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.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering