Absence of mixed valency for Pr in pristine and hole-doped PrNiO2

Abstract

Infinite-layer nickelates $(R{\mathrm{NiO}}_{2})$ exhibit some distinct differences as compared to cuprate superconductors, leading to a debate concerning the role of rare-earth ions $(R=\mathrm{La},\mathrm{Pr},\mathrm{Nd})$ in the low-energy many-body physics. Although rare-earth $4f$ orbitals are typically treated as inert ``core'' electrons in studies, this approximation has been questioned. An active participation of $4f$ states is most likely for ${\mathrm{PrNiO}}_{2}$ based on an analogy to cuprates where Pr cuprates differ significantly from other cuprates. Here, we adopt density functional plus dynamical mean-field theory to investigate the role of Pr $4f$ orbitals and more generally the correlated electronic structure of ${\mathrm{PrNiO}}_{2}$ and its hole-doped variant. We find that the Pr $4f$ states are insulating and show no evidence for either a Kondo resonance or Zhang-Rice singlet formation as they do not have any hybridization channels near the Fermi energy. The biggest effects of hole doping are to shift the Pr $5d$ and $4f$ states further away from the Fermi energy whereas enhancing the Ni $3d\text{\ensuremath{-}}\mathrm{O}$ $2p$ hybridization, thus, reducing correlation effects as the O $2p$ states get closer to the Fermi energy. We again find no evidence for either Kondo or Zhang-Rice physics for the $4f$ states upon hole doping. We conclude by commenting on implications for other reduced valence nickelates.