Orbital characters of bands in the iron-based superconductor BaFe1.85Co0.15As2

The unconventional superconductivity in the newly discovered iron-based superconductors is intimately related to its multiband/multiorbital nature. Here we report the comprehensive orbital characters of the low-energy three-dimensional electronic structure in BaFe${}_{1.85}$Co${}_{0.15}$As${}_2$ by studying the polarization and photon-energy dependence of angle-resolved photoemission data. While the distributions of the $d_{\mathit{xz}}$, $d_{\mathit{yz}}$, and $d_{3z^2-r^2}$ orbitals agree with the prediction of density functional theory, those of the $d_{\mathit{xy}}$ and $d_{x^2-y^2}$ orbitals show remarkable disagreement with theory. Our results point out the inadequacy of the existing band structure calculations and, more importantly, provide a foundation for constructing the correct microscopic model of iron pnictides.