Zero-Resistance States Induced by Electromagnetic-Wave Excitation in   GaAs/AlGaAs Heterostructures
  We report the detection of novel zero-resistance states induced by electromagnetic wave excitation in ultra high mobility GaAs/AlGaAs heterostructure devices, at low magnetic fields, $B$, in the large filling factor limit. Vanishing resistance is observed in the vicinity of $B = [4/(4j+1)] B_{f}$, where $B_{f} = 2\pi\textit{f}m^{*}/e$, where m$^{*}$ is the effective mass, e is the charge, and \textit{f} is the microwave frequency. The dependence of the effect is reported as a function of \textit{f}, the temperature, and the power. 
R. G. Mani