Phonon mechanism of pairing and high temperature superconducting oxides

The Eliashberg theory gives the basis to study the electron-phonon system. The authors note that any kind of excitations (excitons, magnons and so on) may play the same role as phonons so long as their energy is smaller than Fermi energy. In the following they will use the termin phonons for such type of excitations also. The limiting case of weak electron-phonon coupling (λ<<1) corresponds to the well-known BCS theory. The intermediate case λ--1 was investigated numerically for concrete compounds with Tc in the interval 10-20K where the difference from the BCS model is quite small. The limit λ>>1 was not studied properly up to now. It is this case which seems to be interesting from the point of view of high Tc oxides and where the authors hope to find the remarkable difference from the BCS model