Impurity charge compensation in graphene and its effect on charge transport near the Dirac point

Charge transport using ferroelectric (FE) gating was investigated in graphene in the temperature range 300K < T < 350K near the Dirac point (DP). Upon increasing the temperature we observed that the conductivity (s) near the DP switched from a positive to a negative temperature gradient. The switch to a negative temperature gradient moved to higher temperatures and weakened upon moving away from the DP. FE polarization induced impurity charge compensation, together with a temperature dependent graphene-impurity charge separation was responsible for the non-monotonicity in s(T). A self-consistent theory for graphene transport with impurity charge scattering, and phonon scattering was used to analyze the results. Non-monotonic charge transport was also observed in the temperature dependence of the residual conductivity (σ_r). Theoretical analysis of both σ and σ_r revealed a temperature independent contribution of  1.16e²/h that was probably inherent to pristine graphene.