  We have studied the transport properties of a large graphene double quantum
dot under the influence of background disorder potential and magnetic field. At
low temperatures, the evolution of the charge-stability diagram as a function
of B-field is investigated up to 10 Tesla. Our results indicate that the
charging energy of quantum dot is reduced, and hence the size of the dot
increases, at high magnetic field. We provide an explanation of our results
using a tight-binding model, which describes the charge redistribution in a
disordered graphene quantum dot via the formation of Landau levels and edge
states. Our model suggests that the tunnel barriers separating different
electron/hole puddles in a dot become transparent at high B-fields, resulting
in the charge delocalization and reduced charging energy observed
experimentally.
