Based on a clear physical picture, a theory of superconductivity capable of treating the simultaneous participation of multiple bosonic modes that mediate the pairing interaction is developed in terms of the dielectric function. The effect of mode damping is then incorporated in a simple manner that is free of the encumbrance of the strong-coupling, Green function formalism usually required for the retardation effect. Explicit formulae including such damping are derived for the critical temperature Tcand the energy gap Delta0showing, in particular, how the ratio 2 Delta0/Tcmay thus vary from sample to sample, a prediction consistent with the recent experimental findings on high-Tcsuperconductors.
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