Paper GR+TF-TuM9
Scanning Tunneling Spectroscopy of a Gated Single-Layer Graphene Device in the Quantum Hall Regime

Tuesday, October 19, 2010, 10:40 am, Room Brazos

We have performed scanning tunneling spectroscopy (STS) measurements to investigate Dirac particle interactions and localization by local impurities in a gated single-layer exfoliated graphene device in the quantum Hall regime at a temperature of 4.3 K. At the Dirac point, electron-hole puddles created by the disorder potential in SiO₂ substrate are observed at zero magnetic field. In an applied magnetic field, the carriers are condensed into well-resolved Landau levels (LLs), whose general evolution as a function of both charge density and magnetic field is well described by the context of ‘massless’ Dirac particles. Tunneling spectroscopy measurements as a function of magnetic field and applied gate potential are shown to give insight into the localization of carriers and their relation to the disorder potential. At low magnetic fields, tunneling spectra display long-range scattering features related to the graphene disorder potential variation. The disorder potential also determines the spatial distribution of LLs in higher magnetic fields. We observe that isolated compressible LL regions surrounded by incompressible strips behave like graphene quantum dots (QDs). Single-electron charging of the QDs is seen as four-fold Coulomb oscillations in individual dI/dV curves. These results show that the plane of the graphene 2DEG breaks into a checkerboard pattern of electron- or hole-rich QDs localized at either maxima or minima of the disorder potential.