Evolution Of Superconducting Gap Anisotropy In Hole-Doped 122 Iron Pnictides

Motivated by recent experimental findings, we investigate the evolution of the superconducting gap anisotropy in 122 iron pnictides as a function of hole doping. Employing both a functional and a weak coupling renormalization group approach (FRG and WRG), we analyze the Fermi surface instabilities of an effective 122 model band structure at different hole dopings x, and derive the gap anisotropy from the leading superconducting instability. In the transition regime from collinear magnetism to s +/--wave, where strong correlations are present, we employ FRG to identify a non-monotonous change of the gap anisotropy in qualitative agreement with new experimental findings. From the WRG, which is asymptotically exact in the weak coupling limit, we find an s +/--wave to d-wave transition as a function of hole doping, complementing previous findings from FRG [Thomale etal., Phys. Rev. Lett. 107, 117001 (2011)]. The gap anisotropy of the s +/--wave monotonously increases towards the transition to d-wave as a function of x. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim