Electromagnetically induced transparency and absorption in metamaterials: self-consistent theory and experiments*

There has recently been a lot of interest in slow-light metamaterials that provide transparency windows combining low absorption with high group delay. This phenomenon was explained by a two-resonator model involving a radiative resonator that couples directly to the incident field and a dark resonator that can only be excited through coupling with the radiative resonator. However, in our most recent experiments on wire/SRR metamaterials, we have observed a much richer behavior---we measure not only transparency windows with incisions in the absorption spectrum (electromagnetically induced transparency), but also narrow spectral features with absorption larger than the background absorption of the radiative element (electromagnetically induced absorption). We have developed a model in which the coupling of the electromagnetic waves to the radiative resonator is treated explicitly. An important attribute of this model, which is in excellent agreement with our experiments and full-wave simulations, is the self-consistent treatment of the spectral broadening of the bright resonator originating from the dipole radiation as opposed to the bare linewidth due to dissipation. We discuss the conditions under which electromagnetically induced transparency/absorption can be observed.