Source zotero
Authors D. Takegami
arXiv / Publisher Not available in this batch.
PDF Not available in this batch.
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Published 2024-03-10
Research paradigm Unknown
Sample form Unknown

Summary

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

Materials

Methods

Not available in this batch.

Keywords

Not available in this batch.

Highlights

Not available in this batch.

Conclusions

Not available in this batch.

Main claims

  • Ni2+/Ni3+ charge disproportionation is absent in La3Ni2O7-δ; instead the ground state is a d8L-d8 mixture, indicating oxygen 2p holes are important.
    • Evidence: 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.
    • Evidence: 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.

Workflow

  • sample_preparation — Sample prepared with known oxygen deficiency.
    • Materials: La3Ni2O7-δ polycrystalline sample (δ≈0.07)
    • Methods: sol-gel method
    • Observations: Clean fracture surface obtained
  • haxpes_measurements — HAXPES probes bulk electronic structure.
    • Materials: Fractured polycrystalline La3Ni2O7-δ
    • Methods: Hard x-ray photoemission spectroscopy (HAXPES) at 6.5 keV; MB Scientific A-1 HE analyzer; Beamline BL12XU SPring-8
    • Observations: 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.
    • Materials: HAXPES core-level and valence band spectra
    • Methods: Subtraction of La 3d5/2 to isolate Ni 2p3/2; Comparison with reference spectra
    • Observations: 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