We studied the absorption of microwave electromagnetic radiation incident normal to a two-dimensional electron system on a dielectric substrate with a metallic back reflector. We have shown that the presence of a back gate strongly modifies the spectrum of plasmon polaritons in such a structure. We observe a transverse plasmon mode which starts from zero frequency at zero magnetic field and follows renormalized cyclotron resonance. This renormalization occurs from the hybridization of plasma modes with Fabry-P & eacute;rot photonic resonances in the substrate, which indicates their transverse nature. Finally, we speculate that the observed modes resemble helicon waves in three-dimensional metals.

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.

We have investigated plasma excitations in a disk-shaped two-dimensional electron system (2DES), the edge of which was covered by an overlaying metallic gate. We have found that the microwave response of the structure is dominated by the proximity plasma mode propagating along the disk edge. Significantly, we find that as the overlap between the 2DES and the gate tends to zero, the frequency of the proximity plasmon makes a transition to that of an ordinary 2D plasmon in the ungated area of the 2DES. We also observe that tuning the electron density under the gate results in a crossover from the proximity to the laterally screened 2D plasmon. The experimental findings are analyzed using the plasmonic lumped-element approach.

An investigation is performed of the relaxation of plasma excitations in two-dimensional electron systems (2D-ESes) in GaAs/AlGaAs heterostructures. The effect radiational and incoherent collisional relaxation mechanisms have on the linewidth of cyclotron magnetoplasma resonance (CR) is studied. CR arises as a pure resonance that does not hybridize with dimensional magnetoplasma excitations. It is shown how magnetoplasma resonances form a CR’s fine structure due to the interaction between coherent radiative and incoherent collisional mechanisms of two-dimensional plasma relaxation. A comparative analysis is performed of the dependences of cyclotron and transport periods of relaxation on both the temperature and electron density of 2D-ESes. It is demonstrated that the period of cyclotron relaxation could exceed that of transport at low electron densities.

We have investigated the spectrum of two-dimensional (2D) plasmon polaritons over the full range of magnetic fields. In our study, we investigate a disk-shaped two-dimensional electron system (2DES) with a metallic gate on the backside of the substrate. Importantly, we show that 2D plasmon polaritons hybridize with the TM$_0$ photonic mode of a dielectric waveguide formed by a sample substrate. We have developed a theory for plasmon-polaritons in an infinite 2DES. We find the experimental data to be in good agreement with the developed theory.

We investigate the electrodynamics of a disk-shaped two-dimensional electron system in the proximity of a screening gate. The two-dimensional plasmons in the system under study exhibit the linear dispersion characteristic of acoustic plasma waves. We experimentally achieve the limit when the velocity of acoustic waves approaches the speed of light. We show that retardation effects lead to strong coupling between acoustic plasmons and the light, which is manifested in the renormalization of the electron effective mass. We develop a theory to substantiate the observed phenomena.

We have studied the microwave response of a high-mobility two-dimensional electron system (2DES) contacted by two side electrodes. Using kinetic inductance of the 2DES and inter-electrode capacitance, we have constructed a subwavelength 2D plasmonic resonator. We have shown that the resonant frequency of this circuit can be controlled by 2D electron density, external magnetic field, or size of the electrodes. This opens up possibilities for using arrays of plasmonic circuits as tunable components in different frequency ranges.