Unconventional Superconductivity and Josephson Effect in Superconductor/Dirty Normal Metal/Superconductor Junctions

抄録

A relation between amplitudes of Josephson current and nodes in excitation-gap of unconventional superconductors is studied in superconductor/dirty normal metal/superconductor junctions. It is found that ensemble average of the Josephson current vanishes when the junction interface is perpendicular to a plane which includes line- or point-zeros of the excitation-gap. A zero-energy state formed at the junction interface is a character of unconventional superconductor junctions and causes large sample-to-sample fluctuations in the Josephson current in low temperatures. The disappearance of the ensemble-averaged Josephson current and the large fluctuations occur at the same time when the Cooper pairs have d- or f-wave pairing symmetries.