  Using a novel structure, consisting of two, independently contacted graphene
single layers separated by an ultra-thin dielectric, we experimentally measure
the Coulomb drag of massless fermions in graphene. At temperatures higher than
50 K, the Coulomb drag follows a temperature and carrier density dependence
consistent with the Fermi liquid regime. As the temperature is reduced, the
Coulomb drag exhibits giant fluctuations with an increasing amplitude, thanks
to the interplay between coherent transport in the graphene layer and
interaction between the two layers.
