Surface plasmon polariton is a coupled electromagnetic wave and material (electron) density wave. This efficient
coupling is the primary means of transforming light to a heavier particle which yields the desired "light slowing". The
dispersion curve of surface plasmonic waves exhibits both wave slowing (phase velocity) and light slowing (group
velocity). We detail the different avenues for light slowing and reversing (backward propagation) in a plasmonic
structure based on a dielectric gap between two metal plates. Light slowing and almost stopping can be achieved as well
as the more intriguing effect of backward propagation, accompanied by negative refraction. These effects in plasmonic
structures can be used for nano virtual cavities (mirrorless cavities) for ultralow volume sensing as well as generating
large local field enhancement.