Pnictogen height as a possible switch between high- T c nodeless and low- T c nodal pairings in the iron-based superconductors

We study the effect of the lattice structure on the spin-fluctuation-mediated superconductivity in the iron pnictides adopting the five-band models of several virtual lattice structures of LaFeAsO, as well as actual materials such as NdFeAsO and LaFePO obtained from the maximally localized Wannier orbitals. Random phase approximation is applied to the models to solve the Eliashberg equation. This reveals that the gap function and the strength of the superconducting instability are determined by the cooperation or competition among multiple spin-fluctuation modes arising from several nestings among disconnected pieces of the Fermi surface, which is affected by the lattice structure. Specifically, the appearance…