Small-q Phonon Mediated Unconventional Superconductivity in the Iron Pnictides

We report self-consistent calculations of the gap symmetry for the iron-based high-temperature superconductors using realistic small-q phonon mediated pairing potentials and four-band energy dispersions. When both electron and hole Fermi surface pockets are present, we obtain the nodeless \(s_\pm\) state that was first encountered in a spin-fluctuations mechanism picture. Nodal gap structures such as \(d_{x^2-y^2}\) and \(s_\pm+d_{x^2-y^2}\) and even a p-wave triplet state, are accessible upon doping within our phononic mechanism. Our results resolve the conflict between phase sensitive experiments reporting a gap changing sign attributed previously only to a non-phononic mechanism and isotope effect measurements proving the involvement of phonons in the pairing.