Oral: Ultrafast Terahertz Spectroscopy of a Frustrated d-Orbital Flat Band in a Kagome Lattice

The kagome lattice has recently garnered widespread interest as a platform for engineering flat bands. When tuned near the Fermi energy, these flat bands serve as an emerging route for realizing strongly correlated physics. The kagome material Ni₃In has phenomenology demonstrating a remarkable analogy with heavy fermion strange metals, where T-linear resistivity and evidence for quantum critical behavior are observed. Such behavior is highly unusual since the material does not possess localized f-electrons and solely relies on the flat bands which arise from the frustrated hopping of d-electrons of the Ni ion. Yet, the mechanism of the putative Kondo hybridization is still unclear. To this end, we use ultrafast terahertz spectroscopy as an optical probe to elucidate the associated low-energy physics. We observed optical conductivity in the terahertz frequency range that exhibits behavior adjacent to critical scaling. Furthermore, dynamical optical-pump terahertz-probe studies allow us to estimate a possible gap energy.