Half-filled layered organic superconductors and the resonating-valence-bond theory of the hubbard-heisenberg model.

We present a resonating-valence-bond theory of superconductivity for the Hubbard-Heisenberg model on an anisotropic triangular lattice. Our calculations are consistent with the observed phase diagram of the half-filled layered organic superconductors, such as the beta, beta', kappa, and lambda phases of (BEDT-TTF)2X [bis(ethylenedithio)tetrathiafulvalene] and (BETS)2X [bis(ethylenedithio)tetraselenafulvalene]. We find a first order transition from a Mott insulator to a dx2-y2 superconductor with a small superfluid stiffness and a pseudogap with dx2-y2 symmetry.