Probing correlated states with plasmonic origami

Understanding the nature of strongly correlated states in flat-band materials (such as moiré heterostructures) is at the forefront of both experimental and theoretical pursuits. While optical techniques are often very successful in probing the properties of the underlying order, the very narrow bandwidth, which makes flat-band systems interesting, makes their optical investigation challenging. Here we propose to leverage strong light-matter coupling present in the flat-band systems to gain insight through dynamical dielectric response into the structure of the interacting state. We argue that as a result of the enlargement of the effective lattice of the system, conventional long-range plasmon becomes "folded" to yield a multiband plasmon spectrum. The structure of the plasmon spectrum is highly sensitive to the underlying order revealing valued insights such as the interaction-driven band gaps and the order periodicity.