Introduction . It is well known that graphene, a single layer of graphite firstly produced by Geim and Novoselov with micromechanical exfoliation1, presents a peculiar electronic band structure, because electrons that move through this 2D material behave as massless Dirac fermions, i.e., they show a linear relation between energy and momentum2 , 3. However, the presence of the Dirac point, namely the K-point in the first Brillouin zone where the valence band touches the con...