Plasmon-induced transparency in twisted Fano terahertz metamaterials

We investigate the effect of tweaking the quality (Q) factor of split ring resonators in a coupled state, giving rise to plasmonic induced transparency (PIT) which has two distinct, individually engineered resonance modes. The Q factor and the amplitude of each resonance are tuned by twisting them mutually in the unit cell consisting of a subradiant and a superradiant resonator. We experimentally observe that introducing a gradual twist in the three U-shape resonators has a dramatic impact on the PIT spectral response, leading to the disappearance of the transparency peak beyond a certain critical degree of twist. This mainly happens due to the change in the in-plane coupling between the resonators as well the variation in coupling of the twisted resonators with the incident electric field. Further investigation based on the Fano model provides good agreement with the experimental results. The scheme presented here for controlling the Q factor of each resonator in the coupled regime is a unique way to tune the PIT response in terahertz metamaterials and can be easily scaled across the entire electromagnetic spectrum. (C) 2011 Optical Society of America