Transport scattering time probed through rf admittance of a graphene capacitor

TL;DR

This study probes electron dynamics in graphene by measuring its admittance across frequencies, revealing a frequency-dependent transition and a constant scattering time, supporting a random mass model for Dirac Fermions.

Contribution

It introduces a method to extract scattering time and other electronic properties of graphene from admittance measurements over a broad frequency range.

Findings

Admittance transitions from RC-like to skin-effect at GHz frequencies.

Scattering time remains energy-independent in the 0-200 meV range.

Results support a random mass model for Dirac Fermions.

Abstract

We have investigated electron dynamics in top gated graphene by measuring the gate admittance of a diffusive graphene 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 by the Thouless energy. The scattering time is found to be independent of energy in the 0 - 200 meV investigated range at room temperature. This is consistent with a random mass model for Dirac Fermions.