Strong interactions and isospin symmetry breaking in a supermoiré lattice

In multilayer moiré heterostructures, the interference of multiple twist angles ubiquitously leads to tunable ultralong-wavelength patterns known as supermoiré lattices. However, their impact on the system's many-body electronic phase diagram remains largely unexplored. We present local compressibility measurements revealing numerous incompressible states resulting from supermoiré lattice-scale isospin symmetry breaking driven by strong interactions. By using the supermoiré lattice occupancy as a probe of isospin symmetry, we observed an unexpected doubling of the miniband filling near [Formula: see text], possibly indicating a hidden phase transition or normal-state pairing proximal to the superconducting phase. Our work establishes supermoiré lattices as a tunable parameter for designing quantum phases and as an effective tool for unraveling correlated phenomena in moiré materials.