Surface plasmon dynamics in an isolated metallic nanoslit.

We present an analytical study of the dynamic interplay among surface plasmon polarization charges, electromagnetic fields, and energy flow in the metal/dielectric interface and metal nanoslit structure. Particular attention is given to the regime where the energy flow in the metal side is significant compared to that in the dielectric side. The study reveals that a vortex-like circulation of energy is an intrinsic feature of surface plasmon propagation supported by a metal/dielectric interface, and, in general, a vortex can form when the permittivity and permeability values of the materials involved satisfy the following condition: {(epsilon(m)/epsilon(d)) < -1 and (mu(m)/mu(d)) > -1} or {(epsilon(m)/epsilon(d)) > -1 and (mu(m)/mu(d)) < -1}.