Correlated and Almost-Flat Hund's Metallic Phase in Kagome Nodal Surface Metal Sc₃Mn₃Al₇Si₅

Kagome lattice has been actively studied for possible realization of frustration-induced two-dimensional flat bands and a number of correlation-induced phases. The commonality of all realistic Kagome systems proposed, however, is that flat bands are quite dispersive and a charge doping is necessary to shift flat bands close to the Fermi level. Search for Kagome systems with nearly dispersionless flat band close to the Fermi level is an ongoing study. Here, by combining theoretical and experimental tools, we present Sc₃Mn₃Al₇Si₅ as a novel realization of correlation-induced almost-flat bands in the Kagome lattice in the vicinity of the Fermi level. Our measurements of magnetic susceptibility, nuclear magnetic resonance, and optical conductivity hint signatures of ferromagnetic fluctuation at very low temperature below 2 K. Below 30 K, temperature dependence of resistivity alludes to development of electronic correlation. Intriguingly, our dynamical mean-field calculations reveal existence of nearly flat band in proximity of Fermi level at <i>k</i>_z=0 plane, induced by electron correlations. Additionally, renormalized nodal surface bands, protected by a product of two-fold screw rotation and time reversal symmetry, exist at <i>k</i>_z=π plane in the Brillouin zone. We observe a transition from a coherent to an incoherent metallic phase, driven by strong Hund's coupling and temperature. With spin-orbit coupling, flat band becomes almost-flat and may potentially host significant spin Hall signatures. These findings broaden a new prospect to harness correlated topological phases in 3<i>d</i>-based Kagome systems.