Outstanding slow-light effect for graphene metasurface in terahertz

•The group index can reach up to 2510 for slow-light effect.•A convenient modulation for PIT can be realized through Fermi level and carrier mobility, and the theoretical results are in well agreement with the numerical results. So as to realize good slow-light effects in a simple graphene-based nano-structure, a n-shaped graphene metasurface is proposed in this paper. Through the detailed studies, plasmon induced transparency (PIT) can be observed in the proposed metasurface, and the bright-dark mode is used to explain the physical mechanism of this phenomenon. Especially, a convenient modulation for PIT can be realized through Fermi level and carrier mobility. In addition, a developed coupled mode theory (CMT) is established for demonstrating the optical responses of the n-shaped graphene metasurface, and the theoretical results are in well agreement with the numerical results. At last, an excellent slow-light effect with ultra-high group index of 2510 can be achieved in the proposed simple graphene-based metasurface. The outstanding performance of slow-light effect may play important roles for designing the plasmonic slow-light devices in terahertz.