Mechanisms of new type quantum Hall breakdown

量子霍尔效应(QHE)击穿有两种类型，一种是击穿电流与沟道宽度成线性关系(线性)，另一种是击穿电流随沟道宽度呈次线性增加(亚线性)。为了研究亚线型击穿的起源，我们用样品研究了QHE击穿：(1)常规霍尔棒，(2)没有样品边缘的科尔比诺几何样品，(3)样品边界的限制势可通过栅极电压调节的侧栅霍尔棒。用线性和亚线性两种类型的GaAs/AlGaAs二维电子系统(2DES)对实验结果进行了比较。在线型样品中，霍尔棒状样品的临界霍尔电场与在Corbino样品中测得的临界电场符合得很好。结果表明，在线型样品中，电流分布均匀。另一方面，亚线型样品的临界电场远小于线型样品，霍尔棒临界电流和科尔比诺临界电压的宽度关系呈现亚线性特征。此外，侧栅电压对击穿电流值的影响很小，这表明QHE击穿与样品边界处的限制势无关，这些实验结果支持了亚线型QHE击穿不是“边缘效应”，而是体2DES的特性。我们还测量了QHe平台上剩余体电导激活能的电流依赖关系。讨论了亚线型QHE击穿的可能来源：体相2DES中的局域电流分布以及电流(电场)对小电势起伏的2DES中激活能的影响。

There are two types of quantum Hall effect(QHE) breakdown ; one is that the breakdown current scales linearly with the channel width (linear type), and the other is that the breakdown current increases sub-linearly with the channel width (sub-linear type). To investigate the origin of sub-linear type breakdown, we have studied the QHE breakdown by using samples ; (1)conventional Hall-bar, (2)Corbino geometry samples without sample edge, and (3)side gated Hall-bar whose confinement potential at the sample boundary is tunable by the gate voltage. Both linear and sub-linear types of the GaAs/AlGaAs two-dimensional electron systems(2DES) are used to compare the experimental results. In the linear type samples, the observed critical Hall electric field in Hall-bar shaped sample is in good agreement with the critical electric field measured in Corbino samples. It demonstrates that the current distribution is uniform in the linear type samples. On the other hand, the critical electric field in the sub-linear type sample is much smaller than those in the linear type samples, and the width dependence of critical current in Hall-bar and the critical voltage in Corbino shows sub-linear feature. Moreover, the value of breakdown current is scarcely affected by changing side gate voltage, which suggests that the QHE breakdown is independent of the confinement potential at the sample boundary.Those experimental results support that the sub-linear type QHE breakdown is not "edge effect" but the properties of bulk 2DES. We also have measured the current dependence of activation energy of residual bulk conductivity at QHE plateau. The possible origin of sub-linear type QHE breakdown ; the localized current distribution in the bulk 2DES and current (electric field) effect on the activation energy in 2DES with small potential fluctuation, is discussed.