Microscopic nature of the charge-density wave in kagome superconductor RbV${}_3$Sb${}_5$

The recently discovered vanadium-based kagome metals AV${}_3$Sb${}_5$ (A = K, Rb, Cs) offer the possibility to study the interplay between competing electronic orderings, such as charge density order and superconductivity. We focus on the former and provide a comprehensive set of ${}^{51}$V, ${}^{87}$Rb, and ${}^{121}$Sb magnetic resonance measurements on an RbV${}_3$Sb${}_5$ single crystal. Elucidating the symmetries and properties of the CDW phase is essential to understanding the unconventional electronic orderings occurring in this material. We establish the structure of the $2\times 2\times 2$ superlattice that describes the system below the charge density wave transition by combining both experimental and computational methods, with a methodology that can be readily applied to the remaining compounds of the same family. Our results give compelling evidence that the CDW structure occurring below 103 K for RbV${}_3$Sb${}_5$ is the so-called Inverse Start of David pattern $\pi$-shifted along the c axis (also known as staggered tri-hexagonal).