The Fe $K$ x-ray absorption near edge structure of ${\mathrm{BaFe}}_{2-x}{\mathrm{Co}}_x{\mathrm{As}}_2$ superconductors was investigated. No appreciable alteration in shape or energy position of this edge was observed with Co substitution. This result provides experimental support to previous ab initio calculations in which the extra Co electron is concentrated at the substitute site and do not change the electronic occupation of the Fe ions. Superconductivity may emerge due to bonding modifications induced by the substitute atom that weakens the spin-density-wave ground state by reducing the Fe local moments and/or increasing the elastic energy penalty of the accompanying orthorhombic distortion.

• Received 5 July 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.267402