Small-q Phonon Mediated Unconventional Superconductivity in the Iron Pnictides

TL;DR

This study demonstrates that small-q phonon interactions can produce various unconventional superconducting gap symmetries in iron pnictides, including nodeless s± and nodal states, aligning with experimental observations.

Contribution

It introduces a phonon-mediated pairing model capable of explaining diverse gap structures in iron-based superconductors, challenging the notion that only spin fluctuations drive pairing.

Findings

Nodeless s± state arises with electron and hole pockets.

Doping induces nodal gap structures like d_{x^2-y^2} and p-wave.

Phonons can account for phase-sensitive experimental results.

Abstract

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.