Microscopic Origin of Pressure-Enhanced and Robust Superconductivity in Infinite-Layer La₀.8Sr₀.2NiO₂

摘要

该研究结合第一性原理计算、压力依赖的双轨道模型以及自洽FLEX和线性化Eliashberg方程，揭示了无限层La₀.₈Sr₀.₂NiO₂中压力增强且稳健超导的微观机制。结果表明，压力升高增大了动能尺度、降低了有效关联强度U/t、增强了层间杂化，并使空穴从La/Sr电荷库转移到关联的Ni区域；在低压下，动能尺度增大和体系趋近最佳中等耦合促进配对，而高压下压力诱导的自掺杂使体系进入过掺杂区，从而抑制超导，形成宽超导穹顶。尽管压缩使费米面显著三维化，与配对相关的自旋磁化率对q_z依赖较弱，仍主要在(π,π)附近出现峰值，因此Ni dx²-y²主导的d波配对态在计算压力范围内保持稳定。这一受限的低能配对框架解释了该材料在兆巴级压缩下超导的异常稳健性。

材料

• La₀.8Sr₀.2NiO₂

方法

• DFT
• maximally localized Wannier functions (MLWFs)
• constrained random-phase approximation (cRPA)
• fluctuation-exchange approximation (FLEX)
• linearized Eliashberg equation
• pressure-dependent two-orbital model

关键词

• superconducting dome
• pressure enhanced superconductivity
• kinetic energy scale
• effective correlation strength u/t
• interlayer hybridization
• hole self doping
• overdoped regime
• spin susceptibility
• d wave pairing
• ni dx2 y2 orbital
• three dimensional fermi surface

亮点

• A unified microscopic interpretation of the broad superconducting dome is provided through the competition among kinetic-energy enhancement, reduced correlation strength, and hole self-doping.
• Interlayer hybridization strongly reshapes the Fermi surface but has only a secondary effect on pairing in this minimal low-energy framework.
• The restricted low-energy manifold of infinite-layer nickelates is proposed as a minimal platform for testing theories of unconventional superconductivity.
• Reducing the nominal Sr concentration may avoid the overdoped regime under pressure and potentially increase the maximum high-pressure T_c.

结论

• Pressure increases the kinetic-energy scale, reduces the effective correlation strength U/t, strengthens interlayer hybridization, and transfers holes from the La/Sr-derived charge reservoir to the correlated Ni sector.
• The initial enhancement of pairing originates from the increasing kinetic-energy scale and the approach to optimal intermediate coupling.
• The high-pressure suppression of superconductivity is primarily caused by pressure-induced hole self-doping that drives the Ni band into the overdoped regime.
• Despite pronounced three-dimensionalization of the Fermi surface, the pairing-relevant spin susceptibility remains weakly dependent on qz and peaked near (π,π).
• The Ni-dx2-y2-dominated d-wave pairing state remains stable over the calculated pressure range, explaining the robustness of superconductivity under megabar compression.

主要论断

• Pressure increases the kinetic-energy scale, reduces the effective correlation strength U/t, strengthens interlayer hybridization, and transfers holes from the La/Sr charge reservoir to the correlated Ni sector.
  • 证据: Pressure increases the kinetic-energy scale, reduces Ux/t1, strengthens interlayer hybridization, and transfers holes from the La/Sr-derived charge reservoir to the correlated Ni sector.,The nearest-neighbor in-plane hopping increases from its ambient-pressure value to its 210 GPa value; interlayer hopping increases even more strongly; the screened interaction remains nearly constant; hole self-doping increases.
• The pressure dependence of superconductivity is dome-shaped: increasing kinetic scale and approach to optimal intermediate coupling enhance pairing at low pressure, while pressure-induced self-doping into the overdoped regime suppresses pairing at high pressure.
  • 证据: At low pressure, the increasing kinetic scale and the approach to optimal intermediate coupling enhance pairing, while self-doping remains weak. Above approximately GPa, accumulated hole self-doping drives the Ni band further into the overdoped regime and generates the descending side of the dome.,The leading Eliashberg eigenvalue initially increases rapidly with pressure, reaches a maximum around GPa, and then decreases, reproducing the qualitative dome-shaped pressure dependence observed experimentally.
• The Ni-dx2-y2-dominated d-wave pairing state remains stable over the calculated pressure range despite pronounced three-dimensionalization of the Fermi surface, because pairing-relevant spin fluctuations remain weakly dependent on q_z and peaked near (pi,pi).
  • 证据: The leading eigenfunction has d-wave symmetry at every pressure investigated.,The spin susceptibility remains peaked near the in-plane wave vector at both pressures and on both q_z planes, and its weak q_z dependence shows that the pairing-relevant spin fluctuations remain predominantly in-plane.,The active correlated sector of La₀.8Sr₀.2NiO₂ remains dominated by a single Ni-dx2-y2 orbital, while the dz2 orbital primarily mediates interlayer dispersion.

研究流程

• model_construction — The low-energy electronic structure is captured by a two-band tight-binding model dominated by the Ni-dx2-y2 orbital, with La/Sr reservoir effects incorporated as a pressure-dependent carrier concentration.
  • 材料: La₀.8Sr₀.2NiO₂; two-orbital Ni-dx2-y2/Ni-dz2 tight-binding Hamiltonian; La/Sr-derived charge reservoir
  • 方法: DFT structure optimizations; virtual-crystal approximation for Sr substitution; maximally localized Wannier functions; constrained random-phase approximation
  • 观察: Wannier Hamiltonian reproduces Ni-dominated DFT bands near Fermi level; Ni-dx2-y2 forms the principal correlated Fermi surface; Ni-dz2 orbital remains nearly fully occupied
• parameter_evolution_extraction — Pressure increases the kinetic-energy scale, reduces U/t, enhances interlayer hybridization, and transfers holes from the La/Sr charge reservoir to the Ni sector.
  • 材料: pressure-dependent two-orbital model; cRPA screened interaction
  • 方法: extracting pressure-dependent hopping parameters from the MLWF Hamiltonian; evaluating screened interaction with cRPA; determining effective hole concentration from La/Sr electron pocket expansion
  • 观察: in-plane hopping increases with pressure; interlayer hopping increases more strongly; screened interaction remains nearly constant; hole self-doping increases
• pairing_calculation — The calculated pairing tendency reproduces the experimentally observed dome-shaped pressure dependence.
  • 材料: FLEX self-energy and susceptibilities; linearized Eliashberg equation
  • 方法: self-consistent FLEX calculations; linearized Eliashberg equation for spin-singlet pairing; selective variation of model parameters; temperature-dependent eigenvalue calculations
  • 观察: leading eigenvalue increases initially, peaks around optimal pressure, then decreases; eigenfunction has d-wave symmetry at every pressure investigated; fixing ambient-pressure carrier concentration removes most high-pressure suppression; fixing interlayer hopping parameters only modestly changes the eigenvalue
• interpretation — The superconducting dome and robustness under megabar compression arise from a preserved low-energy Ni-dx2-y2-dominated d-wave pairing framework.
  • 材料: Ni-dx2-y2 spectral function; static spin susceptibility
  • 方法: comparison of spectral function and spin susceptibility at ambient and high pressure; identification of dominant pairing trends from selective parameter variation
  • 观察: spin susceptibility remains peaked near (pi,pi) and weakly q_z dependent; pressure substantially modifies the one-particle electronic structure; correlated sector remains dominated by a single Ni-dx2-y2 orbital