Gate-Controlled Terahertz Modulation in Graphene-Integrated Bi ₂ Se ₃ Microstructure

Terahertz (THz) spectroscopy can characterize the collective oscillations of free particles in two-dimensional (2D) materials. The resonant response appearing in the transmitted THz spectra is relevant to the 2D plasmon mode. Here, we investigate the spectral extinction of the THz wave transmitted through the graphene-integrated Bi₂Se₃ microstructure, where the bias voltage applied to the gate electrode controls the device sheet conductance. Comparing the spectral response of the device with the EM wave simulation result, we observe a consistent spectral modulation as a function of the input particle density. The simulation result further characterizes the Bi₂Se₃ Dirac plasmon polariton (DPP) coupled to graphene. We find that the large graphene polarizability enables efficient control of the Bi₂Se₃ DPP mode up to 70% using a moderate gate voltage range of -1 to 1 V. Our result can be used to understand the interlayer long-range Coulomb interaction between Dirac materials.