Enhanced and robust superconductivity in La₀.8Sr₀.2NiO₂ membranes compressed up to 210 GPa

摘要

研究人员制备了自由站立式 La₀.₈Sr₀.₂NiO₂ 薄膜，并利用金刚石对顶砧在高达 210 GPa 的超高压下进行电阻测量。实验发现，超导起始转变温度呈穹顶状演化：从常压下的约 16 K 开始，随压力升高而单调上升，至 146 GPa 时达到峰值 74.5 K，随后缓慢下降，在 210 GPa 时仍保持 57.4 K。通过导数分析和磁场抑制实验证实，这种转变温度的提高源于超导的内禀增强，而非过渡宽度的简单展宽。与 Nd₀.₈₅Sr₀.₁₅NiO₂ 膜的对比显示，两者在 60 GPa 以下均线性增压，斜率相近，但在更高压力下行为出现差异；然而两者最高起始温度均约 75 K，表明 NiO₂ 平面主导超导，而稀土 f 轨道磁矩的影响甚微。该工作首次在氧化物超导体中观察到如此宽压力范围内的鲁棒超导电性，说明无限层镍酸盐的配对强度在极端压缩下未受抑制，为理解非常规超导机制提供了重要线索。

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

• Superconductivity in freestanding La₀.8Sr₀.2NiO₂ membranes is robust up to 210 GPa with a dome-like T_c onset, peaking at 74.5 K at 146 GPa.
  • 证据: Fig. 2c–f: R(T) at various pressures show persistent resistive drops; T_c[onset] values extracted and plotted in Fig. 5.
• The enhancement is intrinsic, not due to transition broadening, as evidenced by derivative analysis and magnetic field suppression.
  • 证据: Fig. 3: dR/dT analysis shows T_c[m] increases significantly; Fig. 4: Hc₂ enhanced at 80 GPa.
• Comparison with Nd₀.85Sr₀.15NiO₂ shows both peak near 75 K, indicating NiO₂ planes govern superconductivity with little influence from rare-earth f-orbitals.
  • 证据: Fig. 5 includes Nd data; both maxima ≈75 K at different pressures; text states f-orbital moment has little impact.
• This robustness is unprecedented among high-T_c oxide superconductors, with most systems suppressed at much lower pressures.
  • 证据: Fig. 5 comparative data: cuprates, bismuthates suppressed below 40 GPa; text mentions only infinite-layer nickelates persist above 200 GPa.

研究流程

• freestanding_membrane_preparation — Freestanding single-crystal La₀.8Sr₀.2NiO₂ membranes are successfully synthesized.
  • 材料: La₀.8Sr₀.2NiO₃ perovskite thin film; SrTiO₃ substrate; Sr₄Al₂O₇ sacrificial layer; CaH₂ reductant
  • 方法: molecular-beam epitaxy; topotactic reduction; chemical release in deionized water
  • 观察: highly oriented (00l) XRD peaks; superconducting transition at ≈16 K before transfer
• high_pressure_device_assembly — Membranes are integrated into DAC devices for high-pressure resistance measurements.
  • 材料: freestanding membrane; diamond anvil cell; gold electrodes
  • 方法: micromanipulator transfer onto diamond culet; electrode deposition
  • 观察: optical image of membrane with four electrodes
• high_pressure_resistance_measurements — Superconducting transition persists up to 210 GPa, with T_c[onset] exhibiting a dome-like pressure dependence.
  • 材料: La₀.8Sr₀.2NiO₂ membrane devices
  • 方法: resistivity measurement under pressure; magnetic field application up to 7T
  • 观察: resistance drops at T_c[onset] values; T_c[onset] increases with pressure up to 146 GPa then decreases
• data_analysis — The increase in T_c[onset] reflects genuine strengthening of superconductivity, not just broadening.
  • 材料: R(T) data; dR/dT curves; magnetic field sweeps
  • 方法: two-line intersection method for T_c[onset]; derivative analysis for T_c[m]; upper critical field determination
  • 观察: T_c[m] increases fourfold; transition width increases but cannot account for T_c[onset] shift; Hc₂ enhanced under pressure
• interpretation — Infinite-layer nickelates exhibit uniquely robust superconductivity under extreme compression, dominated by NiO₂ planes.
  • 材料: phase diagram data from multiple samples and literature
  • 方法: construction of P-T phase diagram; comparison with Nd₀.85Sr₀.15NiO₂ and other superconductors
  • 观察: dome-like behavior with maximum 74.5 K at 146 GPa; both La and Nd nickelates peak at ≈75K; other oxides show suppression at much lower pressures