Josephson effect in low-capacitance superconductor-normal-metal-superconductor systems

The transport properties of a small superconductor-normal-metal-superconducting tunnel junction can be controlled by a gate electrode coupled capacitively to the central island. The critical Josephson current I sub c through such a system as a function of the gate voltage V sub g taking into account parity effects in the superconductors was evaluated. The dependence I sub c (V sub g ) shows resonant singularities and has a qualitatively different character for Delta < E sub C and Delta > E sub C , Delta being the superconducting gap and E sub C = e exp 2 /2C being the charging energy. Due to the sweeping of the gate voltage, the system can be driven to states which are metastable with respect to a change of the number of electrons on the central island. Since the lifetime of the metastable states can be macroscopically large, one can observe a remarkable bistability of the Josephson current. A weak magnetic field suppresses the interference of the electrons propagating through the central electrode, and, consequently, the magnitude of the critical current.