We have generalized the scattering–matrix theory of multiple Andreev reflections in mesoscopic Josephson junctions to the multiple-mode case, and applied it to short superconductor–normal-metal–superconductor (SNS) junctions with diffusive electron transport. Both the dc and ac current-voltage characteristics are analyzed for a wide range of bias voltages $V$. For voltages smaller than the supeconducting gap the dc differential conductance of the SNS junction is predicted to diverge as $1/\sqrt{V}$.

• Received 9 July 1997

DOI:https://doi.org/10.1103/PhysRevB.56.R8518