Nonreciprocal Dyakonov-wave propagation supported by topological insulators

The propagation of Dyakonov waves guided by the planar interface of a columnar thin film and a topological insulator was investigated by numerically solving the associated canonical boundary-value problem. The topological insulator was modeled as an isotropic dielectric material endowed with a nonzero surface admittance. The propagation directions for the Dyakonov waves, as well as the decay constants and phase speeds of the waves, were significantly modulated by varying the magnitude of the surface admittance. Most significantly, a Dyakonov wave propagating along the direction of a vector u_ has a different phase speed and different decay constants as compared with the Dyakonov wave which propagates along the direction of - u_. This nonreciprocity, with respect to interchanging the direction of Dyakonov-wave propagation, is not exhibited when the topological insulator is replaced by an isotropic dielectric material of the same refractive index but with a nonzero surface conductivity instead of a surface admittance.