Josephson effects in superconducting conventional/unconventional tunnel junctions and weak-links

Abstract

The a.c. Josephson effect is perhaps the most striking manifestation of long-range phase coherence (broken gauge symmetry) in superconductors. Superconductivity in which gauge symmetry is broken in combination with one or more additional symmetries of the normal metallic state ( unconventional superconductivity) may also occur. We discuss the Josephson effect for several models of an unconventional superconductor in contact with a conventional superconductor. An unconventional order parameter leads to qualitative changes in the current-phase relation which could be detected with a SQUID in which one arm of the interferometer is an unconventional superconductor. We also compare the current-phase relation for a tunnel junction with that of a weak-link connecting a conventional and unconventional superconductor. Selection rules for unconventional order parameters which enforce zero supercurrent in a tunnel junction are not relevant for weak-links connecting the same unconventional and conventional superconductor. We discuss the the a.c. Josephson effect for several popular models of unconventional superconductivity relevant to the CuO and heavy fermion superconductors.