Small-q phonon-mediated superconductivity in organic k-BEDT-TTF compounds -: art. no. 117005

We propose a new picture for superconductivity in kappa-(BEDT-TTF)(2) X salts arguing that small-q electron-phonon scattering dominates the pairing. We reproduce the distinct X-shaped d-wave gap reported recently by magneto-optic measurements and we argue that the softness of the momentum structure of the gap and the near degeneracy of s- and d-wave gap states may be at the origin of the experimental controversy about the gap symmetry. We show that a magnetic field applied parallel to the planes may induce extended gapless regions on the Fermi surface accounting for the experimental signatures of a Fulde-Ferrel- Larkin-Ovchinikov state and it may induce gap symmetry transitions as well.