Renormalization of the cyclotron frequency in a screened two-dimensional electron system with strong retardation

Resonant microwave absorption by two-dimensional electron systems based on GaAs/AlGaAs heterostructures with a metallic back gate is investigated. The regime where the velocity of a screened plasma wave in a two-dimensional system calculated in the quasi-static approximation exceeds the speed of light in the substrate is obtained. It is established that relativistic retardation-related effects in this situation lead to significant changes in the dispersion and magnetic-field behavior of screened two-dimensional plasmons. It is found that the retardation effects result in the pronounced renormalization of the cyclotron and plasma frequencies. There is good agreement between the experimental results and the existing theory.