Fermi surface nesting induced strong pairing in iron-based superconductors

TLDR

High‑temperature superconductivity in iron pnictides suggests an unconventional multiband mechanism, and Fermi‑surface–dependent nodeless gaps imply that inter‑Fermi‑surface interactions are crucial for pairing. We show that electron doping in BaFe₁.₈₅Co₀.₁₅As₂ reverses the Fermi‑surface nesting from the α to the β pocket because hole and electron pockets change size oppositely. Consequently, the strongest pairing (2Δ/Tc≈6) shifts to the nested β pocket, confirming that Fermi‑surface nesting drives superconducting pairing in iron‑based superconductors.

Abstract

The discovery of high-temperature superconductivity in iron pnictides raised the possibility of an unconventional superconducting mechanism in multiband materials. The observation of Fermi-surface (FS)-dependent nodeless superconducting gaps suggested that inter-FS interactions may play a crucial role in superconducting pairing. In the optimally hole-doped Ba(0.6)K(0.4)Fe(2)As(2), the pairing strength is enhanced simultaneously (2Delta/T(c) approximately 7) on the nearly nested FS pockets, i.e., the inner hole-like (alpha) FS and the 2 hybridized electron-like FSs, whereas the pairing remains weak (2Delta/T(c) approximately 3.6) in the poorly nested outer hole-like (beta) FS. Here, we report that in the electron-doped BaFe(1.85)Co(0.15)As(2), the FS nesting condition switches from the alpha to the beta FS due to the opposite size changes for hole- and electron-like FSs upon electron doping. The strong pairing strength (2Delta/T(c) approximately 6) is also found to switch to the nested beta FS, indicating an intimate connection between FS nesting and superconducting pairing, and strongly supporting the inter-FS pairing mechanism in the iron-based superconductors.