Double Dome Superconductivity in Kagome Metal CsV₃Sb_5-xSn_x

The new <i>A</i>V₃Sb₅ (<i>A</i> = K, Rb, Cs) family of kagome metals are candidates for unconventional superconductivity and chiral charge density wave (CDW) order, both of which are thought to arise due to the proximity of saddle points in their band structures to the Fermi energy. In CsV₃Sb₅, a superconducting transition is observed at 2.5 K and a CDW transition at 94 K. Here we use chemical substitution in CsV₃Sb₅ to explore the relationship between the superconducting and CDW states and generate a phase diagram for CsV₃Sb_5-<i>x</i>Sn<i>_x</i> for 0 ≤ <i>x</i> ≤ 1.5 that illustrates the impact of hole-doping the system. As the Sn content is increased, a nonmonotonic evolution of the superconduting <i>T</i>_C is observed, and two distinct superconductivity domes are observed, with local maxima of 3.6 K at <i>x </i>= 0.03 and 4.1 K at <i>x</i> = 0.35. By <i>x</i> = 1, the superconducting phase vanishes. Simultaneously, the onset temperature of the CDW instability is found to be rapidly suppressed with Sn substitution until the CDW phase vanishes by <i>x</i> = 0.06. The first peak in <i>T</i>_C coexists with the CDW state, suggesting that the SC and CDW orders are related in an unconventional manner.