Measurement of Scattering Rate and Minimum Conductivity in Graphene

The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of $1--20\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{sec}$. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from $2--15\ifmmode\times\else\texttimes\fi{}{10}^{11}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. In the low carrier density limit, the conductivity exhibits values in the range of $2--12{e}^{2}/h$, which can be related to the residual density induced by the inhomogeneous charge…