Accidental nodes in the order parameter of the iron superconductors due to Coulomb repulsion

The nature of the order parameter in the iron superconductors is not fully elucidated. There is a general agreement that the order parameter is a spin singlet state. There is evidence for a fully gapped sign changing $s_{\pm}$ order parameter in some iron superconductors. However, there is also evidence for line nodes in some samples that might indicate a different symmetry. In this paper, we present a model that shows accidental nodes can appear within the $s_{\pm}$ order parameter scenario due to a competition between the pairing interaction and Coulomb repulsion.