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 YBa₂{Cu}₃O_7-δ at temperatures between 10 and 300 K. The pulses possess a usable bandwidth extending from {~}0.1 to 1.5 THz (3.3--50 cm^-1). Below Tc 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/Tc{)}^{{{α}}}$, where {λ}(0)=148 nm and {α}=2.