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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ at temperatures between 10 and 300 K. The pulses possess a usable bandwidth extending from ∼0.1 to 1.5 THz (3.3–50 ${\mathrm{cm}}^{\mathrm{-}1}$). 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 (λ(0)/λ(T)${)}^2$=1-(T/${\mathit{T}}_{\mathit{c}}$ ${)}^{\mathrm{\alpha }}$, where λ(0)=148 nm and α=2.