Pairing mechanism and superconductivity in pressurized La₅Ni₃O₁₁

摘要

通过密度泛函理论（DFT）和随机相位近似（RPA）计算，该研究系统分析了高压下La₅Ni₃O₁₁的电子性质与超导机制。DFT能带结构显示，这种交替堆叠双层和单层NiO₂面的材料存在两组近乎解耦的子能带，分别来自双层子系统和单层子系统。RPA分析表明，超导配对主要发生在双层子系统内，并呈现与加压La₃Ni₂O₇类似的s±波配对对称性；而单层子系统主要通过极弱的层间约瑟夫森耦合（IJC）作为桥梁，连接相邻双层以实现沿c轴的相位相干。在低压下，压力增强使IJC显著提升，从而抬升体态超导转变温度（T_c）；当压力足够高时，γ-pocket的态密度降低导致T_c逐渐下降。这一机制自然解释了实验中观测到的穹顶状T_c-压力依赖关系，并揭示了混合相与纯相镍酸盐超导体不同的压力响应。

材料

• La₅Ni₃O₁₁

方法

• DFT
• RPA
• tight-binding modeling
• Wannier downfolding

关键词

• s± wave pairing
• interlayer josephson coupling
• pressure dome
• hybrid phase nickelate

亮点

• Provides a natural understanding of the dome-shaped T_c pressure dependence in La₅Ni₃O₁₁.
• Shows that the alternating bilayer-single-layer structure leads to extremely weak interlayer Josephson coupling.
• Establishes a unified framework for hybrid phase nickelate superconductors.

结论

• Superconducting pairing primarily occurs in the bilayer subsystem with s±-wave symmetry, similar to pressurized La₃Ni₂O₇.
• The single-layer subsystem serves as a bridge for inter-bilayer phase coherence via weak interlayer Josephson coupling.
• The dome-shaped pressure dependence of T_c arises from the interplay between enhanced IJC at low pressure and reduced DOS on the γ-pocket at high pressure.
• The hybrid phase exhibits distinct pressure response compared to pure bilayer nickelates.

主要论断

• Superconductivity in La₅Ni₃O₁₁ primarily occurs in the bilayer subsystem with s±-wave pairing symmetry
  • 证据: From abstract: 'SC in this material occurs primarily within the bilayer subsystem exhibiting an s± wave pairing symmetry similar to that observed in pressurized La₃Ni₂O₇'
• Single-layer subsystem serves as a bridge facilitating inter-bilayer phase coherence via interlayer Josephson coupling, leading to dome-shaped T_c vs pressure
  • 证据: From abstract: 'the single-layer subsystem mainly serves as a bridge facilitating the inter-bilayer phase coherence through the interlayer Josephson coupling (IJC)… dome-shaped pressure dependence of T_c observed experimentally is naturally understood'

研究流程

• density_functional_theory_calculations — Electronic structure consists of two nearly decoupled subsystems: bilayer and single-layer
  • 材料: La₅Ni₃O₁₁
  • 方法: DFT with PBE functional; VASP
  • 观察: band structure; Fermi surface
• tight_binding_model_construction — Constructed trilayer two-orbital tight-binding model
  • 材料: DFT band structure
  • 方法: Wannier downfolding
  • 观察: hopping integrals
• random_phase_approximation_analysis — s±-wave pairing dominates in bilayer subsystem; single-layer mediates interlayer Josephson coupling
  • 材料: Tight-binding model for bilayer subsystem
  • 方法: RPA for spin susceptibility and pairing
  • 观察: pairing eigenvalue; gap symmetry