Electronic correlations and evolution of the charge density wave in the kagome metals AV3Sb5 (A=

The kagome metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ $(A\phantom{\rule{4pt}{0ex}}=\phantom{\rule{4pt}{0ex}}\mathrm{K},\phantom{\rule{4pt}{0ex}}\mathrm{Rb},\phantom{\rule{4pt}{0ex}}\mathrm{Cs})$ have attracted enormous interest as they exhibit an intertwined charge density wave (CDW) and superconductivity (SC). We report optical studies of $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ across the whole family. With increasing alkali-metal atom radius from K to Cs, the CDW gap ${\mathrm{\ensuremath{\Delta}}}_{\text{CDW}}$ increases monotonically, whereas ${T}_{\text{CDW}}$ first rises and then drops, failing to establish a scaling relation with ${\mathrm{\ensuremath{\Delta}}}_{\text{CDW}}$. While the Fermi surface gapped by the CDW grows, ${T}_{c}$ is elevated in $\mathrm{Cs}{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, indicating that the interplay between the CDW and SC is not simply a competition for the density of states near ${E}_{\text{F}}$. More importantly, we observe an enhancement of electronic correlations in $\mathrm{Cs}{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, which suppresses the CDW but enhances SC, accounting for all the above peculiar observations. Our results suggest electronic correlations as an important factor in manipulating the CDW and its entanglement with SC in $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$.