Fluctuation conductivity in YBa2Cu3O7-y films of various oxygen content.I.Optimally and weakly doped YBCO films

The fluctuation-induced conductivity measured for YBa₂Cu₃O_7-y (YBCO)films of various oxygen concentration is analyzed using different theoretical models describing weak fluctuations in high-T_c superconductors and considering both the Aslamazov-Larkin and Maki-Thompson terms in the clean limit approach.A clear crossover from the MT to AL fluctuation mechanism is revealed for all the samples studied as temperature approaches T_c. Using the crossover temperature T₀ the coherence lengh along the c-axis x_c(0), and the phase-relaxation time of the fluctuating pairs, t_j (100 K), are determined. Despite the fact that T_c decreases from 87.4 down to 54.2 K with oxygen depletion t_j (100 K)=(335±0,01)×10^-13 s is obtained in all the cases.The x_c vs T_c dependence is found to follow the standard superconductivity theory. Possible mechanisms of charge scattering, mainly based on the NAFL model description and of superconducting pairing are also considered.

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