The recently discovered superconductivity in ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ provides a new opportunity for studying strongly correlated unconventional superconductivity. The single-hole ${\mathrm{Ni}}^{+}$ $\left(3d^9\right)$ configuration in the parent compound ${\mathrm{NdNiO}}_2$ is similar to that of ${\mathrm{Cu}}^{2+}$ in cuprates. We suggest that after doping, the intraorbital spin-singlet and interorbital spin-triplet double-hole (doublon) configurations of ${\mathrm{Ni}}^{2+}$ are competing, and we construct a two-band Hubbard model by including both the $3d_{x^2-y^2}$ and $3d_{xy}$ orbitals. The effective spin-orbital superexchange model in the undoped case is a variant of the $\text{SU}\left(4\right)$ Kugel-Khomskii model augmented by symmetry-breaking terms. Upon doping, the effective exchange interactions between spin-$\frac{1}{2}$ single holes, spin-1 (triplet) doublons, and singlet doublons are derived. Possible superconducting pairing symmetries are classified in accordance to the $D_{4h}$ crystalline symmetry, and their connections to the superexchange interactions are analyzed.

• Received 7 October 2019

DOI:https://doi.org/10.1103/PhysRevResearch.1.032046

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Published by the American Physical Society