Interaction induced by nonuniform self-fields in stacks of two long Josephson junctions

We fabricated and tested devices consisting of two long stacked Josephson junctions with direct access to the intermediate electrode, whose thickness is smaller than London penetration depth /spl lambda//sub L/. The electrodes are patterned so that the junctions can be independently biased in the overlap configuration. In the absence of an external magnetic field, we measured the critical current of one junction in the stack as a function of the bias current in the other junction, while the latter was either in the zero voltage state or in the McCumber state. The results indicate that mutual interaction takes place anyway, i.e. when both the junctions or only one of them is in the zero voltage state. To account for the observed phenomena we propose a model that takes into account the nonuniform self-fields generated by the bias currents in this special three-terminal device.