Frequency Dependence of the a c Josephson Effect in Small Dayem Bridges

The current-voltage characteristics of superconducting thin-film indium microbridges (Dayem bridges) and their microwave-induced constant-voltage steps have been investigated at several frequencies. The results are well described by a resistively shunted Josephson junction model, which differs from the usual resistively shunted Josephson junction model only in having a current-phase relation of the form $I=I_0\left(\dot{\varphi }\right) sin\varphi +I_1\left(\dot{\varphi }\right)\times cos\varphi +I_2\left(\dot{\varphi }\right)$, where the functions $I_0$, $I_1$, and $I_2$ are derived from time-dependent Ginzburg-Landau theory.