Active control of graphene plasmon-induced transparency (GPIT) metamaterial structures, composed of periodically patterned monopolar graphene and dipolar graphene, are presented and investigated. Numerical results reveal that the resonant frequency of GPIT structures can be dynamically tuned by varying the Fermi level of the T-shape graphene strip through controlling the voltage of the electrostatic gating. Coupled Lorentz oscillator model is applied to explore the physical mechanism of the frequency tunable GPIT. Furthermore, the group index of terahertz light can be controlled to exceed 350 in the THz region. It is also found that the interaction strength between the dipolar graphene and the monopolar graphene can be tuned by changing the distance between the radiative mode and the dark mode as well as the degree of the symmetry breaking. These tunable features of the GPIT devices are significant and may offer new opportunity to design active devices in the THz region, such as ultrasensitive sensors, slow light devices, and spectral filters.
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