Magnetism typically arises from the joint effect of Fermi statistics and repulsive Coulomb interactions, which favours ground states with non-zero electron spin. As a result, controlling spin magnetism with electric fields—a longstanding technological goal in spintronics and multiferroics 1 , 2 —can be achieved only indirectly. Here we experimentally demonstrate direct electric-field control of magnetic states in an orbital Chern insulator 3 – 6 , a magnetic system in which non-trivial band topology favours long-range order of orbital angular momentum but the spins are thought to remain disordered 7 – 14 . We use van der Waals heterostructures consisting of a graphene monolayer rotationally faulted with respect to a Bernal-stacked bilayer to realize narrow and topologically non-trivial valley-projected moiré minibands 15 – 17 . At fillings of one and three electrons per moiré unit cell within these bands, we observe quantized anomalous Hall effects 18 with transverse resistance approximately equal to h /2 e 2 (where h is Planck’s constant and e is the charge on the electron), which is indicative of spontaneous polarization of the system into a single-valley-projected band with a Chern number equal to two. At a filling of three electrons per moiré unit cell, we find that the sign of the quantum anomalous Hall effect can be reversed via field-effect control of the chemical potential; moreover, this transition is hysteretic, which we use to demonstrate non-volatile electric-field-induced reversal of the magnetic state. A theoretical analysis 19 indicates that the effect arises from the topological edge states, which drive a change in sign of the magnetization and thus a reversal in the favoured magnetic state. Voltage control of magnetic states can be used to electrically pattern non-volatile magnetic-domain structures hosting chiral edge states, with applications ranging from reconfigurable microwave circuit elements to ultralow-power magnetic memories. Non-volatile electrical switching of magnetic order in an orbital Chern insulator is experimentally demonstrated using a moiré heterostructure and analysis shows that the effect is driven by topological edge states.

中文翻译：

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轨道陈绝缘体中磁序的电转换

磁性通常来自费米统计和排斥库仑相互作用的联合效应，这有利于具有非零电子自旋的基态。因此，通过电场控制自旋磁性——自旋电子学和多铁性 1 、 2 的长期技术目标——只能间接实现。在这里，我们通过实验证明了轨道陈绝缘体中磁态的直接电场控制 3 – 6 ，这是一个磁性系统，其中非平凡的带拓扑有利于轨道角动量的长程有序，但自旋被认为保持无序 7 – 14 . 我们使用范德瓦尔斯异质结构，由石墨烯单层组成，相对于伯纳尔堆叠双层旋转断层，以实现狭窄且拓扑上非平凡的谷投影莫尔微带 15-17。在这些带内每个莫尔晶胞填充一个和三个电子时，我们观察到量化的异常霍尔效应 18，横向电阻大约等于 h /2 e 2（其中 h 是普朗克常数，e 是电子上的电荷），即表示系统自发极化成单谷投影带，陈数等于 2。在每个莫尔晶胞填充三个电子时，我们发现量子反常霍尔效应的符号可以通过化学势的场效应控制来反转；此外，这种转变是滞后的，我们用它来证明非易失性电场引起的磁态反转。理论分析 19 表明该效应来自拓扑边缘状态，这会导致磁化符号发生变化，从而导致有利的磁性状态发生逆转。磁状态的电压控制可用于对具有手征边缘状态的非易失性磁畴结构进行电图案化，其应用范围从可重新配置的微波电路元件到超低功耗磁存储器。使用莫尔异质结构实验证明了轨道陈绝缘体中磁序的非易失性电切换，分析表明该效应是由拓扑边缘状态驱动的。