A terahertz graphene metamaterial based on polarization-insensitive plasmon-induced transparency for sensing application

A graphene metamaterial based on polarization-insensitive plasmon-induced transparency (PIT) in the terahertz region is theoretically presented. The graphene metamaterial comprises a cross-shaped and four other identical graphene strips, and a distinct narrow PIT window resulted from the bright-bright coupling is obtained when the electric field is along both x and y polarization directions. Surface current distributions and the two-particle model are used to elucidate the physical mechanism of the PIT effect, where the theoretical results of the two-particle model agree well with the simulation transmission spectra. In addition, the amplitude and resonant frequency of the PIT window can be modulated by tuning the Fermi level of graphene without varying the geometric parameters. Moreover, a high group delay of 1.545 ps can be achieved at the fixed Fermi level of 1 eV. As a function of the terahertz (THz) sensor, the PIT structure exhibits excellent sensing performances with the maximum sensitivity of 0.8 THz per refractive index unit (RIU) and figure of merit (FOM) of 17.28 RIU−1. Therefore, these features indicate that this work paves the way for designing polarization-insensitive and high-performance PIT sensors in the THz region.