Twisted van der Waals heterostructures with flat electronic bands have recently emerged as a platform for realizing correlated and topological states with a high degree of control and tunability. In graphene-based moiré heterostructures, the correlated phase diagram and band topology depend on the number of graphene layers and the details of the external environment from the encapsulating crystals. Here, we report that the system of twisted monolayer–bilayer graphene (tMBG) hosts a variety of correlated metallic and insulating states, as well as topological magnetic states. Because of its low symmetry, the phase diagram of tMBG approximates that of twisted bilayer graphene when an applied perpendicular electric field points from the bilayer towards the monolayer graphene, or twisted double bilayer graphene when the field is reversed. In the former case, we observe correlated states that undergo an orbitally driven insulating transition above a critical perpendicular magnetic field. In the latter case, we observe the emergence of electrically tunable ferromagnetism at one-quarter filling of the conduction band, and an associated anomalous Hall effect. The direction of the magnetization can be switched by electrostatic doping at zero magnetic field. Our results establish tMBG as a tunable platform for investigating correlated and topological states.

具有平坦电子带的扭曲范德华异质结构最近成为一种平台，用于以高度控制和可调谐性来实现相关和拓扑状态。在基于石墨烯的莫尔异质结构中，相关的相图和能带拓扑取决于石墨烯层的数量以及封装晶体的外部环境细节。在这里，我们报道了扭曲的单层-双层石墨烯（tMBG）系统具有各种相关的金属和绝缘态以及拓扑磁态。由于其低对称性，当施加的垂直电场从双层指向单层石墨烯时，tMBG的相图近似于扭曲的双层石墨烯；当电场反转时，tMBG的相图近似于扭曲的双层双层石墨烯。在前一种情况下，我们观察到在临界垂直磁场上方经历轨道驱动的绝缘跃迁的相关状态。在后一种情况下，我们观察到在导带的四分之一填充处出现了电可调铁磁性，并伴有异常的霍尔效应。可以通过在零磁场下进行静电掺杂来切换磁化方向。我们的结果将tMBG确立为研究相关拓扑状态的可调平台。可以通过在零磁场下进行静电掺杂来切换磁化方向。我们的结果将tMBG确立为研究相关拓扑状态的可调平台。可以通过在零磁场下进行静电掺杂来切换磁化方向。我们的结果将tMBG确立为研究相关拓扑状态的可调平台。