Fluctuation conductivity and inhomogeneity in granularYBa2Cu3O7−y/Ag composite thick films

Abstract

We analyse the effect of interplay of the different types of inhomogeneities and the thermalfluctuation of the superconducting order parameter on the excess conductivity in a set ofYBa2Cu3O7−y/Ag composite thick films. We show that the mesoscopic inhomogeneities arising due tomost of the Ag residing at the grain boundaries strongly influence the tailingand the critical regions below and above the mean field transition temperature,Tc, respectively. A small fraction of Ag diffusing into the grains also produces microscopicinhomogeneities. Though these inhomogeneities are not expected to influence the SCOPF, we foundthat TLD, corresponding to the transition from the two to three dimensional fluctuation of the orderparameter in the mean field region, as well as the inter-planar coupling strength, stronglydepend on the Ag content in the composites. The effect of Ag induced inhomogeneities onthe temperature window corresponding to different phases in the mean field and thecritical regions are depicted in the form of a phase diagram. The large variation ofTLD, and nearinvariance of Tc with Ag content in the films as seen in the phase diagram, are explained by invoking therole of Ag in modifying the overall electronic structure of the grains.