DISORDER, ANISOTROPY, AND THE LOSS OF COHERENCE IN SUPERCONDUCTING WIRE NETWORKS

We have investigated the effects of disorder and anisotropy on the sup erconducting transitions of square aluminum wire networks. We have fou nd that disorder in the network tile areas induces a crossover to a gl assy incoherent state in which T-c is independent of the applied field , and we can accurately model this behavior by considering only the en ergy cost of the frustration-induced supercurrents. On networks made a nisotropic by widening the horizontal wires of the square network, we find even more striking results. Numerous measurements (including tran sport: T-c(H) phase boundary, and AC susceptibility) indicate that the narrow wires exhibit the same behavior as the wide wires only at stro ngly commensurate fields; away from these fields, the narrow wires rem ain resistive far below the temperature al which the wide wires lose r esistive sensitivity, Furthermore, this weakening of superconductivity along the narrow wires at incommensurate fields becomes more extreme as the anisotropy is increased, even though the anisotropy is introduc ed by adding superconducting material to make the other set of wires w ider, We describe these results in terms of anisotropic localization o f the superconducting order parameter.