利用Ni $L_3$边共振非弹性X射线散射（RIXS），该工作系统研究了在相干压应变La$_{3-x}$Sr$_x$Ni$_2$O$_7$/SrLaAlO$_4$薄膜中电子与自旋激发随载流子掺杂的演变，覆盖了超导（$x=0,0.09,0.21$）与过掺杂非超导（$x=0.38$）区间。在超导薄膜中，色散自旋激发沿$[H,H]$和$[H,0]$方向持续存在，色散几乎不随掺杂变化且阻尼很小，谱权重仅适度降低，表明双条纹自旋关联保持稳健。然而在$x=0.38$的非超导薄膜中，磁响应强烈展宽和减弱，阻尼显著增强，谱权重下降约50%，标志着相干双条纹自旋激发崩溃。磁相干性随超导电性的同步消失，直接建立了层状镍酸盐薄膜中掺杂控制的磁性与超导电性之间的关联。
本文采用最小双层两轨道模型与随机相近似，研究加压La₃Ni₂O₇中超导配对对称性及其掺杂演化。未掺杂体系中，最有利的配对态为s±波，其间隙函数在不同费米口袋间发生符号反转；分析表明该非常规配对源于双层镍酸盐磁奇模介导的排斥相互作用。空穴掺杂使γ费米口袋扩大，磁偶模驱动的口袋内排斥逐渐增强并主导配对相互作用，最终在重空穴掺杂区驱动配对对称性由s±波转变为dxy波。与之相反，电子掺杂下s±波配对持续存在，甚至在发生Lifshitz转变的深电子掺杂区仍保持稳定，说明γ费米口袋并非双层镍酸盐超导出现的必需条件；由于α与β口袋间的有利嵌套增强自旋涨落，s±波在无γ口袋时反而更加稳健。该研究揭示了掺杂对配对对称性的调控，为检验加压La₃Ni₂O₇的超导配对机制提供了新途径。
通过μ子自旋旋转/弛豫和电阻率测量，结合氧同位素替代，系统研究了三层Ruddlesden-Popper镍酸盐La₄Ni₃O₁₀中密度波转变的压力和同位素效应。常压下观察到两个不相称自旋密度波（SDW）转变，分别发生在132 K和80-90 K；磁结构显示外层两个Ni层呈反铁磁耦合SDW序，内层磁矩较小，且在T以下磁矩出现c轴分量。TSDW处内场突现表明SDW转变类似于一级相变，并与同一温度发生的电荷密度波（CDW）紧密交织。施加压力后，TSDW、T和TCDW均以约-13 K/GPa的速率均匀抑制，不同于双层La₃Ni₂O₇中压力增大SDW与CDW间距的行为。¹⁶O→¹⁸O替代使TCDW升高；在CDW与SDW交织区域，TSDW亦呈现显著同位素效应且与TCDW位移相近，而在T*处SDW独立演化时则无同位素效应。这些结果揭示了La₄Ni₃O₁₀中SDW与CDW的强交织本质，并指出压力诱导CDW序的抑制可能是Ruddlesden-Popper镍酸盐中高压超导的关键机制。
通过第一性原理密度泛函理论计算，系统研究了双层Ruddlesden-Popper型镍酸盐La₃Ni₂O₇薄膜中四价元素替代的电子掺杂效应。研究发现，与铜氧化物不同，铈（Ce）掺杂难以有效向低能带引入电子载流子，而锆（Zr）、铪（Hf）和钍（Th）可作为高效电子掺杂剂。这些元素替代能显著增大Ni-dz²轨道间的层间跳跃积分t⊥，可能增强层间超交换耦合J⊥，进而潜在提高超导转变温度Tc。利用约束随机相位近似评估了相互作用参数，发现电子掺杂使得低能轨道（包括Ni-dx²-y²和dz²及其杂化氧轨道）的占据增加，并改变了层内与层间轨道的电子填充比例。结构分析显示，掺杂剂离子半径的差异导致Ni-O键长变化，其中Zr和Hf引起晶格收缩，而Th掺杂效果最强。结果表明，Zr、Hf、Th是实现La₃Ni₂O₇电子掺杂的候选材料，为澄清该体系中电子配对机制的争议提供了新途径。
通过结合密度泛函理论和动力学平均场理论，研究了无限层镍酸盐LaNiO₂在电子掺杂和空穴掺杂下电子结构、磁性与关联效应的演化。结果显示，由于稀土5d态的存在，Ni-d_{x²-y²}带的自掺杂效应呈现显著不对称：空穴掺杂强烈抑制自掺杂，而电子掺杂虽增大稀土5d电子口袋尺寸，却未有效空穴掺杂Ni-d_{x²-y²}带。这一差异直接影响磁性响应——空穴掺杂迅速压制反铁磁序，电子掺杂则使反铁磁态保持为基态。尽管存在这些差异，两种掺杂下的电子关联均由Ni-d_{x²-y²}轨道主导，表明单带描述在电子和空穴掺杂区均可能适用。
预测超导转变温度（Tc）仍面临挑战。本研究提出可解释且结构、化学感知的高斯过程模型 GP-Tc，通过图元直方图编码局部键合环境，并结合地球移动距离构建有效核，实现带不确定度的 Tc 预测。分析表明，仅需相邻原子间电子亲和势差分布、原子间距及少量元素特征即可预测不同超导家族的 Tc，揭示电子亲和势差是连接局域键合与宏观超导性的关键化学参数，且机制无关。该模型复现了无限层镍酸盐 Nd0.8Sr0.2NiO2 的实验 Tc 范围，并预测化学计量 PtPb3Bi 的超导性，实验证实 Tc≈3 K。此外，GP-Tc 通过网页接口开放，并识别出 SrNiO2 与 K(PRh)2 等高优先级候选材料。
研究人员利用臭氧辅助原子层外延技术，在NdAlO3衬底上生长了La2PrNi2O7薄膜，引入了高达-2.14%的极端压缩应变，实现了起始临界温度达60 K、零电阻温度33 K和20 K处抗磁转变的高温超导性，磁输运测量确认其为准二维超导态。对比应变片与高压块材的相图发现，尽管两者都通过抑制自旋密度波驱动超导，但晶格响应存在分歧：薄膜在其c轴参数窗口显著发散，而面内参数与块材一致。关键的是，霍尔测量揭示了电子性质的二分性，最佳超导薄膜呈现负霍尔系数的类电子特征，与高压块材和非超导拉伸正系数的类空穴特征截然对立。这表明应变与压力策略均能有效调控潜在关联调制，超越特定费米面拓扑的限制，从而驱动超导性。这项工作建立了一个研究镍酸盐多轨道物理的宏观平台，为探索高温超导机制提供了新维度。
High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3 $${d}_{{x}^{2}-{y}^{2}}$$, Ni 3 $${d}_{{z}^{2}}$$, and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 $${d}_{{z}^{2}}$$orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor.
Trilayer Ruddlesden-Popper phase La4Ni3O10 has been observed with Tc of ∼30 K at high pressure in a recent experiment, which further expanded the family of nickelate superconductors. In this study, we explored the effects of electronic correlations in La4Ni3O10 using density functional theory plus dynamical mean-field theory at ambient and high pressures. Our derived spectral functions and Fermi surface of the ambient pressure phase are nicely consistent with the experimental results by angle-resolved photoemission spectroscopy, which emphasized the importance of electronic correlations in La4Ni3O10. We also found the electronic correlations in pressurized La4Ni3O10 are both orbital-dependent and layer-dependent due to the presence of Hund’s rule coupling. There is a competition between the Hund’s rule coupling and the crystal-field splitting, and therefore, the Ni–O layers with weaker crystal-field splitting energy would have stronger electronic correlations.
The discovery of superconductivity with a critical temperature of about 80 K in La3Ni2O7 single crystals under pressure has received enormous attention. La3Ni2O7 is not superconducting under ambient pressure but exhibits a transition at T ∗ ≃ 115 K. Understanding the electronic correlations and charge dynamics is an important step towards the origin of superconductivity and other instabilities. Here, our optical study shows that La3Ni2O7 features strong electronic correlations which significantly reduce the electron’s kinetic energy and place this system in the proximity of the Mott phase. The low-frequency optical conductivity reveals two Drude components arising from multiple bands at the Fermi level. The transition at T ∗ removes the Drude component exhibiting non-Fermi liquid behavior, whereas the one with Fermi-liquid behavior is barely affected. These observations in combination with theoretical results suggest that the Fermi surface dominated by the Ni- $${d}_{3{z}^{2}-{r}^{2}}$$orbital is removed due to the transition at T ∗. Our experimental results provide pivotal information for understanding the transition at T ∗ and superconductivity in La3Ni2O7.