Linda Ye, Stanford University

The notion of an electronic flat band refers to a collectively degenerate set of quantum
mechanical eigenstates in periodic solids. The vanishing kinetic energy of flat bands relative to
the electron-electron interaction is expected to result in a variety of many-body quantum
phases of matter. Despite intense theoretical interest, systematic design and experimental
realization of such flat band-driven correlated states in natural crystals have remained a
challenge. Here we report the realization of a partially filled flat band in a new single crystalline
kagome metal Ni 3 In. This flat band is found to arise from the Ni-orbital wave functions localized
at triangular motifs within the kagome lattice plane, where an underlying destructive
interference among hopping paths flattens the dispersion. We observe unusual metallic and
thermodynamic responses suggestive of the presence of local fluctuating magnetic moments
originating from the flat band states, which together with non-Fermi liquid behavior indicate
proximity to potential quantum criticalities. These results demonstrate a cooperative lattice
and orbital engineering approach to designing flat band-based many-body phenomena, which
may be applied as a novel means of accessing electronic and magnetic instabilities and
integrating correlation with topology.
Reference: L. Ye et al., arXiv/2106.10824