Role of density of states in the fluctuation conductivity of Bi2Sr2Ca Cu2O8 and Tl2Ba2CaCu2O8 single crystals

The out-of-plane resistivity ρc (T,B) of Bi2Sr2CaCu2O8 and Tl2Ba2CaCu2O8 single crystals has been measured in weak magnetic fields applied perpendicular to the ab-plane. The measurement show a well pronounced peak at a temperature Tm. The external magnetic field shifts Tm towards lower temperatures and increases the magnitude of the peak. We demonstrate that the ρc (T,O) is well described by the fluctuation theory, developed by Dorin et al., in the Gaussian approximation over a wide range of temperature, but in the presence of field, fluctuations are better described in Hartree approximation. (author)