Contrasting Momentum-Selective Spin-Density-Wave Gaps in Bilayer and Trilayer Nickelates

摘要

利用偏振分辨电子拉曼散射技术，本研究系统测绘了三层镍氧化物La₄Ni₃O₁₀中自旋密度波（SDW）能隙的动量选择性。实验观察到SDW引起的谱权重重分布同时出现在布里渊区中心的α口袋和靠近区边界的一部分β口袋上，对应的能隙能量约为55 meV；而β口袋沿对角线方向的区域未观察到可比的谱权重抑制，表明该区域几乎没有能隙打开。这一动量空间能隙拓扑与双层镍氧化物La₃Ni₂O₇中仅β口袋出现各向异性SDW能隙的特征形成鲜明对比。上述结果确立了双层与三层镍氧化物间不同的动量空间能隙拓扑结构，为密度波不稳定性的有序波矢和与超导电性相关的机理提供了新的约束。

材料

• La₄Ni₃O₁₀

方法

• polarization-resolved electronic Raman scattering

关键词

• spin density wave gap
• momentum space gap topology
• α pocket
• β pocket

亮点

• New constraints on ordering wave vector and density-wave mechanism relevant to superconductivity.

结论

• In trilayer La₄Ni₃O₁₀, SDW gaps open on α pocket and part of β pocket, contrasting with La₃Ni₂O₇ where gaps only on β pocket, establishing distinct gap topology between bilayer and trilayer nickelates.

主要论断

• In La₄Ni₃O₁₀, SDW gaps open on both the α pocket and the β pocket near X/Y points, with gap energies approximately 55 meV.
  • 证据: Raman spectra: A₁g channel shows spectral weight loss (α pocket), B₁g channel shows dip-hump structure (β pocket near X/Y).
• No significant gap opens on the diagonal region of β pockets in La₄Ni₃O₁₀.
  • 证据: B₂g channel shows no change across T_SDW.
• The SDW gap topology is qualitatively different between La₄Ni₃O₁₀ and La₃Ni₂O₇.
  • 证据: Direct comparison of Raman data: La₄Ni₃O₁₀ gaps on α and β near X/Y, La₃Ni₂O₇ gaps only on β with anisotropic coupling.

研究流程

• sample_growth — High-qualityLa₄Ni₃O₁₀ single crystals grown.
  • 材料: La₂O₃; NiO; oxygen
  • 方法: vertical optical-image floating-zone furnace
  • 观察: La₄Ni₃O₁₀ single crystals with DW transition near 140K
• Raman_spectroscopy — SDW-induced spectral weight redistribution observed in multiple channels.
  • 材料: single crystals
  • 方法: polarization-resolved Raman scattering; confocal geometry; 532 nm laser
  • 观察: Electronic continuum in all channels; Spectral weight loss below 1000 cm-1 in xx, x'x', x'y' channels below 140K; No change in xy channel
• symmetry_decomposition_and_analysis — Gaps open on α pocket and β pocket near X/Y points, but not on diagonal β pocket.
  • 方法: spectral decomposition into A₁g, B₁g, B₂g using pseudo-D₄h symmetry; difference spectra analysis
  • 观察: A₁g: dip below 800 cm-1 (gap on α pocket); B₁g: dip-hump crossing at 800 cm-1 (gap on β pocket near X/Y); B₂g: no change (no gap on diagonal β pocket); Gap energies: A₁g ≈56 meV, B₁g ≈55 meV
• comparison_with_bilayer — Distinct SDW gap topology between bilayer and trilayer nickelates.
  • 方法: comparison with La₃Ni₂O₇ Raman results
  • 观察: In La₄Ni₃O₁₀: gaps on α and β near X/Y; in La₃Ni₂O₇: gaps only on β with anisotropy; different coherence strength