How close can one approach the Dirac point in graphene experimentally?

TL;DR

This study demonstrates that in high-mobility suspended graphene devices, the Dirac point can be approached within 1 meV, with minimal charge inhomogeneity and no insulating state observed down to 1 K, providing insights into graphene's intrinsic electronic properties.

Contribution

The paper provides an experimental method to approach the Dirac point in graphene with unprecedented precision, revealing intrinsic properties and setting limits on charge inhomogeneity and bandgap presence.

Findings

Charge inhomogeneity as low as 10^8 cm^-2

Dirac point approached within 1 meV

No insulating state observed down to 1 K

Abstract

The above question is frequently asked by theorists who are interested in graphene as a model system, especially in context of relativistic quantum physics. We offer an experimental answer by describing electron transport in suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with the onset of Landau quantization occurring in fields below 5 mT. The observed charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state with a few charge carriers per entire micron-scale device. Above liquid helium temperatures, the electronic properties of such devices are intrinsic, being governed by thermal excitations only. This yields that the Dirac point can be approached within 1 meV, a limit currently set by the remaining charge inhomogeneity. No sign of an insulating state is observed down to 1 K, which establishes the upper limit on a possible bandgap.