Abstract
We report capacitance measurements in top-gated graphene sheets as a function of charge carrier density. A measurement method using an LC-circuit provides high sensitivity to small capacitance changes and hence allows the observation of the quantum part of the capacitance. The extracted density of states has a finite value of 1×1017 m− 2 eV−1 in the vicinity of the Dirac point, which is in contrast to the theoretical prediction for ideal graphene. We attribute this discrepancy to fluctuations of the electrostatic potential with a typical amplitude of 100 meV in our device.
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