Screening in a two-band model for superconducting infinite-layer nickelate

Starting from an effective two-dimensional two-band model for infinite-layered nickelates, consisting of bands obtained from $d$- and $s$- like orbitals, we investigate to which extent it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant $s$-like band as an important driver. In the absence of screening one strongly correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the $s$ band so that the undoped nickelate remains a Mott insulator with half-filled $d$ orbitals. This regime markedly differs from the observations in high-$T_{c}$ cuprates and pairing with $s$-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the $s$ and $d_{x^{2}-y^{2}}$ bands are both partly filled and couple only weakly, so that one approximately finds a self-doped $d$ band as well as tendencies toward $d$-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second $s$ band is also partly filled. We thus find that both one-band physics and a Kondo-lattice-like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the $s$-band pocket

Interplay between Zhang-Rice singlets and high-spin states in a model for doped NiO2_2 planes

Superconductivity found in doped NdNiO$_2$ is puzzling as two local symmetries of doped NiO$_2$ layers compete, with presumably far-reaching implications for the involved mechanism: a cuprate-like regime with Zhang-Rice singlets {\cblue is replaced by local triplet states at realistic values of charge-transfer energy, which would suggest a rather different superconductivity scenario from high-$T_c$ cuprates}. We address this competition by investigating Ni$_4$O$_8$ clusters with periodic boundary conditions in the parameter range relevant for the superconducting nickelates. With increasing value of charge-transfer energy we observe upon hole doping the expected crossover from the cuprate regime dominated by Zhang-Rice singlets to the local triplet states. We find that smaller charge-transfer energy $\Delta$ is able to drive this change of the ground state character when realistic values for nickel-oxygen repulsion $U_{dp}$ are taken into account. For large values of the charge-transfer energy, oxygen orbitals are less important than in superconducting cuprates as their spectral weight is found only at rather high excitation energies. However, a second Ni($3d$) orbital can easily become relevant, with either the $xy$ or the $3z^2-r^2$ orbitals contributing in addition to the $x^2-y^2$ orbital {\cblue to the formation of triplet states. In addition,} our result that $U_{dp}$ (acting between Ni and O) favors onsite triplets implies that correlation effects beyond purely onsite interactions should be taken into account when obtaining effective two-band models.Comment: 12 pages, 11 figures, under revie

Character of doped holes in Nd1−xSrxNiO2Nd_{1−x}Sr_{x}NiO_{2}

We investigate charge distribution in the recently discovered high-$T_c$ superconductors, layered nickelates. With increasing value of charge-transfer energy we observe the expected crossover from the cuprate to the local triplet regime upon hole doping. We find that the $d-p$ Coulomb interaction $U_{dp}$ plays a role and makes Zhang-Rice singlets less favorable, while the amplitude of local triplets is enhanced. By investigating the effective two-band model with orbitals of $x^2-y^2$ and $s$ symmetries we show that antiferromagnetic interactions dominate for electron doping. The screened interactions for the $s$ band suggest the importance of rare-earth atoms in superconducting nickelates.Comment: 8 pages, 5 figures, submitte

Single-band versus two-band description of magnetism in infinite-layer nickelates

We present a weak-coupling analysis of magnetism in infinite-layer nickelates, where we compare a single-band description with a two-band model. Both models predict that (i) hybridization due to hopping is negligible, and (ii) the magnetic properties are characterized by very similar dynamic structure factors, S($\vec{k}$,w), at the points ($\pi, \pi, 0$) and ($\pi, \pi, \pi$). This gives effectively a two-dimensional description of the magnetic propertie

Hubbard subbands and superconductivity in the infinite-layer nickelate

An effective two-dimensional two-band model for infinite-layer nickelates consists of bands obtained from $d_{x^2-y^2}$ and $s$--like orbitals. We investigate whether it could be mapped onto a single-band Hubbard model and the filling of Hubbard bands. We find that both one-band physics and a Kondo-lattice regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the filling of the itinerant $s$-band. Next we investigate one-particle excitations by changing the screening. First, for weak screening the strong correlations push electrons out of the $s$-band so that the undoped nickelate is similar to a cuprate. Second, for strong screening the $s$ and $d_{x^2-y^2}$ bands are both partly filled and weakly couple. Particularly in this latter regime mapping to a one-band model gives significant spectral weight transfer between the Hubbard subbands. Finally we point out that the superconducting phases may have either $d$-wave or $s$-wave symmetry.Comment: 6 pages, 5 figures, conference. arXiv admin note: substantial text overlap with arXiv:2208.0328