Microwave resonance in a high-quality GaAs/AlGaAs two-dimensional electron system in the low-density and low-mobility condition

Radiation induced magnetoresistance oscillations are well known and readily observable in the high-quality two-dimensional (2D) electron system. Here, we report unexpected photoexcited transport, under a low-carrier density, low-mobility condition, in the high-quality GaAs/AlGaAs devices that exhibit the above-mentioned oscillations. This study reveals enhanced nonresonant magnetoresistance as well as microwave resonance that appear unrelated to the above-mentioned radiation-induced magnetoresistance oscillations. The positions of the resonance along the $B$ axis depends on the microwave power, the microwave frequency, and the direction of sweep of the magnetic field, as the photoexcited diagonal resistance is prominently enhanced over the dark value. Most remarkably, the observed microwave-induced resonance becomes unobservable below a characteristic cutoff frequency. These features suggest a bulk magnetoplasmon origin for the observed resonances. A picture including bottlenecks in transport within 2D electron systems and microwave modified tunneling at bottlenecks is suggested to help understand some aspects of experiment.