Tunable plasmon-induced transparency terahertz metasurface with Ge₂Sb₂Te₅-controlled mode intercoupling

We presented an electrically-controlled scheme of tunable plasmon-induced transparency (PIT) terahertz metasurface by exploiting the phase change of Ge₂Sb₂Te₅ (GST). The PIT metasurface consists of a two-dimensional periodic array of hybrid unit cells with a split-ring resonator (SRR) and a cut wire (CW), which undergoes only a electro-resonance coupling mechanism sensitive to changes in surrounding dielectric parameters. The strong PIT effect is produced by the destructive interference between the electric quadrupole resonance of the SRR and the electric dipole resonance of the CW. Three kinds of GST-integrated configurations were analyzed to tune the PIT spectra, with GST strips integrated at the gap of SRR, on the top of CW, and both. When the phase transition of GST trips are electrically controlled from the amorphous to crystalline state, the intercoupling and dumping coefficients of hybrid unit cell can be effectively adjusted to affect the PIT response in frequency and amplitude. A temporal coupled-mode theory was employed to quantitatively discuss the variant coupling effect between the electric quadrupole and dipole resonance modes. Such scheme of GST-tuned PIT can be used to develop optical logic gate for terahertz communication.