Transport mechanisms in HTS junctions

Transport mechanisms in HTS Josephson Junctions are discussed theoretically. Two types of conductive channels are considered: geometrical constrictions and localized electronic states (LS). Temperature dependencies of excess and critical currents in ScS, SNcNS and SIS junctions are calculated in the framework of the models assuming transport via geometrical constrictions or resonant tunnelling via LS. The consequences of d-wave pairing symmetry are discussed qualitatively. We argue that both regimes of large and small widths of a channel in the momentum space are relevant to different types of HTS interfaces. The first regime is possibly realized at grain boundaries and HTS/noble metal interfaces, while the other — in semiconducting barriers. We discuss an applicability of these models to description of the data for critical currents in YBCO/PBCO ramp junctions and HTS SNS junctions.