  The electronic transport of graphene p-n junctions under perpendicular
magnetic field is investigated in theory. Under low magnetic field, the
transport is determined by the resonant tunneling of Landau levels and
conductance versus magnetic field shows a Shubnikov-de Haas oscillation. At
higher magnetic field, the p-n junction subjected to the quasi-classical regime
and the formation of snake states results in periodical backscattering and
transmission as magnetic field varies. The conductance oscillation pattern is
mediated both by magnetic field and the carrier concentration on bipolar
regions. For medium magnetic field between above two regimes, the combined
contributions of resonant tunneling, snake states oscillation and Aharanov-Bohm
interference induce irregular oscillation of conductance. At very high magnetic
field, the system is subjected to quantum Hall regime. Under disorder, the
quantum tunneling at low magnetic field is slightly affected and the
oscillation of snake states at higher magnetic field is suppressed. In the
quantum Hall regime, the conductance is a constant as predicted by the mixture
rule.
