  We report precision measurements of the gradient of the Casimir force between
an Au-coated sphere and graphene sheet deposited on a silica plate. The
measurement data are compared with exact theory using the polarization tensor
found in the framework of the Dirac model including effects of the nonzero
chemical potential and energy gap of the graphene sample with no fitting
parameters. The very good agreement between experiment and theory demonstrates
the unusually big thermal effect at separations below 1 mum which has never
been observed for conventional 3D materials. Thus, it is confirmed
experimentally that for graphene the effective temperature is determined by the
Fermi velocity rather than by the speed of light.
