Electronic Properties of BaFe$_2$As$_2$ upon Doping and Pressure: The Prominent Role of the As $\it p$ Orbitals

International audienceUsing high-resolution, lifetime removed, x-ray absorption spectroscopy at the As $\it K$ edge, we evidencethe strong sensitivity of the As electronic structure upon electron doping with Co or pressure change inBaFe$_2$As$_2$ at room temperature. Our results unravel the prominent role played by As$\it 4p$ orbitals in theelectronic properties of the Fe pnictide superconductors. We propose a unique picture to describe theoverall effect of both external parameter doping and pressure, resolving the apparent contradiction betweenangle-resolved photoemission spectroscopy, transport, and absorption results, with the As$\it p$ states as a keyingredien