Microwave response of superconducting variable-thickness microbridges

We report on the microwave response of variable-thickness tin and lead microbridges, the best of which can show microwave-induced Josephson steps up to 4.2 mV at low temperatures, limited primarily by heating effects. By examining the temperature dependence of the number of steps observed, we find agreement with the theory of such heating effects of Tinkham, Octavio, and Skocpol. We also show that the size and periodicity with microwave power of the steps at low voltages can be affected by heating. Finally, we show that closely spaced pairs of such variable-thickness microbridges can couple strongly together, and apparently can synchronize their oscillations on a Josephson step over a wider range of currents than can single bridges.