Photo-excited zero-resistance states in the GaAs/AlGaAs system
  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. 
R. G. Mani