轨道Chern绝缘体中磁序的电开关
Electrical switching of magnetic order in an orbital Chern insulator
摘要：
磁性通常来自费米统计和排斥库仑相互作用的联合效应，其有利于具有非零电子自旋的基态。因此，用电场控制自旋磁性-自旋电子学和多铁性学长期以来的技术目标-只能间接实现。在这里，我们实验证明了直接电场控制的磁态在轨道陈绝缘体，磁系统中，非平凡的能带拓扑有利于轨道角动量的长程序，但自旋被认为是保持无序。我们使用范德华异质结构组成的石墨烯单层旋转故障相对于Bernal堆叠的双层实现狭窄的和拓扑非平凡的谷投影莫尔迷你带。在这些带内每个莫尔晶胞填充一个和三个电子时，我们观察到横向电阻约等于$h/2e^2$的量子化异常霍尔效应，这表明系统自发极化成陈数等于2的单谷投影带。在每个摩尔单元格填充三个电子时，我们发现量子反常霍尔效应的符号可以通过场效应控制化学势来反转;此外，这种转变是滞后的，我们用它来证明非易失性电场诱导的磁态反转。理论分析表明，这种效应来自于拓扑边缘状态，它驱动磁化强度的符号变化，从而使有利的磁状态反转。磁状态的电压控制可用于电图案化具有手性边缘状态的非易失性磁畴结构，其应用范围从可重构微波电路元件到超低功率磁存储器。
英文摘要：
Magnetism typically arises from the joint effect of Fermi statistics and repulsive Coulomb interactions, which favors ground states with non-zero electron spin. As a result, controlling spin magnetism with electric fields---a longstanding technological goal in spintronics and multiferroics---can be achieved only indirectly. Here, we experimentally demonstrate direct electric field control of magnetic states in an orbital Chern insulator, a magnetic system in which non-trivial band topology favors long range order of orbital angular momentum but the spins are thought to remain disordered. 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 nontrivial valley-projected moiré minibands. At fillings of one and three electrons per moiré unit cell within these bands, we observe quantized anomalous Hall effects with transverse resistance approximately equal to $h/2e^2$, 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 nonvolatile electric field induced reversal of the magnetic state. A theoretical analysis 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 favored magnetic state. Voltage control of magnetic states can be used to electrically pattern nonvolatile magnetic domain structures hosting chiral edge states, with applications ranging from reconfigurable microwave circuit elements to ultralow power magnetic memory.
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