Topinka M A, LeRoy B J, Westervelt R M, Shaw S E, Fleischmann R, Heller E J, Maranowski K D, Gossard A C
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Nature. 2001 Mar 8;410(6825):183-6. doi: 10.1038/35065553.
Semiconductor nanostructures based on two-dimensional electron gases (2DEGs) could form the basis of future devices for sensing, information processing and quantum computation. Although electron transport in 2DEG nanostructures has been well studied, and many remarkable phenomena have already been discovered (for example, weak localization, quantum chaos, universal conductance fluctuations), fundamental aspects of the electron flow through these structures have so far not been clarified. However, it has recently become possible to image current directly through 2DEG devices using scanning probe microscope techniques. Here, we use such a technique to observe electron flow through a narrow constriction in a 2DEG-a quantum point contact. The images show that the electron flow from the point contact forms narrow, branching strands instead of smoothly spreading fans. Our theoretical study of this flow indicates that this branching of current flux is due to focusing of the electron paths by ripples in the background potential. The strands are decorated by interference fringes separated by half the Fermi wavelength, indicating the persistence of quantum mechanical phase coherence in the electron flow. These findings may have important implications for a better understanding of electron transport in 2DEGs and for the design of future nanostructure devices.
基于二维电子气（2DEG）的半导体纳米结构有望成为未来传感、信息处理和量子计算设备的基础。尽管人们已经对2DEG纳米结构中的电子输运进行了深入研究，并且发现了许多显著的现象（例如，弱局域化、量子混沌、普遍电导涨落），但迄今为止，电子在这些结构中流动的基本特性仍未得到明确阐释。然而，近来利用扫描探针显微镜技术直接对2DEG器件中的电流进行成像已成为可能。在此，我们运用这种技术来观测电子在2DEG中的一个狭窄收缩处——量子点接触中的流动情况。图像显示，从量子点接触流出的电子流形成了狭窄的分支束，而非平滑扩展的扇形。我们对这种流动的理论研究表明，电流通量的这种分支现象是由背景势中的波纹对电子路径的聚焦作用所导致的。这些束被间隔为费米波长一半的干涉条纹所修饰，这表明电子流中量子力学相位相干性的持续存在。这些发现可能对更好地理解2DEG中的电子输运以及未来纳米结构器件的设计具有重要意义。
