Fluctuation conductivity in YBa2Cu3O7−y films with different oxygen content. I. Optimally and lightly doped YBCO films

Fluctuation conductivity in YBa2Cu3O7−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 Tc. The values of the transition temperature are used to determine the coherence length ξc(0) along the c axis and the phase relaxation time τφ(100K) of the fluctuational pairs. Despite the decrease of Tc from 87.4 to 54.2 K with decreasing oxygen content in the samples studied, a value τφ(100K)=(3.35±0.01)×10−13 s is obtained for all the samples. It is shown that the dependence of ξc(0) on Tc conforms to the standard theory of superconductivity. The mechanisms for the scattering of charge carriers and for superconducting pairing in high-Tc superconductors are analyzed.