CURRENT-PHASE RELATION IN AN INTERMEDIATELY COUPLED SUPERCONDUCTOR-SUPERCONDUCTOR JUNCTION

The limiting configuration of the S-N-S' junction in which the N-layer thickness is of the order of the screening length in metals (approxim ate to 1-2 Angstrom) may serve as a model for a clean S-S' interface. This configuration supports one N-layer-attached gap state (manifold), with eigenenergy close to and less than the smaller superconducting g ap. This gap state is interpreted as the excitation associated with br eakage of interface-attached Cooper pairs, comprised of one electron f rom each side of the thin-N layer. The corresponding junction's curren t-phase (psi) relation is calculated. The gap state is shown to contri bute an appreciable ''sin(2 psi)'' correction term to the ''sin(psi)'' Josephson term. The corresponding maximum-current magnetic-flux depen dence of a two-junction configuration (SQUID) is predicted to have zer os shifted from their common loci at half-integer flux quanta.