Measurements of the Riedel peak in superconducting aluminum tunnel junctions (mixers)

The Riedel singularity in thin-film aluminum tunnel junctions was measured from temperature behavior of the zero voltage step and the RF-induced Josephson steps at around the gap frequency. From these experiments the author derived a value of the imaginary gap parameter to be about 1% of the gap parameter value at the gap edge when the temperature was 0.7 of the transition temperature. The author believes that, using magnetic field for tuned superconductor-insulator-superconductor (SIS) mixers with relatively large area, the Riedel singularity should not play an important role for frequencies around the gap frequency at finite temperatures.<
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