Synthetic Axion Response with Space-Time Crystals

Here, we show that space-time modulations provide an exciting route to realize complex nonreciprocal couplings, and, in particular, the elusive axion response. We develop an analytical formalism to homog-enize anisotropic space-time crystals in the long wavelength limit. It is found that space-time crystals with suitable glide-rotation symmetry can have a giant axion-type response, several orders of magnitude larger than in natural materials. The nonreciprocal axion response may have interesting applications in optics, for example, in electromagnetic isolation, and in addition may enable exciting forms of light-wave interactions.

Automated summary

We demonstrate that space-time modulations can be used to achieve complex nonreciprocal couplings, particularly the elusive axion response. We develop an analytical formalism for homogenizing anisotropic space-time crystals in the long wavelength limit and find that space-time crystals with appropriate glide-rotation symmetry can exhibit a giant axion-type response, several orders of magnitude larger than in natural materials. The nonreciprocal axion response has interesting potential applications in optics, such as electromagnetic isolation, and can enable exciting forms of light-wave interactions.