  The microwave-excited high mobility two-dimensional electron system exhibits,
at liquid helium temperatures, vanishing resistance in the vicinity of $B =
[4/(4j+1)] B_{f}$, where $B_{f} = 2\pi\textit{f}m^{*}/e$, m$^{*}$ is an
effective mass, e is the charge, and \textit{f} is the microwave frequency.
Here, we summarize some experimental results.
