Active Modulation of Electromagnetically Induced Transparency in Terahertz Spiral Metamaterial

We propose and demonstrate terahertz (THz) spiral metamaterial (TSM) with square (TSM-1) and hexagonal (TSM-2) meta-atom arrangements. By applying a directcurrent (dc) bias voltage on TSM-1, it exhibits the active modulation of electromagnetically induced transparency (EIT) with a tuning range of 0.12 THz. Furthermore, to facilitate the flexibility and applicability of TSM, the unit cell of TSM with different $\theta$ is superimposed to form TSM-2. TSM-2 possesses the combination of electromagnetic behaviors generated by each unit cell of TSM with different $\theta$. This study provides a design of complementary THz metamaterial to have EIT analog characteristics, which shows single-digital and multi-digital signals for the programmable metamaterial application.