We report on some unusual behavior of the measured current-voltage characteristics (CVC) in artificially prepared two-dimensional unshunted array of overdamped Nb- AlOx -Nb Josephson junctions. The obtained nonlinear CVC are found to exhibit a pronounced (and practically temperature independent) crossover at some current Icr = (1/2 ΒC-1) I C from a resistance R dominated state with VR =R I 2 - IC2 below Icr to a capacitance C dominated state with VC = /4eC I-IC above Icr. The origin of the observed behavior is discussed within a single-plaquette approximation assuming the conventional resistively shunted junction model with a finite capacitance and the Ambegaokar-Baratoff relation for the critical current of the single junction.
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We are indebted to R. S. Newrock, P. Barbara and C. J. Lobb for helpful discussions and for providing SIS samples. This work has been financially supported by the Brazilian agencies CNPq, CAPES, and FAPESP.
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