Cu-O chains in YBa2Cu3O7-δ and the phonon mechanism of high Tc superconductivity

Within the phonon mechanims the effect of the interplay of high and low frequency quasi-local modes, involving the longitudinal and transversal vibrations of oxygen atoms in the Cu-O chains on the superconductivity in YBa2Cu3O7-δ is studied. The possibility of enhancing Tc due to this interplay is demonstrated numerically. A strong normal isotope effect is predicted. The adiabatic potential for the high-frequency mode is obtained by considering the cluster (Cu-O-Cu)2+ by the Hartree-Fock method with pseudopotential. It is shown that the in-chain copper lons are 1+ valence state. The calculations including vectorized codes have been performed on the array processor EC 2706. 4 tabs