SPATIALLY-RESOLVED OBSERVATION OF THE RESISTIVE TRANSITION IN SUPERCONDUCTING WIRE NETWORKS

We obtained spatially resolved images of the resistive transition of c urrent-biased two-dimensional Nb wire networks in zero external magnet ic field by applying low-temperature scanning electron microscopy. At temperatures well below the superconducting transition temperature the se networks show a hysteretic steplike current-voltage characteristic. We present two-dimensional images of the resistive areas of the netwo rks at various bias points and of the spatial distribution of the supe rcurrent below the critical current, showing the Meissner effect. Abov e the critical current, the voltage is localized at single rows of the network, oriented perpendicular to the transport current By increasin g the bias current, we always observe adjacent rows switching into the resistive state. The observed dynamics of the networks can be explain ed by the creation of localized phase-slip centers in the wires of the network. At temperatures close to the transition temperature the step s in the current-voltage characteristic disappear and the networks sho w a resistive behavior typical for wide superconducting bridges. We in terpret the transition between the two temperature regimes as a transi tion from a quasi-one-dimensional to a two-dimensional behavior.