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The recent observation of high-𝑇𝑐 superconductivity in the bilayer nickelate La3⁢Ni2⁢O7 under pressure has garnered significant interest. While researches have predominantly focused on the role of electron-electron interactions in the superconducting mechanism, the impact of electron-phonon coupling (EPC) has remained elusive and unexplored. In this Letter, we perform first-principles calculations to study the phonon spectrum and electron-phonon coupling within La3⁢Ni2⁢O7 under pressure and explore the interplay between EPC and electronic interactions on the superconductivity by employing functional renormalization group (FRG) approach. Our calculations reveal that EPC alone is insufficient to trigger superconductivity in La3⁢Ni2⁢O7 under pressure. We identify unique out-of-plane and in-plane breathing phonon modes which selectively couple with the Ni 𝑑𝑧2 and 𝑑𝑥2−𝑦2 orbitals, showcasing an orbital-selective EPC. Within the bilayer two-orbital model, it is revealed that solely electronic interactions foster 𝑠±-wave pairing characterized by notable frustration in the band space, leading to a relatively low transition temperature. Remarkably, we find that the out-of-plane EPC can act in concert with electronic interactions to promote the interlayer pairing in the 𝑑𝑧2 orbital, partially releasing the pairing frustration and thus elevating 𝑇𝑐. In contrast, the inclusion of in-plane EPC only marginally affects the superconductivity, distinct from the cuprates. Potential experimental implications in La3⁢Ni2⁢O7 are also discussed.

The discovery of pressurized superconductivity at 80 K in La3Ni2O7 officially brings nickelates into the family of high-temperature superconductors, which gives rise to not only new insights but also mysteries in the strongly correlated superconductivity. More recently, the sibling compound La4Ni3O10 was also shown to be superconducting below about 25 K under pressure, further boosting the popularity of nickelates in the Ruddlesden-Popper phase. In this study, combining high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structures of La4Ni3O10 at ambient pressure. We reveal a high resemblance of La4Ni3O10 with La3Ni2O7 in the orbital-dependent fermiology and electronic structure, suggesting a similar electronic correlation between the two compounds. The temperature-dependent measurements imply an orbital-dependent energy gap related to the density-wave transition in La4Ni3O10. By comparing the theoretical pressure-dependent electronic structure, clues about the superconducting high-pressure phase can be deduced from the ambient measurements, providing crucial information for deciphering the unconventional superconductivity in nickelates.

该研究利用扫描超导量子干涉显微镜对无限层镍基超导体Nd₀.₈Sr₀.₂NiO₂薄膜进行局域磁化率与磁通成像，以揭示零温超流密度与超导转变温度之间的关联。由于样品存在微米尺度的不均匀性，研究通过空间统计分析发现：当局部T_c高于8K时，T_c与ρ_s0呈线性关系；而当T_c低于8K时，二者呈亚线性依赖（近似T_c∝ρ_s0^{1/2}）。这一整体关系与过掺杂铜氧化物超导体中的观测结果高度相似，暗示了无限层镍基超导体与铜氧化物超导体在超导机制上可能存在密切的内在联系。

该研究基于双层两轨道Hubbard模型，采用时间依赖变分原理团簇微扰理论（TDVP-CPT）与大尺度密度矩阵重正化群（DMRG）方法，系统探究了La₃Ni₂O₇中电子关联对费米面拓扑与超导配对对称性的影响。TDVP-CPT在包含多达16个物理位点的团簇上计算发现，电子关联驱动了显著的轨道选择性低能谱重构：d_{z²}轨道的谱权重逐渐耗尽，γ能带下沉至费米能级以下，而α和β能带则出现赝隙，最终在强耦合下形成以d_{x²-y²}轨道为主的费米弧。DMRG计算进一步揭示，主导的超导配对关联与该费米面重构一致演化，从弱耦合下的d_{z²}轨道主导的层间自旋单态配对转变为强耦合下的d_{x²-y²}轨道主导的配对，但始终保持s±波对称性。研究表明，γ费米面的消失非但不抑制超导电性，反而标志着关联驱动的配对通道转变，其关键中介机制包括层间反铁磁涨落、Hund耦合与轨道间杂化。

该研究针对加压La₃Ni₂O₇中超导配对对称性尚未定论的问题，采用四轨道Wannier哈密顿量，将单格点双轨道动力学平均场理论（DMFT）的自能引入随机相近似（RPA），构建自能重整化粒子－空穴气泡以替代裸气泡，保持相同的局域Slater-Kanamori相互作用顶点。普通RPA计算显示主导配对属于B₂g的dxy通道，而一旦包含DMFT自能，配对层级发生反转：A₁g符号改变的s±态成为主导，B₁g dx²-y²通道次之，原先的B₂g不稳定性被强烈抑制。口袋对分解和轨道分辨磁化率表明，该反转源于d3z²-r²轨道的选择性重整化，它滤除了有利于dxy配对的γ口袋散射过程，同时保留了有利于s±的分布性口袋间散射。进一步利用双Bethe-Salpeter方程结合局域DMFT顶点计算静态自旋磁化率，得到宽广的有限动量磁响应且在Γ点附近较弱，从两粒子层面强化了s±态的自旋涨落背景。结果表明，在La₃Ni₂O₇中强关联效应并非次要修正，恰当处理关联重整化的准粒子对于准确预测超导配对对称性至关重要。

本文报道了在Eu基无限层镍酸盐（EuxNd1-xNiO₂和EuxPr1-xNiO₂）中实现的超过液氦冷却极限的逆超导转变。通过磁场调控，在过掺杂和欠掺杂区域均观察到超导零电阻态被限制在较低临界温度（Tc-inv约2.6–5.4 K）与较高正常Tc之间，升温或增加电流密度可从电阻态驱动进入超导态，并在更高温度和电流下再次消失。系统变温输运测量表明，这一Kelvin区间的逆超导转变源于温度变化引起的Eu²⁺4f⁷相关补偿有效磁场与上临界场的交替主导，并得到了磁场下约300 mK处超导重现所形成的温度诱导重入超导现象的支持。该工作建立了磁相互作用重构的高温超导体系作为探索逆转热退相干范式的量子现象的平台，也为量子相变器件的反向设计开拓了应用场景。

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