Orbital-selective electron correlations in high-Trm c bilayer nickelates: from a global phase diagram to implications for spectroscopy

Summary

B_y constructing the global phase diagram of a bilayer two-orbital Hubbard model, we investigate the orbital-selective electron correlations in the bilayer nickelate La₃Ni₂O₇. At half-filling the system undergoes a Mott transition, and at the physical electron filling it exhibits strong orbital selectivity, manifested as interlayer spin singlet formation among z²-orbital electrons. This effect leads to significant band-structure renormalization with dramatic bandwidth narrowing, while the splitting between the z² bonding and antibonding bands remains at about 1 eV. These correlation features naturally explain the orbital-dependent effective mass enhancement and the sinking of the z² bonding band below the Fermi level observed in ARPES experiments, as well as the puzzling contrast in optical conductivity where the Drude weight drops sharply yet the interband peak position barely shifts. Theoretical analysis reveals that interlayer antiferromagnetic superexchange plays a key role in maintaining the band splitting, and intralayer correlations drive the z² band away from the Fermi surface. This work provides a unified microscopic picture for understanding the normal-state properties and the mechanism of high-temperature superconductivity in multilayer nickelates.

Materials

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Methods

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Keywords

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Highlights

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Conclusions

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Main claims

• La₃Ni₂O₇ exhibits strong orbital-selective electron correlations, with z2 electrons more correlated than x2-y2 electrons.
  • Evidence: Calculated orbital-resolved quasiparticle weights at n=1.5 show Z(z2) << Z(x2-y2) for U >= 2.5 eV (Fig. 1c).,The orbital selectivity is linked to a Mott transition at half filling (Fig. 1b).,ARPES experiment (Yang et al. 2024b) reports orbital-dependent band renormalization; our calculated effective mass enhancements semi-quantitatively match the ARPES values (Table 1).
• Interlayer antiferromagnetic spin singlets form between electrons in z2 orbitals.
  • Evidence: Interlayer spin correlator for z2 electrons saturates at large U to ~-0.5, indicating AFM correlations (Fig. 2).,Extracted superexchange coupling J_perp is sizable at U ≈ 2.5 eV (Fig. S₄b).
• The orbital-selective correlations and interlayer singlet formation explain the key spectroscopic observations: strong band renormalization, sinking of the bonding z2 band below EF, suppressed Drude weight, and a largely unshifted interband optical peak near 1 eV.
  • Evidence: Band structure at U=2.5 eV shows overall bandwidth renormalization and bonding z2 band shifted below EF (Fig. 3b), consistent with ARPES.,Optical conductivity shows Drude weight suppressed by factor ≈6-9 (Fig. 4a) and interband peak remaining at ≈1 eV (Fig. 4b), matching experiments (Liu et al. 2024).,The bonding-antibonding splitting is maintained by superexchange interaction, preventing a large shift of the interband peak despite strong correlations.

Workflow

• model_construction — A bilayer two-orbital Hubbard model with realistic tight-binding parameters describes the low-energy electronic structure of La₃Ni₂O₇.
  • Materials: bilayer two-orbital Hubbard model; tight-binding parameters from DFT for La₃Ni₂O₇
  • Methods: slave-spin method; Gutzwiller variational method
  • Observations: model captures low-energy bands dominated by Ni e_g orbitals
• phase_diagram_calculation — A global phase diagram reveals orbital-selective correlations anchored by a Mott insulator at half filling.
  • Materials: quasiparticle spectral weight Z; electron filling n
  • Methods: slave-spin computation of orbital-resolved Z
  • Observations: Mott transition at half filling for U≈4 eV; strong orbital selectivity at n=1.5 with Z(z2) << Z(x2-y2)
• spin_correlation_analysis — Quasi-localized z2 moments form interlayer spin singlets driven by superexchange.
  • Materials: interlayer spin-spin correlation function
  • Methods: calculation of equal-time spin correlator
  • Observations: spin correlator saturates to ~-0.5, consistent with interlayer AFM spin singlet formation
• electronic_structure_calculation — Orbital-selective correlations cause orbital-dependent effective mass enhancement and maintain large bonding-antibonding splitting.
  • Materials: renormalized band dispersion
  • Methods: slave-spin calculation of quasiparticle bands
  • Observations: overall bandwidth narrowing; bonding z2 band sinks ≈50 meV below EF; bonding-antibonding splitting remains ≈1 eV
• optical_response_calculation — Strong correlations simultaneously explain suppressed Drude weight and nearly unshifted interband peak via superexchange-enhanced splitting.
  • Materials: Drude weight and interband optical conductivity
  • Methods: computation of in-plane and out-of-plane optical conductivity
  • Observations: Drude weight reduced by factor 6-9 relative to DFT; interband peak remains near 1 eV with slight shift