Abstract

The cuprate high temperature superconductivity problem has resisted solution for over 20 years. The experimental challenge comprises not only Tc’s of up to 150 K, but exotic features such as d-wave pairing symmetry and the existence of a pseudogap above Tc. Conventional electron-phonon coupling seems too weak to provide the pairing mechanism, while the Hubbard model has recently been shown not to be a high temperature superconductor. What is it about the CuO2 plane, known to be the active element in HiTc superconductors, that is driving these systems? Chemists are familiar with the strong vibrational excitation and anomalous scattering when electrons hop into the antibonding orbital of a molecule. We propose a similar scenario for itinerant electrons coupling into the Cu-O-Cu bond. Taking into account symmetry restrictions, the result is a model – supported by ab initio calculations – with a novel strong, local, nonlinear interaction between electrons and the O-coordinate. In mean field, the model leads to the pseudogap and its characteristic temperature T* via an unusual symmetry-breaking that has been recently observed. The pairing interaction supports strong d-wave pairing, and is also in accord with various experiment regarding other properties including isotope shifts.