ELECTRONIC PAIRING MECHANISM DUE TO BAND MODIFICATION WITH INCREASINGPAIR NUMBER

It is shown that a shift of an electron band with electron occupation number n, which is changing during the transition to the superconducti ng state, can lower the total energy of the system. In fact it will br ing a negative contribution to the pairing potential, which is proport ional to the product of the electron band shift with occupation number and the charge transfer during the transition to the superconducting state. The shift of the electron band comes from the change of stresse s and the change of correlation effects in the CuO2 plane with n, that in turn is caused by the changing oxygen concentration. This model ex plains the phenomenological success of Hirsch's model, which gives no explanation how the band shift in energy can give rise to superconduct ivity.