The constriction model for SNS Josephson junctions

Abstract

The approach developed by Blonder, Tinkham and Klapwijk (BTK) for calculation of the quasiparticle (qp) current in NcS contacts is generalized to the case of ScNS and SNcNS contacts with disordered NS electrodes. Amplitudes of Andreev and normal reflections at the ballistic constriction are calculated. The relation between the qp current and energy spectrum of NS proximity sandwich is found for arbitrary transparencies of the constriction and NS interfaces. The appearance of new series of subharmonic peaks associated with the two-gap structure in the density of states of NS electrodes is demonstrated. The model is also applied to calculation of the critical and the excess currents in ScNS and SNcNS for different interface parameters. The relevance of the model to transport mechanisms in step-edge HTS SNS contacts is discussed.