“…As graphene is a zero gap semiconductor, under the widely used experimental conditions, when large contact area electrodes are used, and the angle of incidence of the wave packets on the interface can vary over a certain range, lower energy spreading states are likely to tunnel, too. An anisotropic conductivity may also appear in conventional transport experiments, however, at energies close to the Fermi energy, because the effect of short-range nonsymmetric defects 33 or because the Rashba spin-orbit coupling 34 caused by impurities 35 or by the interaction with the support surface. 36 A very important factor that may affect the propagation of charge carriers 37,38 in graphene is the presence of grain boundaries.…”