3D FLUCTUATION CONDUCTIVITY IN THE 2-BAND MODEL - THEORY AND EXPERIMENT

The formulae for the temperature dependence of the 3D paraconductivity in the vicinity of a superconducting phase transition are derived usi ng the linearized Ginzburg-Landau equations for a two-band model takin g into account interband scattering of pairs within the Kubo formalism . In general there exist two correlation lengths. However, only one of them is critical and determines the fluctuation conductivity Delta si gma(T). The Aslamazov-Larkin formulae are modified in the two-band mod el. After calculating from available data the various terms and amplit udes, our theory is compared with experimental data on La-123, Y-123 a nd Bi-2212 based films.