Structural and Fluctuation Induced Excess Conductivity in R:1113 Superconductors

Abstract

We report here the fluctuation-induced excess conductivity in RBaSrCu3O7-δ (R = Y, Gd, Nd, and La) superconductor. It is found that Y and Gd samples are orthorhombic, while the Nd and La samples are quasi-tetragonal. The oxygen content is found to be close to 7 for all R:1113 samples. The logarithmic plots of ∆σ and reduced temperature Є reveal two different exponents corresponding to crossover temperature due to shifting the order parameter from (2D/1D) to (3D). The critical temperature, mean field temperature, crossover temperature, out of plane coherence length, and interlayer coupling are decreased as the ionic size increases. While the in plane and effective coherence lengths, and anisotropy are increased. We have also estimated several physical parameters such as upper critical magnetic fields in both a-b- and c-axis (Bab and BC), and critical current density J (0 K), and their values are found to be decrease as the ionic size increases. The results are discussed in terms of oxygen rearrangement, localization of carriers, coherence lengths, and anisotropy which are produced as the ionic size increases.