Gap symmetry in KFe2As2 and the cos 4θ gap component in LiFeAs

We revisit the issue of the gap symmetry in KFe2As2, which is an Fe pnictide superconductor with only hole pockets. Previous theoretical studies mostly argued for a d-wave gap in KFe2As2 since transport and thermodynamic measurements point to the presence of the gap nodes. However, a d-wave gap is inconsistent with recent laser-based angle-resolved photoemission measurements. We propose a scenario for a nodal s-wave superconductivity induced by a nonmagnetic intraband and interband interactions between fermions near hole pockets. The superconducting gap changes sign between the hole pockets and has cos 4 theta angular dependence and accidental nodes on one or several hole pockets. We argue that strong angle dependence is the consequence of near-degeneracy between interpocket and intrapocket interaction on the hole pockets. We also analyze the cos 4 theta angular dependence of the gap in other Fe pnictides and compare theoretical results with the photoemission experiments of LiFeAs.