Flat bands and ferromagnetic fluctuations via orbital-selective electron correlations in Mn-based kagome metal

Kagome lattice has been actively studied for the possible realization of frustration-induced two-dimensional flat bands and the resulting correlation-induced phases. The search for kagome systems with a nearly dispersionless flat band close to the Fermi level is an ongoing study. By combining theoretical and experimental tools, here we present Sc₃Mn₃Al₇Si₅ as a novel realization of correlation-induced almost-flat bands in the kagome lattice near the Fermi level. Our magnetic susceptibility, ²⁷Al nuclear magnetic resonance, transport, and optical conductivity measurements indicate a correlated metallic phase with tantalizing ferromagnetic instability. Our dynamical mean-field calculations suggest that such ferromagnetic instability observed originates from the formation of nearly flat dispersions close to the Fermi level, where electron correlations induce strong orbital-selective renormalization and manifestation of the kagome-frustrated bands. In addition, a significant negative magnetoresistance signal is observed, which can be attributed to the suppression of flat-band-induced ferromagnetic fluctuation, which further supports the formation of flat bands in this compound. These findings broaden a new prospect to harness correlated topological phases via multiorbital correlations in 3d-based kagome systems.