Pairing due to Spin Fluctuations in Layered Organic Superconductors

Abstract

I show that, for a $\kappa$-type organic $(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F}{)}_{2}X$ molecular crystal, a superconducting state with $T_{\mathrm{c}}\approx 10\mathrm{K}$ 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 $\kappa$-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.