AN ORDER-DISORDER CROSSOVER IN GRANULAR SUPERCONDUCTORS

On nanometric scale, even HTCS thin films with very sharp transitions show a granular structure and the existence of a continuos network of grain boundaries. Coupling through grain boundaries is distributed, and the geometry of the network is practically random. In the presence of a magnetic field also the frustration should be taken in account. Is it possible to estimate quantitatively the relevance of any one of the above elements in determining the properties of the sample? We have investigated this problem on simple 2D model systems. Here, we present a discussion of the interplay between disorder and frustration, and of their influence on the loss of coherence in granular materials. Size and shape effects on the response of the arrays are also briefly considered.