High-Frequency Behavior of "Ideal" Superconducting Point Contacts

Abstract

We have studied niobium point contacts which are very consistent and reproducible from junction to junction, in both their dc and high-frequency behavior. We find a strong correlation between the sharpness of the gap structure and the ac Josephson effect, and we present the first quantitative measurements of the far-infrared frequency dependence of the Josephson effect above the energy gap. The measured $I-V$ curves are also compared with available theoretical models.