  Multiple compound surface plasmon-polariton (SPP) waves can be guided by a
structure consisting of a sufficiently thick layer of metal sandwiched between
a homogeneous isotropic dielectric (HID) material and a dielectric structurally
chiral material (SCM). The compound SPP waves are strongly bound to both
metal/dielectric interfaces when the thickness of the metal layer is comparable
to the skin depth but just to one of the two interfaces when the thickness is
much larger. The compound SPP waves differ in phase speed, attenuation rate,
and field profile, even though all are excitable at the same frequency. Some
compound SPP waves are not greatly affected by the choice of the direction of
propagation in the transverse plane but others are, depending on metal
thickness. For fixed metal thickness, the number of compound SPP waves depends
on the relative permittivity of the HID material, which can be useful for
sensing applications.
