Anisotropy, disorder, and commensurability in superconducting networks

We report on recent experiments on electron beam lithographically prepared superconducting wire networks. In square networks we have found that along with the dips in the T_c vs. φ/φ₀ phase boundary at rational fields, there is an even more pronounced effect of rationality on the width of the resistive transition. We have disordered several types of networks, fit the phase boundary excellently with the J² model and shown that there is no critical field or amount of disorder above which the phase boundary loses periodic structure. We have introduced anisotropy into the square lattice by varying the thickness of the horizontal and vertical wires. This produces an anisotropic “phase boundary”, dependent on the direction inn which the anisotropy is probed, that is in good agreement with calculations for anisotropic tight binding bands in a strong field. We have found a unique way to disorder a quasi-crystalline network and used it to demonstrate that commensurate states are directly related to the inflation properties of the network.