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Coulomb interactions, Dirac sea polarization and $SU(4)$ symmetry breaking of the integer quantum Hall states of graphene

We investigate effects of the filled Dirac sea on the $SU(4)$ symmetry breaking in the integer quantum Hall states of graphene with long-ranged Coulomb interactions. Our model also includes Hubbard and nearest neighbour repulsive interactions with strengths $U$ and $V$ respectively. We find that the symmetry breaking of the $n=0$ Landau levels induces an $SU(4)$ polarization of the Dirac sea. This results in several phases which are absent when the effects of the Dirac sea are neglected. We compute the phase diagram in the $U$-$V$ space. We also calculate the excitation gaps in tilted magnetic fields for all the phases. We compare our model results with experiments and find a range of $U$ and $V$ that are consistent with them.