Abstract:
This talk will be divided into two parts. In the first part, I will show the effect of topological defects on the transport properties of a narrow graphene ribbon. The results show that the conductance vanishes at several discrete Fermi energies where the system develops loop orbital electric currents with certain chirality. The chirality depends on the direction of the applied bias voltage and the sign of the local curvature created by the topological defects. In the second part, electronic localization properties in disordered graphene with strong long-range impurities will be demonstrated. We find that states near the Dirac points are localized for sufficiently strong disorder (therefore inevitable intervalley scattering) and the transition between the localized and delocalized states is of Kosterlitz-Thouless type. Our results show that the transition originates from bounding and unbounding of local current vortices.