  We have investigated tunneling current through a suspended graphene Corbino
disk in high magnetic fields at the Dirac point, i.e. at filling factor $\nu$ =
0. At the onset of the dielectric breakdown the current through the disk grows
exponentially before ohmic behaviour, but in a manner distinct from thermal
activation. We find that Zener tunneling between Landau sublevels dominates,
facilitated by tilting of the source-drain bias potential. According to our
analytic modelling, the Zener tunneling is strongly affected by the gyrotropic
force (Lorentz force) due to the high magnetic field
