Terahertz spectroscopy of high temperature superconductors and their photonic applications

Development of the ultrashort pulse lasers made it possible to realize the terahertz (THz) generation and detection in a broad frequency range between 0.1 and 30 THz. Extensive studies of the superconducting materials have been performed from basic sciences to the photonic applications because the THz frequencies span the gap in the electromagnetic spectrum between the electronic and the photonic technologies. Especially, the ultrashort pulses allow us to monitor the non-equilibrium dynamics of the superconductors and develop the ultrafast switching. Starting from a brief overview of the cuprate superconductor, we review the basic optical properties and photonic applications of the superconductors in a wide range of THz frequencies. It should be noted that numerous equilibrium and non-equilibrium THz spectroscopic measurements of the high temperature superconductors demonstrated the existence of the superconducting gap and its recovery dynamics and also terahertz electromagnetic wave modulation combined with the concept of metamaterials. These superconducting metamaterials will pave the way for better understanding of the new material properties and giving new ideas in application aspects