Microscopic nature of the charge-density wave in the kagome superconductor RbV₃Sb₅

The recently discovered vanadium-based Kagome metals AV₃Sb₅ (A = K, Rb, Cs) undergo a unique phase transition into charge-density wave (CDW) order which precedes both unconventional superconductivity and time-reversal symmetry breaking. Therefore the essential first step in building a full understanding of the role of CDW in establishing these unconventional phases is to unveil the symmetries and the microscopic nature of the charge-ordered phase. Here, we determine the exact structure of the 2×2×2 superlattice that develops below the charge-density wave ordering temperature (TCDW) in RbV₃Sb₅. We present a comprehensive set of ⁵¹V, ⁸⁷Rb, and ¹²¹Sb nuclear magnetic resonance (NMR) measurements and density functional theory simulations of NMR observables to provide a unique site-selective view into the local nature of the charge-ordered phase. The combination of these experimental results with simulations provides compelling evidence that the CDW structure prevailing below 103 K in RbV₃Sb₅ is the so-called inverse Star of David pattern, π-shifted along the c axis. These findings put severe constraints on the topology of these Kagome compounds and thus provide essential guidance for the development of an appropriate theoretical framework for predicting properties of exotic electronic orders arising within the CDW phase.

近期发现的基于钒的Kagome金属AV₃Sb₅（A = K, Rb, Cs）在经历独特的相变进入电荷密度波（CDW）有序状态时，这一状态先于非常规超导性和时间反演对称破缺出现。因此，在全面理解电荷密度波在建立这些非常规相中所起作用的过程中，首要步骤是揭示电荷有序相的对称性和微观本质。在本研究中，我们确定了RbV₃Sb₅在电荷密度波有序温度（TCDW）以下形成的2×2×2超晶格的确切结构。我们通过一系列的⁵¹V、⁸⁷Rb和¹²¹Sb核磁共振（NMR）测量以及NMR可观测量的密度泛函理论模拟，提供了对电荷有序相局部性质的独特位点选择性视角。这些实验结果与模拟的结合，为RbV₃Sb₅在低于103 K时存在的CDW结构是所谓的倒置大卫之星图案，沿c轴π移位提供了强有力的证据。这些发现对Kagome化合物的拓扑结构提出了严格的限制，从而为构建预测CDW相内出现的奇异电子序性质的理论框架提供了至关重要的指导。