Spin fluctuation-induced superconductivity in organic compounds

Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as kappa-(ET)(2)X is investigated using a simplified dimer Hubbard model with a right-angled isosceles triangular lattice (transfer matrices -tau, -tau'). The dynamical susceptibility and the self-energy are calculated self-consistently within the fluctuation exchange approximation: and the value for T-c obtained by solving the linearized Eliashberg-type equations is in good agreement with experimental results. The pairing symmetry is of the d(x2-y2) type. The calculated (U/tau)dependence of T-c compares qualitatively well with the observed pressure dependence of T-c. Varying the value for tau/tau' from 0 to 1, we interpolate between the square lattice and the regular triangular lattice and find first that relative values of T-c for kappa-(ET)(2)X and cuprates are reasonably explained and second that T-c tends to decrease with increasing tau/tau'. No superconductivity is found for tau'/tau = 1, the regular triangular lattice.