Giant Linear Nonreciprocity, Zero Reflection, and Zero Band Gap in Equilibrated Space-Time-Varying Media

This study provides a rigorous analytical solution for electromagnetic wave propagation within and scattered from a slab of engineered material possessing general space-time modulation. In contrast to the weak photonic transitions in conventional space-time permittivity-modulated media, an equilibrated space-time-varying medium provides energy and momentum for strong, unidirectional photonic transitions from the excited mode to its four adjacent modes. Equilibrium in the electric and magnetic properties of such a medium yields various interesting phenomena, pointing the way to optimal insulators, nonreciprocal integrated systems, and subharmonic frequency generators.