Percolating granular superconductor in a magnetic field

An array of Josephson tunnel junctions is studied as a model for granular superconductors. We determine the critical line in the (H, T)-plane, separating the phase-coherent and incoherent region as a function of the magnetic field. Both positional disorder and junction-dilution are treated. Approaching the percolation threshold from above, the critical exponent of the upper critical field is found to be 0.60±0.03. © 1988 Springer-Verlag.