GAP FUNCTION AND DENSITY OF STATES IN THE STRONG-COUPLING LIMIT FOR AN ELECTRON-BOSON SYSTEM

We have calculated the frequency-dependent gap function for a superconductor in the strong-coupling limit lambda >> 1, where lambda 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, lambda almost-equal-to 1, where structure occurs on an energy scale determined by the boson frequency.