LASER PROBING OF HIGH-TC SUPERCONDUCTING THIN-FILMS

The spatial inhomogeneity of the electrical characteristics of hihg-T thin films was studied by optical laser probing. It was shown that the characteristic length L of inhomogeneous current distribution in high-T(c) films may be much larger than the grain size a, e.g. in polycrystalline YBa2Cu3O7-x film with critical current densities j(4.(2)2K3) approximately 10(3)-10(4)A/cm2 and grain size a approximately 1-mu-m the characteristic length L was equal to approximately 15-mu-m at T > T and approximately 100-mu-m at T < T(c). The large values of L are related to the large-scale percolation in the system of intergrain Josephson junctions with very wide distribution of critical currents I(ci) and normal-state resistances R (ni).