Static and dynamic properties of short, narrow, variable-thickness microbridges

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Abstract
The electrical properties, including the Josephson-effect response to microwave radiation, have been studied for extremely small, high-resistance microbridges of Pb-In alloy and unalloyed In, with dimensions ranging from 300& to 2000&. The IcR product of In and Pb-In microbridges decreases smoothly as the bridge cross section is reduced, approaching the Ginzburg-Landau limit of 0.64 mV/K for the smallest bridges. The voltage range of microwave response and the temperature range of hysteresis-free operation both increase (improve) as the bridge is made narrower, in agreement with Joule heating theory. For example, an 8 ohm Pb0.9In0.1bridge with all dimensions &500 & has a maximum step voltage ofV_{\max} = 1.5mV and a nonhysteretic temperature range of\DeltaT_{no hyst} = 1.2K. Bridges of unalloyed In can show still better response due to a longer coherence length, and nonhysteretic operation over the full temperature range below Tcis possible.