Novel tunable terahertz graphene metamaterial with an ultrahigh group index over a broad bandwidth

We propose a grating-coupled graphene metamaterial structure at a terahertz band. An obvious tunable plasmon-induced transparency can be achieved by changing the graphene Fermi level, and there is a very high absorption peak in the spectrum. Thus, this structure can be used to realize a terahertz modulator or absorption device with two outstanding functions. Using phase changes, we have also studied the slow light effect, and we find that there is a broad ultrahigh-group-index band, and the maximum group index can reach 216. This research may open up new avenues for slow light devices. (C) 2018 The Japan Society of Applied Physics