conducta nce at high-voltage bias does not increase with increasing voltage. Th e tunneling results, together with the well-behaved magnetic field dep endence of the critical Josephson current, hysteresis, and Fiske-type resonances in current-voltage curves, indicate a dielectric behavior o f the grain boundary junction, i.e., a tunnel junction. (C) 1996 Ameri can Institute of Physics.