Suppression of superconductivity by Néel-type magnetic fluctuations in the iron pnictides

Motivated by the recent experimental detection of Néel-type [(π, π)] magnetic fluctuations in some iron pnictides, we study the impact of competing (π, π) and (π, 0) spin fluctuations on the superconductivity of these materials. We show that, counterintuitively, even short-range, weak Néel fluctuations strongly suppress the s^+- state, with the main effect arising from a repulsive contribution to the s ^+- pairing interaction, complemented by low-frequency inelastic scattering. Further increasing the strength of the Néel fluctuations leads to a low-T_c d-wave state, with a possible intermediate s+id phase. The results suggest that the absence of superconductivity in a series of hole-doped pnictides is due to the combination of short-range Néel fluctuations and pair-breaking impurity scattering and also that T_c of optimally doped pnictides could be further increased if residual (π, π) fluctuations were reduced.