Absence of Ni₂/Ni₃ charge disproportionation and possible roles of O₂ p holes in La₃Ni₂O₇−δ revealed by hard x-ray photoemission spectroscopy

摘要

Absence of Ni₂/Ni₃ charge disproportionation and possible roles of O₂ p holes in La₃Ni₂O₇−δ revealed by hard x-ray photoemission spectroscopy

材料

• La₃Ni₂O₇-δ

方法

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关键词

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亮点

本批次暂无数据。

结论

本批次暂无数据。

主要论断

• Ni₂+/Ni₃+ charge disproportionation is absent in La₃Ni₂O₇-δ; instead the ground state is a d8L-d8 mixture, indicating oxygen 2p holes are important.
  • 证据: Ni 2p HAXPES spectra do not show a double-peak structure with 3–4 eV splitting; the main peak and satellite resemble LaNiO₃ (d8L) more than NiO (d8).
• The density wave transition and superconductivity are likely associated with correlated carriers of Ni 3d and O 2p character.
  • 证据: Spectral weight at Fermi level is suppressed even above the density wave transition (150 K), suggesting a pseudogap due to electron-electron or excitonic interactions.

研究流程

• sample_preparation — Sample prepared with known oxygen deficiency.
  • 材料: La₃Ni₂O₇-δ polycrystalline sample (δ≈0.07)
  • 方法: sol-gel method
  • 观察: Clean fracture surface obtained
• haxpes_measurements — HAXPES probes bulk electronic structure.
  • 材料: Fractured polycrystalline La₃Ni₂O₇-δ
  • 方法: Hard x-ray photoemission spectroscopy (HAXPES) at 6.5 keV; MB Scientific A-1 HE analyzer; Beamline BL₁₂XU SPring-8
  • 观察: Wide scan shows La, Ni, O, C peaks; O 1s sharp peak at 529 eV with FWHM 0.75 eV; Ni 2p spectra overlapped with La 3d; after subtraction, resembles NiO and LaNiO₃
• spectral_analysis — No charge disproportionation; ground state is d8L-d8 mixture with oxygen 2p holes.
  • 材料: HAXPES core-level and valence band spectra
  • 方法: Subtraction of La 3d5/2 to isolate Ni 2p3/2; Comparison with reference spectra
  • 观察: Ni 2p main peak and satellite match LaNiO₃ (d8L) rather than NiO (d8); No double-peak structure indicative of Ni₂+/Ni₃+ charge disproportionation; Valence band pseudogap: spectral weight at Fermi level close to zero