Clustered impurities and carrier transport in supported graphene
  We investigate the effects of charged impurity distributions and carrier-carrier interactions on electronic transport in graphene on SiO$_2$ by employing a self-consistent coupled simulation of carrier transport and electrodynamics. We show that impurity clusters of characteristic width 40--50 nm generate electron--hole puddles of experimentally observed sizes. In the conductivity versus carrier density dependence, the residual conductivity and the linear-region slope are determined by the impurity distribution, and the measured slope can be used to estimate the impurity density in experiment. Furthermore, we show that the high-density sublinearity in the conductivity stems from carrier-carrier interactions. 
N. Sule, S. C. Hagness, and I. Knezevic
cond-mat.mes-hall