  We have investigated the cross-over from Zener tunneling of single charge
carriers to avalanche type of bunched electron transport in a suspended
graphene Corbino disk in the zeroth Landau level. At low bias, we find a
tunneling current that follows the gyrotropic Zener tunneling behavior. At
larger bias, we find avalanche type of transport that sets in at a smaller
current the larger the magnetic field is. The low-frequency noise indicates
strong bunching of the electrons in the avalanches. On the basis of the
measured low-frequency switching noise power, we deduce the characteristic
switching rates of the avalanche sequence. The simultaneous microwave shot
noise measurement also reveals intrinsic correlations within the avalanche
pulses and indicate decrease of correlations with increasing bias.
