来源 自动抓取
作者 Lauro B. Braz, Daniel D. Rivera, Emmanuel V. C. Lopes, George B. Martins, Gustavo M. Dalpian, Luis G. G. V. Dias da Silva
arXiv / 出版方 https://arxiv.org/abs/2609.05185
PDF https://arxiv.org/pdf/2609.05185
相关度评分 5.701
主分类 cond-mat.supr-con
发布日期 2026-09-07
研究范式 理论研究
样品形态 未知

摘要

该研究针对高压双层镍酸盐La3Ni2O7超导配对对称性的争议，采用一种基于正交化投影的全谱模型（Oroj方法），将Kohn-Sham态投影到局域Ni-e_g轨道上，在保持密度泛函理论能带结构的同时，把谱权重重新分布到更宽的能量范围，从而纳入Ni-O杂化及远离费米面的电子态贡献。与仅描述费米面附近低能带的Wannier模型相比，该全谱模型显著增强了层间自旋涨落，并给出公度的磁不稳定性；在自旋涨落框架下，这种特征有利于形成符号改变的s±波超导态，而低能模型则倾向于d波配对。结果表明，全能量描述中的层间耦合和Ni-O杂化对双层镍酸盐超导配对对称性的理论预测具有重要稳定作用。

材料

方法

  • DFT
  • orthonormalized projections (Oroj)
  • matrix random-phase approximation (mRPA)
  • Wannierization
  • maximally localized Wannier functions
  • Fermi surface nesting analysis
  • RPA spin and charge susceptibility calculations

关键词

亮点

  • The Oroj method uses the complete set of Kohn-Sham bands as the non-interacting basis, reducing the many-band problem to a few-orbital model without altering the DFT eigenvalues.
  • The full-spectrum treatment reveals strong interlayer spin fluctuations that are absent or underestimated in low-energy Wannier models.
  • The predicted s± pairing from the full-spectrum weak-coupling treatment aligns with strong-coupling results, helping resolve discrepancies among low-energy tight-binding models.
  • The model attributes the stabilization of s± pairing to an extra electron arising from hybridization with oxygen states far from the Fermi level.

结论

  • The orthonormalized-projection full-spectrum model preserves the density-functional band structure while redistributing spectral weight over a wide energy range, naturally including Ni-O hybridization and states away from the Fermi level.
  • Compared with the low-energy Wannier model, the full-spectrum Oroj description yields enhanced interlayer spin fluctuations and a commensurate magnetic instability.
  • Within the spin-fluctuation framework, the full-spectrum features favor a sign-changing s± superconducting state, whereas low-energy models tend to stabilize d-wave pairing.
  • The Oroj electron occupation is consistent with a Ni-O molecular-orbital picture with five holes per Ni-O dimer, and the additional hybridized electron stabilizes interlayer pairing.
  • Interlayer coupling in full-energy models plays an important role in shaping the predicted pairing symmetry of bilayer nickelates.

主要论断

  • The full-spectrum Oroj model includes Ni-O hybridization and high-energy spectral weight, changing the effective Ni orbital occupation relative to low-energy Wannier models.
    • 证据: The Oroj construction preserves the DFT band structure while redistributing spectral weight over a wide energy range.,Oroj naturally includes contributions from Ni-O hybridized bands located well below/above the Fermi level, adding spectral weight and increasing overall Ni orbital occupation.,Wannier models restricted to low-energy bands yield lower orbital occupations and omit oxygen-derived weight.
  • The Oroj full-spectrum model gives enhanced interlayer spin fluctuations and a commensurate magnetic instability.
    • 证据: Compared to a low-energy description, this approach yields enhanced interlayer spin fluctuations and a commensurate magnetic instability.,Oroj susceptibility matrix shows diverging spin-density terms plus well-pronounced interlayer terms; Wannier model shows irrelevant interlayer terms.,The Oroj magnetic order parameter includes interlayer spin-bond order absent in the Wannier model.
  • Within the spin-fluctuation framework, the full-spectrum Oroj model favors sign-changing s± superconductivity, whereas low-energy models favor d-wave pairing.
    • 证据: Within a spin-fluctuation framework, these features favor a sign-changing s± superconducting state, whereas low-energy models tend to stabilize d-wave pairing.,Fig. 9 shows robust s± symmetry for the Oroj model and d-wave symmetry for the Wannier model.,The Oroj solution aligns with strong-coupling results predicting s±-wave superconductivity.
  • Interlayer coupling and apical-oxygen-mediated hybridization play an important stabilizing role in theoretical predictions of pairing symmetry in bilayer nickelates.
    • 证据: Interlayer coupling in full-energy models may play an important role in shaping the predicted pairing symmetry.,The interlayer fluctuations are highly influenced by the apical oxygen site that connects dz2 orbitals in both layers.,In a simplified bilayer molecular-orbital model, bonding/antibonding gaps directly relate interlayer and intralayer pairing components, and interlayer pairing is essential for s±.
  • Truncated Wannier-based weak-coupling models can produce fragile d-wave pairing due to distorted Fermi-surface nesting and sensitivity to perturbations.
    • 证据: The Wannier Fermi surface shows smaller and slightly distorted pockets, leading to incorrect magnetic nesting vector.,In Wannier-based tight-binding models, superconducting pairing is highly sensitive to the range of hopping amplitudes.,Emergence of d-wave superconductivity in truncated Wannier models is likely accidental and dependent on fine-tuned band structures.

研究流程

  • model_construction — Full-spectrum projected models capture Ni-O hybridization and high-energy spectral weight absent in low-energy Wannier models.
    • 材料: La3Ni2O7 high-pressure bilayer nickelate; Ni e_g orbitals (dx2-y2, dz2); oxygen hybridized states
    • 方法: density functional theory Kohn-Sham eigenstates; orthonormalized projections (Oroj) onto local orbitals; maximally localized Wannier functions for low-energy comparison
    • 观察: Oroj preserves the DFT band structure and redistributes spectral weight over a wide energy range; Wannier model reproduces only four low-energy bands and distorts Fermi surface pockets; Oroj yields larger projected Ni orbital occupation, corresponding to an extra electron compared with Wannier
  • electronic_structure_analysis — The full-spectrum Oroj approach gives a more faithful Fermiology and electron occupation than truncated low-energy Wannier models.
    • 材料: La3Ni2O7 Fermi surface; Oroj spectral weights; Wannier band structure
    • 方法: band structure and Fermi surface comparison; orbital-resolved spectral function and density of states; integrated electron occupation analysis
    • 观察: Oroj and DFT Fermi surfaces show nesting between the nearest alpha and beta pockets; Wannier Fermi surface has smaller, distorted pockets and incorrect nesting vector; Oroj orbital occupations for dx2-y2 and dz2 are similar, unlike Wannier values
  • magnetic_susceptibility_analysis — The Oroj full-spectrum model enhances interlayer spin fluctuations and produces a commensurate magnetic instability.
    • 材料: interacting multiorbital model with Hubbard and Hund interactions; Oroj and Wannier non-interacting bases
    • 方法: matrix random-phase approximation (mRPA); bare and interacting spin susceptibility calculations; generalized Stoner criterion and susceptibility eigen-decomposition
    • 观察: Oroj has a susceptibility peak at a commensurate magnetic ordering vector; Wannier model peaks at incommensurate vector and lacks strong interlayer susceptibility terms; Oroj order parameter includes interlayer spin-bond order; Wannier does not
  • superconducting_pairing_analysis — Ni-O hybridization and interlayer coupling stabilize s± superconductivity in La3Ni2O7, whereas low-energy models favor d-wave.
    • 材料: Oroj and Wannier interacting models; spin-fluctuation pairing interaction
    • 方法: multiorbital RPA pairing interaction; linearized gap equation solved using spectral-weight formulation
    • 观察: Oroj yields a sign-changing s± gap; Wannier model yields d-wave pairing; Oroj s± solution is connected to interlayer pairing and remains robust