It is shown that the Josephson current in a pure superconducting-normal-superconducting (SNS) sandwich with normal layer thickness large compared with the coherence distance can be calculated easily from the quasiparticle spectrum by use of Galilean invariance. The results agree with Ishii at $T=0\mathrm{}°$K and with an expression of Kulik for the bound-state contribution, but we do not find a larger contribution from states with $E$ near ${\Delta }_0$ as suggested by Kulik. The expected current decreases very rapidly with increase in temperature so that it would be necessary to go to very low temperatures to observe the effect.

• Received 7 July 1971

DOI:https://doi.org/10.1103/PhysRevB.5.72