Transport scattering time probed through rf admittance of a graphene capacitor

(Received 4 November 2010; published 17 March 2011)We have investigated electron dynamics in top gated graphene by measuring the gate admittance of a diffusivegraphene capacitor in a broad frequency range as a function of carrier density. The density of states, conductivity,and diffusion constant are deduced from the low-frequency gate capacitance, its charging time, and their ratio.The admittance evolves from an rc-like to a skin-effect response at GHz frequency with a crossover given bythe Thouless energy. The scattering time is found to be independent of energy in the 0- to 200-meV investigatedrange at room temperature. This is consistent with a random mass model for Dirac fermions.DOI: 10.1103/PhysRevB.83.125408 PACS number(s): 72