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

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 300Å to 2000Å. The I
c
R 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 Pb
0.9
In
0.1
bridge with all dimensions ≤500 Å has a maximum step voltage of
V_{\max} = 1.5
mV and a nonhysteretic temperature range of
\DeltaT_{no hyst} = 1.2
K. Bridges of unalloyed In can show still better response due to a longer coherence length, and nonhysteretic operation over the full temperature range below T
c
is possible.