Possible three dimensional nodes in the $s{\pm}$ superconducting gap of BaFe$_2$(As$_{1-x}$P$_x$)$_2$

TL;DR

This paper models the three-dimensional superconducting gap in BaFe$_2$(As$_{1-x}$P$_x$)$_2$, revealing nodal structures in the gap related to Fermi surface warping and orbital character, explaining material-dependent gap variations.

Contribution

It introduces a 3D ten orbital model for BaFe$_2$(As$_{1-x}$P$_x$)$_2$ and analyzes the nodal structures in the superconducting gap within a spin fluctuation framework.

Findings

Superconducting gap is mainly s± with sign change between electron and hole Fermi surfaces.

Nodal structures appear on warped hole Fermi surfaces with specific orbital characters.

Results explain the material dependence of the superconducting gap in iron pnictides.

Abstract

We examine theoretically the superconducting state of BaFe$_2$(As$_{1-x}$P$_x$)$_2$, an isovalent doping 122 iron pnictide superconductor. We construct a three dimensional ten orbital model from first principles band calculation, and investigate the superconducting gap within the spin fluctuation mediated pairing mechanism. The gap is basically $s\pm$, where the gap changes its sign between electron and hole Fermi surfaces, but three dimensional nodal structures appear in the largely warped hole Fermi surface having strong $Z^2/XZ/YZ$ orbital character. The present result, together with our previous study on 1111 systems, explains the strong material dependence of the superconducting gap in the iron pnictides.