Spatially resolved observation of the resistive transition in superconducting wire networks

We obtained spatially resolved images of the resistive transition of current-biased two-dimensional Nb wire networks in zero external magnetic field by applying low-temperature scanning electron microscopy. At temperatures well below the superconducting transition temperature these networks show a hysteretic steplike current-voltage characteristic. We present two-dimensional images of the resistive areas of the networks at various bias points and of the spatial distribution of the supercurrent below the critical current, showing the Meissner effect. Above the critical current, the voltage is localized at single rows of the network, oriented perpendicular to the transport current By increasing the bias current, we always observe adjacent rows switching into the resistive state. The observed dynamics of the networks can be explained by the creation of localized phase-slip centers in the wires of the network. At temperatures close to the transition temperature the steps in the current-voltage characteristic disappear and the networks show a resistive behavior typical for wide superconducting bridges. We interpret the transition between the two temperature regimes as a transition from a quasi-one-dimensional to a two-dimensional behavior.