Role of asymmetric environment on the dark mode excitation in metamaterial analogue of electromagnetically-induced transparency.

An otherwise dark magnetic dipole resonance in a split-ring resonator can be excited electrically with a Fano-type profile once the symmetric environment for this resonator is broken with respect to the polarized electric-field direction of incident waves. When this asymmetrically induced narrow resonance coincides with a broad dipolar resonance at an identical frequency regime, the metamaterial analogue of electromagnetically-induced transparency (EIT) window can be formed. We demonstrate that this environmental-asymmetry condition can be introduced dielectrically as well as plasmonically, either resonantly or nonresonantly, which indicates the plasmon coupling between different resonant modes is not responsible for the dark mode excitation. Thus, this result should contribute to the physical understanding on dark-mode excitation pathway for EIT-like phenomenon in plasmonic metamaterials.