We study the existence and topological stability of Fermi points in a graphene layer and stacks with many layers. We show that the discrete symmetries (space-time inversion) stabilize the Fermi points in monolayer, bilayer, and multilayer graphenes with orthorhombic stacking. The bands near $k=0$ and $ϵ=0$ in multilayers with the Bernal stacking depend on the parity of the number of layers, and Fermi points are unstable when the number of layers is odd. The low-energy changes in the electronic structure induced by commensurate perturbations which mix the two Dirac points are also investigated.

• Received 19 February 2007

DOI:https://doi.org/10.1103/PhysRevB.75.155424