  We point out that plasmons in doped graphene simultaneously enable low-losses
and significant wave localization for frequencies below that of the optical
phonon branch $\hbar\omega_{Oph}\approx 0.2$ eV. Large plasmon losses occur in
the interband regime (via excitation of electron-hole pairs), which can be
pushed towards higher frequencies for higher doping values. For sufficiently
large dopings, there is a bandwidth of frequencies from $\omega_{Oph}$ up to
the interband threshold, where a plasmon decay channel via emission of an
optical phonon together with an electron-hole pair is nonegligible. The
calculation of losses is performed within the framework of a random-phase
approximation and number conserving relaxation-time approximation. The measured
DC relaxation-time serves as an input parameter characterizing collisions with
impurities, whereas the contribution from optical phonons is estimated from the
influence of the electron-phonon coupling on the optical conductivity. Optical
properties of plasmons in graphene are in many relevant aspects similar to
optical properties of surface plasmons propagating on dielectric-metal
interface, which have been drawing a lot of interest lately because of their
importance for nanophotonics. Therefore, the fact that plasmons in graphene
could have low losses for certain frequencies makes them potentially
interesting for nanophotonic applications.
