We report on the stability of the quantum Hall plateau in very large Hall bars (100 μm width) made from a chemically gated graphene film grown on SiC substrate. The ν=2 quantized plateau of the Hall appears from B⋍5T and persists up to B≃80 T. We relate this extreme broad plateau to the presence of charge reservoirs from which electrons are transferred to graphene as the magnetic field increases. This mechanism allows the Fermi energy to remain always above the two-fold degenerated zero-energy Landau level and ensures the stability of the Hall plateau at low temperature. On the other hand, the temperature dependence of the magneto-resistance suggests some limitations to the charge transfer model and the onset of a localization-delocalization transition. At high current density, the longitudinal resistance displays small and periodic oscillations when plotted versus 1/B, with a 2π Berry phase. The extracted carrier density is consistent with as-grown graphene on SiC, e.g. without the chemical gate. We assume that the oscillating features originate from inhomogeneous doping across the sample where patches of pristine (undoped) graphene are present. Numerical simulations, based on a charge transfer between the graphene patches, reproduce well the experimental data and indicate that undoped graphene covers up to 30% of the total sample’s surface.

Ming Yang is currently an PhD student in LNCMI-T(Laboratoire National des Champs Magnétiques Intenses-Toulouse). He is primarily interested in the transport properties under high magnetic field of two-dimensional electron gas such as graphene. He received his B.S. degree in Physics from Huazhong University of Science and Technology(China) (2012). After two years' study as a PhD student in Wuhan National High Magnetic Center, he got a scholarship from the China Scholarship Council and joint the Nano-group in LNCMI-T in 2014.