Surface plasmon excitation and non-zero induced surface current density

We study the general conditions for the surface plasmon excitation at the interface between two media with non-zero input electromagnetic fields. Using the boundary conditions for electromagnetic waves allowing for non-zero induced surface charge and surface current densities, we recover the same surface plasmon resonance condition for the cases of dielectric-metal interfaces, but with non-zero surface current densities and therefore discontinuous tangential components of the magnetic field across the boundary. This is in sharp contrast to the conventional understanding of the surface plasmon where the tangential components of both the electrical and magnetic fields are continuous across the boundary. The similarities and differences between the excited surface plasmon involving non-zero surface current densities and the traditional self-sustained surface plasmon are discussed and a united picture is provided.