| Автор | Yu A Izyumov |
| Автор | B M Letfulov |
| Автор | E V Shipitsyn |
| Дата выпуска | 1994-07-04 |
| dc.description | The equations for a mean-field-type approximation in the (t-J) model are formulated in terms of a diagrammatic technique with Hubbard X-operators. With their help, equations for the order parameters are derived in ferromagnetic and antiferromagnetic phases of a metal. In both cases, two coupled order parameters exist: a magnetization m and a gap Delta in the electron spectrum. They reflect a dual behaviour of a strongly correlated system: it is simultaneously an itinerant and a localized magnet. Formulae for Curie temperature T<sub>C</sub> and Neel temperature T<sub>N</sub> are derived, from which the different nature of ferromagnetic and antiferromagnetic ordering is explicitly seen. For a simple cubic lattice the electron concentration n dependences of T<sub>C</sub> and T<sub>N</sub> are numerically calculated. It is shown that T<sub>N</sub> rapidly falls with deviation from half-filling, when n=1. Magnetic correlation length l<sub>c</sub> varies at low temperature as approximately (1-n)<sup>- 1</sup>2 /. Such behaviour corresponds to that observed in experiments in copper oxide high-T<sub>c</sub> superconductors. The magnetic phase diagram is constructed on the (t/U, n) plane. The equations for the coupled order parameters are solved for T=0 and the dependences of the order parameters m and Delta on n are presented in a wide interval of electron concentrations. They indicate the growing degree of itinerancy with deviation from half-filling. It is shown that the critical concentration n<sub>c</sub> for a crossover from itinerant magnetism to magnetism with localized magnetic moments should be a peculiar point where perturbation theory breaks down. |
| Формат | application.pdf |
| Издатель | Institute of Physics Publishing |
| Название | A mean-field-type approximation for the (t-J) model |
| Тип | paper |
| DOI | 10.1088/0953-8984/6/27/022 |
| Electronic ISSN | 1361-648X |
| Print ISSN | 0953-8984 |
| Журнал | Journal of Physics: Condensed Matter |
| Том | 6 |
| Первая страница | 5137 |
| Последняя страница | 5154 |
| Аффилиация | Yu A Izyumov; Inst. of Metal Phys., Acad. of Sci., Ekaterinburg, Russia |
| Аффилиация | B M Letfulov; Inst. of Metal Phys., Acad. of Sci., Ekaterinburg, Russia |
| Аффилиация | E V Shipitsyn; Inst. of Metal Phys., Acad. of Sci., Ekaterinburg, Russia |
| Выпуск | 27 |
