Interplay of electric field and electronic correlations in pairing competition in bilayer nickelates

摘要

本研究基于双层双轨道Hubbard模型，利用基态约束路径量子蒙特卡洛方法，考察了垂直电场（层间势差）与电子关联对双层镍酸盐中层间s^±与层内d波配对竞争的调控机制。结果显示，增大层间势差通常增强d波配对顶点贡献并抑制s^±配对，使配对偏好向d波通道转移；增大晶场分裂则增强s^±配对的相对竞争力，而增大Hund耦合在弱偏置下有利于s^±配对，在大偏置下则增强d波配对。微观分析表明，电场主要引起各轨道扇区内层间电荷重分布，伴随反铁磁自旋结构因子及Hund耦合诱导的局域轨道间平行自旋关联增强。这些发现揭示了电荷重分布、磁关联与配对竞争之间的潜在联系，为理解层极化及多轨道相互作用如何影响双层镍酸盐的相对配对倾向提供了理论依据。

材料

• bilayer nickelates
• La₃Ni₂O₇

方法

• constrained-path quantum Monte Carlo
• ground-state constrained-path quantum Monte Carlo
• bare static Lindhard susceptibility

关键词

• pairing competition
• layer polarization
• interlayer s± pairing
• intralayer d wave pairing
• charge redistribution
• antiferromagnetic spin structure factor
• hund's coupling
• crystal field splitting
• orbital occupations

亮点

• The study identifies layer polarization as a means of tuning the competition between interlayer and intralayer pairing in bilayer nickelates without changing chemical composition.
• Step-like enhancements in the antiferromagnetic spin structure factor and lower-layer orbital occupation are observed in similar field intervals, suggesting a connection between charge redistribution and magnetic response.
• The bare static susceptibility exhibits similar step-like variations to the interacting observables, indicating that finite-size electronic structure may play a role in the observed magnetic response.

结论

• Increasing the effective layer potential difference generally enhances the finite-size pairing vertex contribution for d-wave pairing and reduces the s± pairing vertex, shifting the relative pairing preference toward the d-wave channel.
• Increasing the onsite repulsion enhances both vertex contributions, more strongly in the d-wave channel, whereas increasing the crystal-field splitting reduces both and makes s± pairing relatively more competitive.
• Hund's coupling increases the relative competitiveness of s± pairing at weak bias, while enhancing the relative strength of d-wave pairing at large bias.
• The electric-field potential difference primarily redistributes charge between layers within each orbital sector, accompanied by an increase in the antiferromagnetic spin structure factor.
• Hund's coupling enhances local interorbital parallel-spin correlations, suggesting a connection between charge redistribution, magnetic correlations, and pairing competition.

主要论断

• Increasing the layer potential difference (\varepsilon) shifts the pairing preference toward the d-wave channel by enhancing V_d and reducing V_s^±.
  • 证据: Figure 2 shows V_d increases and V_s^± decreases with \varepsilon.,Text states: 'increasing \varepsilon generally enhances the finite-size pairing vertex contribution V_d and reduces V_s^±, shifting the relative pairing preference toward the d-wave channel.'
• Onsite repulsion (U) enhances both pairing vertex contributions, with a stronger effect on the d-wave channel.
  • 证据: Figure 3 shows V_d increases more than V_s^± as U increases from 2 to 3.,Text states: 'Increasing the onsite repulsion enhances both vertex contributions, more strongly in the d-wave channel.'
• Crystal-field splitting reduces both pairing vertex contributions, making s^± pairing relatively more competitive.
  • 证据: Figure 3(c) and (d) show the crossover boundary shifts as crystal-field splitting increases.,Text states: 'increasing the crystal-field splitting reduces both and makes s^± pairing relatively more competitive.'
• Hund's coupling increases the relative competitiveness of s^± pairing at weak bias but enhances d-wave pairing at large bias.
  • 证据: Figure 4 shows the crossover field changes with Hund's coupling.,Text states: 'Hund's coupling increases the relative competitiveness of s^± pairing at weak bias, while enhancing the relative strength of d-wave pairing at large bias.'
• The electric field primarily redistributes charge between layers within each orbital sector, accompanied by increased antiferromagnetic spin correlations.
  • 证据: Figure 5 shows layer-resolved orbital occupations change with \varepsilon while total orbital occupations remain nearly constant.,Figure 6(a) shows the antiferromagnetic spin structure factor increases with \varepsilon.,Text states: 'The bias primarily redistributes charge between layers within each orbital sector, accompanied by an increase in the antiferromagnetic spin structure factor.'

研究流程

• model_definition — The model captures the essential multiorbital physics and external field tuning of bilayer nickelates.
  • 材料: Bilayer two-orbital Hubbard model; Layer potential-energy difference (effective perpendicular electric field); Onsite repulsion; Crystal-field splitting; Hund's coupling
  • 方法: Hamiltonian construction with density-density Hund interaction; Parameter selection based on first-principles Wannier downfolding
• numerical_simulation — CPMC provides accurate ground-state properties for the interacting multiorbital system.
  • 材料: Ground-state constrained-path quantum Monte Carlo (CPMC); Slater determinant walkers; Trial wave function from noninteracting Hamiltonian
  • 方法: Importance-sampled branching random walk in imaginary time; Hubbard-Stratonovich transformation; Constrained-path approximation to control fermion sign problem; Back propagation for equal-time observables
  • 观察: Systematic error typically within a few percent; Statistical error bars smaller than symbol size
• observable_analysis — The interplay of electric field and electronic correlations shifts the pairing preference between interlayer s^± and intralayer d-wave channels.
  • 材料: Pairing vertex contributions (V_d, V_s^±); Orbital occupations; Antiferromagnetic spin structure factor; Local interorbital parallel-spin correlations; Bare static Lindhard susceptibility
  • 方法: Calculation of equal-time correlation functions; Subtraction of disconnected single-particle contributions; Evaluation of layer- and orbital-resolved densities; Comparison of interacting and noninteracting susceptibilities
  • 观察: Increasing \varepsilon enhances V_d and reduces V_s^±; Increasing U enhances both vertices, more strongly in d-wave; Increasing crystal-field splitting reduces both vertices, making s^± more competitive; Hund's coupling increases s^± competitiveness at weak bias and d-wave at large bias; Charge redistribution occurs primarily between layers within each orbital sector; Antiferromagnetic spin structure factor increases with \varepsilon
• interpretation — Layer polarization and multiorbital interactions influence relative pairing tendencies through charge redistribution and magnetic correlations.
  • 材料: Charge redistribution patterns; Magnetic correlation enhancements; Pairing vertex trends
  • 方法: Correlation analysis between charge, spin, and pairing observables; Comparison with noninteracting reference
  • 观察: Layer imbalance reduces relative advantage of interlayer pairing at large bias; Hund's coupling links magnetic responses of orbitals, promoting interlayer pairing at weak bias