Static properties of stacked Josephson junctions: Comparison of experiments with the inductively coupled sine-Gordon model

We report on the static properties of twofold stacks of long Josephson junc tions fabricated with the Nb/Al-AlOx/Nb technology. The current-voltage cha racteristics of these structures typically show three different values of t he critical current for a constant external magnetic field. This property c an be explained by the inductive coupling model. Numerical calculations-bas ed on a system of coupled sine-Gordon equations show that the effective mag netic field in one of the junctions depends on whether the other junction i s in the zero voltage state or not. This leads to different critical curren ts for each junction. This phenomenon was observed for the annular and stra ight overlap junctions with various parameters. [S0163-1829(99)03902-8].