AVS 57th International Symposium & Exhibition
    Graphene Focus Topic Thursday Sessions
       Session GR+AS+TF+MI-ThA

Paper GR+AS+TF+MI-ThA4
Atomic-Scale Maps of Quantum Hall States in Epitaxial Graphene

Thursday, October 21, 2010, 3:00 pm, Room Brazos

Session: Graphene: Surface Characterization
Presenter: D.L. Miller, Georgia Institute of Technology
Authors: D.L. Miller, Georgia Institute of Technology
K.D. Kubista, Georgia Institute of Technology
G.M. Rutter, National Institute of Standards and Technology
M. Ruan, Georgia Institute of Technology
W.A. de Heer, Georgia Institute of Technology
P.N. First, Georgia Institute of Technology
J.A. Stroscio, National Institute of Standards and Technology
Correspondent: Click to Email
When a perpendicular magnetic field is applied to a graphene sheet, the resulting eigenenergies (Landau Levels or LLs) have a nonlinear energy distribution that includes a four-fold degenerate zero-energy state (LL0). Maps of the energy-resolved local density of states (LDOS) acquired via cryogenic scanning tunneling spectroscopy (STS) provide atomic-scale imaging of the LL spatial distribution. Focusing on LL0, we use STS maps to image the localized and extended quantum Hall states. Unexpectedly, we find atomic-scale variations of the LDOS above a critical magnetic field. We attribute this to an energy gap in LL0 and show how it depends on the local A-B lattice symmetry. The gap is observed only within patches of at least a few magnetic lengths in size, which forces the splitting to “turn off” below the critical field. This behavior implies a breaking of the local sublattice symmetry imposed by moiré layer stacking.