Electrodynamics ofYBa2Cu3O7films deduced from submillimeter synchrotron-radiation transmittance measurements

Transmission measurements on ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ films in the spectral range 25 to 100 ${\mathrm{cm}}^{\mathrm{-}1}$ have been performed using synchrotron radiation. In the normal state, the classical Drude conductivity function successfully explains the rise in transmission with frequency. The spectra below ${\mathit{T}}_{\mathit{c}}$ show a strong supercurrent screening of the infrared field. A temperature-dependent penetration depth is calculated from the transmission spectra using the local-limit-response kernel and a quasiparticle conductivity rising as (T/${\mathit{T}}_{\mathit{c}}$ ${)}^4$. Depending on the film quality, the zero-temperature penetration depth varies from 234 to 340 nm.