The technology to build reproducible and accurately defined structuresconsisting of many lumped junctions has become available only recently,therefore extended investigations are relatively new. However, beside theinterest of such discrete structures per se, it has been suggested soon afterthe discovery of high-Tc superconductivity that granular superconductorsmight be modelled as superconducting islands surrounded bynon-superconducting material and weakly coupled to each other. Thisprogram has been vigorously carried on, and models of planar Josephsonjunction arrays (JJAs) have been successfully used to mimic the magneticbehaviour of granular superconductors. The JJA model has been comparedto continuous models of non-granular superconductors. We will show howto derive the height of pinning barriers in the JJA model and compare theresults with the continuous model. In particular, the existence of currentdependent activation energy has been proved to be a key characteristic tounderstand fluxon motion.
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