Small-q phonon-mediated unconventional superconductivity in the iron pnictides

We report self-consistent calculations of the gap symmetry for 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(+/-) state that was first encountered in a spin-fluctuation mechanism picture. Nodal s(+/-) as well as other gap structures such as d(x2-y2), s(+/-) + d(x2-y2), 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 nonphononic mechanism, and isotope effect measurements proving the involvement of phonons in the pairing.