Theory of Strongly Correlated Systems in the Limit of Large On-Site Coulomb Repulsion |
| Yu.A. Izyumov Institute for Metal Physics, Ural Division of the Russian Academy of Sciences, Kovalevskaya 18, 620219 Ekaterinburg, Russia |
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| A strongly correlated electronic system is studied within the framework of the t-J model with the help of diagram technique for the Hubbard X-operators. The summing of some series of diagrams is suggested, corresponding to the following three types of approximations: the generalized random phase approximation, the mean field approximation, and the low density approximation. In generalized random phase approximation the dynamic magnetic susceptibility of paramagnetic phase is calculated, and boundaries of stability of this phase are found on the plane of Hamiltonian parameters and electron concentration n. It is shown that at some critical concentration nc the system undergoes a crossover from the itinerant magnetism (n < nc) to the magnetism with localized magnetic moments (n > nc). Simultaneously, the system transfers from the Fermi-liquid behaviour to the regime of strong electron correlations with nonquasiparticle states. In mean field approximation equations for the order parameters were derived and phase transitions temperatures in a ferromagnetic and antiferromagnetic phases were obtained. In low density approximation a state of the saturated ferromagnetism was investigated and a critical concentration ns was calculated when the nonsaturated ferromagnetism follows the saturated ferromagnetism. |
| DOI: 10.12693/APhysPolA.85.103 PACS numbers: 75.10.Lp, 75.30.Cr |