THz transmission through superconducting periodic structures (invited talk)

We study THz transmission through two kinds of periodic structures, metamaterial and the array of subwavelength periodic holes, made from the superconducting (SC) NbN thin films. Due to the low loss of superconducting films, we got very high unloaded quality factor of THz metmaterial at 8 K. A large tuning range is displayed when the temperature is just below the superconducting transition temperature. Based on the SC THz MM, we designed and fabricated planar terahertz (THz) MMs to mimic electromagnetically induced transparency (EIT) system. High transmittance and large delay-bandwidth product at transparency window is demonstrated. We also report the extraordinary THz transmission through superconducting subwavelength hole array. As temperature drops below superconducting transition temperature, the transmission spectra experience distinct changes. The extraordinary transmission is greatly enhanced in superconducting state due to the enhancement of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs).