Dirac cones reshaped by interaction effects in suspended graphene

TL;DR

This study measures the cyclotron mass in suspended graphene, revealing that electron-electron interactions significantly modify the Dirac spectrum and increase the Fermi velocity at low carrier concentrations, challenging the single-particle model.

Contribution

It provides experimental evidence of interaction-induced renormalization of the Dirac cones in graphene, showing a substantial increase in Fermi velocity at low densities.

Findings

Fermi velocity reaches ~3x10^6 m/s at low carrier density

Electron-electron interactions cause nonlinear spectral behavior

Upper limit of ~0.1 meV on possible energy gap in graphene

Abstract

We report measurements of the cyclotron mass in graphene for carrier concentrations n varying over three orders of magnitude. In contrast to the single-particle picture, the real spectrum of graphene is profoundly nonlinear so that the Fermi velocity describing the spectral slope reaches ~3x10^6 m/s at n <10^10 cm^-2, three times the value commonly used for graphene. The observed changes are attributed to electron-electron interaction that renormalizes the Dirac spectrum because of weak screening. Our experiments also put an upper limit of ~0.1 meV on the possible gap in graphene.