  Observations of electron-hole asymmetry in transport through graphene devices
at high magnetic field challenge prevalent models of the graphene quantum Hall
effect. Here, we study this asymmetry both in conventional magnetotransport and
in scanning gate microscopy maps measured in an encapsulated graphene
constriction. We reveal that the presence of upstream modes and local doping in
the vicinity of electrical contacts leads to a totally different picture of
topological breakdown for electrons and holes, explaining the observed
asymmetry.
