Electrodynamics of high-temperature superconductors investigated with coherent terahertz pulse spectroscopy

Recent experimental investigations of the electrodynamic properties of high-temperature superconductors in the terahertz regime are reviewed. Transmission measurements were performed with use of coherent terahertz pulse spectroscopy, which enables us to extract directly the frequency-dependent complex conductivity σ1+iσ2. Investigations of both pure YBa2Cu3O7-δ and the related alloy Y1-xPrxBa2Cu3O7-δ were conducted over a temperature range from 300 K down to 10 K. From these measurements we can extract the temperature-dependent London penetration depth λL(T), the plasma frequency ωp, and the quasi-particle scattering time τ(T). The implications of our measurements for contemporary theories of high-Tc superconductivity are discussed.