Using high-resolution, lifetime removed, x-ray absorption spectroscopy at the As $K$ edge, we evidence the strong sensitivity of the As electronic structure upon electron doping with Co or pressure change in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, at room temperature. Our results unravel the prominent role played by As-$4p$ orbitals in the electronic properties of the Fe pnictide superconductors. We propose a unique picture to describe the overall effect of both external parameter doping and pressure, resolving the apparent contradiction between angle-resolved photoemission spectroscopy, transport, and absorption results, with the As-$p$ states as a key ingredient.

• Received 15 July 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.177001