Pairing due to Spin Fluctuations in Layered Organic Superconductors

I show that, for a κ-type organic (BEDT-TTF)₂X molecular crystal, a superconducting state with Tc≈10K and gap nodes on the Fermi surface can be caused by short-ranged antiferromagnetic spin fluctuations. Using a two-band description for the antibonding orbitals on a BEDT-TTF dimer of the κ-type salt, and an intermediate local Coulomb repulsion between two holes on one dimer, the magnetic interaction and the superconducting gap function are determined self consistently within the fluctuation-exchange approximation. The pairing interaction is predominantly caused by interband coupling and additionally affected by spin excitations of the quasi-one-dimensional band.