Effect of the Shunt Capacitance on the ac Josephson Effect in Nb Point Contacts

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Abstract
The ac Josephson effects in Nb point contacts were measured using optically pumped sub-millimeter-wave laser. Laser-induced constant voltage steps (Shapiro steps) were observed on the dc I–V curves of the hysteretic junction as well as non-hysteretic junctions. We found that the height of the fundamental step normalized to the critical current at no irradiation in hysteretic junctions was considerably larger than that previously reported. The enhancement of the step observed can be explained by taking the effect of the shunt capacitance into consideration.