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

摘要

通过构建双层两轨道哈伯德模型的全域相图，研究了双层镍酸盐La₃Ni₂O₇中的轨道选择性电子关联。在半填充时体系发生莫特转变，在物理电子数下呈现强轨道选择性，表现为z²轨道电子形成层间自旋单重态。该效应导致能带结构显著重整化，带宽大幅收缩，而z²成键与反键带间的分裂仍维持在约1 eV。这些关联特征自然解释了ARPES实验观测到的轨道依赖有效质量增强和z²成键带下沉至费米能级以下，以及光学电导率中Drude权重急剧降低而带间峰位几乎不移动的矛盾现象。理论分析表明，层间反铁磁超交换作用在维持带分裂中起关键作用，且层内关联使z²带脱离费米面。该工作为理解多层镍酸盐的常态性质和高温超导机制提供了统一的微观图像。

材料

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方法

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关键词

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亮点

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结论

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主要论断

• La₃Ni₂O₇ exhibits strong orbital-selective electron correlations, with z2 electrons more correlated than x2-y2 electrons.
  • 证据: 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.
  • 证据: 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.
  • 证据: 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.

研究流程

• model_construction — A bilayer two-orbital Hubbard model with realistic tight-binding parameters describes the low-energy electronic structure of La₃Ni₂O₇.
  • 材料: bilayer two-orbital Hubbard model; tight-binding parameters from DFT for La₃Ni₂O₇
  • 方法: slave-spin method; Gutzwiller variational method
  • 观察: 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.
  • 材料: quasiparticle spectral weight Z; electron filling n
  • 方法: slave-spin computation of orbital-resolved Z
  • 观察: 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.
  • 材料: interlayer spin-spin correlation function
  • 方法: calculation of equal-time spin correlator
  • 观察: 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.
  • 材料: renormalized band dispersion
  • 方法: slave-spin calculation of quasiparticle bands
  • 观察: 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.
  • 材料: Drude weight and interband optical conductivity
  • 方法: computation of in-plane and out-of-plane optical conductivity
  • 观察: Drude weight reduced by factor 6-9 relative to DFT; interband peak remains near 1 eV with slight shift