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 analytical formalism homogenize anisotropic crystals long wavelength limit. It is found with suitable glide-rotation symmetry can have a giant axion-type response, several orders of magnitude larger than natural materials. The response may interesting applications optics, for example, electromagnetic isolation, and addition enable forms light-wave interactions.