Electronic correlations and magnetic interactions in infinite-layer ${\mathrm{NdNiO}}_2$

The large antiferromagnetic exchange coupling in the parent high-$T_{\mathrm{c}}$ cuprate superconductors is believed to play a crucial role in pairing the superconducting carriers. The recent observation of superconductivity in hole-doped infinite-layer (IL-) ${\mathrm{NdNiO}}_2$ brings to the fore the relevance of magnetic coupling in high-$T_{\mathrm{c}}$ superconductors, particularly because no magnetic ordering is observed in the undoped IL-${\mathrm{NdNiO}}_2$, unlike in parent copper oxides. Here, we investigate the electronic structure and the nature of magnetic exchange in IL-${\mathrm{NdNiO}}_2$ using state-of-the-art many-body quantum chemistry methods. From a systematic comparison of the electronic and magnetic properties with isostructural cuprate IL-${\mathrm{CaCuO}}_2$, we find that the on-site dynamical correlations are significantly stronger in IL-${\mathrm{NdNiO}}_2$ compared to the cuprate analog. These dynamical correlations play a critical role in the magnetic exchange resulting in an unexpectedly large antiferromagnetic nearest-neighbor isotropic $J$ of 77 meV between the ${\mathrm{Ni}}^{1+}$ ions within the $ab$ plane. While we find many similarities in the electronic structure between the nickelate and the cuprate, the role of electronic correlations is profoundly different in the two. We further discuss the implications of our findings in understanding the origin of superconductivity in nickelates.

Figure 1

(a) Square planar ${\mathrm{NiO}}_4$ plaque and (b) the oxygen environment around the ${\mathrm{Nd}}^{3+}$ in IL-${\mathrm{NdNiO}}_2$. (c) Crystal field levels of the ${\mathrm{Ni}}^{1+}$ as computed from our calculations, and the energies in eV are also shown.

Figure 2

(a) and (c) Single-orbital entropy $s{\left(1\right)}_i$. (b) and (d) Mutual orbital information $I_{i,j}$ between a few strongly entangled pairs of CASSCF natural orbitals (also shown) for IL-${\mathrm{NdNiO}}_2$ and IL-${\mathrm{CaCuO}}_2$, respectively. $I_{i,j}$ for all orbital pairs is shown in SM [31]. In (a) and (c) the green and magenta colors represent the two different set of orbitals, occupied (at the HF level) and the corresponding double shell (virtual), respectively. The thicknesses of the black, blue, and pink lines in (b) and (d) denote the strength of $I_{i,j}$, and the size of the dots is proportional to $s{\left(1\right)}_i$.