Charge balance and relaxation effects in the Fe based supercondutors*

Doping this family of compounds with electrons (substitution of Fe for Co) destroys the magnetic order of the parent compound and progressively introduces superconductivity. The extra electrons from Co are possibly inserted in the Fe As plane the one responsible for superconductivity. The evolution of the electronic structure as seen from the atomic point of view is an important piece of information for understanding these compounds. Core level photoemission (XPS) has the capability of catching some aspects of the electron dynamic at the Fermi surface by means of relaxation and screening effects. In my contribution, I will show and discuss a series of core level spectra whose data have been collected at 30 K and with and high resolution (40meV), thus achieving a high detail of information which will show the intricate interplay among different degrees of freedom.