High field quantum hall effect in disordered graphene near the dirac point

We investigate on the conductance properties of low mobility graphene in the quantum Hall regime at filling factor less than v = 2. For this purpose, we compare the high-field longitudinal and Hall resistances of two graphene samples with different mobility. We show that the presence of “charge density puddles”, most probably due to charged impurities, particularly affect the fundamental high field electronic properties of graphene. In particular, the Hall resistance plateau at R = h/2e2 is unstable and shows a non-monotonic behaviour when the system is driven close to the Dirac point. This phenomenon is ascribed to as Fermi level pinning in the Landau Level sub-bands of graphene, in the presence of disorder.