Moiré graphene systems have attracted considerable attention in the past 3 years because they exhibit exotic phenomena including correlated insulating states, unconventional superconductivity and the quantum anomalous Hall effect. All these phenomena are intimately related to the valley-spin-degenerate and topologically non-trivial flat bands in moiré graphene systems. When time-reversal symmetry is broken spontaneously, such flavour-degenerate topological flat bands exhibit unconventional orbital magnetism associated with real-space current-loop patterns on the moiré length scale. In this Perspective, we first survey key experimental progress on the correlated insulating states and the quantum anomalous Hall phenomena. Most of these phenomena are related to the moiré orbital magnetic states, which originate from the topological nature of the moiré flat bands. Finally, we discuss theoretical progress in the understanding of the correlated insulating and quantum anomalous Hall phenomena from the perspective of spontaneous symmetry breaking.

莫尔石墨烯系统在过去三年中引起了相当大的关注，因为它们表现出奇特的现象，包括相关的绝缘态，非常规的超导性和量子异常霍尔效应。所有这些现象都与莫尔石墨烯系统中的自旋简并的谷状自旋平带密切相关。当时间反转对称性自发地破裂时，这种变质退化的拓扑平坦带会显示出与莫尔长度尺度上的真实空间电流回路模式相关的非常规轨道磁。在此透视图中，我们首先调查了相关绝缘态和量子异常霍尔现象的关键实验进展。这些现象大多数与摩尔纹轨道磁态有关，这源自莫尔条纹平坦带的拓扑性质。最后，我们从自发对称破坏的角度讨论了在理解相关的绝缘和量子异常霍尔现象方面的理论进展。