No abstract

We present an experimental investigation of arrays with long-range interaction, together with a model to explain observed deviations from the predictions of earlier theoretical work. These arrays consist of N horizontal and N vertical superconducting filaments arranged in two parallel planes separated by an oxide layer, so that every wire is Josephson coupled to every other wire in the array as nearest-or nextnearest neighbors. We have performed ac-susceptibility and dc-transport measurements on both ordered and disordered arrays. Our ac measurements show a strong feature at a temperature T"which we interpret as a transition to the macroscopically phase-coherent state. We find that this feature is field dependent in ordered arrays, but not in disordered arrays. dc-transport measurements reveal that these arrays have unexpectedly low critical currents and show voltage steps in their I-V curves; moreover, they are hysteretic despite the fact that they consist of nonhysteretic junctions. Our analysis of these results shows that the finite ratio of the wire inductance to the Josephson inductance cannot be ignored since it limits the effective number of Josephson junctions along a wire to N, ff ((N.

We theoretically investigate ordered and disordered Josephson-junction arrays with long-range interaction. These arrays consist of two orthogonal sets of N parallel superconducting wires that are Josephson coupled to each other at every point of crossing. In this configuration, all wires, regardless of spatial separation, are nearest-or next-nearest neighbors. Using a mean-field approximation we show that the arrays undergo a phase transition to a macroscopically phase-coherent state at a temperature T, =NEJ/2k& in the zero-field case. When a magnetic field, corresponding to a strongly commensurate number of flux quanta per unit cell, f =p/q, is introduced in an ordered array, we find that

When rf and dc bias currents are injected diagonally into an NxM Josephson-junction array and a