Marginal-Fermi-Liquid-like Behavior without Pseudogap in Infinite-Layer Nickelates

摘要

本研究通过角分辨光电子能谱（ARPES）对无限层镍酸盐超导体 La₀.8Ca₀.2NiO₂ 及其母体 LaNiO₂ 薄膜的低能电子结构进行测量，利用改进的表面处理工艺首次在该体系中分辨出清晰的准粒子峰。在 La₀.8Ca₀.2NiO₂ 中，电子自能虚部与能量呈近似线性关系，其斜率从 (π/2, π/2) 到 (π, 0) 方向逐渐增大，显示出动量依赖的边际费米液体样散射特征。两种薄膜均表现出从对角线方向向反节点区域逐步抑制的低能谱权重，母体中的抑制更强，然而整个费米面上始终保留有限的费米能级谱权重，未见到能带前沿位移或背弯现象，表明不存在铜氧化物中典型的赝能隙。这些结果表明，动量选择性关联和边际费米液体样散射可以在无可检测赝能隙的情况下发生，为甄别高温超导正常态所必需的电子要素提供了关键基准，并暗示赝能隙并非必需，电荷转移能级和掺杂载流子轨道特征可能起着决定性作用。

材料

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方法

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关键词

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亮点

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结论

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主要论断

• La₀.8Ca₀.2NiO₂ exhibits marginal-Fermi-liquid-like scattering with linear-in-energy Im Σ.
  • 证据: 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.
  • 证据: 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.
  • 证据: 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.
  • 证据: Comparisons with cuprate pseudogap energy scales (10–50 meV) and recent three-orbital calculations suggest charge-transfer energy suppresses pseudogap-like features.

研究流程

• sample_preparation — Optimized surface treatment enables quasiparticle-resolved ARPES on infinite-layer nickelates.
  • 材料: La₀.8Ca₀.2NiO₂ thin film; LaNiO₂ thin film; (Nb:)SrTiO₃ substrate; gold for electrical grounding
  • 方法: 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
  • 观察: 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.
  • 方法: 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
  • 观察: 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.
  • 方法: 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
  • 观察: 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-T_c superconductivity.