Nonlinear growth in the amplitude of radiation-induced magnetoresistance oscillations

We report the observation of inverse magnetic field periodic, radiation-induced magnetoresistance oscillations in GaAs/AlGaAs heterostructures prepared in W. Wegscheider's group, compare their characteristics with similar oscillations in V. Umansky's material, and describe the lineshape variation vs the radiation power, $P$, in the two systems. We find that the radiation-induced oscillatory resistance, $\ensuremath{\Delta}{R}_{xx}$, in both materials, can be described by $\ensuremath{\Delta}{R}_{xx}=\ensuremath{-}A\text{ }\text{exp}(\ensuremath{-}\ensuremath{\lambda}/B)\text{sin}(2\ensuremath{\pi}F/B)$, where $A$ is the amplitude, $\ensuremath{\lambda}$ is the damping parameter, and $F$ is the oscillation frequency. Both $\ensuremath{\lambda}$ and $F$ turn out to be insensitive to $P$. On the other hand, $A$ grows nonlinearly with $P$.