Condensed Matter Seminar: Light–matter interactions in strongly correlated quantum materials at ultralow temperatures

Moiré quantum engineering in twisted two-dimensional (2D) materials enables profound superlattice modulations of electronic band structures, interactions, and topological properties. While the influence of these modulations on ground-state formation has been extensively studied, optical excitations associated with the moiré bands at their characteristic energy scale—the far-infrared (FIR) regime—serve as essential probes of interacting electrons but have remained largely unexplored due to extreme experimental challenges. In this talk, I will describe the detection of low-temperature excitations of interacting electrons in magic-angle graphene, enabled by our newly developed millikelvin FIR detection platform. We resolve the low-energy FIR excitation spectrum, revealing sharp resonances that characterize this strongly correlated system—observed for the first time since its discovery eight years ago. I will discuss our findings in the context of recent advances in the heavy-fermion picture of magic-angle graphene and highlight new features that remain to be understood. Finally, I will outline future opportunities enabled by our platform to explore previously inaccessible regimes of light–matter interactions, particularly in materials with flat bands and fractionalized states.