Orbital and spin character of doped carriers in infinite-layer nickelates

The discovery of superconductivity in infinite-layer nickelate thin films has produced fervent theoretical research about the doping evolution of their electronic structure. Here, by means of x-ray spectroscopy and atomic multiplet calculations, the authors show that doped holes are mainly introduced in Ni sites in a spin-singlet configuration. The dominant role of the Ni 3d_x²-y² band implies that infinite-layer nickelates are likely a strongly correlated electronic system, reminiscent of their cuprate siblings.