发表机构
SOLEIL Synchrotron; Université Paris-Saclay; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences; School of Physical Sciences, University of Chinese Academy of Sciences（索雷尔同步辐射中心; 巴黎萨克雷大学; 中国科学院物理研究所凝聚态物理国家实验室; 中国科学院大学物理科学学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过红外-可见光反射率测量，揭示了La$_3$Ni$_2$O$_7$在无倾斜转变时电子结构发生显著重构，光谱权重转移及带间激发合并表明双层Ni $3d_{z^2}$态重组，为理解其高温超导机制提供关键参考。
AI 中文摘要
加压La$_3$Ni$_2$O$_7$中高温超导的出现与抑制NiO$_6$八面体倾斜的结构转变密切相关，但其对电子结构的影响仍知之甚少。本文通过环境压力下覆盖15 meV至3.2 eV光子能量的宽带红外至可见光反射率测量，探测了$T_{st}\simeq 544$ K处无倾斜转变的电子响应。我们观察到在异常宽的能量范围内光谱权重发生显著重新分布，光谱权重从1至3 eV之间的激发转移到1 eV以下的低能激发。最引人注目的是，两个低能带间激发在进入无倾斜相时逐渐收敛并合并，揭示了有限能量电子结构的显著重构。这些变化指向双层Ni $3d_{z^2}$衍生电子态的重构，其层间耦合对La$_3$Ni$_2$O$_7$中提出的超导机制至关重要。我们的结果确立了无倾斜转变作为重组与高温超导相关的电子自由度的直接途径，并为超导态的电子结构提供了环境压力参考。
英文摘要
The emergence of high-$T_c$ superconductivity in pressurized La$_3$Ni$_2$O$_7$ is intimately linked to a structural transition that suppresses the tilts of the NiO$_6$ octahedra, yet its impact on the electronic structure remains poorly understood. Here, we probe the electronic response across this tilt-free transition at $T_{st}\simeq 544$ K using broadband infrared-to-visible reflectivity at ambient pressure, covering photon energies from 15 meV to 3.2 eV. We observe a pronounced redistribution of spectral weight over an exceptionally broad energy range, with spectral weight transferred from excitations between 1 and 3 eV toward low-energy excitations below 1 eV. Most strikingly, two low-energy interband excitations progressively converge and merge upon entering the tilt-free phase, revealing a substantial reconstruction of the finite-energy electronic structure. These changes point to a reconstruction of the bilayer Ni $3d_{z^2}$-derived electronic states, whose interlayer coupling is central to proposed mechanisms of superconductivity in La$_3$Ni$_2$O$_7$. Our results establish the tilt-free transition as a direct route to reorganizing the electronic degrees of freedom implicated in high-$T_c$ superconductivity and provide an ambient-pressure reference for the electronic structure of the superconducting state.
