Role of interstitial $s$ orbital in a model of infinite-layer nickelates

Abstract

Motivated by recent angle-resolved photoemission spectroscopy (ARPES) experiments on infinite-layer (IL) nickelates, we employ determinant quantum Monte Carlo (DQMC) to study the three-orbital Emery model ($d$-$p$ model) coupled to an additional interstitial $s$ orbital retaining the three-dimensional dispersion. Our large-scale simulations reveal that: (1) the interstitial $s$-orbital-derived electron pocket is significantly reduced by the strong interaction but persists upon 20\% hole doping, reaching a size comparable to experimental observations; (2) the $d_{x^2-y^2}$-orbital dispersion is strongly renormalized by interactions, leading to a weak $k_z$ dependence consistent with ARPES measurements. Furthermore, compared with the conventional three-orbital $d$-$p$ model, the $d$-$p$-$s$ model exhibits enhanced short-range antiferromagnetic correlations. These results highlight the crucial role of strong correlations and multi-orbital effects in shaping the low-energy electronic structure and many-body correlations in IL nickelates, and demonstrate the necessity of treating interaction-driven many-body physics within a realistic multi-orbital framework.

Figures (3)

• Figure 1: Schematic illustration of (top) the $d$-$p$-$s$ model and (bottom) the $d$-$p$ (Emery) model. The signs of the corresponding orbital wavefunctions are indicated by red (positive) and blue (negative). Black and gray dashed lines distinguish the $d$-$p$ plane hybridization from the $p$-$s$ hybridization.
• Figure 2: The non-interacting band structure projected onto the $d_{x^2-y^2}$ and $s$ orbitals with the high-symmetry path displayed in the inset. Here the $d_{x^2-y^2}$ orbital exhibits a pronounced $k_z$ dispersion between points $X$ and $R$, while the interstitial $s$ orbital forms electron pockets at both the $\Gamma$ and $A$ points. The blurry bands between -5 and -6 eV originate from the hybridization to $p$ orbitals, whose dispersions are omitted since their energies lie far away from the Fermi level. The two red horizontal dashed lines indicate the Fermi levels corresponding to the parent compound LaNiO$_2$ (upper) and the 20% Ca doped case (lower) li_observation_2025.
• Figure :