JOSEPHSON EFFECT IN LOW-CAPACITANCE SUPERCONDUCTOR NORMAL-METAL SUPERCONDUCTOR SYSTEMS

The transport properties of a small superconductor-normal-metal-superc onducting tunnel junction can be controlled by a gate electrode couple d capacitively to the central island. We evaluate the critical Josephs on current I(c) through such a system as a function of the gate voltag e V(g) taking into account parity effects in the superconductors. The dependence I(c)(V(g)) shows resonant singularities and has a qualitati vely different character for DELTA < E(C) and DELTA > E(C), DELTA bein g the superconducting gap and E(C) = e2/2C being the charging energy. Due to the sweeping of the gate voltage, the system can be driven to s tates which are metastable with respect to a change of the number of e lectrons on the central island. Since the lifetime of the metastable s tates can be macroscopically large, one can observe a remarkable bista bility of the Josephson current. A weak magnetic field supresses the i nterference of the electrons propagating through the central electrode , and, consequently, the magnitude of the critical current.