SCANNING TUNNELING SPECTROSCOPY OF A GATED GRAPHENE DEVICE IN THE QUANTUM HALL REGIME
Gregory M. Rutter1, Suyong Jung1,2, Nikolai B. Zhitenev1, Joseph A. Stroscio1
1CNST, NIST, Gaithersburg, MD
2Maryland NanoCenter, UMD, College Park, MD
In this work, scanning tunneling spectroscopy is used to investigate the magnetic quantization of a single-layer exfoliated graphene device at a temperature of 4.3 K in magnetic fields up to 8 T. Exfoliated graphene samples were fabricated by removing graphene layers from natural graphite, then placing them onto a SiO2/Si substrate. A gold electrode, used for the tunneling bias, was deposited using a stencil mask. Single-layer graphene is then probed with both the application of a perpendicular magnetic field and with an external gate voltage applied to the Si substrate below the graphene. Under high magnetic field conditions, charge carriers in graphene are condensed into well-defined degenerate states called Landau levels (LL), which have an energy dependence of (where n is the Landau index and B is the magnetic field). The Landau level distribution is centered around the n = 0 LL, which resides at the charge neutrality point in graphene, called the Dirac point. By varying the charge density (ne) with the externally applied gate potential, we can move the LL distribution with respect to the Fermi energy (EF) allowing the filling of different Landau levels. Detailed plots of the differential conductance, dI/dV(E, ne), show a combination of plateaus followed by discrete steps at each Landau level as the carrier density (gate potential) is varied. This behavior, observed in GaAs heterostructures, has been attributed to chemical potential jumps as each Landau level is pinned to EF. Additional sharp peaks observed in the dI/dV measurements, which originate from different types of localized states, will be also discussed.
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