Flavor-Sensitive Optical Imaging of Flat Band Graphene*

Isospin polarization plays a crucial role in flatband graphene systems. Here, we report a novel optical sensing technique of flavor (isospin) polarization based on short-range interaction with excitons. Through a systematic study across crystalline and moiré graphene systems, we demonstrate the capability of our technique to distinguish between flavor polarization and other types of Fermi surface changes, which would give similar responses in compressibility measurements. With wide-field optical imaging, our technique also enables high-throughput mapping of flavor polarization domains across a broad temperature range and device structures.