PRECISION-MEASUREMENT OF THE INPLANE PENETRATION DEPTH LAMBDA(AB)(T) IN YBA2CU3O7-DELTA USING GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

We have determined the temperature dependence of the ab-plane penetrat ion depth lambda(ab) in epitaxial YBa2Cu3O7-delta films by measuring t he magnetic-field dependence of the critical current of YBa2Cu3O7-delt a bicrystal grain-boundary Josephson junctions. Using this de techniqu e the change of the penetration depth with varying temperature has bee n measured between 4.2 and 60 K with a resolution of 0.2 Angstrom. We found a linear lambda(ab)(T) dependence at temperatures below about 10 K. This linear dependence is consistent with lines nodes of the gap f unction.