  We study the electromagnetic properties of a metamaterial consisting of
polarizable (nano)particles and a single graphene sheet placed at the interface
between two dielectrics. We show that the particle's polarizability is
renormalized because of the electromagnetic coupling to surface plasmons
supported by graphene, which results in a dispersive behavior, different for
the polarizability components corresponding to the induced dipole moment,
parallel and perpendicular to the graphene sheet. In particular, this effect is
predicted to take place for a metallic particle whose bare polarizability in
the terahertz (THz) region is practically equal to the cube of its radius
(times $4\pi \varepsilon_0$). This opens the possibility to excite surface
plasmons in graphene and enhance its absorption in the THz range by simply
using a monolayer of metallic particles randomly deposited on top of it, as we
show by explicit calculations.
