Temperature and magnetic field dependence of critical currents in granular superconductors

We analyze the critical current density J/sub c/ of a two-dimensional granular superconductor by a Josephson junction network approach, taking into account shielding current effects. We show that the temperature and field dependence of J/sub c/ is not directly given by the corresponding dependences of the maximum Josephson current of a single junction. By a critical state picture we discuss the temperature and magnetic field dependence of the effective energy barrier U/sub /spl gamma// for flux motion in the array. From the knowledge of U/sub /spl gamma//, calculated in the presence of currents flowing through the junctions, the magnetic field and temperature dependence of the critical current is derived.<
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