We have calculated the frequency-dependent gap function for a superconductor in the strong-coupling limit λ≫1, where λ is the electron-boson mass-renormalization parameter. We find a multipeaked function which leads to a spectral function with quasiparticle-like resonances on an energy scale determined by the gap. This is in contrast to the moderate-coupling regime, λ≊1, where structure occurs on an energy scale determined by the boson frequency.

• Received 10 September 1990

DOI:https://doi.org/10.1103/PhysRevB.43.5355