Manipulating quantum Hall edge channels in graphene through Scanning Gate Microscopy

We show evidence of the backscattering of quantum Hall edge channels in a narrow graphene Hall bar, induced by the gating effect of the conducting tip of a Scanning Gate Microscope, which we can position with nanometer precision. Moreover, we see intriguing junctions arise between regions of different charge carrier density, due to the gradual spatial variation of the gating potential, which manifests itself in values of the longitudinal resistance $R_{xx}$ that have not been observed before in devices based on top-- or split--gates. The solution of the corresponding quantum scattering problem is presented to substantiate these results, and possible follow--up experiments are discussed.