Phase Diagram of Extended Hubbard Model with Intraatomic Attraction

Abstract

We have used a canonical transformation to derive an effective extended Hubbard Hamiltonian with intraatomic repulsion and Ising-type interatomic exchange interaction in an effective external magnetic field from the extended Hubbard model with intraatomic attraction. The absence of magnetic ordering in the original Hamiltonian is transformed into the condition of one quasiparticle per atom, though the bare electron density in the original Hamiltonian is arbitrary. In the strong intraatomic attraction limit, we can further derive from the transformed Hamiltonian an antiferromagnetic anisotropic Heisenberg Hamiltonian in an external field and with a given value of magnetization. A phase diagram of the charge ordered, the singlet superconducting, the mixed and the non-ordered phases is then obtained with the mean field approximation. All transition among various phases are second order. For some special cases our results reduce to the known results or to the exact solutions.