  Gapless spectrum of graphene allows easy spatial separation of electrons and
holes with an external in-plane electric field. Guided collective plasmon modes
can propagate along the separation line, whose amplitude decays with the
distance to it. Their spectrum and direction of propagation can be controlled
with the strength and direction of in-plane electric field. In case of a
bilayer graphene additional control is possible by the perpendicular electric
field that opens a gap in the band spectrum of electrons. We investigate guided
plasmon spectra in bilayer p-n junctions using hydrodynamics of charged
electron liquid.
