Source capture
Authors Yu Fan, Zhitong An, Xiang Ding, Xingtian Sun, Yutong Chen, Zhihui Chen, Shenglin Tang, Chihao Li, Jiahao Ye, Timur Kim, Haichao Xu, Rui Peng, Donglai Feng
arXiv / Publisher https://arxiv.org/abs/2607.16852
PDF https://arxiv.org/pdf/2607.16852
Relevance score 5.366
Primary category cond-mat.supr-con
Published 2026-07-21
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Summary

Using angle-resolved photoemission spectroscopy (ARPES) with an optimized surface treatment, we probe the low-energy electronic structure of the infinite-layer nickelate superconductor La0.8Ca0.2NiO2 and its parent LaNiO2 thin films, resolving clear quasiparticle peaks for the first time in this system. In La0.8Ca0.2NiO2, the imaginary part of the electron self-energy exhibits a roughly linear dependence on energy with a slope that progressively increases from the (π/2, π/2) to the (π, 0) direction, revealing momentum-dependent marginal-Fermi-liquid-like scattering. Both films display low-energy spectral weight that is gradually suppressed from the diagonal toward the antinodal region, with stronger suppression in the parent compound; however, finite Fermi-level spectral weight persists over the entire Fermi surface, and no leading-edge shift or back-bending is observed, indicating the absence of the pseudogap typical of cuprates. These findings demonstrate that momentum-selective correlations and marginal-Fermi-liquid-like scattering can emerge without a detectable pseudogap, providing a crucial benchmark for identifying the essential electronic ingredients of the high-Tc normal state and suggesting that the pseudogap is not a requirement, while charge-transfer energy and the orbital character of doped carriers may play decisive roles.

Materials

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Methods

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Keywords

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Highlights

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Conclusions

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Main claims

  • La0.8Ca0.2NiO2 exhibits marginal-Fermi-liquid-like scattering with linear-in-energy Im Σ.
    • Evidence: Self-energy extracted from ARPES shows approximately linear energy dependence over 150 meV, deviating from quadratic Fermi-liquid behavior.
  • No pseudogap is observed in either superconducting La0.8Ca0.2NiO2 or parent LaNiO2.
    • Evidence: Finite spectral weight persists at EF across entire Fermi surface; no leading-edge shift or back-bending in any measured momentum cut.
  • Momentum-dependent correlations suppress spectral weight toward (π,0) without gap opening.
    • Evidence: Polar plots show continuous intensity decrease toward antinodal region, with weight ratio (π,0)/(π/2,π/2) = 0.81 (doped) and 0.71 (parent).
  • The absence of pseudogap in nickelates may be linked to distinct charge-transfer energetics and doped-hole orbital character.
    • Evidence: Comparisons with cuprate pseudogap energy scales (10–50 meV) and recent three-orbital calculations suggest charge-transfer energy suppresses pseudogap-like features.

Workflow

  • sample_preparation — Optimized surface treatment enables quasiparticle-resolved ARPES on infinite-layer nickelates.
    • Materials: La0.8Ca0.2NiO2 thin film; LaNiO2 thin film; (Nb:)SrTiO3 substrate; gold for electrical grounding
    • Methods: oxide molecular beam epitaxy; in-situ atomic hydrogen topotactic reduction; protective mask with fine apertures during reduction; gold deposition on substrate edges and side facets
    • Observations: sharp XRD peaks characteristic of infinite-layer phase; superconducting transition at ≈7.8K; linear-in-T normal-state resistivity (exponent 1.14); well-defined quasiparticle peaks in ARPES
  • measurement — ARPES reveals gapless Fermi crossings and absence of pseudogap in both superconducting and parent nickelate films.
    • Methods: angle-resolved photoemission spectroscopy (ARPES); Fermi surface mapping with multiple photon energies and sample orientations; high-resolution energy distribution curve (EDC) measurements; momentum distribution curve (MDC) analysis
    • Observations: dispersive bands crossing EF at all measured momenta; no leading-edge shift or back-bending in EDCs; finite Fermi-level spectral weight around entire Fermi surface; matrix-element-induced intensity modulation but no Fermi arcs
  • analysis — Momentum-dependent marginal-Fermi-liquid-like scattering and antinodal spectral-weight suppression coexist with gapless excitations.
    • Methods: extraction of imaginary part of electron self-energy Im Σ(ω); quantitative EDC leading-edge comparison; polar plot of spectral weight in [-50 meV, +10 meV] window; MDC dispersion tracking to detect back-bending
    • Observations: Im Σ(ω) approximately linear in energy over 0–150 meV range; slope of Im Σ increases from (π/2, π/2) to (π, 0); spectral weight suppression toward (π, 0) stronger in LaNiO2 than La0.8Ca0.2NiO2; no back-bending in MDC dispersion
  • interpretation — Momentum-selective correlations and marginal-Fermi-liquid behavior can emerge without a detectable cuprate-like pseudogap, and the pseudogap is not a necessary ingredient for high-Tc superconductivity.