Electrons in moiré flat band systems can spontaneously break time-reversal symmetry, giving rise to a quantized anomalous Hall effect. In this study, 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 micrometer-scale domains pinned to structural disorder.

莫尔平带系统中的电子可以自发地破坏时间反转对称性，从而产生量化的反常霍尔效应。在这项研究中，我们使用超导量子干涉装置对与六方氮化硼对齐的扭曲双层石墨烯中的杂散磁场进行成像。我们发现每个电荷载流子有几个玻尔磁子的磁化，这表明磁性主要是轨道性质的。我们的测量结果表明，随着化学势扫过量子反常霍尔间隙，磁化强度发生了很大变化，这与手征边缘态对轨道陈绝缘体磁化强度的预期贡献一致。绘制场驱动磁反转的空间演化图，我们发现了一系列可重复的微米级域，这些域与结构无序有关。