Polaron coherence as origin of the pseudogap phase in high temperature superconducting cuprates

Within a two-component approach to high T c copper oxides including polaronic couplings, we identify the pseudogap phase as the onset of polaron ordering. This ordering persists in the superconducting phase. A huge isotope effect on the pseudogap onset temperature T * is predicted and in agreement with experimental data. The anomalous temperature dependence of the mean square copper-oxygen ion displacement observed above, at and below T c , stems from an s-wave superconducting component of the order parameter, whereas a pure d-wave order parameter alone can be excluded.