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Journal of Applied Physics

Nonresonant detection of Josephson radiation from thin-film microbridges

O. H. Soerensen, J. Mygind, N. F. Pedersen, Vladimir N. Gubankov, Mogens T. Levinsen, P. E. Lindelöf

Published Dec 1, 1977• 7 citations
Publisher

Abstract

Measurements are reported of the Josephson radiation from microbridges coupled to an X-band receiver via a nonresonant microwave transformer. Although closely coupled to the bridge, the transformer does not modify the bridge properties. We find that near the transition temperature the radiation linewidth is proportional to the square of the dynamic resistance, which is also predicted by the resistively shunted junction model. The effective noise temperature determined by the linewidth is 19±3 K and the measured maximum integral power is 5×10−12 W.

DOI
10.1063/1.323542

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The temperature and field variation of the photoresponse of tin Josephson film microbridges are studied in experiments in which the microbridges are irradiated in the centimeter and millimeter ranges. Experiments have been carried out under conditions that correspond to narrow-band and wide-band detection. Certain features of the response which are due to stimulation of superconductivity in the microbridges by the microwave radiation and a direct current are studied. In heterodyne detection these features disappear at a high power level of the heterodyne oscillator, and a substantial increase is observed in the response, this is caused by a higher differential resistance of the microbridge. The maximum sensitivity (approx.10/sup 4/ V/W) is achieved with selective detection.

Technical Physics•Apr 1, 1979•0 citations
Measurements are reported of the Josephson radiation from microbridges coupled to an X-band receiver via a nonresonant microwave transformer. Although closely coupled to the bridge, the transformer does not modify the bridge properties. We find that near the transition temperature the radiation linewidth is proportional to the square of the dynamic resistance, which is also predicted by the resistively shunted junction model. The effective noise temperature determined by the linewidth is 19±3 K and the measured maximum integral power is 5×10−12 W.
Measurements at 3 GHz of the microwave properties of a superconducting thin-film microbridge coupled to a narrowly tuned strip-line resonator (coupled Q approximately 10 3 ) indicate that such a device displays the same variations in small-signal impedance as predicted by the resistively shunted junction model of a Josephson weak-link. Whenever this impedance becomes negative the microbridge is found to generate microwave radiation whose frequency is determined not by the junction bias voltage but by the natural resonance of the strip-line.
Amplification, down-conversion and detection of the microwaves in thin-film Josephson variable thickness bridges of submicron dimensions have been investigated experimentally. The results for indium and tin bridges are discussed taking into account the influence of the nonequilibrium electrons in a weak link region. The same experiments were carried out with SNS variable thickness Nb-Al-Nb bridges. They showed that the properties of SNS bridges agreed better with the theoretical predictions of the resistively shunted junction model in a wide temperature range. Moreover the parameters of the Nb-Al-Nb bridges have possessed better stability and reliability.
The temperature and field variation of the photoresponse of tin Josephson film microbridges are studied in experiments in which the microbridges are irradiated in the centimeter and millimeter ranges. Experiments have been carried out under conditions that correspond to narrow-band and wide-band detection. Certain features of the response which are due to stimulation of superconductivity in the microbridges by the microwave radiation and a direct current are studied. In heterodyne detection these features disappear at a high power level of the heterodyne oscillator, and a substantial increase is observed in the response, this is caused by a higher differential resistance of the microbridge. The maximum sensitivity (approx.10/sup 4/ V/W) is achieved with selective detection.