Conductivity magnetooscillations in 2D electron-impurity system under microwave irradiation: role of magnetoplasmons

It is developed a many-electron approach to explain the recently observed conductivity magnetooscillations in very high mobility 2D electron systems under microwave irradiation. For the first time a theory takes into account the microwave-induced renormalization of the screened impurity potential. As a result this potential has singular, dynamic and non-linear in electric field nature. That changes the picture of scattering of electrons at impurities in a ``clean'' 2D system essentially: for appearence of the rectified dissipative current responsible are excitations of 2D magnetoplasmons rather than one-electron transitions between Landau levels. In a ``dirty'' 2D system the role of electron-electron interaction diminishes, so the collective excitations cease to exist, and our results turn into the well-known ones, which were obtained in the one-electron approach.