Superconductivity onset above 60 K in ambient-pressure nickelate films

摘要

本研究采用巨大氧化原子层外延法，在极端非平衡条件下于SrLaAlO₄衬底上生长(La,Pr)₃Ni₂O₇薄膜，实现了常压下约63 K的超导起始转变温度，零电阻温度达约37 K，抗磁信号起始约23 K。该方法通过高温和原位充分氧化克服了亚稳态超导相的结构不稳定性，X射线衍射和扫描透射电镜证实薄膜具有大范围晶态纯度。输运测量显示正常态电阻温度幂律指数α从低起始转变温度样品的费米液体行为（α≈2）向高起始转变温度样品的奇异金属行为（α≈1）系统演化，直接将增强的超导性与非费米液体行为关联。互电感技术绘制的涡旋熔化相图揭示二维熔化极限被抑制至近零，层间耦合强度显著强于铋系铜氧化物。这些结果表明镍酸盐是常压下具有强层间耦合的奇异金属高温超导体。

材料

• (La、Pr)₃Ni₂O₇

方法

• gigantic-oxidative atomic-layer-by-layer epitaxy (GAE)
• X-ray diffraction (XRD)
• synchrotron XRD
• reciprocal space mapping
• STEM
• energy-dispersive X-ray spectroscopy (EDS)
• transport measurements (R-T)
• mutual inductance technique
• power-law fitting for resistivity exponent

关键词

• strange metal behavior
• linear in t resistivity
• vortex melting
• interlayer coupling
• non equilibrium growth
• coherent interface
• oxygen stoichiometry
• berezinskii kosterlitz thouless (bkt) transition

亮点

• The GAE method creates an extreme non-equilibrium growth regime that decouples the conflict between crystallinity and oxygenation.
• Mapping the vortex melting phase diagram reveals the 2D melting limit suppressed to near zero, demonstrating significantly stronger interlayer coupling than that of cuprates.
• The nickelates are identified as an ambient-pressure strange-metal high-temperature superconductor with strong interlayer coupling.

结论

• We report ambient-pressure superconductivity onset at ≈63 K in epitaxial (La,Pr)₃Ni₂O₇ thin films.
• Transport measurements reveal a zero-resistance temperature reaching ≈37 K, while mutual inductance measurements demonstrate a robust diamagnetic transition starting at ≈23 K.
• These films exhibit a systematic evolution in their normal-state resistivity-temperature curve: the power-law exponent α evolves from Fermi-liquid-like (α≈2) at lower T_c,onset to strange-metal-like (α≈1) in higher T_c,onset samples.

主要论断

• Ambient-pressure superconductivity onset at ≈63 K and zero-resistance at ≈37 K is achieved in (La,Pr)₃Ni₂O₇ films via extreme non-equilibrium GAE method.
  • 证据: abstract: 'ambient-pressure superconductivity onset at ≈63 K' and 'zero-resistance temperature reaching ≈37 K',full_text Fig. 1c: S₁ film shows Tc_onset = 63 K, Tc_zero ≈ 30 K (S₁) and 37 K (S₂)
• The normal-state resistivity exponent α evolves from Fermi-liquid-like (α≈2) at lower Tc_onset to strange-metal-like (α≈1) at higher Tc_onset, directly linking enhanced superconductivity to non-Fermi liquid behavior.
  • 证据: abstract: 'the power-law exponent α evolves from Fermi-liquid-like (α ≈2) at lower Tc_onset to strange-metal-like (α ≈1) in higher Tc_onset samples',full_text Fig. 1d,e: clear correlation shown for 90 samples with various La:Pr ratios
• Mutual inductance measurements reveal a robust diamagnetic transition at ≈23 K and a vortex melting phase diagram with 2D melting limit suppressed to near zero, indicating much stronger interlayer coupling than cuprates (e.g., Bi-2212).
  • 证据: abstract: 'Mapping the vortex melting phase diagram… reveals 2D melting limit suppressed to near zero, which demonstrates significantly stronger interlayer coupling than that of cuprates',full_text Fig. 2: TM onset at 23 K, Bcr≈200 T from fitting, compared to Bi-2212 Bcr ≈2T
• The enhanced performance is enabled by pushing GAE into an extreme non-equilibrium regime that simultaneously improves crystallinity and achieves full oxygenation.
  • 证据: abstract: 'This T_c leap is enabled by pushing our GAE method into an extreme non-equilibrium growth regime',full_text: 'GAE accesses a unique high-temperature and high-oxidation regime' and STEM/XRD confirm large-scale crystalline purity

研究流程

• film_growth — Extreme non-equilibrium GAE enables single-step synthesis with Tc_onset >60 K.
  • 材料: (La,Pr)₃Ni₂O₇ thin films on SrLaAlO₄ (001) substrates
  • 方法: gigantic-oxidative atomic-layer-by-layer epitaxy (GAE); alternating ablation of (La,Pr)O_x and NiO_x targets
  • 观察: RHEED oscillations show layer-by-layer growth; Films are superconducting as-grown without post-annealing
• transport_and_mutual_inductance_measurements — Enhanced superconductivity correlates with strange-metal normal state and strong interlayer coupling.
  • 材料: (La,Pr)₃Ni₂O₇ films with various oxygen stoichiometries
  • 方法: four-terminal AC lock-in transport; two-coil mutual inductance technique; XRD and STEM
  • 观察: Tc_onset up to 63 K, Tc_zero up to 37K; Normal-state exponent α evolves from ≈2 to ≈1 with increasing Tc_onset; Vortex melting temperature TM ≈23 K at zero field, strong interlayer coupling