We demonstrate experimentally that graphene quantum capacitance $C_{ \mathrm{ q}}$ can have a strong impact on transport spectroscopy through the interplay with nearby charge reservoirs. The effect is elucidated in a field-effect-gated epitaxial graphene device, in which interface states serve as charge reservoirs. The Fermi-level dependence of $C_{ \mathrm{ q}}$ is manifested as an unusual parabolic gate voltage ($V_{ \mathrm{ g}}$) dependence of the carrier density, centered on the Dirac point. Consequently, in high magnetic fields $B$, the spectroscopy of longitudinal resistance ($R_{ xx}$) vs. $V_{ \mathrm{ g}}$ represents the structure of the unequally spaced relativistic graphene Landau levels (LLs). $R_{ xx}$ mapping vs. $V_{ \mathrm{ g}}$ and $B$ thus reveals the vital role of the zero-energy LL on the development of the anomalously wide $\nu=2$ quantum Hall state.
Categories: cond-mat.mes-hall cond-mat.dis-nn cond-mat.mtrl-sci cond-mat.other