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 dominated. The I(V) exhibit marked oscillations with applied gate voltage which are characteristic of single- electron charging. The feature associated with the Josephson currents shows both this effect and also SQUID-related oscillations with applied magnetic field. The behavior can be understood through an extension of the usual model for single-electron charging effects in such circuits to include two-electron transitions. The effects are distinct from but related to the Bloch oscillation phenomena of single-junction circuits.