The Complete Quantum Hall Trio
The Complete Quantum Hall Trio
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DOI：
10.1126/science.1237215
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发表时间：
2013-04
期刊：
影响因子：
56.9
通讯作者：
Seongshik Oh
中科院分区：
文献类型：
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作者：
Seongshik Oh
在没有外部磁场的情况下观察到量子化的电阻状态，就完成了三个与量子霍尔相关的效应。[另见Chang等人的报告]当电流I流过放置在与流动方向垂直的外部磁场H中的导体平板时，磁场使携带电流的电荷粒子偏转到导体的边缘，并在样品上产生横向电压VT。这种由埃德温·霍尔于1879年发现的效应被称为霍尔效应。由于横向电阻(或霍尔电阻)定义为VT/I与H/n成正比，其中n是样品的片状载流子密度，因此霍尔效应已被广泛用于量化电子材料的载流子类型(电子或空穴)、密度和迁移率。然而，在20世纪80年代，人们发现，当载流子被限制在二维系统(或薄片)中时，只要H/n接近特定值(2)，霍尔电阻就在h/(νe2)处精确量子化，其中h是普朗克常数，e是电子电荷，ν是正整数。这种现象被称为量子霍尔效应(QHE)，总是需要一个外部磁场。本期(3)第167页，Chang等人。他们发现，即使在没有外部磁场的情况下，横向电阻中的这种精确量子化也可以发生在薄铁磁拓扑绝缘体上；结果证实了人们期待已久的量子反常霍尔效应(QAHE)，这是量子霍尔三重奏的最后成员(见图)。
Observation of a quantized resistance state in the absence of an external magnetic field completes a trio of quantum Hall related effects. [Also see Report by Chang et al.] When an electric current I flows through a slab of conductor placed in an external magnetic field H perpendicular to the flow direction, the magnetic field deflects the current-carrying charge particles toward the edge of the conductor and a transverse voltage VT develops across the sample. This effect, discovered by Edwin Hall in 1879 (1), is called the Hall effect. Because the transverse resistance (or Hall resistance) defined as VT/I is proportional to H/n, where n is the sheet carrier density of the sample, the Hall effect has been widely used to quantify the carrier type (electron or hole), density, and mobilities of electronic materials. However, in the 1980s it was found that when the charge carriers are confined to a two-dimensional system (or sheet), the Hall resistance becomes exactly quantized at h/(νe2), where h is the Planck constant, e is the electron charge, and ν is a positive integer, whenever H/n approaches specific values (2). This phenomenon, called the quantum Hall effect (QHE), always requires an external magnetic field. On page 167 this issue (3), Chang et al. have discovered that such exact quantization in the transverse resistance can occur even without an external magnetic field on a thin ferromagnetic topological insulator; the result confirms the long-awaited quantum anomalous Hall effect (QAHE), the final member of the quantum Hall trio (see the figure).