Figure 1

Band structure and Fermi surfaces of (a) the ten-orbital model in the original Brillouin zone of the BCT lattice structure and (b) the five-orbital model of KFe${}_2$As${}_2$ presented in the unfolded Brillouin zone of the ST lattice structure. The dots in the left are the original first-principles band calculation, while the solid lines are the tight-binding model band dispersion obtained by using maximally localized Wannier orbitals. The horizontal cuts of the Fermi surface at $k_z=0$ and $k_z=\pi$ are presented in the bottom panels of (a) and (b). Translating the left (right) panel of the five-orbital Fermi surface (b) by $(\pi ,\pi ,\pi )$ and superposing it to the right (left) corresponds to the ten-orbital Fermi surface shown in the right (left). (c) The BCT and the ST lattice structure. The former (latter) unit cell with two (one) iron(s) is adopted for the ten (five)-orbital model. The figure has been produced using vesta (Ref. 27). (d) The Brillouin zone correspondence between the ten-orbital (black line) and five-orbital (blue line) models. The Z point of the second Brillouin zone of the BCT structure coincides with the M point of the unfolded Brillouin zone.Reuse & Permissions

Figure 2

(Top) The band structure of the five-orbital model of KFe${}_2$As${}_2$ refolded into the original Brillouin zone (solid red), and the band structure of the ten-orbital model (dashed black). (Bottom panels) Horizontal cuts of the Fermi surface for the ten-orbital (upper) and five-orbital (lower) models. The thickness represents the $z^2$, $xz/yz$, and $xy$ orbital characters.Reuse & Permissions

Figure 3

Comparison of the spin susceptibility between the ten-orbital (top) and five-orbital (bottom) models along the wave vector $(0,0)$ to ($\pi$,0). $T=0.07$ eV with $16\times 16\times 16$ $k$-point meshes.Reuse & Permissions

Figure 4

Comparison of the $s\pm$ gap function between (a) the ten-orbital and (b) the five-orbital models at $T=0.07$ eV with $16\times 16\times 16$ $k$-point meshes. Contour plots are shown for five horizontal cuts around $\Gamma$-Z and X-P-X in the original Brillouin zone of the BCT lattice. The five-orbital results, obtained originally in the unfolded Brillouin zone, are refolded into this Brillouin zone. Solid black lines are the Fermi surface and the red dashed lines are the nodal lines of the gap. The Brillouin zone is shown along with the regions where the gap is presented.Reuse & Permissions

Figure 5

The spin susceptibility for the five-orbital models at $T=0.04$ eV with (a) $n=5.5$ (KFe${}_2$As${}_2$), (b) $n=5.8$ (Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$), and (c) $n=6.1$ [Ba(Fe${}_{0.9}$Co${}_{0.1}$)${}_2$As${}_2$]. (d) The Stoner factor against the band filling for the models of KFe${}_2$As${}_2$ and BaFe${}_2$As${}_2$. The dots indicate the positions of the actual band filling of the corresponding material. At $n=5.8$, we adopt the model of Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$.Reuse & Permissions

Figure 6

The orbital character distribution on the Fermi surface for $k_z=0$. $xy$ (a),(c) and $yz$ (b),(d) orbitals for the band fillings $n=5.5$ (a),(b) and $n=6.1$ (c),(d). The arrows indicate the wave vectors connecting the portions of the Fermi surface having similar orbital character. These arrows correspond to the peak position in the spin susceptibility.Reuse & Permissions

Figure 7

The contour plots of gap function of the five-orbital model for $s$-wave (a) and $d_{x^2-y^2}$-wave (b) at $T=0.04$ eV. The solid black lines represent the Fermi surfaces,while dashed red lines are the nodes of the gap. (c) A schematic figure of the horizontal nodes in the ${\alpha }_1$ Fermi surface in the case of $s$-wave pairing. The arrow indicates the intraband scattering that drives the sign change.Reuse & Permissions