Stationary charge imbalance effect in a system of coupled Josephson junctions.

We investigate the stationary charge imbalance effect in the system of coupled overdamped Josephson junctions. We show that the stationary charge imbalance in the resistive state brings to a decrease in the Josephson frequency in the junctions of the stack. The formed difference in frequencies leads to a nonuniform switch of junctions along the stack to the Shapiro step regime in the presence of external electromagnetic radiation. On the other hand, such nonuniform switching leads to the appearance of voltage spikes on the IV-characteristic of the stack. We show that the stationary charge imbalance is responsible for a slope in the Shapiro step due to the difference of the nonequilibrium potentials at the edges of the step. The obtained results have been compared with the voltage bias coupled Josephson junctions and experimental results. [ABSTRACT FROM AUTHOR]