  We study the mid-infrared plasmonic response in Bernal-stacked bilayer
graphene. Unlike its monolayer counterpart, bilayer graphene accommodates
optically active phonon modes and a resonant interband transition at infrared
frequencies. They strongly modifies the plasmonic properties of bilayer
graphene, leading to Fano-type resonances, giant plasmonic enhancement of
infrared phonon absorption, narrow window of optical transparency, and a new
plasmonic mode at higher energy than the classical plasmon.
