Josephson-oscillator spectrum and the reentrant phase transition in granular superconductors

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Abstract
The superconductive phase transition in a granular superconductor, modeled as a Josephson-junction array, is studied using a self-consistent mean-field theory. In the case when the Josephson oscillator was treated as a pendulum with discrete energy levels, no reentrant behavior was found. In the opposite extreme when it was treated as a quantum particle in a periodic field, having a band-energy spectrum, there exists a reentrance from the superconductive to the normal state as the temperature is further lowered.