Impact of graphene quantum capacitance on transport spectroscopy

TL;DR

This paper experimentally shows how graphene quantum capacitance influences transport spectroscopy by interacting with charge reservoirs, affecting Landau level structure and quantum Hall states in epitaxial graphene.

Contribution

It reveals the significant impact of quantum capacitance on transport measurements and Landau level observation in graphene with interface charge reservoirs.

Findings

Quantum capacitance causes parabolic gate voltage dependence of carrier density.

Landau level structure is clearly observed in resistance measurements.

Zero-energy Landau level plays a key role in quantum Hall state development.

Abstract

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.