  We propose Hybridizable Discontinuous Galerkin (HDG) methods for solving the
frequency-domain Maxwell's equations coupled to the Nonlocal Hydrodynamic Drude
(NHD) and Generalized Nonlocal Optical Response (GNOR) models, which are
employed to describe the optical properties of nano-plasmonic scatterers and
waveguides. Brief derivations for both the NHD model and the GNOR model are
presented. The formulations of the HDG method are given, in which we introduce
two hybrid variables living only on the skeleton of the mesh. The local field
solutions are expressed in terms of the hybrid variables in each element. Two
conservativity conditions are globally enforced to make the problem solvable
and to guarantee the continuity of the tangential component of the electric
field and the normal component of the current density. Numerical results show
that the proposed HDG methods converge at optimal rate. We benchmark our
implementation and demonstrate that the HDG method has the potential to solve
complex nanophotonic problems.
