SUPERCONDUCTING, FLUX AND ANTIFERROMAGNETIC PHASE IN A 2D EXTENDED HUBBARD-MODEL

The superconducting phase of the s-, the d- and the mixed symmetry, the ordered phase of magnetic fluxes induced by rotating electron currents, and the antiferromagnetism are studied for the extended Hubbard model on the square lattice and within mean-field approximation. A stability diagram for these phases is analyzed in the space of the parameters of the Hamiltonian. The different phases can coexist depending on the parameters and on temperature. The superconducting phase of the mixed sd-type symmetry has the order parameters Δx and Δy in the x- and the y-directions with different phases. Their relative difference may be in the range (π/2, π). It is shown that there is a variety of phase transitions in the system. In many cases, the phase transition to the sd-superconductivity is a phase transition of a first-kind. Critical temperature dependence of the order parameters are also determined. © 1990.