  The immunity of microwave-induced magneto-resistance oscillations and corresponding zero resistance regions to the direction of (circular) polarization of microwave is studied in this paper. We propose that a spontaneous circular motion of the whole electron fluid would stabilize the system and minimize the polarization sensitivity of the oscillatory DC resistance. Results of a self-consistent calculation capture the qualitative features of the experimental observation. 
On the (circular) polarization-independence of microwave-induced   resistance oscillations and zero resistance state