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.