Coexisting Kagome and Heavy Fermion Flat Bands in YbCr$_6$Ge$_6$

Abstract: Flat bands, emergent in strongly correlated electron systems, stand at the frontier of condensed matter physics, providing fertile ground for unconventional quantum phases. Recent observations of dispersionless bands at the Fermi level in kagome lattice open the possibility of unifying the disjoint paradigms of topology and correlation-driven heavy fermion liquids. Here, we report the unprecedented coexistence of these mechanisms in the layered kagome metal YbCr6Ge6. At high temperatures, an intrinsic kagome flat band-arising from the frustrated hopping on the kagome lattice-dominates the Fermi level. Upon cooling, localized Yb 4f-states hybridize with the topological kagome flat bands, transforming this state into the Kondo resonance states that are nearly dispersionless across the entire Brillouin zone. Crystalline symmetry forbids hybridization along specific high-symmetry lines, which stabilizes Dirac crossings of heavy-fermion character. Topological analysis of the resulting gaps reveals both trivial and nontrivial Z2 invariants, establishing the emergence of a Dirac-Kondo semimetal phase. Taken together, these results identify YbCr6Ge6 as a prototype of a topological heavy-fermion system and a platform where geometric frustration, strong correlations, and topology converge, with broad implications for correlated quantum matter.