Doping-dependent pairing symmetry in the Iron-Pnictides

TL;DR

This study uses the functional renormalization group to analyze how doping and interaction anisotropy influence pairing symmetry in iron-pnictides, revealing a narrow nodal s-wave regime and an exotic d-wave instability.

Contribution

It provides a detailed phase diagram showing doping-dependent pairing symmetries and highlights the impact of interaction anisotropy on superconducting states in iron-pnictides.

Findings

Narrow parameter regime for nodal s-wave in electron-doped cases

Absence of nodal s-wave in hole-doped cases, favoring d-wave

Interaction anisotropy causes sensitivity of pairing symmetry

Abstract

We use the functional renormalization group method to analyze the phase diagram of a 4-band model for the iron-pnictides subject to band interactions with certain A_{1g} momentum dependence. We determine the parameter regimes where an extended s-wave pairing instability with and without nodes emerges. On the electron-doped side, the parameter regime in which a nodal gap appears is found to be much narrower than recently predicted in arXiv:0903.5547. On the hole-doped side, the extended s-wave pairing never becomes nodal: above a critical strength of the intra-band repulsion, the system favors an exotic extended d-wave instability on the enlarged hole pockets at much lower T_c. At half filling, we find that a strong momentum dependence of inter-band pair hopping yields an extended s-wave instability instead of spin-density wave (SDW) ordering. These results demonstrate that an interaction anisotropy around the Fermi surfaces generally leads to a pronounced sensitivity of the pairing state on the system parameters.