Controlling Dirac fermions optics in high mobility graphene by scanning gate microscop

Abstract

Among the exotic properties of Dirac excitations in graphene, Klein tunneling appears to be a remarkable one, and its full understanding and control is aprerequisite to build graphene-based electron optics devices. With the advent of high mobility suspended or encapsulated graphene devices, various optical-likebehavior of charge carriers have been reported, such as for examples electron guiding or Fabry-Pérot interferences in n-p-n junctions. So far the p-n junctionsused to guide or reflect electrons are often realized by metallic or graphite gates. Hence their sharpness is fixed and governed mostly by the gate-to-graphenedistance. Here we investigate electron and hole transport through a 300nm wide encapsulated graphene constriction. Using the polarized tip of a cryogenicscanning probe microscope, we can create a local n-p-n or p-n-p junction. By changing tip voltage and distance to the graphene flake, we can control at will theexact shape and sharpness of the junction, hence play with the reflection, transmission and refraction of charge carriers at the p-n interfaces. We present amethod to accurately characterize the exact carrier density profile under the tip influence, and reach a full determination of the tip-induced potential. We observesignatures of electron focusing on the circular tip potential, as well as Fabry-Pérot interference phenomena depending on the tip voltage and position. Theseobservations demonstrate that Scanning Gate Microscopy is a very powerful tool to study and control Klein tunneling in high mobility graphene devices, paving theway to high precision electron optics experiments