INPLANE MAGNETORESISTIVITY ANOMALIES NEAR THE AVERAGE SUPERCONDUCTINGTRANSITION IN YBA2CU3O7-DELTA AND BI2SR2CACU2O8 CRYSTALS WITH NONUNIFORMLY DISTRIBUTED T-C-INHOMOGENEITIES

We present detailed measurements of the in-plane magnetoresistivity, r ho(ab)(T, H), around the average superconducting transition in inhomog eneous YBa2Cu3O7-delta (Y-123) and Bi2Sr2CaCu2O8 (Bi-2212) crystals wi th small T-c-inhomogeneities non-uniformly distributed in the sample v olume, associated with small oxygen-content inhomogeneities. In zero a pplied magnetic field, our results confirm the presence in these inhom ogeneous Y-123 crystals of sharp resistivity peaks just above the aver age T-c, and they also show for the first time the presence of similar anomalies in inhomogeneous Bi-2212 crystals. Our measurements for mag netic fields, H, applied perpendicularly or parallel to the CuO2 (ab-) planes show that in these inhomogeneous superconductors the so-called magnetoresistivity excess, rho(ab)(T, H) - rho(ab)(T, O), is negative and very anisotropic near the average T-c. By using two-dimensional e lectrical resistor networks, this behaviour is explained, simultaneous ly and consistently for both directions of the applied magnetic field, in terms of temperature dependent current density redistributions ass ociated with the presence of non-uniformly distributed T-c-inhomogenei ties in the crystals.