Derivation of the t-J model: Electron spectrum and exchange interactions in narrow energy bands

[摘要] A derivation of the t-J model of a highly-correlated solid is given starting from the general many-electron Hamiltonian with explicit picking out of the corrections owing to the nonorthogonality of atomic wave functions. Asymmetry of the Hubbard subbands (i.e., of electron and hole cases) for a nearly half-filled bare band is demonstrated. The nonorthogonality effects are shown to lead to strong modifications of indirect antiferromagnetic exchange interaction in the limit of large on-site Coulomb repulsion. Consequences of this treatment for the magnetism formation in narrow energy bands are discussed. Peculiarities of the case of frustrated lattices, which contain equilateral triangles of nearest neighbors, are considered.

[关键词] HUBBARD-MODEL;PARTICLE SPECTRUM;ANTIFERROMAGNET;INSTABILITY;STATE