Discrete symmetry in graphene: the Dirac equation and beyond
  In this pedagogical paper we review the discrete symmetries of the Dirac equation using elementary tools, but in a comparative order: the usual 3 + 1 dimensional case and the 2 + 1 dimensional case. Motivated by new applications of the 2d Dirac equation in condensed matter, we further analyze the discrete symmetries of a full tight-binding model in hexagonal lattices without conical approximations. We touch upon an effective CPT symmetry breaking that occurs when deformations and second-neighbor corrections are considered. 
Emerson Sadurn\'i, Eladio Rivera-Moci\~nos, Alfonso Rosado
cond-mat.other hep-th quant-ph