THE HUBBARD-MODEL IN THE REGIME OF STRONG ELECTRONIC CORRELATIONS

An up-to-date study is made of the Hubbard model, a main model of strongly correlated electron systems. It is shown that in the regime of strong correlations U similar to W the following principal correlation effects appear: metal-insulator phase transition, appearance of localized magnetic moments, violation of the fermi-liquid behavior. Different approaches to the problem, not basing on perturbation theory with respect to a small parameter U/W or W/U, are discussed. A new method in the theory of the strongly correlated system is brought to light, which is based on the limit of the infinite space dimension d = infinity. Physical results obtained by this method are compared with ones obtained by other traditional approaches. On overview of the behaviour of strongly correlated systems is given in the wide interval of the parameters U, W and the electronic concentration n.