  We report the results of a combined microwave polarization-dependence and
power-dependence study of the microwave-radiation-induced magnetoresistance
oscillations in high mobility GaAs/AlGaAs heterostructure devices at liquid
helium temperatures. The diagonal resistance was measured with the magnetic
field fixed at the extrema of the radiation-induced magnetoresistance
oscillations, as the microwave power was varied at a number of microwave
polarization angles. The results indicate a nonlinear relation between the
oscillatory peak or valley magnetoresistance and the microwave power, as well
as a cosine square relation between the oscillatory peak or valley
magnetoresistance and the microwave polarization angle. The main features are
briefly compared with the predictions of existing models.
