SUPERCONDUCTIVITY, GAPLESS STATE AND ISOTOPE EFFECT IN THE CUPRATES

The removal of oxygen from YBa2Cu3O7-x has a profound impact on variou s properties of this compound. The model of induced two gap supercondu ctivity that we developed previously allows us to describe these prope rties. For example, for compositions between 0 < x <0.15, the energy g ap on the chains changes drastically, and in fact. becomes gapless. Ho wever, T(c) remains relatively constant, because it is determined most ly by the properties of the planes. We find from specific heat measure ments that the electron-phonon coupling on the planes is sufficient to account for the high T(c) in YBa2Cu3O7-x. Furthermore we can explain the unusual doping dependence of the isotope shift to effects of non-a diabaticity of oxygen motion in these compounds.