Electron Phonon Interaction and Strong Correlations in High-Temperature Superconductors: One can not avoid unavoidable

摘要

The important role of the electron-phonon interaction (EPI) in explaining theproperties of the normal state and pairing mechanism in high-T$_{c}$superconductors (HTSC) is discussed. A number of experimental results areanalyzed such as: dynamical conductivity, Raman scattering, neutron scattering,ARPES, tunnelling measurements, isotope effect and etc. They give convincingevidence that the EPI is strong and dominantly contributes to pairing in HTSCoxides. It is argued that strong electronic correlations in conjunction withthe pronounced (in relatively weakly screened materials) EPI are unavoidableingredients for the microscopic theory of pairing in HTSC oxides. I present thewell defined and controllable theory of strong correlations and the EPI. It isshown that strong correlations give rise to the pronounced \textit{forwardscattering peak} in the EPI - the FSP theory. The FSP theory explains in aconsistent way several (crucial) puzzles such as much smaller transportcoupling constant than the pairing one ($\lambda_{tr}\ll \lambda$), which arepresent if one interprets the results in HTSC oxides by the oldMigdal-Eliashberg theory for the EPI. The ARPES shift puzzle where the nodalkink at 70 meV is unshifted in the superconducting state, while the anti-nodalone at 40 meV is shifted can be explained at present only by the FSP theory. Anumber of other interesting predictions of the FSP theory are also discussed.