Cr-Substitution-Driven Correlation Enhancement and Hund's Metallicity in CsV_3-xCr_xSb₅

The Kagome metal CsV_3Sb_5 transitions from a weakly correlated state to a strongly correlated state upon Cr substitution; however, the mechanism driving this enhancement remains an open question. Here, we employed a combination of density functional theory and dynamical mean-field theory (DFT+DMFT) to systematically investigate the evolution of electronic correlations in the CsV_3-xCr_xSb_5 (x=0, 1, and 3) series. Our calculations revealed that Cr doping drives the system into a strongly correlated Hund's metal phase, which is characterized by significant and orbital-dependent enhancements in the quasiparticle effective masses and electronic scattering rates. We trace the origin of this transition to the doping-induced shift from low-to high-spin atomic configurations. This preference for high-spin states, which is promoted by near-half-filling of the Cr-d orbitals, induces a pronounced orbital blocking effect that strengthens the correlations. Our findings establish that Hund's coupling is the decisive factor governing the rich correlation physics in the CsV_3-xCr_xSb_5 family, providing a tunable platform for exploring Hund's metallicity.