  We demonstrate that plasmons in graphene can be manipulated using a DC
current. A source-drain current lifts the forward/backward degeneracy of the
plasmons, creating two modes with different propagation properties parallel and
antiparallel to the current. We show that the propagation length of the plasmon
propagating parallel to the drift current is enhanced, while the propagation
length for the antiparallel plasmon is suppressed. We also investigate the
scattering of light off graphene due to the plasmons in a periodic dielectric
environment and we find that the plasmon resonance separates in two peaks
corresponding to the forward and backward plasmon modes. The narrower linewidth
of the forward propagating plasmon may be of interest for refractive index
sensing and the DC current control could be used for the modulation of
mid-infrared electromagnetic radiation.
