Fluctuation conductivity in YBa[sub 2]Cu[sub 3]O[sub 7-y] films with different oxygen content. I. Optimally and lightly doped YBCO films.

Fluctuation conductivity in YBa[SUB2]Cu[SUB3]O[SUB7-y] (YBCO) films with different oxygen concentrations is investigated. All of the samples exhibit a clear transition from the Maki-Thompson mechanism of scattering of fluctuational pairs to the Aslamazov-Larkin mechanism as the temperature approaches T<SUBc>. The values of the transition temperature are used to determine the coherence length ξ<SUBc>(0) along the c axis and the phase relaxation time τφ(100K) of the fluctuational pairs. Despite the decrease of T<SUBc> from 87.4 to 54.2 K with decreasing oxygen content in the samples studied, a value τφ(100K) = (3.35 ± 0.01) x 10<SUP-13> s is obtained for all the samples. It is shown that the dependence of ξ<SUBc>(0) on T<SUBc> conforms to the standard theory of superconductivity. The mechanisms for the scattering of charge carriers and for superconducting pairing in high-T<SUBc> superconductors are analyzed. [ABSTRACT FROM AUTHOR]