Symmetries and nonreciprocity: a light wave's perspective

Symmetries of crystals often give them fascinating and useful physical properties. It is especially true in the optical domain, where breaking or introducing symmetries can result in new qualitative phenomena. We will examine the effect of broken time reversal and spatial inversion symmetries in a medium on the propagation of light and find nonreciprocal absorption and refractive index in such situations. We will also see how such nonreciprocity can be enhanced in resonance with spin transitions and by artificial chiral structures.