We propose a novel terahertz metamaterial structure based on patterned monolayer graphene. This structure produces an evident dual plasmon-induced transparency (PIT) phenomenon due to destructive interference between bright and dark modes. Since the Fermi level of graphene can be adjusted by an external bias voltage, the PIT phenomenon can be tuned by adjusting the voltage. Then the coupled-mode theory (CMT) is introduced to explore the internal mechanism of the PIT. After that, we investigate the variation of absorption rate at different graphene carrier mobilities, and it shows that the absorption rate of this structure can reach 50%, which is a guideline for the realization of graphene terahertz absorption devices. In addition, through the study of the slow-light performance for this structure, it is found that its group index is as high as 928, which provides a specific theoretical basis for the study of graphene slow-light devices.
Dual plasmon-induced transparency (PIT) is realized in the simple multilayer structure consisting of three graphene layers. The coupling mechanism between the three modes of three graphene layers is analyzed in detail. It is revealed that the dual PIT originates from the resonators with different quality factors by analog electromagnetic induction transparency (EIT) analysis and coupling mode theory (CMT). After that, the dual PIT expresses dynamic tunability by tuning applied bias voltage, which indicates that the structure proposed has potential application in modulators. Moreover, dual PIT in our proposed structure can be applied in the biosensor, and significantly improved sensitivity and figure of merit (FOM) as high as 16,660 nm/RIU and 31.0924 have been obtained, which has obvious enhancement compared with many reported sensors. This work can deepen our understanding of PIT and pave the way to the design of graphene dual PIT sensors.
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