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.
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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.
We employ a density-functional theory plus dynamical mean-field theory framework to investigate the correlated electronic structure of the alternating single-layer–trilayer (1313) polymorph of La3Ni2O7, which becomes superconducting under pressure. At ambient pressure, the single layer is in a Mott-insulating regime and the low-energy physics is dominated by the trilayer block. Under pressure, the gap in the single-layer block closes due to orbital-selective physics, enabling charge transfer into the trilayer block. This change in effective doping of the trilayer block could be linked to the higher 𝑇𝑐 obtained in La3Ni2O7−1313 (∼80 K) when compared to the nominal trilayer La4Ni3O10 compound (∼30 K). We conclude that correlation-driven layer differentiation is crucial in the La3Ni2O7−1313 polymorph and that its low-energy physics aligns closely with the trilayer La4Ni3O10 compound (in spite of the apparent differences in nominal filling) rather than with the conventional bilayer La3Ni2O7.
研究人员利用偏振超快泵浦-探测光谱，对比研究了常压下双层La₃Ni₂O₇和三层La₄Ni₃O₁₀单晶的正常态电子动力学。两种材料均表现出密度波转变并伴随准粒子弛豫瓶颈的打开，但其电子响应具有显著不同的对称性：三层La₄Ni₃O₁₀在整个温区内保持光学各向同性，而双层La₃Ni₂O₇在低温下则展现出明显的二重（C₂）旋转对称性破缺，即电子向列性。这种向列性体现在准粒子慢弛豫动力学和有效能隙尺度的各向异性中，并且其在115 K以下与一个次级各向同性序相互竞争，导致向列信号随温度呈非单调变化。该工作揭示了双层镍酸盐中电子向列涨落的存在，而三层体系中并未出现这一现象，暗示了电子向列性与La₃Ni₂O₇高压超导配对之间可能存在的紧密关联，为深入理解这类镍基超导体的微观机制提供了关键信息。
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该工作利用常压宽带红外至可见光反射率谱（15 meV–3.2 eV）并结合高温拉曼测量，研究了La3Ni2O7在约544 K从NiO6八面体倾斜相到无倾斜结构转变前后的电子响应。结果显示，光谱权重在极宽能量范围内发生显著重新分布，由1–3 eV激发转移至1 eV以下低能激发；尤其两个低能带间激发随进入无倾斜相逐步靠近并合并，表明有限能量电子结构发生大幅重构。Drude–Lorentz分析进一步指认这些变化主要来自有限能量激发而非Drude响应，并指向双层Ni 3d_{z^2}衍生电子态的重构，其层间耦合被认为是La3Ni2O7超导机制的核心。作者据此认为，无倾斜转变可直接重组与高温超导相关的电子自由度，并为超导态电子结构提供常压参考。