Niobium point-contact Josephson-junction behavior at 604 GHz

Abstract
We have measured the ac Josephson effect in Nb point contacts at 604 GHz (496 μm). We find the coupling of the far‐infrared radiation to the point contact to depend in a simple manner on the resistance of the contact. The behavior of the high‐resistance point contacts (50⩽R⩽200 Ω) is very reproducible, allowing a quantitative comparison of the data to the frequency‐dependent Werthamer theory. We also account for the effects of noise and heating and compare these to Tinkham’s heating theory.