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 junctions fabricated with the Nb/Al-AlOx/Nb technology. The current-voltage characteristics of these structures typically show three different values of the critical current for a constant external magnetic field. This property can be explained by the inductive coupling model. Numerical calculations-based on a system of coupled sine-Gordon equations show that the effective magnetic field in one of the junctions depends on whether the other junction is in the zero voltage state or not. This leads to different critical currents for each junction. This phenomenon was observed for the annular and straight overlap junctions with various parameters.