  By numerical simulations and analytical studies, we show that the phenomenon
of microwave-induced resistance oscillations can be understood as a classical
memory effect caused by re-collisions of electrons with scattering centers
after a cyclotron period. We develop a Drude-like approach to magneto-transport
in presence of a microwave field, taking account of memory effects, and find an
excellent agreement between numerical and analytical results, as well as a
qualitative agreement with experiment.
