kagome金属CsV$_3$Sb$_5$中的3/8电荷密度波不稳定性
3/8 charge-density wave instability in the kagome metal CsV$_3$Sb$_5$
- University of Minnesota（明尼苏达大学）
- Harvey Mudd College（哈维穆德学院）
- University of Toronto（多伦多大学）
- University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
该研究通过DFPT计算和朗道理论分析，揭示了kagome金属CsV$_3$Sb$_5$在压力下出现3/8波矢电荷密度波不稳定性及其单斜畸变机制，解释了超导穹顶凹陷现象。
AI中文摘要：
kagome金属CsV$_3$Sb$_5$表现出电荷密度波（CDW）和超导转变，两者都受到压力的显著影响。最近的X射线衍射实验在超导穹顶凹陷对应的压力下识别出一种新的电荷有序相。该CDW相显示出独特的波矢$\mathbf{Q} = (3/8, 0, 1/2)$和单斜对称性，与常压下报道的$2\times2\times 2$和$2\times2\times 4$有序形成对比。在本信中，我们展示了在精细倒空间网格上的密度泛函微扰理论（DFPT）计算预测CsV$_3$Sb$_5$的主要晶格不稳定性出现在该波矢处。有限位移计算揭示，虽然非谐效应在常压下稳定了常规的$L_2^-$ CDW，但竞争的3/8不稳定性在约1 GPa以上变得能量上有利，与实验观察一致。有趣的是，嵌套函数在同一波矢处显示出峰值。朗道自由能分析解释了X射线衍射中观察到的单斜畸变的出现，此外还解释了若干可能与超导$T_c$观察趋势相关的键序模式。
英文摘要：
The kagome metal CsV$_3$Sb$_5$ exhibits charge density wave (CDW) and superconducting transitions, both of which are substantially affected by pressure. Recent x-ray diffraction experiments identify a new charge-ordered phase at a pressure coinciding with the dip of the superconducting dome. This CDW phase displays a distinctive wavevector $\mathbf{Q} = (3/8, 0, 1/2)$ and monoclinic symmetry, in contrast to the $2\times2\times 2$ and $2\times2\times 4$ orders reported at ambient pressure. In this letter, we show that density functional perturbation theory (DFPT) calculations on a fine reciprocal-space grid predict the leading lattice instability of CsV$_3$Sb$_5$ to be at this wavevector. Finite-displacement calculations reveal that while anharmonic effects stabilize the conventional $L_2^-$ CDW at ambient pressure, the competing $3/8$ instability becomes energetically favorable above $\sim$1 GPa, consistent with experimental observations. Interestingly, the nesting function displays a peak at the same wavevector. A Landau free energy analysis explains the emergence of the monoclinic distortion observed in x-ray diffraction, in addition to several bond-ordering patterns that may be relevant to the observed trends in the superconducting $T_c$.
