Direct imaging of coherent quantum transport in graphene p−n−p junctions

We use electrostatic lithography to fabricate a graphene p-n-p junction and exploit the coherence of weakly confined Dirac quasiparticles to image the underlying scattering potential using low-temperature scanning gate microscopy. The tip-induced perturbation to the junction potential modifies the condition for resonant scattering, enabling us to detect localized Fabry-Perot subcavities from the focal point of halos in scanning gate images. In addition to halos over the bulk, we also observe ones spatially registered to the physical edge of the graphene. Guided by quantum transport simulations, we attribute these to modified resonant scattering at the edges within elongated cavities that form due to focusing of the electrostatic field.