Critical current in granular superconductor C-Si-W with peak-like re-entrant superconductivity.

Some granular disordered superconductors, namely diamond-like carbon-silicon films containing tungsten, show one or more small, clearly detectable peaks in resistivity curves at lower temperatures than that of the superconducting main transition, T-c. Based on the concept of cluster superconductivity and on the percolation theory, we carried out extensive numerical simulations that relate the appearance of the peak-type re-entrant superconductivity to the absence of superconducting percolative paths crossing the entire sample. The numerical determination of such paths allowed us to compute the maximum supercurrent density j(c) to flow through the sample in the temperature region below T-c.