Observation of combined Josephson and charging effects in small tunnel junction circuits

Experiments on small superconducting tunnel junctions in a Giaever-Zeller-plus-SQUID geometry clearly show an I(V) feature due to Josephson supercurrent in a regime where single-electron charging effects are dominant. The I(V) data exhibit marked oscillations with gate voltage characteristic of single-electron charging. The Josephson feature shows both this effect and SQUID-related oscillations with applied magnetic field. The behavior can be understood through the usual model for charging effects in such circuits, extended to include two-electron transitions.