Influence of the Nb middle layer on the current of a double Josephson junction

We have investigated the relation between the Josephson current and the thickness of the Nb middle layer in a double Josephson junction. The characteristics of the sample are somewhat different even though the sample is made under the same conditions. So we have changed only the thickness of the Nb middle layer in the double Josephson junction in the same substrate with the shutter between the sample and the target. We fabricated the double Josephson junction completely under the same conditions except for the thickness of the Nb middle layer. The Josephson current increased as the Nb middle layer became thinner. However, no Josephson current was observed without an Nb middle layer