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 YBa2Cu3O7−δ at temperatures between 10 K and 300 K. The pulses possess a usable bandwidth extending from ∼0.1 – 1.5 THz (3.3 cm – 50 cm). 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 it agrees well with a functional form (λ(0)/λ(T )) = 1 − (T/Tc), where λ(0) = 148 nm, and α = 2. (a) also at Odense Universitet, DK-5230 Odense M, Denmark (b) permanent address: Hughes Research Laboratories, Malibu, CA, USA. (c) permanent address: P. N. Lebedev Physics Institute, Moscow, Russia.