Systems of Strongly Correlated Electrons Interacting with Each Other and with Phonons. Diagram Approach

Abstract

The features of materials leading to the effect of strong correlation and the phenomena realized in them, namely, the metal-insulator Mott transition and high-temperature superconductivity, were considered. The history of their study was traced. Special attention was paid to the study of the role of the interorbital correlation effect and Hund’s coupling in multi-orbital systems, as well as of the electron-phonon interaction in the systems with both strong electron-phonon and Coulomb interactions. The development of the method of the diagram technique of a strong coupling was analyzed, and the results obtained on the base of that approach are presented.