The evolution of pairing correlation with 3d_z2 electron filling in a bilayer two-orbital model for La₃Ni₂O₇

摘要

通过密度矩阵重正化群方法，该工作在一维最小几何结构上系统研究了加压双层镍氧化物La₃Ni₂O₇中有效双层双轨道模型的超导配对关联随Ni 3dz²轨道填充的演化。通过调节轨道化学势差异，将3dz²轨道从1/12掺杂连续调控至近半填充，发现超导关联在半填充附近被显著抑制，表明该轨道的巡游性有利于配对。此外，在电荷涨落较大的区域配对关联增强，暗示电荷序与超导之间存在竞争。这些结果支持了既有的理论图像：层间反铁磁超交换提供配对胶水，而巡游的3dz²轨道通过杂化将配对传递并建立长程相干性。研究明确了3dz²轨道巡游性对超导的关键作用，为理解该体系中非常规配对机制提供了重要依据。

材料

• La₃Ni₂O₇

方法

• DMRG

关键词

• pairing correlation
• charge fluctuations
• charge order
• superconductivity
• itinerancy
• 3dz2 orbital

亮点

• The study clarifies the crucial role of the itinerancy of the 3dz2 orbital in superconductivity, providing important evidence for understanding the unconventional pairing mechanism in La₃Ni₂O₇.
• The pairing correlation is enhanced at regions with large charge fluctuations, indicating a competition between charge order and superconductivity.

结论

• The evolution of pairing correlation with electron filling in an effective bilayer two-orbital model for La₃Ni₂O₇ shows significant suppression when the 3dz2 orbital approaches half-filling.
• The itinerancy of the 3dz2 orbital is favorable for superconductivity in the bilayer two-orbital model.
• Pairing correlation is enhanced in regions where charge fluctuations are large, suggesting competition between charge order and superconductivity.

主要论断

• Itinerancy of the 3dz2 orbital is favorable for superconducting pairing in the bilayer two-orbital model of La₃Ni₂O₇.
  • 证据: B_y systematically varying the 3dz2 orbital filling from 1/12 doping to half-filling, a pronounced suppression of superconducting correlations near half-filling is observed (abstract).,DMRG results show that the pairing exponent K_sc increases as the dz2 orbital approaches half-filling, indicating weaker pairing (Section III, Figs. 4-5).
• Pairing correlations are enhanced in regions where charge fluctuations are large, suggesting competition between charge order and superconductivity.
  • 证据: Pairing correlation is enhanced around two singularity points in Fig. 2, which correspond to large charge fluctuations and changes in charge density wave patterns (Section III).,At these points, charge density wave wavelength changes or phase shifts, indicating charge order competition (abstract and supplementary figures).

研究流程

• Model construction — The model serves as a minimal model to investigate the role of dz2 orbital filling on pairing correlations.
  • 材料: Bilayer two-orbital Hamiltonian for La₃Ni₂O₇; Ni 3dx2-y2 and 3dz2 orbitals
  • 方法: Effective bilayer two-orbital model derived from DFT calculations
  • 观察: Model captures low-energy physics of pressurized La₃Ni₂O₇
• DMRG simulation — DMRG results reveal evolution of pairing correlations with dz2 orbital filling.
  • 材料: One-dimensional chain geometry; DMRG with bond dimension up to 12288 and truncation error ≈10-9
  • 方法: Density matrix renormalization group (DMRG)
  • 观察: Computed orbital-resolved charge density and spin profiles; Calculated inter-layer and intra-layer pair-pair correlation functions
• Pairing correlation analysis — Superconducting correlations are suppressed near half-filling and enhanced at charge fluctuation regions, indicating itinerancy of dz2 orbital favors pairing and competition with charge order.
  • 材料: Pair-pair correlation data for vertical (inter-layer) and intra-layer bonds
  • 方法: Power-law fit to extract pairing exponent K_sc; Finite truncation error extrapolation
  • 观察: Pairing exponent K_sc increases as dz2 filling approaches half-filling for both dz2 and dx2-y2 orbitals; Dips in K_sc at two singularity points (μ_diff ≈ 1.8 and 2.8) corresponding to large charge fluctuations