Phase Coherence and Critical Resistance in Superconducting Granular Films
A granular superconductor is an ensemble of small superconducting grains, the sizes and shapes of which are randomly distributed to some extent. The grains are interacting with each other through the Josephson coupling which is also random. The physical properties of granular superconductors depend largely on the mean size of grains, d, and the mean Josephson coupling energy, E J . Usually, d is smaller than the coherence length. Therefore each grain is a so-called zero dimensional superconductor. In the limit of large size and weak coupling, the system can be regarded as a random Josephson network, while in the opposite limit, it is a homogeneously disordered superconductor. Many interesting phenomena are expected between these two limits. In this paper, the experiments of two-dimensional (2 D) thin films of granular superconductors are reviewed.
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