On the relation between the energy gap and the critical temperature

It is shown that the ratio β = epsilon/Tsub(c) (epsilon is the energy gap at T = OK) saturates with increasing strength of the electron-phonon interaction; the value βsub(max) is calculated. The special case of a multigap superconductor is discussed. New high-Tsub(c) superconductors present a unique opportunity to observe a multigap structure. (author)