Antiferromagnetism and superconductivity in layered organic conductors:: Variational cluster approach

The kappa-(ET)(2)X layered conductors (where ET stands for BEDT-TTF) are studied within the dimer model as a function of the diagonal hopping t' and Hubbard repulsion U. Antiferromagnetism and d-wave superconductivity are investigated at zero temperature using variational cluster perturbation theory (VCPT). For large U, Neel antiferromagnetism exists for t' < t'(c2), with t'(c2) similar to 0.9. For fixed t', as U is decreased (or pressure increased), a d(x2 - y2) superconducting phase appears. When U is decreased further, then a d(xy) order takes over. There is a critical value of t'(c1) similar to 0.8 of t' beyond which the AF and dSC phases are separated by the Mott disordered phase.