Explanation for the isotropy of the Dirac cone in graphene
Abstract
It is shown that in the absence of spontaneous symmetry breaking the Dirac cones in the system of interacting electrons on honeycomb lattice are isotropic at low energies. The effect is due to the Z3 subgroup of the D3 symmetry group of the dispersion relation of Dirac quasiparticles. Consequences of the violations of the Z3 or the sublattice symmetry are discussed.
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