Hidden negative dc conductivity induced by cyclotron resonance excitation in a 2D electron gas on liquid helium

We report a theoretical study of dc magnetoconductivity of a highly correlated 2D electron gas on the free surface of liquid helium in the presence of nonuniform cyclotron resonance (CR) excitation. To describe the system of overheated electrons, a two-fraction model of electrons differently affected by the ac electric field is proposed. For dark electrons, we found a novel inelastic effect that strongly increases longitudinal conductivity with increasing electron temperature. A small fraction of electrons directly affected by the CR excitation can exhibit the negative conductivity effect, which causes instability of the uniform-density state. We found that even a small energy exchange with a scatterer could shift the conductivity minimum and zero-resistance states to the opposite side of the CR line. The proposed theoretical model could explain the puzzling CR-induced redistribution of electrons observed experimentally.