Kinetic inductance and penetration depth of thin superconducting films measured by THz-pulse spectroscopy.

We measure the transmission of THz pulses through thin films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ at temperatures between 10 and 300 K. The pulses possess a usable bandwidth extending from \ensuremath{\sim}0.1 to 1.5 THz (3.3\char21{}50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). Below ${\mathit{T}}_{\mathit{c}}$ we observe pulse reshaping caused by the kinetic inductance of the superconducting charge carriers. From transmission data, we extract values of the London penetration depth, as a function of temperature, and find that they agree well with a functional form (\ensuremath{\lambda}(0)/\ensuremath{\lambda}(T)${)}^{2}$=1-(T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{\alpha}}}$, where \ensuremath{\lambda}(0)=148 nm and \ensuremath{\alpha}=2.