Importance of the Electron-Phonon Interaction with the Forward Scattering Peak for Superconducting Pairing in Cuprates

摘要

Basic experimental facts related to ARPES, tunnelling, optics ad neutronscattering measurements are discussed. They give evidence for the relevance ofthe electron-phonon interaction (EPI) in pairing mechanism of HTSC cuprates. Acontrollable theory for strong correlations and their effects on EPI isdiscussed which is based on the 1/N expansion method in the t-J model. Strongcorrelations renormalize EPI and other charge-fluctuation properties (byincluding nonmagnetic impurity scattering) and the forward scattering peak(FSP) appears in the effective interactions. Pronounced FSP in EPI of HTSCcuprates reconciles many puzzling results. The theory of EPI with FSP givesthat the couplings in the s- and d-wave pairing channel are of the samemagnitude near and below the optimal hole doping. FSP in the nonmagneticimpurity scattering potential is responsible for robustness of d-wave pairingin cuprates. The ARPES kink and the isotope effect in the nodal and anti-nodalpoints and the collapse of the elastic impurity scattering in thesuperconducting state, are explained by this theory. It also explains why thenodal kink is not-shifted in the superconducting state while the anti-nodalkink is shifted by the maximal superconducting gap. In systems with FSP in EPIbesides the classical phase fluctuations there are also internal fluctuationsof Cooper pairs giving rise to an additional contribution to the pseudogap.