Generalization of fluctuation induced conductivity in polycrystalline Y1-xCaxBa2Cu3Oy and Bi2Sr2Ca1Cu2O8+delta superconductors

We have investigated the fluctuation induced conductivity (FIC) of two high -T-c superconductors (HTSC) namely Bi2Sr2Ca1Cu2O8+delta and Y1-xCaxBa2Cu3Oy . The effective medium theory is used to formulate the Aslamazov-Larkin typ e equations for these polycrystalline superconductors. For the three dimens ional case the temperature exponent remains unaltered since both the expone nts for the ab plane and c direction FICs in the crystal are same. But the situation is more complex in the two dimensional case where the counterpart s in the crystal have different temperature dependencies. The FIC is evalua ted and compared with the theoretically obtained values from the model prop osed. We have also evaluated the exponents, the coherence lengths, and the crossover temperature. The analysis based on the present model reveals that these two superconductors are similar concerning their nature of fluctuati ons. The extent of a particular fluctuation region of course differs from o ne HTSC to another. (C) 1999 American Institute of Physics. [S0021-8979(99) 03217-X].