Engineering terahertz surface magnon-polaritons in hyperbolic antiferromagnets

Abstract

Magnetic crystals were recently studied as a route to hyperbolic dispersion and the effects associated with it. These studies, however, concentrated on bulk waves and frequencies where transmission is possible and where negative refraction occurs. Here, in contrast, we concentrate on geometries which sample regions of the dispersion relations where bulk propagation is not possible. This is done by controlling the orientation of the uniaxial anisotropy axis with respect to the surface of the crystal. Furthermore, we find that new magnetic surface polaritons exist in these regions, and we investigate the nature of these waves. In addition, significant tunability can be introduced by applying an external field perpendicular to the easy axes of a uniaxial antiferromagnet, creating a canted structure and generally shifting the frequencies to higher values. This externally applied field dramatically changes the nature of both surface and bulk polaritons, making them highly nonreciprocal.

Far-Infrared Reflection from Heterostructures Made of Ultrathin Ferromagnetic Layers

“…[18,55] A related phenomenon that is often seen in magnetic insulators in this frequency range is the existence of surface waves. [56][57][58] Although this nonreciprocity on reflection is related to surface effects, we found that true surface waves only appear in this composite material if the conductivity was made smaller (σ < 10 4 S·m −1 ) and if the composite was made 100 µm thick. Neither of these parameters are realistic for this specific study as we focus on iron (a metal) and because 100 µm corresponds to over 10,000 repeats of the ultrathin iron layers.…”

Electromagnetic Waves in Canted Magnets

“…By doing so, it is possible to open up gaps of non-propagating regions where surface polaritons can appear as shown in Fig. 15(f) [46]. As demonstrated recently, this rotation allows for the existence of surface waves even at zero external field which could be used as a way to enhance Goos-Hänchen shifts.…”

Oriented Asymmetric Wave Propagation and Refraction Bending in Hyperbolic Media

“…In magnets, however, the nature of the off-diagonal components is distinctively different, in which case additional nonreciprocal effects, associated with the particular form of the permeability tensor, may further modify the behavior. [33][34][35] We believe that our findings on the oriented asymmetric transmission can also be used as a potential avenue for applications on optical devices such as direction dependent electromagnetic filters.…”