Impact of the two Fe unit cell on the electronic structure measured by ARPES in iron pnictides

In all iron pnictides, the positions of the ligand alternatively above and below the Fe plane create 2 inequivalent Fe sites. This results in 10 Fe 3d bands in the electronic structure. However, they do not all have the same status for an ARPES experiment. There are interference effects between the 2 Fe that modulate strongly the intensity of the bands and that can even switch their parity. We give a simple description of these effects, notably showing that ARPES polarization selection rules in these systems can not be applied by reference to a single Fe ion. We show that ARPES data for the electron pockets in Ba(Fe sub(0.92)Co sub(0.08)) sub(2)As sub(2) are in excellent agreement with this model as well as with direct calculation of the spectral weight. We observe both the total suppression of some bands and the parity switching of some other bands. Once these effects are properly taken into account, the structure of the electron pockets, as measured by ARPES, becomes very clear and simple. By combining ARPES measurements in different experimental configurations, we clearly isolate each band forming one of the electron pockets. We identify a deep electron band along one ellipse axis with the d sub(xy) orbital and a shallow electron band along the perpendicular axis with the d sub(xz)/d sub(yz) orbitals, in good agreement with band-structure calculations. We show that the electron pockets are warped as a function of k sub(z) as expected theoretically, but that they are much smaller than predicted by the calculation.