Imaging orbital ferromagnetism in a moire Chern insulator

Electrons in moire flat band systems can spontaneously break time reversal symmetry, giving rise to a quantized anomalous Hall effect. Here we use a superconducting quantum interference device to image stray magnetic fields in twisted bilayer graphene aligned to hexagonal boron nitride. We find a magnetization of several Bohr magnetons per charge carrier, demonstrating that the magnetism is primarily orbital in nature. Our measurements reveal a large change in the magnetization as the chemical potential is swept across the quantum anomalous Hall gap consistent with the expected contribution of chiral edge states to the magnetization of an orbital Chern insulator. Mapping the spatial evolution of field-driven magnetic reversal, we find a series of reproducible micron scale domains, pinned to structural disorder.  

Methods
This dataset contains scanning SQUID measurements and electronic transport measurements of a twisted bilayer graphene sample supporting an orbital Chern magnet phase.  The scanning SQUID measurements were collected using a cryogenic nanoSQUID microscope.