Spin Fluctuation-Induced Superconductivity in Organic Compounds

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Abstract
Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as κ-( ET) 2 X is investigated using a simplified dimer Hubbard model with a right-angled isosceles triangular lattice (transfer matrices -τ, -τ ′ ). 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 the experimental results. The pairing symmetry is of the d x 2 - y 2 type. The calculated ( U /τ )-dependence of T c compares qualitatively well with the observed pressure dependence of T c . Varying the value for τ ′ /τ 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 κ-( ET) 2 X and cuprates are reasonably explained and second that T c tends to decrease with increasing τ ′ /τ. No superconductivity is found for τ ′ /τ = 1, the regular triangular lattice.