Surface waves (SWs) are localized waves that travel along the planar interface between two different mediums
when certain dispersion relations are satisfied. If both mediums have purely dielectric constitutive properties,
the characteristics of SW propagation are determined by the anisotropy of both mediums. Surface waves are then
called Dyakonov SWs (DSWs), after Dyakonov who theoretically established the possibility of SW propagation
at the planar interface of an isotropic dielectric and a positive uniaxial dielectric. Since then, DSW propagation
guided by interfaces between a variety of dielectrics has been studied. With an isotropic dielectric on one
side, the dielectric on the other side of the interface can be not only positive uniaxial but also biaxial. DSW
propagation can also occur along an interface between two uniaxial or biaxial dielectrics that are twisted about
a common axis with respect to each other but are otherwise identical.
Recently, DSW propagation has been studied taking (i) uniaxial dielectrics such as calomel and dioptase
crystals; (ii) biaxial dielectrics such as hemimorphite, crocoite, tellurite, witherite, and cerussite; and (iii)
electro-optic materials such as potassium niobate. With materials that are significantly anisotropic, the angular
regime of directions for DSW propagation turns out to be narrow. In the case of naturally occurring crystals,
one has to accept the narrow angular existence domain (AED). However, exploiting the Pockels effect not only
facilitates dynamic electrical control of DSW propagation, but also widens the AED for DSW propagation.