Antiferromagnetism and Superconductivity in Layered Organic Conductors: Variational Cluster Approach

The κ-(ET)₂X 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, N\'eel antiferromagnetism exists for t^'<tc2^', with tc2^'~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 dxy order takes over. There is a critical value of tc1^'~0.8 of t^' beyond which the AF and dSC phases are separated by the Mott disordered phase.