  Dragging of light by moving dielectrics was predicted by Fresnel and verified
by Fizeau's celebrated experiments with flowing water. This momentous discovery
is among the experimental cornerstones of Einstein's special relativity and is
well understood in the context of relativistic kinematics. In contrast,
experiments on dragging photons by an electron flow in solids are riddled with
inconsistencies and so far eluded agreement with the theory. Here we report on
the electron flow dragging surface plasmon polaritons (SPPs): hybrid
quasiparticles of infrared photons and electrons in graphene. The drag is
visualized directly through infrared nano-imaging of propagating plasmonic
waves in the presence of a high-density current. The polaritons in graphene
shorten their wavelength when launched against the drifting carriers. Unlike
the Fizeau effect for light, the SPP drag by electrical currents defies the
simple kinematics interpretation and is linked to the nonlinear electrodynamics
of the Dirac electrons in graphene. The observed plasmonic Fizeau drag enables
breaking of time-reversal symmetry and reciprocity at infrared frequencies
without resorting to magnetic fields or chiral optical pumping.
