▎ 摘　　要

Graphene exhibits quantum Hall ferromagnetism in which an approximate SU(4) symmetry involving spin and valley degrees of freedom is spontaneously broken. We construct a set of integer and fractional quantum Hall states that break the SU(4) spin (valley) symmetry, and study their neutral and charged excitations. Several properties of these ferromagnets can be evaluated analytically in the SU(4) symmetric limit, including the full collective-mode spectrum at integer fillings. By constructing explicit wave functions we show that the lowest-energy skyrmion states carry charge +/- 1 for any integer filling, and that skyrmions are the lowest-energy-charged excitations for graphene Landau-level index parallel to n parallel to