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本研究系统性地分析了Ruddlesden-Popper镍酸盐La_{n+1}Ni_nO_{3n+1}（n=1,2,3,∞）系列单晶及粉末样品，结合粉末与单晶X射线衍射、热容、差示扫描量热等多种实验手段，在2–1000 K宽温域内揭示了此前被忽视的高温相变。对n=2和n=3化合物，在约560 K处观测到明显的晶格参数异常，例如双层2222相中面外晶格常数突增、面内收缩，表明八面体倾斜的突然释放；单层-三层1313多形体则表现为各向同性的体积骤缩；三层相n=3在该温度附近单斜角β出现清晰拐折，热容与DSC数据也证实该转变的热力学特征。该转变与已知的高温四方相变及低温密度波相变截然不同，且n=∞钙钛矿LaNiO₃未呈现类似行为。研究确认该高温相变是镍酸盐RP系列的普遍特性，强调在探索超导电性时必须重视此高温结构不稳定性对低温物性的潜在影响。

该研究利用时间分辨光学光谱技术，在环境压力下10 K至室温范围内探索了双层镍氧化物La₃Ni₂O₇中高能电子激发的超快动力学。研究识别出源于不同带间跃迁的两个高能电子激发，能量分别位于约1.8 eV和2.4 eV，并揭示它们具有不同的密度波（DW）能隙，分别为约54 meV和67 meV。这两个激发态的弛豫动力学可由Rothwarf-Taylor模型很好地描述。此外，实验观测到四个相干拉曼活性声子模式，这些模式与不同的电子激发表现出不同的耦合强度。升温引起的声子软化在约100 K至室温之间可用包含热膨胀和非谐声子-声子耦合的半定量模型解释；而在低温下，测量到的声子频率与模型拟合的偏差暗示了电子-声子耦合的额外贡献。该工作直接证明了该材料中复杂的能隙结构和声子动力学，为理解其密度波机制及多体效应提供了关键见解。

本研究在(Sm,Eu,Ca,Sr)NiO₂无限层镍酸盐薄膜中发现了高磁场稳定的重入超导电性。通过电阻和射频感应测量，在低场超导态外，于高场区域观察到另一个电阻急剧下降的超导态，其转变温度在低Tc样品中约9.6–11.7 K，高Tc样品（最高31.7 K）中则表现为低场与高场超导相融合，上临界磁场远超泡利顺磁极限。利用修正了内交换场的Werthamer-Helfand-Hohenberg（WHH）模型可精确描述相图，表明该现象源于Eu²⁺磁矩产生的内交换场抵消外加磁场的Jaccarino-Peter补偿机制。这项发现首次在具有较高超导转变温度的材料中实现场诱导重入超导，为开发可在数十特斯拉磁场下工作的超导磁体与器件提供了新路径。

Single crystals of Ruddlesden–Popper nickelates La4Ni3O10 were grown by means of the floating-zone technique at oxygen pressure of 20 bar. Our results reveal the effects of the annealing process under pressure on the crystal structure. We present the requirements for crystal growth and show how a reported ferromagnetic impurity phase can be avoided. The different growth and post-annealing processes result in two distinct phases 𝑃 21∕𝑎 and Bmab in which the metal-to-metal transitions occur at 152 K and 136 K, respectively.

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研究人员开发了一种将自由站立无限层Nd₀.₈₅Sr₀.₁₅NiO₂薄膜集成到金刚石对顶砧中的技术，从而克服了薄膜在高压环境中测量的困难。通过对该薄膜施加高达约90 GPa的压力，他们观测到超导转变温度（T_c）从常压下的约17 K单调线性提升至约74.2 K，增强速率约为0.65 K/GPa，且未出现饱和迹象。这一线性的、非饱和的T_c压力演化趋势与大多数铜氧化物超导体及双层镍酸盐中观察到的压力诱导过掺杂导致的T_c下降行为显著不同，表明无限层镍酸盐的配对强度可被提升至出乎意料的高水平。此外，上临界场和相干长度的测量进一步证实了超导态随压力增强。该研究提供了通过晶格压缩持续增强超导电性的新途径，且所开发的自由薄膜高压技术有望广泛应用于其他二维材料。

Recent experimental observations have showed some signatures of superconductivity close to 80 K in La3Ni2O7 under pressure and have raised the hope of achieving high-temperature superconductivity in bulk nickelates. However, a zero-resistance state—a key characteristic of a superconductor—was not observed. Here we show that the zero-resistance state does exist in single crystals of La3Ni2O7−δ using a liquid pressure medium at up to 30 GPa. We also find that the system remains metallic under applied pressures, suggesting the absence of a metal–insulator transition proximate to the superconductivity. Moreover, analysis of the normal state T-linear resistance reveals a link between this strange-metal behaviour and superconductivity. The association between strange-metal behaviour and high-temperature superconductivity is very much in line with other classes of unconventional superconductors, including the cuprates and Fe-based superconductors. Further investigations exploring the interplay of strange-metal behaviour and superconductivity, as well as possible competing electronic or structural phases, are essential to understand the mechanism of superconductivity in this system.