  Plasmon induced transparency (PIT) effect in a terahertz graphene
metamaterial is numerically and theoretically analyzed. The proposed
metamaterial comprises of a pair of graphene split ring resonators placed
alternately on both sides of a graphene strip of nanometer scale. The PIT
effect in the graphene metamaterial is studied for different vertical and
horizontal configurations. Our results reveal that there is no PIT effect in
the graphene metamaterial when the centers of both the split ring resonators
and the graphene strip are collinear to each other. This is a noteworthy
feature, as the PIT effect does not vanish for similar configuration in a
metal-based metamaterial structure. We have further shown that the PIT effect
can be tuned by varying the Fermi energy of graphene layer. A theoretical model
using the three level plasmonic system is established in order to validate the
numerical results. Our studies could be significant in designing graphene based
frequency agile ultra-thin devices for terahertz applications.
