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

摘要

本研究利用共振非弹性X射线散射（RIXS）直接对比了三层镍酸盐La₄Ni₃O₁₀与双层La₃Ni₂O₇的电子和磁激发性质。结果显示，La₄Ni₃O₁₀表现出更强的巡游性，如更宽的Ni d-d轨道激发和更强的荧光背景，表明其电子关联弱于双层体系。尽管关联较弱，仍可观测到清晰的集体自旋激发，包括色散的声学和光学磁振子支以及非公度自旋密度波（SDW）。通过线性自旋波理论分析，提取出其层间超交换相互作用Jz约为22 meV，远小于La₃Ni₂O₇中的值。较弱的电子关联和减弱的层间磁交换共同解释了三层化合物超导转变温度（约30 K）显著低于双层（约80 K）的原因。该研究确立了层间磁耦合和电子关联作为层状镍酸盐超导性的关键参数，为理解这类新兴家族的超导配对机制提供了重要约束。

材料

• La₄Ni₃O₁₀
• La₃Ni₂O₇

方法

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

关键词

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

亮点

• 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.

结论

• 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).

主要论断

• La₄Ni₃O₁₀ exhibits more itinerant behavior with weaker electronic correlations than bilayer La₃Ni₂O₇, evidenced by broader Ni d-d orbital excitations and stronger fluorescence background.
  • 证据: 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).
  • 证据: 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'

研究流程

• Sample preparation and characterization
  • 材料: La₄Ni₃O₁₀ single crystals
  • 方法: High-oxygen-pressure floating-zone technique
  • 观察: Monoclinic/orthorhombic structure; Density wave transition at ≈135K
• RIXS measurements — Trilayer is more itinerant with weaker correlations
  • 材料: Single crystals
  • 方法: Ni L-edge resonant inelastic X-ray scattering; Polarization analysis; Momentum-dependent scans
  • 观察: 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
  • 材料: Extracted magnon dispersion
  • 方法: Bilayer Heisenberg model; SpinW fitting
  • 观察: Interlayer superexchange Jz ≈ 22 meV; In-plane J₁ ≈ 29.5 meV, J₂ ≈ -21 meV, J₃ ≈ 4 meV