  Recently, type-II Dirac fermions characterized by strongly titled Dirac cones
have been proposed. The new fermions exhibit unique physical properties
different from the type-I Dirac fermions in graphene, and thus attract
tremendous attentions. Up to date, all type-II fermions are only found in the
heavy compounds with strong spin obit coupling. Here, we propose that both
type-I and type-II Dirac fermions can exist in the graphene embedding
nitrogen-molecule line defects (NMLDs). While the types of Dirac fermions are
determined by the size W of graphene nanoribbons between the line defects. By
comparing the two types of Dirac fermions, their different physical properties
and originations are revealed directly. Remarkably, the type-I Dirac points
induce one Fermi arc corresponding to edge states along the armchair direction,
while the type-II Dirac points induce two Fermi arcs corresponding to two sets
of edge states along the zigzag direction. These results not only expand our
views on the Dirac fermions in two-dimensional structures, but also extend
their applications in electronics.
