Department of Physics, National Taiwan University, Taipei 106, Taiwan.
Nanoscale Res Lett. 2013 May 6;8(1):214. doi: 10.1186/1556-276X-8-214.
We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field Bc, an approximately temperature-independent point in the measured longitudinal resistivity ρxx, which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility μq of our device. It is found that at the direct I-QH transition, μqBc ≈ 0.37 which is considerably smaller than 1. In contrast, at Bc, ρxx is close to the Hall resistivity ρxy, i.e., the classical mobility μBc is ≈ 1. Therefore, our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D.
我们对多层石墨烯薄片进行了磁输运测量。在交叉磁场 Bc 处，观察到测量的纵向电阻率 ρxx 中出现一个近似温度无关的点，这归因于直接绝缘量子霍尔（I-QH）转变。通过分析磁阻振荡的幅度，我们能够测量我们器件的量子迁移率 μq。结果发现，在直接 I-QH 转变处，μqBc ≈ 0.37，这明显小于 1。相比之下，在 Bc 处，ρxx 接近霍尔电阻率 ρxy，即经典迁移率 μBc ≈ 1。因此，我们的结果表明，在多层石墨烯中观察到的直接 I-QH 转变需要引入不同的迁移率。结合在各种材料系统中获得的现有实验结果，我们在石墨烯上获得的数据表明，直接 I-QH 转变是二维中的普遍效应。
