Properties of HTS step-edge SNS junctions

The critical current and current-voltage characteristics of step-edge HTS SNS junctions are discussed theoretically. In accordance with the experimental data it is assumed that the current transport through both NS interfaces takes place in ab-direction. In the bottom interface ((001) surface of YBCO) the ab-coupling may occur due to atomic steps which play a role of constrictions for the current flow. Therefore the contact is modelled as SNS structure with system of constrictions located at both interfaces. The I_cR_N product and the excess current I_ex are calculated as a function of temperature, interface transparency and N layer thickness. It is shown that in accordance with the experimental data the I_ex and I_c are of the same order of magnitude in a broad parameter range.