Stabilization of singlet hole-doped state in infinite-layer nickelate superconductors

Motivated by the recent x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) experi-ments, we use a detailed impurity model to explore the nature of the parent compound and hole-doped states of (La, Nd, Pr)NiO2 by including the crystal field splitting, the Ni-3d multiplet structure, and the hybridization between Ni-3d, O-2p, and Nd-5d orbitals. For simplicity and stimulated by the recent electronic structure calculations, the latter are formally replaced with symmetric orbitals centered at the missing O sites in the Nd layer, forming a two-dimensional band strongly hybridizing with the Ni-3dz92 state. This hybridization pushes the main part of the 3dz92 spectral function up in energy by several eV and stabilizes the singlet with considerable dz92 and other configurational components. For the parent compound, we find that states of Ni-3dz92 character spread over a large energy range in the spectra, and cannot and should not be represented by a single orbital energy, as suggested in other approximations. This is qualitatively consistent with the RIXS measurements showing a broad distribution of the Ni-3dz92 hole state, although the shape of the Ni-3dz92 related structure is much more complicated requiring reinterpretations of the RIXS data. For the hole-doped systems, we show that adding these additional ingredients can still result in the lowest-energy hole-doped state having a singlet character.

Automated summary

By studying (La, Nd, Pr)NiO2 system using an impurity model, the nature of the parent compound and hole-doped states have been explored by considering crystal field splitting, Ni-3d multiplet structure, and orbital hybridization. For the parent compound, Ni-3dz92 states are found to spread over a large energy range in the spectra and cannot be represented by a single orbital energy. Adding additional ingredients in the hole-doped systems can still result in the lowest-energy hole-doped state having a singlet character.