Evolution of superconducting gap anisotropy in hole-doped 122 iron pnictides

Abstract

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 analyse 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_{\pm}-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_{\pm}-wave to d-wave transition as a function of hole doping, complementing previous findings from FRG [Thomale et al., Phys. Rev. Lett. 107, 117001 (2011)]. The gap anisotropy of the s_{\pm}-wave monotonously increases towards the transition to d-wave as a function of x.