Hopping frustration-induced flat band and strange metallicity in a kagome metal

The introduction of localized electronic states into a metal can alter its physical properties, for example enabling exotic metal physics including heavy fermion and strange metal behavior. A common source of localized states in such systems are partially filled 4f and 5f shells because of the inherently compact nature of those orbitals. The interaction of electrons in these orbitals with the conduction sea is well described by the Kondo framework. However, there have also been observations of Kondo-like behavior in 3d transition metal oxides and in 4d and 5d-containing van der Waals heterostructures. This calls for a broader consideration of the physical requirements for Kondo systems. Here we show transport and thermodynamic hallmarks of heavy fermion and strange metal behavior that arise in kagome metal Ni3In, wherein the source of localized states is destructive interference-induced band flattening of partially filled Ni 3d states. With magnetic field and pressure tuning, we also find evidence that the system is proximate to quantum criticality, extending the analogy to f-electron Kondo lattices. These observations highlight the role of hopping frustration in metallic systems as a potential source for strong correlations. Additionally, this suggests a lattice-driven approach to realizing correlated metals with non-trivial band topology.