发表机构
Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences; University of Science and Technology of China; High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences; Collaborative Innovation Center of Microstructures, Nanjing University（中国科学院合肥物质科学研究院固体物理研究所材料物理重点实验室; 中国科学技术大学; 中国科学院合肥物质科学研究院高磁场实验室; 南京大学微结构协同创新中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究结合机器学习力场分子动力学与模式分辨电声耦合分析，揭示笼目金属YRu$_3$Si$_2$和LaRu$_3$Si$_2$的电荷密度波由模式选择型电声耦合驱动，解释了二者电荷密度波转变温度的差异。
AI 中文摘要
YRu$_3$Si$_2$和LaRu$_3$Si$_2$是笼目金属中电荷密度波（CDW）转变温度最高的材料，其$T_{\text{CDW}}$分别约为800 K和400 K，对应的传播矢量$Q_{\text{CDW}}$分别约为(1/2,0,0)和(1/4,0,0)。这一创纪录转变温度背后的微观机制此前尚未得到解决。本研究结合机器学习力场驱动分子动力学提取的非简谐声子重整化，与模式分辨的电声耦合（EPC）分析来确定该机制。CDW由模式选择型EPC驱动：Ru的面外声子模式耦合Ru-$d_{xz}/d_{yz}$轨道与Si-$p_x/p_y$轨道，且声子线宽在$Q_{\text{CDW}}$处出现尖锐峰值，而无特征的电子磁化率排除了费米面嵌套的可能。声子非简谐性会使CDW熔化，非简谐声子谱能很好地重现$Q_{\text{CDW}}$和$T_{\text{CDW}}$，与实验结果吻合良好。分子动力学模拟还能在实空间中可视化CDW的熔化过程。化学键分析进一步表明，较小的Y$^{3+}$半径会增强Ru-Ru键，提高晶格刚性，从而解释了YRu$_3$Si$_2$的$T_{\text{CDW}}$是LaRu$_3$Si$_2$两倍的原因。本研究结果为笼目金属YRu$_3$Si$_2$和LaRu$_3$Si$_2$中CDW的形成与熔化建立了统一的微观图像。
英文摘要
YRu$_3$Si$_2$ and LaRu$_3$Si$_2$ host the highest charge density wave (CDW) transition temperatures ever reported in kagome metals, $T_{\mathrm{CDW}}\approx 800$ and 400~K, with propagation vectors $Q_{\mathrm{CDW}}\approx(1/2,0,0)$ and $(1/4,0,0)$, respectively. The microscopic mechanism behind these record values has remained unresolved. Here, we combine anharmonic phonon renormalization extracted from molecular dynamics driven by a machine-learned force field with mode-resolved electron-phonon coupling (EPC) analysis to identify this mechanism. The CDW is driven by mode-selective EPC: the Ru out-of-plane phonon modes couple the Ru-$d_{xz}/d_{yz}$ and Si-$p_x/p_y$ orbitals, and the phonon linewidth peaks sharply at $Q_{\mathrm{CDW}}$, while the featureless electronic susceptibility rules out Fermi-surface nesting. Phonon anharmonicity melts the CDW, and the anharmonic phonon spectra reproduce both $Q_{\mathrm{CDW}}$ and $T_{\mathrm{CDW}}$ in good agreement with experiments. Molecular dynamics simulations also visualize the CDW melting in real space. Chemical bonding analysis further shows that the smaller Y$^{3+}$ radius strengthens the Ru-Ru bonds, enhancing lattice rigidity and accounting for the factor-of-two higher $T_{\mathrm{CDW}}$ of YRu$_3$Si$_2$. Our results establish a unified microscopic picture of CDW formation and melting in kagome metals YRu$_3$Si$_2$ and LaRu$_3$Si$_2$.
