Electronic structure and two-orbital model of the quadlayer La₅Ni₄O₁₃

摘要

通过密度泛函理论（DFT）与随机相近似（RPA）计算，系统研究了四层Ruddlesden–Popper镍氧化物La₅Ni₄O₁₃在常压、5%各向同性压缩应变和4% c轴单轴应变下的电子结构，并基于Wannier下折叠构建了四层两轨道模型。DFT表明，各向同性应变展宽Ni-e_g能带并引起O-p向Ni-d的电荷转移；c轴单轴应变则选择性上移d_z2衍生的bonding1能带，而d_x2-y2色散几乎不变。该两轨道模型可重现低能Ni-e_g能带。常压和5%各向同性应变下，费米面由两个电子口袋（α、δ）和三个空穴口袋（β、β′、β″）组成；单轴应变下出现具有d_z2轨道特征的γ空穴口袋。RPA计算显示，主导自旋响应从常压的q≈(2π/3,2π/3)转为两种应变下的q≈(π,π)，且在c轴压缩下增强。作者据此认为，c轴压缩可能为四层镍氧化物提供类似于双层和三层镍氧化物的有利超导路径。

材料

• La₅Ni₄O₁₃

方法

• DFT
• RPA
• Wannier downfolding
• VASP
• PAW
• PBE
• GGA
• WANNIER90
• quadlayer two-orbital tight-binding model

关键词

• ruddlesden popper nickelates
• pressure induced superconductivity
• ni e_g bands
• charge transfer
• fermi surface
• electron pockets
• hole pockets
• lifshitz transition
• spin susceptibility
• spin fluctuations
• interlayer coupling
• uniaxial strain
• isotropic strain

亮点

• Systematically compares ambient pressure, 5% isotropic compressive strain, and 4% c-axis uniaxial strain in the quadlayer Ruddlesden-Popper nickelate La₅Ni₄O₁₃.
• Constructs a quadlayer two-orbital model via Wannier downfolding that captures the strain evolution of the Fermi surface.
• Identifies a strain-induced Lifshitz transition under c-axis uniaxial strain, where a d_z²-derived γ hole pocket emerges, unlike under ambient or isotropic strain.
• Shows that c-axis compression enhances the spin susceptibility at (π, π), suggesting a possible superconducting pairing channel analogous to bilayer and trilayer nickelates.

结论

• DFT calculations show that 5% isotropic strain broadens the Ni-e_g bands and induces charge transfer from O-p to Ni-d orbitals, whereas 4% c-axis uniaxial strain selectively shifts the d_z²-derived bonding1 band upward while leaving the d_x²-y² dispersion nearly unchanged.
• A quadlayer two-orbital model constructed by Wannier downfolding reproduces the low-energy Ni-e_g bands and shows that the d_z²-derived hole pocket remains absent under ambient pressure and isotropic strain but emerges around the M point under 4% c-axis uniaxial strain, signaling a strain-induced Lifshitz transition.
• RPA calculations reveal that the leading spin response shifts from q approximately (2π/3, 2π/3) at ambient pressure to q approximately (π, π) under both strain conditions and is enhanced under c-axis compression.
• The results suggest that c-axis compression may provide a favorable route to superconductivity in quadlayer La₅Ni₄O₁₃ analogous to that in bilayer and trilayer nickelates, and that uniaxial compression is more efficient than hydrostatic pressure for generating the d_z²-derived hole pocket.

主要论断

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研究流程

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