Electronic correlations, layer distinction, and electron doping in the alternating single-layer--trilayer La₃Ni₂O₇ polymorph

Summary

We employ a density-functional theory plus dynamical mean-field theory framework to investigate the correlated electronic structure of the alternating single-layer–trilayer (1313) polymorph of La₃⁢Ni₂⁢O₇, which becomes superconducting under pressure. At ambient pressure, the single layer is in a Mott-insulating regime and the low-energy physics is dominated by the trilayer block. Under pressure, the gap in the single-layer block closes due to orbital-selective physics, enabling charge transfer into the trilayer block. This change in effective doping of the trilayer block could be linked to the higher 𝑇𝑐 obtained in La₃⁢Ni₂⁢O₇−1313 (∼80 K) when compared to the nominal trilayer La₄⁢Ni₃⁢O₁₀ compound (∼30 K). We conclude that correlation-driven layer differentiation is crucial in the La₃⁢Ni₂⁢O₇−1313 polymorph and that its low-energy physics aligns closely with the trilayer La₄⁢Ni₃⁢O₁₀ compound (in spite of the apparent differences in nominal filling) rather than with the conventional bilayer La₃⁢Ni₂⁢O₇.

Materials

• La₃Ni₂O₇-1313 polymorph

Methods

• density functional theory plus dynamical mean-field theory (DFT+DMFT)

Keywords

• mott insulating regime
• orbital selective physics
• charge transfer
• effective doping
• layer differentiation

Highlights

• Higher T_c in 1313 polymorph (≈80 K) compared to La₄Ni₃O₁₀ (≈30 K) linked to charge transfer under pressure.

Conclusions

• Correlation-driven layer differentiation is crucial; low-energy physics of 1313 polymorph aligns with trilayer La₄Ni₃O₁₀ rather than conventional bilayer La₃Ni₂O₇.

Main claims

• At ambient pressure, the single-layer block in La₃Ni₂O₇-1313 is in a Mott-insulating state, and low-energy physics is dominated by the trilayer block.
  • Evidence: Abstract: 'At ambient pressure, the single layer is in a Mott-insulating regime and the low-energy physics is dominated by the trilayer block.',Full text: 'the single layer is in a Mott-insulating regime (with gaps in both orbital sectors)' and 'the low-energy physics of La₃Ni₂O₇-1313 is subsequently dominated by the trilayer block'.
• Under pressure, the single-layer gap closes via orbital-selective physics (dx2-y2 becomes metallic while dz2 remains insulating), enabling charge transfer into the trilayer.
  • Evidence: Abstract: 'Under pressure, the gap in the single-layer block closes due to orbital-selective physics, enabling charge transfer into the trilayer block.',Full text: 'We find that the Mott-insulating nature of the single-layer block at ambient pressure transitions into an orbital-selective Mott state with the Ni-dx2-y2 orbital exhibiting metallic behavior' and 'pressure induces a charge redistribution from the single-layer into the trilayer'.
• The pressurized La₃Ni₂O₇-1313 can be viewed as electron-doped La₄Ni₃O₁₀, which may explain its higher T_c.
  • Evidence: Abstract: 'This change in effective doping of the trilayer block could be linked to the higher T_c obtained in La₃Ni₂O₇-1313 (≈80 K) when compared to the nominal trilayer La₄Ni₃O₁₀ compound (≈30 K).',Full text: 'pressurized La₃Ni₂O₇-1313 can be thought of as electron-doped La₄Ni₃O₁₀' and 'The effective electron doping could be connected to the larger superconducting T_c of La₃Ni₂O₇-1313'.

Workflow

• DFT Calculations — DFT provides the noninteracting starting point for correlated calculations.
  • Materials: La₃Ni₂O₇-1313 polymorph (P₄/mmm); La₂NiO₄ (I₄/mmm); La₄Ni₃O₁₀ (I₄/mmm)
  • Methods: All-electron DFT (WIEN₂k); Downfolding to Ni-eg Wannier functions
  • Observations: Noninteracting band structure with Ni-eg bands crossing Fermi level; Layer-dependent electronic structure
• DMFT Simulations — DMFT captures correlation-driven layer differentiation and Mott physics.
  • Materials: Ni-eg correlated space (dz2, dx2-y2)
  • Methods: Single-site dynamical mean-field theory (DMFT); CT-HYB impurity solver; Hubbard-Kanamori interactions (U=5 eV, JH=1 eV)
  • Observations: Self-energies on Matsubara axis; k-resolved spectral functions; Site-resolved orbital occupations and atomic histograms
• Analysis of Correlated Electronic Structure — Pressure induces orbital-selective Mott transition in the single layer and effective electron doping of the trilayer.
  • Materials: La₃Ni₂O₇-1313 at ambient and 30 GPa
  • Methods: Comparison with constituent materials (La₂NiO₄, La₄Ni₃O₁₀); Mass enhancement calculations from self-energies
  • Observations: At ambient: single layer is Mott-insulating; trilayer is correlated metallic with layer dependence; Under pressure: single layer becomes orbital-selective Mott (dx2-y2 metallic, dz2 remains insulating); Charge transfer from SL to TL under pressure