A Disconnected Superconducting Regime at the Parent Limit of Infinite-Layer Nickelates

摘要

本研究发现，在无阳离子取代且化学计量比的 PrNiO₂ 薄膜中，无需覆盖层即可观察到零电阻和抗磁响应，从而确认了无限层镍氧化物母体的本征超导性。通过异质结构工程插入非超导缓冲层，排除了衬底界面效应的贡献。等价位三价 La 替代同样能保持超导，表明该现象并非 PrNiO₂ 独有。然而，微量的二价 Sr 或 Ca 替代（约 3% 以内）会迅速抑制超导，使其不再出现。结合角分辨光电子能谱测量，揭示这一超导相局限于母体 PrNiO₂ 额外空穴掺杂 3% 以内的极窄区间。该超导相与先前在约 20% 二价掺杂处建立的超导穹顶之间存在一个非超导区域，在相图上形成彼此分离的两个超导区。此外，母体超导相的上临界场各向异性显著更强。这些结果表明，无限层镍氧化物并非简单的铜氧化物类似物，而是拥有独特的超导物理和分离的超导区域。

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

• Pristine stoichiometric PrNiO₂ exhibits intrinsic superconductivity with zero resistance and diamagnetism.
  • 证据: Figure 1b shows zero resistance below ≈7 K.,Figure 1f shows diamagnetic frequency shift in TDO.
• Superconductivity is not an interfacial effect from the SrTiO₃ substrate.
  • 证据: Figure 1h: heterostructure with non-superconducting Ca-doped spacer retains robust zero-resistance transition.
• The superconducting phase is confined to within 3% additional hole doping from the parent state.
  • 证据: Figure 2e,f: superconductivity suppressed by 3% Sr or Ca substitution, insulating behavior for Ca.
• This new superconducting regime is disconnected from the previously established hole-doped dome.
  • 证据: Figure 4a phase diagram shows a non-superconducting gap between the near-parent regime and the dome at ≈20% doping.
• The parent superconducting regime exhibits enhanced upper-critical-field anisotropy compared to the hole-doped dome.
  • 证据: Figure 4b: in-plane Hc₂ far exceeds Pauli limit and anisotropy γ ≈68 near T_c, stronger than reported for optimally doped nickelates.

研究流程

• sample_synthesis — High-quality stoichiometric PrNiO₂ films are essential for observing intrinsic superconductivity.
  • 材料: PrNiO₂; SrTiO₃ substrate
  • 方法: pulsed laser deposition (inferred); stoichiometry tuning (Pr/Ni ratio)
  • 观察: low normal-state resistivity below quantum of resistance; suppressed low-temperature resistivity upturn
• transport_characterization — Uncapped PrNiO₂ shows reproducible zero-resistance superconductivity.
  • 材料: PrNiO₂ films; magnetic field system up to 9T
  • 方法: four-probe resistivity vs. temperature; magnetic field sweeps in-plane and out-of-plane
  • 观察: zero resistance below ≈7K; superconducting transition progressively suppressed by magnetic field
• diamagnetic_measurement — Diamagnetic response confirms bulk superconductivity with both hallmarks (zero resistance and Meissner effect).
  • 材料: PrNiO₂ film; tunnel diode oscillator (TDO) circuit
  • 方法: TDO frequency shift detection
  • 观察: clear frequency shift indicating diamagnetic shielding
• interface_exclusion — Superconductivity is intrinsic to PrNiO₂, not driven by substrate interface effects.
  • 材料: PrNiO₂; Pr₀.97Ca₀.03NiO₂; SrTiO₃
  • 方法: insertion of 3-uc non-superconducting Ca-doped spacer layer
  • 观察: robust zero-resistance transition persists with comparable T_c
• doping_dependence — Superconducting phase exists only within 3% hole doping from parent state, distinct from higher-doped dome.
  • 材料: La_xPr_1-xNiO₂ films; Pr_1-xSr_xNiO₂ films; Pr_1-xCa_xNiO₂ films
  • 方法: transport measurements with substitution
  • 观察: superconductivity preserved under La; rapid suppression by Sr or Ca at 3%, insulating behavior for Ca; no superconductivity for x ≥ 0.03
• electronic_structure — Superconducting parent PrNiO₂ is self-doped with ≈9% holes; Ca doping adds holes without significant disorder.
  • 材料: PrNiO₂ and Pr₀.95Ca₀.05NiO₂ films
  • 方法: angle-resolved photoemission spectroscopy (ARPES); Hall effect measurements
  • 观察: hole-like α pocket and electron-like β pocket at EF; hole doping ≈9% in Ni 3dx2-y2 from Luttinger volume; negligible MDC broadening upon Ca substitution; negative Hall coefficient in PrNiO₂
• phase_diagram_analysis — Infinite-layer nickelates host two disconnected superconducting regimes with distinct critical field anisotropy.
  • 材料: resistivity vs. doping data; high-field transport up to 35T
  • 方法: construction of hole-doping phase diagram; extraction of upper critical field Hc₂ and anisotropy
  • 观察: two disjoint superconducting regions separated by non-superconducting gap; in-plane Hc₂ exceeds Pauli limit, out-of-plane Hc₂ shows upturn; anisotropy γ = Hc₂[ab]/Hc₂[c] ≈68 near T_c