  Singular graphene metasurfaces, conductivity gratings realized by
periodically suppressing the local doping level of a graphene sheet, have
recently been proposed to efficiently harvest THz light and couple it to
surface plasmons over broad absorption bands, achieving remarkably high field
enhancement. However, the large momentum wavevectors thus attained are
sensitive to the nonlocal behaviour of the underlying electron liquid. Here, we
extend the theory of singular graphene metasurfaces to account for the full
nonlocal optical response of graphene and discuss the resulting impact on the
plasmon resonance spectrum. Finally, we propose a simple local analogue model
that is able to reproduce the effect of nonlocality in local-response
calculations by introducing a constant conductivity offset, which could prove a
valuable tool in the modelling of more complex experimental graphene-based
platforms.
