Critical Analyses of the Resistivity in High Tc- Superconductors: For the Case of Single Crystalline Bi2Sr2CaCu2O8+δ

We have performed the precise resistivity measurements of single crystalline Bi2Sr2CaCu2O8+δ by the six terminal method. Because of the huge anisotropy in the normal state and the superconducting state, the true resistivity can only be obtained by taking the inhomogeneous current distribution in the sample into account. In addition, both in-plane and c-axis resistivities have a tendency to merge at a single temperature T irr, which corresponds to the irreversibility temperature. This fact as well as the I-V characteristics strongly suggests existence of the single phase transition at T irr in Bi2Sr2CaCu2O8+δ, which is in strong contrast with YBa2Cu3O7+δ.