Effects of External RF Radiation on Josephson Tunnel Junctions.

D. N. Langenberg, William H. Parker, Barry N. Taylor

Clark A. Hamilton

Sergio Nicola Erne, A. Ferrigno, Thomas F. Finnegan +1 more

The frequency and power of the microwave radiation detected from long in-line Josephson tunnel junctions when dc biased on low order singularities or self-induced steps have been measured as a function of bias current and externally applied magnetic field. The preliminary experimental results reported here show that the magnetic tuning of the emitted radiation may be considerably greater than that obtained in similar junctions of overlap geometry.

Thomas F. Finnegan, J. Wilson, J. Toots

A major factor in the practical utilization of any Josephson device for microwave and higher frequency applications (such as the generation and detection of electromagnetic radiation) is the success with which the junction device can be coupled to an external transmission line. As part of an experimental investigation of the electrodynamics of small arrays of Josephson tunnel junctions, the properties of the coherent radiation emitted both by individual junctions and by coupled junction systems have been studied at frequencies between 2 and 12 GHz. Near 9 GHz, more than 10-9 W of coherent radiation has been detected from a single Pb-Pb oxide-Pb junction coupled via waveguide. The development of thin film devices in which the tunnel junctions form part of a microstrip line have made it feasible to observe directly (in a single device) the radiation emitted both at the fundamental geometrical frequency and at the low order harmonics. The observed temperature dependence of the junction cavity Q indicate the low temperature losses are primarily due to cavity loading of the external transmission line.

Katsuya Kikuchi, Hiroaki Myoren, Takeshi Iizuka +1 more

The magnetic field dependence of the Josephson current of a Josephson tunnel junction whose shape was a normal distribution is analyzed for superconducting tunnel junction (STJ) photon detector applications. It was found that the Josephson current of a normal distribution junction is very sensitive to the external magnetic field and follows a function of exp (-B 2), while a conventional rectangular STJ exhibits the well-known Fraunhofer pattern of sin x/x. Numerical calculations show that the Josephson current of the normal distribution junction can be suppressed by an external magnetic field that is one tenth of that needed for conventional rectangular junctions. Calculations of a normal distribution junction approximated with a 1 µm mesh also show that the Josephson current is sufficiently suppressed by a small magnetic field. The effect of the misalignment of the angle between the junction and the magnetic field was evaluated. It was found that for a normal-distribution-shaped junction, misalignment of the magnetic field is allowed within ± 5°, suppressing the Josephson effect by two orders of magnitude more than that of a rectangular junction.

D. N. Langenberg, Douglas J. Scalapino, Barry N. Taylor +1 more