dc Josephson Effect for Strong-Coupling Superconductors

The maximum zero-voltage (Josephson) current $I_s$ in identical-superconductor tunnel junctions is shown to be related to the response of the bulk superconductor to ac fields. Strong-coupling effects reduce $I_s$ to 78.8% of the weak-coupling prediction for Pb and to 91.1% of that for Sn, corresponding to similar strong-coupling reductions in the bulk supercurrent response of these materials.