A UNIFIED THEORY OF CLEAN JOSEPHSON-JUNCTIONS

The general formula for the do Josephson current is obtained, which is written by means of the probability amplitude of the Andreev reflection. Applying the formula to a simple model, we obtain the result which includes those of Ambegaokar-Baratoff, Kulik-Omel'yanchuk, and Ishii as a special case. It is found that the current carrying states appear in the energy gap, which are localized around the tunnel barrier, when the phases of two superconductors do not coincide with each other. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.