Comparison of Nb Thin-Film Point-Contact Josephson Junction Characteristics with the Stewart-McCumber Model

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Abstract
This paper compares the measured characteristics of a three-dimensional Nb thin-film point-contact junction with those predicted by the Stewart-McCumber model. The erratic microwave-induced I-V characteristic we observed at low microwave power levels was also evident in a digital simulation –based on the Stewart-McCumber model–of the time dependence of the junction voltage and the phase space trajectory. Subharmonic steps V=(n/m)(h f/2e) were observed when a 70 GHz signal was applied, but the usual condition ωC R n≃1 for substeps was not fulfilled. Substeps were also observed in the digital simulation even when the current-phase relationship was purely sinusoidal.