A novel diagrammatic technique for strongly correlated electron systems

Abstract

We dedicate this paper to the memory of the outstanding Moldavian scientist and remarkable person Academic Vsevolod Moskalenko, who deceased so early but whose papers and monographs left a deep trace in science, contributing remarkably to the theory of multiband superconductivity, polaron theory, multiparticle physics, etc. V. A. Moskalenko and colleagues elaborated a new approach to the theory of strongly correlated electrons using the original diagram methods for the Hubbard model of the main model of strongly correlated electron systems. He was the one to formulate a new concept of correlation functions as the carriers of all quantum spin, charge and couple fluctuations of the system on the basis of which he managed to derive the equation of the Dyson type for the full single-particle propagators. The new type of investigations made it possible to determine a number of significant properties of transformations such as a metal-dielectric transition, the wave of a spin density and superconductivity. He contributed greatly to the development of the polaron theory in the strongly correlated systems.