Multiple surface-plasmon-polariton waves guided jointly by a metal and a   hyperbolic, dielectric, structurally chiral material
  The planar interface of a metal and a hyperbolic, dielectric, structurally chiral material can support the propagation of none, one, or multiple surface-plasmon-polariton (SPP) waves, at a specified frequency and along a specified direction in the interface plane. When multiple SPP waves can exist, they differ in phase speed, propagation length, degree of localization to the interface, and spatial profiles of the associated electromagnetic fields. 
Akhlesh Lakhtakia, Muhammad Faryad
physics.optics