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基于对三层镍酸盐La₄Ni₃O₁₀高压超导的发现，该研究利用密度泛函理论结合动力学平均场理论（DFT+DMFT）设计并计算了钴基类似物La₄Co₂NiO₈Cl₂。通过将高压相La₄Co₃O₁₀内层Co替换为Ni并掺入Cl实现电子掺杂，该化合物获得了与超导La₄Ni₃O₁₀相似的晶体结构及强关联电子特征：外层Co轨道呈现强有效质量增强和非费米液体行为，内层Ni则表现为弱关联费米液体；在M点附近出现源于外层Co轨道且接近费米能级的平带；同时具有显著的轨道选择性以及高自旋与低自旋态混合的局域自旋涨落。这些特性与La₄Ni₃O₁₀的关键电子态高度吻合，表明La₄Co₂NiO₈Cl₂有望成为钴基层状化合物中实现高温超导电性的候选材料，为后续实验探索提供了理论依据。

本文采用DFT+动力学平均场理论方法，研究了电子关联和外延应变对双层Ruddlesden-Popper镍酸盐La₃Ni₂O₇正常态电子结构、准粒子重整化、费米面及磁关联的影响。结果表明Ni 3d能带存在显著的轨道选择性重整化和强非相干性，Ni的x²−y²与3z²−r²态接近轨道选择性局域化。电子性质对面内应变高度敏感：拉伸应变和约−2%以内的中等压缩应变均能显著增强磁关联；而在约−4%的大压缩应变下，体系发生Lifshitz转变，γ费米面片消失，该费米面片与几乎完全占据的、浅的成键Ni 3z²−r²平带相关，并导致磁关联急剧下降，暗示超导被抑制。总体上，结果支持自旋/电荷密度波条纹不稳定性由费米面嵌套驱动的图像，并表明压力和应变可有效调控自旋-电荷密度波有序，从而增强自旋涨落。

It has been recently shown that under pressure trilayer Ruddlesden-Popper nickelate La4⁢Ni3⁢O10 (LNO) becomes superconducting below a critical temperature ≈20 K, in addition to the infinite-layer and bilayer systems. Motivated by this observation, we explore the effects of electron correlations on its electronic structure and magnetic properties using the advanced density functional theory plus dynamical mean-field theory approach. Our results for the normal-state electronic structure and correlation effects in LNO show much in common with the infinite-layer and bilayer nickelates, with remarkable site- and orbital-dependent renormalizations of the Ni 3⁢𝑑 bands and notable incoherence of the Ni 𝑑3⁢𝑧2−𝑟2 states, caused by correlation effects. Our analysis of the Fermi surface and magnetic correlations suggests the emergence of competing spin and charge stripe states, implying the importance of in-plane spin fluctuations to explain superconductivity in this material.

Motivated by the recent observation of superconductivity in the pressurized trilayer Ruddlesden-Popper (RP) nickelate La4⁢Ni3⁢O10, we explore its structural, electronic, and magnetic properties as a function of hydrostatic pressure from first-principles calculations. We find that an orthorhombic (monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity. The electronic structure of La4⁢Ni3⁢O10 can be understood using a molecular trimer basis wherein 𝑛 molecular subbands arise as the 𝑑𝑧2 orbitals hybridize strongly along the 𝑐 axis within the trilayer. The magnetic tendencies indicate that the ground state at ambient pressure is formed by nonmagnetic inner planes and stripe-ordered outer planes that are antiferromagnetically coupled along the 𝑐 axis, resulting in an unusual ↑, 0, ↓ stacking that is consistent with the spin density wave model previously suggested by neutron diffraction. Such a state is destabilized at the pressure where superconductivity arises. Despite the presence of 𝑑𝑧2 states at the Fermi level, the 𝑑𝑥2−𝑦2 orbitals also play a key role in the electronic structure of La4⁢Ni3⁢O10. This active role of the 𝑑𝑥2−𝑦2 states in the low-energy physics of the trilayer RP nickelate, together with the distinct electronic behavior of the inner and outer planes, resembles the physics of multilayer cuprates.

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。

Signatures of superconductivity under pressure have recently been reported in the bilayer La3⁢Ni2⁢O7 and trilayer La4⁢Ni3⁢O10 Ruddlesden-Popper (RP) nickelates with the general chemical formula La𝑛+1⁢Ni𝑛⁢O3⁢𝑛+1 (𝑛 = number of perovskite layers along the 𝑐-axis). The emergence of superconductivity is always concomitant with a structural transition in which the octahedral tilts are suppressed, bringing the apical Ni-O-Ni angle to 180∘ and causing an increase in the out-of-plane 𝑑𝑧2 orbital overlap. Due to this strong interlayer coupling, a flat band of pure 𝑑𝑧2 character crosses the Fermi level. Here, using first-principles calculations, we explore biaxial strain (both compressive and tensile) as a means to mimic the electronic structure characteristics of RP nickelates (up to 𝑛=5) under hydrostatic pressure. Our findings highlight that strain enables the decoupling of the structural and electronic structure effects obtained under hydrostatic pressure: While compressive strain brings the apical Ni-O-Ni angle closer to 180∘, it shifts the 𝑑𝑧2 flat bands away from the Fermi energy, giving rise to a more cupratelike electronic structure. In contrast, tensile strain reduces the apical Ni-O-Ni angle (to values of ∼160∘), but it recovers the flat 𝑑𝑧2 band at the Fermi level appearing in the bilayer and trilayer RP nickelates under pressure. Overall, strain represents a promising way to tune the electronic structure of RP nickelates and could be an alternative route to achieve superconductivity at ambient pressure in this family of materials.

本文采用第一性原理DFT+U方法，研究了不同稀土元素（Pr、Nd、Sm）掺杂La₃Ni₂O₇的晶体结构和电子性质趋势。计算表明，掺杂原子优先占据岩盐层中的La位，随掺杂离子半径减小（Pr→Sm），化学压力效应使晶胞体积单调递减，单斜到四方的结构转变压力依次升高，且该转变与超导电性的出现基本吻合，与实验观测一致。在高压四方相中，d_{z²}能带平坦化并穿越费米能级，出现d_{z²}特征的空穴型费米面，被视为超导电性的关键电子标志。随稀土离子尺寸减小，面内跳跃积分增强，而由于顶端Ni-O键长缩短，面外跳跃积分反而减弱。这些发现为理解稀土掺杂对双层Ruddlesden-Popper镍酸盐电子结构的影响及其与超导转变温度的关联提供了微观机理见解。

本研究采用DFT+DMFT方法，系统探讨了交替单层-双层Ruddlesden-Popper型镍酸盐La₅Ni₃O₁₁（1212-LNO）在正常态的电子结构和磁相关性。结果表明，结构上不同的单层和双层Ni离子表现出显著差异：双层Ni离子中的e_g态形成了强烈重整化的准粒子能带，其中Ni的x²-y²和3z²-r²轨道有效质量增强因子分别达到约3.5和4.2；而单层Ni离子的e_g态则呈现轨道选择莫特绝缘态，其中Ni的3z²-r²轨道具有窄能隙，x²-y²轨道则表现为金属性且强非相干（非费米液体）行为。磁相关分析表明，双层NiO₆板中可能形成自旋与电荷密度波交织的条纹，主要不稳定性对应波矢Q=(1/3,1/3)的“上-下-0”自旋图案，并与(1/4,1/4)的“上-上-下-下”双列条纹态竞争。单层Ni的3d电子则倾向于形成奈尔型磁序。在压力下，1212-LNO经历轨道选择莫特绝缘体-金属相变，伴随单层Ni e_g态的金属化，其近费米能级处呈现强非相干的非费米液体行为。总体而言，关联效应显著重构了磁相关性，使其从DFT预测的单层主导转变为双层主导，强调了层间约束和轨道依赖关联的关键作用。

本文采用基于第一性原理瓦尼尔函数的二轨道双层模型和连续格林函数方法，理论分析了超导双层镍酸盐薄膜的扫描隧道显微镜谱。研究发现，多轨道特性和瓦尼尔函数的空间各向异性导致局域态密度对针尖位置高度敏感：随着针尖高度增加，不同能带相干峰的相对权重发生显著变化，从而可通过距离依赖测量区分处于争议中的γ带与β带相干峰的轨道来源。此外，在含杂质的系统中，准粒子干涉图样能清晰分辨s波和d波超导序参量的对称性。该工作为实验上识别超导能隙的能带归属及配对对称性提供了明确的理论指导。

该研究通过结合密度泛函理论、Wannier紧束缚建模和旋转不变奴隶玻色子计算，系统探讨了超导材料La₅Ni₃O₁₁中插层La₂NiO₄（214）层的电子角色。针对嵌入的214层，基于PBE与HSE06泛函提取的实际电子参数构建了双轨道模型，并利用奴隶玻色子方法计算了其关联基态相图。结果显示，在现实的晶体场劈裂和库仑相互作用区间内，该层倾向于处于反铁磁绝缘态或能带绝缘态，而非顺磁金属态，其低能谱权重被完全压制。进一步分析包含La₃Ni₂O₇（327）块与214层的耦合模型时发现，层间杂化并不能在费米能级附近恢复任何源自214层的有效态密度。因此，La₅Ni₃O₁₁的低能电子结构主要由327块主导，插层的214层在电子学上保持惰性，不参与形成费米面。这一发现厘清了该混层镍氧化物的最小低能有效模型，并为理解插层Ruddlesden-Popper镍酸盐中的超导机制提供了统一图像。