Mechanisms of new type quantum Hall breakdown

量子霍尔效应（QHE）击穿有两种类型；一种是击穿电流随通道宽度呈线性增长（线性型），另一种是击穿电流随通道宽度呈亚线性增长（亚线性型）。为了探讨亚线性击穿的起源，我们采用样本方法研究了QHE击穿；(1)常规霍尔棒，(2)没有样品边缘的Corbino几何样品，(3)样品边界约束电位可通过栅极电压调节的侧门控霍尔棒。采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。在线性型样品中，霍尔棒状样品中观测到的临界霍尔电场与Corbino样品中测量到的临界电场吻合较好。结果表明，在线性型样品中，电流分布是均匀的。另一方面，亚线性型样品的临界电场比线性型样品小得多，Hall-bar临界电流与Corbino临界电压的宽度依赖关系呈现亚线性特征。此外，击穿电流的值几乎不受侧栅电压变化的影响，这表明QHE击穿与样品边界的约束势无关。这些实验结果支持了亚线性型QHE击穿不是“边缘效应”，而是块体2DES的性质。我们还测量了QHE平台上剩余体积电导率活化能的电流依赖性。亚线性型QHE击穿的可能成因讨论了体态2DES中的局部电流分布，以及电流（电场）对小电位波动2DES中活化能的影响。

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.