Fermi level tuning and double-dome superconductivity in the kagome metal CsV3Sb5-xSnx

The recently reported AV3Sb5 (A = K, Rb, Cs) family of kagome metals are candidates for unconventional superconductivity and chiral charge density wave (CDW) order; both potentially arise from nested saddle points in their band structures close to the Fermi energy. Here, we use chemical substitution to introduce holes into CsV3Sb5 and unveil an unconventional coupling of the CDW and superconducting states. Specifically, we generate a phase diagram for CsV3Sb5−xSnx that illustrates the impact of hole doping the system and lifting the nearest van Hove singularity toward and above EF. Superconductivity exhibits a nonmonotonic evolution with the introduction of holes, resulting in two “domes” peaked at 3.6 and 4.1 K and the rapid suppression of three-dimensional CDW order. The evolution of CDW and superconducting order is compared with the evolution of the electronic band structure of CsV3Sb5−xSnx, where the complete suppression of superconductivity seemingly coincides with an electronlike band comprised of Sb pz orbitals pushed above EF.