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 BaFe1.85Co0.15As2 by studying the polarization and photon-energy dependence of angle-resolved photoemission data. While the distributions of the d(xz), d(yz), and d(3z2-r2) orbitals agree with the prediction of density functional theory, those of the d(xy) and d(x2-y2) 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.