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 $I={I}₀({ ̇ \.{}{}}{{φ}}) sin{φ}+{I}₁({ ̇ \.{}{}}{{φ}})×{}cos{φ}+{I}₂({ ̇ \.{}{}}{{φ}})$, where the functions ${I}₀$, ${I}₁$, and ${I}₂$ are derived from time-dependent Ginzburg-Landau theory.