Realization of the Axion Insulator State in Quantum Anomalous Hall Sandwich Heterostructures
Realization of the Axion Insulator State in Quantum Anomalous Hall Sandwich Heterostructures
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DOI：
10.1103/physrevlett.120.056801
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发表时间：
2018-01-31
影响因子：
8.6
通讯作者：
Chang, Cui-Zu
中科院分区：
文献类型：
--
作者：
Xiao, Di;Jiang, Jue;Chang, Cui-Zu
“磁电效应”是由材料的磁性和电性之间的耦合产生的。拓扑绝缘体（TIs）的Z(2)不变量导致了这种现象的量子化版本，称为拓扑磁电（TME）效应。这种效应可以在一种称为“轴子绝缘子”的新拓扑相中实现，其表面状态都是间隙的，但内部仍然服从时间反转对称。我们在量子反常霍尔（QAH）夹层异质结构中使用电输运测量证明了这种相位，其中两个组成不同的磁性TI层被未掺杂的TI层分开。同一样品的磁力显微镜图像显示，在不同的矫顽力场下，顶层和底层的顺序磁化逆转，这是由于间隔层导致的层间交换耦合弱的结果。当磁化强度为反平行时，霍尔电阻和霍尔电导均为零平台，同时纵向电阻大，纵向电导消失，表明实现了轴子绝缘子状态。因此，我们的发现提供了一个与已建立的QAH状态不同的物质阶段的证据，并为实现TME效应提供了一个有希望的平台。
The "magnetoelectric effect" arises from the coupling between magnetic and electric properties in materials. The Z(2) invariant of topological insulators (TIs) leads to a quantized version of this phenomenon, known as the topological magnetoelectric (TME) effect. This effect can be realized in a new topological phase called an "axion insulator" whose surface states are all gapped but the interior still obeys time reversal symmetry. We demonstrate such a phase using electrical transport measurements in a quantum anomalous Hall (QAH) sandwich heterostructure, in which two compositionally different magnetic TI layers are separated by an undoped TI layer. Magnetic force microscopy images of the same sample reveal sequential magnetization reversals of the top and bottom layers at different coercive fields, a consequence of the weak interlayer exchange coupling due to the spacer. When the magnetization is antiparallel, both the Hall resistance and Hall conductance show zero plateaus, accompanied by a large longitudinal resistance and vanishing longitudinal conductance, indicating the realization of an axion insulator state. Our findings thus show evidence for a phase of matter distinct from the established QAH state and provide a promising platform for the realization of the TME effect.