Origin of Spin Stripes in Bilayer Nickelate La₃Ni₂O₇

摘要

针对双层镍酸盐La₃Ni₂O₇在常压下的非常规磁序，本文提出了一个忠实反映其晶体对称性的微观哈密顿量。通过大规模密度矩阵重正化群计算表明，在较大的Hund耦合JH作用下，由于隐藏的准一维性，模型中出现了(π/2,π/2)自旋条纹序，并在一定电子浓度范围内持续存在。在更对称的高压区域，当层间反铁磁耦合J⊥足够强时，模型表现出增强的层间配对倾向。该研究揭示了对角自旋条纹的微观起源，并确认Hund耦合JH和层间耦合J⊥是控制La₃Ni₂O₇磁序和配对倾向的关键要素。

材料

• La₃Ni₂O₇

方法

• density matrix renormalization group (DMRG)
• microscopic Hamiltonian

关键词

• spin stripe order
• hund's coupling
• interlayer antiferromagnetic coupling

亮点

• Hidden quasi-one dimensionality of spin stripe order.
• Indispensable role of Hund's coupling.

结论

• Spin stripe order (π/2,π/2) emerges in La₃Ni₂O₇ with sizable Hund's coupling, and superconducting tendency appears when interlayer antiferromagnetic coupling becomes large under pressure.

主要论断

• A microscopic model with non-uniform hopping and Hund's coupling reproduces the (π/2,π/2) spin stripe order observed in La₃Ni₂O₇.
  • 证据: Full text: DMRG calculations show (π/2,π/2) spin stripe order in the model for t' < t and large U.,Abstract: 'Using state-of-the-art density matrix renormalization group calculations, we show that (π/2,π/2) spin stripe order emerges in our model'
• Superconductivity in La₃Ni₂O₇ requires large interlayer antiferromagnetic coupling, which naturally occurs under pressure.
  • 证据: Abstract: 'Our model exhibits superconducting tendency only when the interlayer antiferromagnetic coupling J⊥ becomes sufficiently large, which naturally occurs under pressure.',Full text: DMRG results show power-law decay of interlayer singlet pairing correlation with exponent Ksc < 2 for J⊥=4t.
• Hund's coupling JH plays an indispensable role in stabilizing the spin stripe order.
  • 证据: Abstract: 'The spin stripe order occurs over a range of electron concentrations, but requires a sizable Hund's coupling JH.',Full text: 'We have confirmed numerically that by taking a smaller JH, one needs a larger U to stabilize the stripe order.'

研究流程

• Model Construction — The model describes the interplay of lattice structure and magnetism in La₃Ni₂O₇.
  • 材料: Microscopic Hamiltonian for La₃Ni₂O₇; dx2-y2 and dz2 orbitals; Hund's coupling JH; interlayer coupling J⊥
  • 方法: Construction of effective bilayer two-orbital model
  • 观察: Model captures strain effects via hopping anisotropy
• DMRG Calculation — DMRG results show (π/2,π/2) spin stripe order emerges when t' < t and U is sufficiently large, and superconductivity appears when J⊥ is large.
  • 材料: GPU-accelerated DMRG; System sizes up to 400 sites; Bond dimension up to 20000
  • 方法: Density matrix renormalization group (DMRG) calculations; Subspace expansion technique
  • 观察: Spin correlation functions F(|ri-rj|); Phase diagrams in t'-U plane for fixed JH
• Phase Diagram Analysis — The spin stripe order requires sizable Hund's coupling, and superconductivity occurs when interlayer coupling is sufficiently large.
  • 材料: Phase diagrams from DMRG; Spin correlation functions
  • 方法: Identification of spin stripe orders (π/2,π/2) and (π,0); Analysis of superconducting correlations (interlayer singlet pairing)
  • 观察: (π/2,π/2) SSO stable when decoupled 1D chains are ferromagnetic; Superconducting power-law decay r-Ksc with Ksc < 2 for large J⊥