  We investigate the plasmons in bilayer black phosphorus (BP) with bias-driven
formation of Dirac cones, by developing an effective two-band Hamiltonian that
captures this electronic transition with great accuracy. We show that the
appearance of the Dirac cones lead to additional linearly dispersing acoustic
plasmon mode, in conjunction to the conventional plasmon. In addition, the
change in the Fermi surface topology from a disc to ring or dual pockets also
modifies the dielectric loss.
