Dissecting superconductivity in the Ruddlesden-Popper nickelates: The role of electron correlation and interlayer magnetic exchange

Summary

This study employs resonant inelastic X-ray scattering (RIXS) to directly compare the electronic and magnetic excitation properties of trilayer nickelate La₄Ni₃O₁₀ and bilayer La₃Ni₂O₇. The results show that La₄Ni₃O₁₀ exhibits more itinerant behavior, evidenced by broader Ni d-d orbital excitations and a stronger fluorescence background, indicating weaker electronic correlations than in the bilayer system. Despite the weaker correlations, clear collective spin excitations are observed, including dispersive acoustic and optical magnon branches as well as incommensurate spin density waves (SDW). Using linear spin-wave theory analysis, the interlayer superexchange interaction Jz is extracted to be approximately 22 meV, significantly smaller than that in La₃Ni₂O₇. The weaker electron correlations and reduced interlayer magnetic exchange together account for the substantially lower superconducting transition temperature of the trilayer compound (about 30 K) compared to the bilayer (about 80 K). This study establishes interlayer magnetic coupling and electronic correlations as key parameters for superconductivity in layered nickelates, providing important constraints for understanding the superconducting pairing mechanism in this emerging family.

Materials

• La₄Ni₃O₁₀
• La₃Ni₂O₇

Methods

• Resonant inelastic X-ray scattering (RIXS)
• Linear spin-wave theory (LSWT)
• X-ray absorption spectroscopy (XAS)

Keywords

• interlayer magnetic exchange
• electronic correlations
• spin density wave
• magnon dispersion
• itinerant character

Highlights

• Our findings establish interlayer magnetic coupling and electronic correlations as key parameters for superconductivity in layered nickelates.
• Provides critical constraints for understanding the pairing mechanism in this emerging family.

Conclusions

• La₄Ni₃O₁₀ exhibits more itinerant behavior and weaker electronic correlations than La₃Ni₂O₇.
• The interlayer superexchange interaction Jz is about 22 meV, significantly smaller than in La₃Ni₂O₇.
• Clear collective spin excitations are observed, including dispersive acoustic and optical magnon branches and an incommensurate spin density wave.
• The weaker electron correlations and reduced interlayer magnetic exchange together account for the substantially lower T_c of the trilayer compound (≈30 K) compared to the bilayer (≈80 K).

Main claims

• La₄Ni₃O₁₀ exhibits more itinerant behavior with weaker electronic correlations than bilayer La₃Ni₂O₇, evidenced by broader Ni d-d orbital excitations and stronger fluorescence background.
  • Evidence: Abstract: 'La₄Ni₃O₁₀ exhibits more itinerant behavior, evidenced by broader Ni d-d orbital excitations and a stronger fluorescence background, indicating weaker electronic correlations'
• The interlayer superexchange interaction Jz in La₄Ni₃O₁₀ is approximately 22 meV, significantly smaller than in La₃Ni₂O₇, and combined with weaker correlations accounts for the lower T_c (≈30 K vs ≈80 K).
  • Evidence: Abstract: 'the interlayer superexchange interaction Jz is extracted to be approximately 22 meV, significantly smaller than that in La₃Ni₂O₇… The weaker electron correlations and reduced interlayer magnetic exchange together account for the substantially lower superconducting transition temperature'

Workflow

• Sample preparation and characterization
  • Materials: La₄Ni₃O₁₀ single crystals
  • Methods: High-oxygen-pressure floating-zone technique
  • Observations: Monoclinic/orthorhombic structure; Density wave transition at ≈135K
• RIXS measurements — Trilayer is more itinerant with weaker correlations
  • Materials: Single crystals
  • Methods: Ni L-edge resonant inelastic X-ray scattering; Polarization analysis; Momentum-dependent scans
  • Observations: Broader orbital excitations than in bilayer La₃Ni₂O₇; Stronger fluorescence background; Dispersive acoustic and optical magnon branches; Incommensurate SDW at Q=(0.31, 0.31)
• Linear spin wave theory analysis — Weaker correlation and reduced interlayer exchange explain lower T_c in trilayer
  • Materials: Extracted magnon dispersion
  • Methods: Bilayer Heisenberg model; SpinW fitting
  • Observations: Interlayer superexchange Jz ≈ 22 meV; In-plane J₁ ≈ 29.5 meV, J₂ ≈ -21 meV, J₃ ≈ 4 meV