Abstract

The high mobility achieved in the mesoscopic graphene devices encapsulated by hexagon boron-nitride (h-BN) enables the ballistic transport over a few micrometers and provides the opportunity to investigate the novel electron optics in Dirac fermion system. The scanning gate microscope (SGM) is a valuable tool to study these ballistic transport phenomena and has been applied to investigate the Fabry-Perot cavity across a graphene np junction [1]. In this talk I will present some works extending the SGM technique to image the ballistic trajectories of the magnetic focusing in a graphene device. By locally varying the carrier concentration through the charged AFM tip at 4K, we are able to 1) image the first and second focusing arcs by diverting the focused electrons away from the collector; and 2) refocus the slightly misaligned electrons back to collector [2]. Our results demonstrate the feasibility of the method and indicate the possibility of manipulating ballistic electron beams with an AFM probe. Another independent but similar work also supports our findings [3]