Electromagnetic Wave Attenuation by Superconducting Fluctuations in a Thin, Granular Aluminum Film.

摘要

The imaginary part of the fluctuating electrical conductivity near the superconducting transition temperature of a thin Al film is measured using a unique technique that was developed for measuring the ultrasonic attenuation of very thin films using surface waves. A 300 A aluminum film is deposited onto a lithium niobate substrate between two sets of interdigital electrodes. In this case the electrodes are used as electromagnetic antennas for transmitting and receiving electromagnetic waves. A minimum in the attenuation of the transmitted waves is observed at the superconducting transition temperature and a theory is presented which ascribes this minimum to a minimum of the imaginary part of the complex conductivity produced by superconducting fluctuations in a thin Al film. The particular geometry of the lithium niobate enhances the magnitude of the effect since at the frequencies of these measurements the lithium niobium due to its high dielectric constant acts like a resonant microwave cavity.