  Spatial separation of electrons and holes in graphene gives rise to existence
of plasmon waves confined to the boundary region. Theory of such guided plasmon
modes within hydrodynamics of electron-hole liquid is developed. For plasmon
wavelengths smaller than the size of charged domains plasmon dispersion is
found to be \omega ~ q^(1/4). Frequency, velocity and direction of propagation
of guided plasmon modes can be easily controlled by external electric field. In
the presence of magnetic field spectrum of additional gapless magnetoplasmon
excitations is obtained. Our findings indicate that graphene is a promising
material for nanoplasmonics.
