  The ground state of the two-dimensional electron systems in Bernal bilayer
and ABC-stacked multilayer graphenes in the presence of a strong magnetic field
is investigated with the Hartree-Fock approximation. Phase diagrams of the
systems are obtained, focusing on charge density wave states including states
with vortices of valley pseudospins (called a Skyrme crystal). The
single-electron states in these stacked graphenes are given by two-component
wave functions. That of the first excited Landau level has the same component
as the lowest Landau level of the ordinary two-dimensional electrons. Because
of this localized wave functions, the Skyrme crystal has low energy in this
first excited level up to four layers of graphene, when the inter-layer
distance is assumed to be infinitesimal. At the same time, bubble crystals are
suppressed, so the phase diagram is different from that of a single-layer
graphene.
