TEMPERATURE AND MAGNETIC-FIELD DEPENDENCE OF CRITICAL CURRENTS IN GRANULAR SUPERCONDUCTORS

We analyze the critical current density J(c) of a two-dimensional gran ular superconductor by a Josephson junction network approach, taking i nto account shielding current effects. We show that the temperature an d field dependence of J(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-gamma for flux motion in the array. From the knowledge of U-gamma, calculated in the presence of currents flowing through the Junctions, the magnetic field and temp erature dependence of the critical current is derived.