Dual-polarization and Fermi-level tunable plasmons induce transparency terahertz metasurface for high-performance sensing applications

Prior research has established that black phosphorus (BP) enhances sensor sensitivity and facilitates the plasmon-induced transparency (PIT) effect. However, BP-based PIT sensors typically suffer from poor tunability and low figures of merit (FOM). To overcome these limitations, this paper proposes a highly sensitive and tunable PIT terahertz metasurface based on a graphene-black phosphorus (GP-BP) hybrid structure. The metasurface comprises two identical patterned layers, each consisting of a cross-shaped resonator coupled with a closed rectangular ring resonator. Using finite-difference time-domain (FDTD) simulations, we demonstrate that the PIT transmission window arises from the coupling between the bright modes of these structures. By varying the ambient refractive index from 1.0 to 1.7, the metasurface achieves a maximum sensitivity of 4.22 THz/RIU and an FOM of 7.495 in the terahertz band. Furthermore, increasing electron doping in BP induces a significant red shift in the sensor's transmission spectrum. The PIT resonance frequency can also be dynamically modulated by adjusting the terahertz wave polarization and the graphene Fermi level. Additionally, the transmission spectrum exhibits minimal sensitivity to variations in the incident angle. These characteristics highlight the proposed sensor's significant potential for terahertz biosensing applications.