Effect of grain boundaries on paraconductivity of YBa2Cu3Ox Original Research Article

To investigate the effect of grain boundaries on paraconductivity of YBa2Cu3Ox, melt-textured and c-axis oriented thin films with controlled grain boundaries (superconducting transition width, ΔT, varying between 0.54 and 2.85 K) were prepared, and dc-conductivity has been measured as a function of temperature. In the logarithmic plots of excess-conductivity (Δσ) and reduced temperature (ϵ), starting from low values of ϵ, we have observed three different regions namely critical region, mean field region and short wave fluctuation region. A correlation is observed between the range of critical region and ΔT, which is found to increase with ΔT. While for ΔT values smaller than 2.5 K only static critical region is observed, for higher ΔTs both static and dynamic critical regions are observed. In the mean field region a crossover from 3D to 2D was observed for all the samples. At ϵ values larger than 0.24, the excess-conductivity decreased sharply as ϵ−3, which suggested the existence of the short wave fluctuations.