Evolution of the linear-polarization-angle-dependence of the radiation-induced magnetoresistance-oscillations with microwave power

We examine the role of the microwave power in the linear polarization angle dependence of the microwave radiation induced magnetoresistance oscillations observed in the high mobility GaAs/AlGaAs two dimensional electron system. Diagonal resistance $R_{xx}$ was measured at fixed magnetic fields corresponding to the photo-excited oscillatory extrema of $R_{xx}$ as a function of both the microwave power, $P$, and the linear polarization angle, $\theta$. Color contour plots of such measurements demonstrate the evolution of the $R_{xx}$ versus $\theta$ line shape with increasing microwave power. We report that the non-linear power dependence of the amplitude of the radiation-induced magnetoresistance oscillations distorts the cosine-square relation between $R_{xx}$ and $\theta$ at high power.