(A = K, Rb, Cs) Kagome Alloys*

The kagome superconductors AV₃Sb₅ (A = K, Rb, Cs) exhibit charge-density wave (CDW) order whose structural manifestation depends on the alkali-metal site. KV₃Sb₅ and RbV₃Sb₅ adopt a 2 x 2 x 2 superstructure in Fmmm with either a tri-hexagonal (TrH) or Star-of-David (SoD) distortion. In contrast, CsV₃Sb₅ undergoes a staged transition, where the 2 x 2 x 2 state competes with and partially transforms into a 2 x 2 x 4 superstructure in Cmmm with mixed TrH and SoD distortions that coexist metastably. Recent work has shown that these three compounds are not isolated phases but the terminal members of a full solid solution, providing a route to probe CDW order in kagome materials through A-site alloying. We utilize single-crystal synthesis and synchrotron x-ray diffraction to design and analyze the CDW order of targeted AV₃Sb₅ alloys as a function of A-site composition. By comparing K-rich and Cs-rich alloys, we track how the 2 x 2 x 2 Fmmm state connects to the 2 x 2 x 4 Cmmm state, clarifying the structural origin of correlated electronic phenomena in kagome superconductors.