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Applied Physics Letters

Subharmonic energy gap structure in the Josephson radiation at 35 GHz from a superconducting thin-film microbridge

Jørn Bindslev Hansen, Mogens T. Levinsen, P. E. Lindelöf, Bjørn Dueholm, J. Mygind, N. F. Pedersen, O. H. Soerensen

Published Jul 1, 1979• 6 citations
Publisher

Abstract

Nonresonant detection of the Josephson radiation 35 GHz from a superconducting thin-film microbridge is reported. The high frequency and the accuracy of these measurements lead to a new important observation: subharmonic energy gap structure in the detected integral power. The maximum integral power measured was as large as 8×10−11 W.
DOI
10.1063/1.90910

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Effect of microwave radiation on the voltage-current characteristics of a variable-thickness Josephson microbridge

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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.
The subharmonic gap structure (SGS) in long-overlap Nb-AlOx-Nb Josephson tunnel junctions has been investigated. The experimental results show peaks in the differential conductance at both odd and even integer fractions of the gap voltage, VG. Furthermore, the conductance peaks at VG/2 has been observed to split into two peaks with different characteristics. At high magnetic fields, the I-V characteristics approach a single curve, while retaining the SGS conductance peaks. The gap structure and the SGS show the same temperature dependence. The SGS can be explained by a Josephson self-coupling effect or multiple Andreev reflections. The results are important for the development of the flux flow oscillator used a local oscillator in integrated all-superconducting 200-800 GHz receivers.
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.