School of Engineering and Applied Sciences and Department of Physics, Harvard University , Cambridge, Massachusetts 02138 United States.
National Institute for Materials Science , 1-1 Namiki, Tsukuba, 305-0044, Japan.
Nano Lett. 2016 Mar 9;16(3):1690-4. doi: 10.1021/acs.nanolett.5b04609. Epub 2016 Feb 10.
Electrons in graphene can travel for several microns without scattering at low temperatures, and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer number of cyclotron diameters away. By tuning the magnetic field B and electron density n in the graphene layer, we observe magnetic focusing peaks. We use a cooled scanning gate microscope to image cyclotron trajectories in graphene at 4.2 K. The tip creates a local change in density that casts a shadow by deflecting electrons flowing nearby; an image of flow can be obtained by measuring the transmission between contacts as the tip is raster scanned across the sample. On the first magnetic focusing peak, we image a cyclotron orbit that extends from one contact to the other. In addition, we study the geometry of orbits deflected into the second point contact by the tip.
在低温下，石墨烯中的电子可以在没有散射的情况下传播数微米，其运动变得弹道式，遵循经典轨迹。当磁场 B 垂直于平面施加时，电子沿回旋轨道运动。当从一个狭窄的接触点注入的电子聚焦在位于整数个回旋直径之外的第二个接触点上时，就会发生磁聚焦。通过调节磁场 B 和石墨烯层中的电子密度 n，我们观察到磁聚焦峰。我们使用冷却扫描门显微镜在 4.2 K 下对石墨烯中的回旋轨迹进行成像。尖端通过偏转附近流动的电子来局部改变密度，从而投射阴影；通过测量尖端在样品上进行光栅扫描时两个接触点之间的传输，可以获得流动的图像。在第一个磁聚焦峰上，我们成像了一个从一个接触点延伸到另一个接触点的回旋轨道。此外，我们还研究了被尖端偏转进入第二个点接触的轨道的几何形状。
