Scattering of electrons in graphene by clusters of impurities

It is shown that formation of clusters of charged impurities on graphene can suppress their contribution to the resistivity by a factor of the order of the number of impurities per cluster. The dependence of conductivity on carrier concentration remains linear. In the regime where the cluster size is large in comparison to the Fermi wavelength, the scattering cross section shows sharp resonances as a function of incident angle and electron wave vector. In this regime, due to the dominant contribution of scattering by small angles, the transport cross section can be much smaller than the total one, which may be checked experimentally by comparison of the Dingle temperature to the electron mean-free path.