Direct observation of the electronic structure of the layered phosphide superconductor ZrP2−xSex

The layered phosphide superconductor, ZrP${}_{2\ensuremath{-}x}$Se${}_{x}$, is an emerging platform that allows various elemental substitutions and incorporates Dirac nodal lines. Here, the authors demonstrate with hard x-ray photoemission spectroscopy that the two phosphorus atoms at the in-plane and mixed-anion sites assume different valence states and that the electron filling is indeed controlled by the anion substitution. The full picture obtained for the electronic structure and the evidence of its tunability provide key insights into the optimization of superconductivity and other properties of the compound.