  The quantum Hall effect is the seminal example of topological protection, as
charge carriers are transmitted through one-dimensional edge channels where
backscattering is prohibited. Graphene has made its marks as an exceptional
platform to reveal new facets of this remarkable property. However, in
conventional Hall bar geometries, topological protection of graphene edge
channels is found regrettably less robust than in high mobility
semi-conductors. Here, we explore graphene quantum Hall regime at the local
scale, using a scanning gate microscope. We reveal the detrimental influence of
antidots along the graphene edges, mediating backscattering towards upstream
edge channels, hence triggering topological breakdown. Combined with
simulations, our experimental results provide further insights into graphene
quantum Hall channels vulnerability. In turn, this may ease future developments
towards precise manipulation of topologically protected edge channels hosted in
various types of two-dimensional crystals.
