  Recent experiments have shown that spatial dispersion may have a conspicuous
impact on the response of plasmonic structures. This suggests that in some
cases the Drude model should be replaced by more advanced descriptions that
take spatial dispersion into account, like the hydrodynamic model. Here we show
that nonlocality in the metallic response affects surface plasmons propagating
at the interface between a metal and a dielectric with high permittivity. As a
direct consequence, any nanoparticle with a radius larger than 20 nm can be
expected to be sensitive to spatial dispersion whatever its size. The same
behavior is expected for a simple metallic grating allowing the excitation of
surface plasmons, just as in Wood's famous experiments. Importantly, our work
suggests that for any plasmonic structure in a high permittivity dielectric,
nonlocality should be taken into account.
