PARITY-INDUCED SUPPRESSION OF THE COULOMB BLOCKADE OF JOSEPHSON TUNNELING

We study the Josephson current through a superconducting grain coupled by two tunnel junctions to macroscopic superconducting leads. As a re sult of the Coulomb blockade we predict the critical Josephson current to have a threshold behavior when the superconducting gap is suppress ed below the charging energy by a magnetic field. This effect is a dir ect consequence of a discrimination by the superconducting ground stat e between odd and even number of electrons on the grain. The critical current is periodically modulated by the voltage of a gate electrostat ically coupled to the grain. We find a characteristic change in this m odulation at the threshold.