Anisotropic Electronic Correlations in the Spin Density Wave State of La₃Ni₂O₇

摘要

本文利用极化分辨电子拉曼散射测量了高质量La₃Ni₂O₇单晶，在150 K以下的密度波转变中观察到显著的、对称性依赖的谱权重重新分布：B₁g通道呈现不对称峰，B₂g通道呈现对称宽峰，分别对应布里渊区X/Y点附近和对角线方向的电子激发。定量分析提取出两组SDW能隙值，B₁g通道能隙约为37.5–40.4 meV（2Δ/k_BT_c≈5.5–5.9），B₂g通道能隙约为23.0 meV（2Δ/k_BT_c≈3.4），表明前者属中等至强耦合，后者属弱耦合。这种动量选择的各向异性耦合强度无法用简单的弱耦合嵌套理论解释，揭示了非常规SDW源于各向异性电子关联。能隙的温度依赖性明显弱于平均场预期，且B₂g通道各向同性与B₁g通道弱各向异性也支持两种不同耦合机制的共存。该工作确立了La₃Ni₂O₇中SDW的电子特性，为理解压力下镍酸盐高温超导的涌现提供了微观基础。

材料

• La₃Ni₂O₇

方法

• polarization-resolved electronic Raman scattering
• quantitative gap analysis

关键词

• spin density wave (sdw) gap
• anisotropic electronic correlations
• momentum selective gap
• brillouin zone x/y points

亮点

• Establishes electronic character of SDW in La₃Ni₂O₇, providing microscopic foundation for understanding superconductivity under pressure.

结论

• SDW gaps in La₃Ni₂O₇ are momentum-selective with intermediate-to-strong coupling near X/Y points and weaker along diagonal, indicating an unconventional SDW driven by anisotropic electronic correlations.

主要论断

• SDW gaps open in La₃Ni₂O₇ below 150 K with different amplitudes on different Fermi surface regions.
  • 证据: Raman spectra show redistribution of spectral weight in B₁g and B₂g channels below 150 K; fitting yields gap values of ≈37-40 meV (B₁g) and ≈23 meV (B₂g).
• The SDW coupling is weak along the diagonal direction (B₂g) and medium-to-strong near X/Y points (B₁g).
  • 证据: 2Δ/kT ratios: 3.4 for B₂g (weak coupling), 5.5-5.9 for B₁g (medium-to-strong coupling); lineshape asymmetry indicates strong correlation in B₁g.
• The SDW transition is primarily electronic (spin) rather than lattice-driven.
  • 证据: No anomalies in phonon modes across transition; no zone-folded phonons; electronic origin supported by lack of lattice signatures.

研究流程

• sample_growth — Single crystals of La₃Ni₂O₇ were grown.
  • 材料: La₂O₃; NiO; O₂
  • 方法: high-pressure optical floating zone furnace; solid-state reaction
  • 观察: High-qualityLa₃Ni₂O₇ single crystals
• Raman_spectroscopy_measurements — SDW gap opening observed in B₁g and B₂g channels.
  • 材料: single crystals
  • 方法: polarization-resolved Raman scattering; confocal geometry; 532 nm laser; Stirling fridge
  • 观察: Electronic Raman response in A₁g, B₁g, B₂g channels; Spectral weight redistribution below 150 K in B₁g and B₂g; No change in A₁g
• analysis_and_fitting — Anisotropic SDW gaps with different coupling strengths on different Fermi surface regions.
  • 方法: memory function fitting; Tsuneto-Maki function; Lorentzian fitting
  • 观察: Gap values: Δ_B₁g=37.5-40.4 meV, Δ_B₂g=23.0 meV; 2Δ/kT ratios: 5.5-5.9 for B₁g, 3.4 for B₂g; Weak coupling in B₂g, medium-to-strong in B₁g