Topological Edge States in Tunable Bulk Gyrotropic Media Composed of Magnetized Low-Temperature Plasma Discharges

Gyrotropic media exhibit several interesting electromagnetic properties, including topologically protected edge states that allow for one-way, back-scattering immune propagation of interfacial electromagnetic waves. Unfortunately, such media are challenging to create for engineering applications since the use of ferromagnetic (gyrotropic) materials limit the range of operating frequencies and a homogeneous bulk magnetized plasma is difficult to produce in practice. In this presentation, we show how a tunable bulk gyrotropic medium can be constructed using magnetized low-temperature plasma discharge tubes in a two-dimensional photonic crystal configuration. Experiments are performed for microwave frequencies in the range of 2-10 GHz. Band structures for both the magnetized and unmagnetized case are compared and confirmed via experimental transmission measurements and numerical simulations of the actual device. Evidence for topologically-protected edge states from local field measurements is presented.