Evolution of Microscopic Localization in Graphene in a Magnetic Field: From Scattering Resonances to Quantum Dots.
Suyong S. Jung, Gregory M. Rutter, Nikolai N. Klimov, David B. Newell, Irene G. Calizo, Angela R. Hight Walker, Nikolai B. Zhitenev, Joseph A. Stroscio
Graphene is a unique material displaying high-mobility transport in monolayer-thin films. However, its properties are strongly dependent on interactions with substrates, local charges and environment. Scanned probe microscopies can be used to locally probe the effects of these interactions on graphene charge carriers, which are directly exposed at the surface. We use scanning tunneling spectroscopy (STS) to obtain a microscopic picture of localization at a level not attainable in previous measurements and identify new signatures of localization and interaction in the STS spectra. In zero magnetic field, we detect weakly localized states in the tunneling spectra, originating from substrate induced disorder, which follow the energy variation of the Dirac-point as the graphene charge density is changed with a gate potential. Under quantum Hall conditions when the electronic states are condensed into well defined Landau levels (LL), the character of the localization changes dramatically; the twodimensional electron gas breaks into a network of interacting quantum dots formed at the potential hills and valleys of the disorder potential.