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.
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该论文将密度泛函理论加哈伯德U修正（DFT+U）与有限位移法相结合，实现了对强关联材料中声子谱和电子-声子矩阵的全哈伯德修正计算。作者将该方法应用于两种典型体系：无限层镍酸盐LaNiO₂和二氧化钌RuO₂。结果表明：在20%空穴掺杂的LaNiO₂中，哈伯德U修正微弱增强其电子-声子相互作用，但总耦合强度仍很小，不足以解释实验中约10-30 K的超导转变温度；这与近期GW修正预言的结果相反，差异源于DFT+U与GW方法所得费米面拓扑不同。在RuO₂中，哈伯德U修正消除了TiO₂衬底应变下的虚声子模，并大幅降低了电子-声子耦合，缓解了理论上过大的电子-声子耦合与实验观测到低超导转变温度之间的矛盾。该工作提供了完整纳入哈伯德U修正的电子-声子性质计算方案，并凸显了费米面形状及关联效应对声子谱和电子-声子矩阵的关键影响。
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Identification of superconductivity in the Ruddlesden-Popper phases of nickelates under high pressure remains challenging. Here, we report a comprehensive study of the crystal structure, electrical resistance, and Meissner effect in single crystals of bilayer nickelate La3Ni2O7 under hydrostatic pressures up to 104 GPa. Using high-pressure X-ray diffraction, we observe a structural transition from an orthorhombic to a tetragonal phase above 40 GPa. Superconductivity emerges with a maximum onset transition temperature Tconset of 83 K at 18.0 GPa, accompanied by zero resistance. The superconducting phase is gradually suppressed and vanishes above 80 GPa, forming a right-triangle-like superconducting region. Direct-current magnetic susceptibility measurements demonstrate the Meissner effect and reveal a superconducting volume fraction of ∼41% at 22.0 GPa and 20 K, confirming the bulk nature of superconductivity in La3Ni2O7. Our results highlight the intricate relationship between superconductivity, oxygen content, and structural transitions in this material.