NONOHMIC I-V BEHAVIOR IN GRANULAR YBA2CU3O7-DELTA AND (BI,PB)(2)SR2CA2CU3O10 HIGH-T-C SUPERCONDUCTORS

Current-voltage measurements performed on granular YBa2Cu3O7-delta and (Bi, Pb)(2)Sr2Ca2Cu3O10 high-T-c superconducting samples below their transition temperatures revealed a power law (V = alpha I-beta) over a wide range of applied voltage. The exponent beta decreases linearly w ith increasing temperature, deviating from linearity at temperature T- nl lower than T-c. Moreover the resistivity (rho) exhibits a slope cha nge in a log(rho)-log(1-T/T-c) plot at a temperature T < T-c. We argu e that T-nl and T may reflect changes in the dynamics of the intergra nular (or Josephson) vortices just below the superconducting transitio n temperatures.