Co-operating multiorbital and nonlocal correlations in bilayer nickelate

摘要

本研究基于有效三轨道模型，采用超越动力学平均场理论的D-TRILEX多体框架，系统分析了高压超导双层镍酸盐La₃Ni₂O₇正常态中多轨道与非局域自能效应的相互作用。结果表明，低能物理场景高度依赖于轨道间相互作用强度：当该强度较弱时，著名的γ准粒子平坦带位于费米能级以下；当强度增强时，该平坦带穿越费米能级，导致电子与铁磁性的顺磁子激发发生散射，形成自旋极化子束缚态。这些束缚态表现为费米能级下方出现的非相干谱权重阴影带。研究的发现揭示了双层镍酸盐中存在额外的竞争电子态，这为解释近期角分辨光电子能谱实验中关于费米面附近谱结构的争议提供了理论依据。

材料

• La₃Ni₂O₇

方法

• D-TRILEX
• DFT
• DMFT
• maximum entropy method

关键词

• spin polaron formation
• non fermi liquid
• flat band
• ferromagnetic paramagnon

亮点

• The low-energy physics is highly dependent on the interorbital interaction strength.
• The findings provide a theoretical basis for resolving ARPES controversies regarding spectral structures near the Fermi surface.

结论

• When the interorbital interaction is strong, the flat γ band crosses the Fermi level, and electrons scatter with ferromagnetic paramagnon excitations, forming spin-polaron bound states.
• These bound states manifest as incoherent spectral weight shadow bands below the Fermi level.

主要论断

• In La₃Ni₂O₇, the position of the flat γ band relative to the Fermi level is controlled by interorbital interaction strength
  • 证据: D-TRILEX calculations show that increasing U₂ reduces occupation of the γ band, shifting its flat part upward; at U₂=4.6 eV the flat band is exactly at Fermi level
• When the flat band crosses the Fermi level, electrons scatter with ferromagnetic spin fluctuations, forming spin-polaron bound states that appear as incoherent shadow bands
  • 证据: The self-energy becomes strongly momentum-dependent near M point; spin susceptibility shows FM-like character; a shadow band appears below Fermi level

研究流程

• Model and method setup — Low-energy physics depends on U₂
  • 材料: Effective three-orbital model for La₃Ni₂O₇
  • 方法: D-TRILEX method incorporating nonlocal correlations beyond DMFT
  • 观察: Spectral function, self-energy, susceptibilities
• Analysis of results — Spin-polaron bound states form from scattering with ferromagnetic paramagnon excitations
  • 方法: Analytic continuation; Bethe-Salpeter eigenvalues
  • 观察: For smaller U₂, flat dz2 band below Fermi level; for larger U₂, flat band crosses Fermi level leading to spin-polaron formation