Variational cluster study of antiferromagnetism and d-wave superconductivity in layered organic superconductors

The interplay between the antiferromagnetism and d-wave superconductivity of kappa(ET)(2)X conductors has been investigated by the variational cluster approach (VCA), based on self-energy-functional approach. The dimer Hubbard model has been studied as a function of the on-site repulsion U and diagonal hopping amplitude t'. Our zero-temperature calculations show a transition from Neel antiferromagnetism to a spin-liquid phase at around t' similar to 0.9. At weak coupling we find d-wave superconductivity. and a transition between d(x)2-(y)2 and d(xy) pairing symmetry as U decreases.