Fluctuation Conductivity of La0.5RE0.5BaCaCu3O7−d (RE=Y, Sm, Dy) Superconductor

Abstract

We report production, conductivity fluctuation and magnetoconductivity fluctuation measurements of the system La0.5RE0.5BaCaCu3O7−δ RE=(Y,Sm,Dy) high-temperature superconductors. Samples were synthesized by the standard solid state reaction recipe. By Rietveld-like refinement of X-ray diffraction patterns we determined that the material crystallizes in a tetragonal structure. DC resistivity measurements show a bulk critical temperature Tc (71, 72 and 72 K for RE=Y, Sm, Dy, respectively) for the analyzed samples. In order to examine the effect of substitution of rare earth into the lanthanum structural sites on the pairing mechanism close to Tc, we performed conductivity fluctuation analysis by using the method of logarithmic temperature derivative of the conductivity excess. We found the occurrence of Gaussian and genuinely critical fluctuations. Our results are in agreement with reports on non-doped systems, but we observe minor values of the coherence length of the fluctuation regimes for the doped case. Correlations of critical exponents with the dimensionality of the fluctuation system for Gaussian regimes were made by using the Aslamazov–Larkin theory. The genuinely critical exponent was interpreted by the 3D-XY.