Dirac cones reshaped by interaction effects in suspended graphene

Understand

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.