• Direct imaging of supermoiré domains in helical trilayer graphene using scanning single-electron transistor (SET) probe.
• Observation of two inequivalent domain types arising from local breaking of C2z symmetry.
• Confirmation of opposite Chern numbers in adjacent domains, indicating topological boundary modes.
• Demonstration of lattice relaxation into triangular domains with uniform moiré wavelength, arranged on a supermoiré scale.