Probing diffusion in a graphene quantum capacitor at high frequency
Résumé
High-frequency properties of a long graphene capacitor have been measured and used to investigate electronic diffusion at room temperature. A quantum capacitance dip is observed at charge neutrality in quantitative agreement with theory except at very low carrier density where the effect of impurities dominates. The conductivity is deduced from the charge relaxation resistance. It follows the quantum capacitance dependence in gate voltage indicating a density-independent diffusion constant. This behavior of top-gated graphene contrasts with the low-temperature linear density dependence reported for long range charge impurity scattering. These results are also useful for the high frequency dynamics of top gated graphene transistors.