Vol 89, No 2 (2025)

We presented a numerical simulation of planar resonators for the subterahertz frequency range, confined by various types of reflectors: Bragg mirrors, grating mirrors, solid metal mirrors. The dependences of the amplification of the electric field strength in the resonator on the structure parameters were constructed for normal incidence of an electromagnetic wave on the surface of the resonator. The physical limitations imposed on the magnitude of the gain are determined.

The properties of a silicon-based plasmonic detector of electromagnetic radiation were examined in the lowfrequency region (0.1-20 GHz). The detector’s sensitive element was embedded within a matched coplanar waveguide, through which the electromagnetic radiation was conveyed. The dependence of the DC voltage observed at the detector’s output on the frequency of the incident radiation was measured. The detector’s power characteristics were measured, and the threshold radiation power at which the detector transitions into a nonlinear regime was determined.

The phase boundary of the “gas – magnetoexciton condensate” transition of an excited two-dimensional electron system placed in a quantizing magnetic field is constructed in the “temperature – excitation density” coordinates. Based on experimental data, it can be concluded that the condensate is a collective, incompressible in real space, excited state of a Hall dielectric.

We presented the results of a study of two-dimensional electron systems implemented in MgZnO/ZnO heterostructures with high interaction parameters. Using the inelastic light scattering method, we observed ferromagnetic transitions and spin textures. We also studied the dispersion dependences of key energy parameters.

The resonance photoluminescence of excited Laughlin liquid at the electron filling factor of 1/3 is studied. It is shown that for a neutral defect in Laughlin liquid consisting of an electron at the upper spin sublevel of the zero Landau level and a valence hole, the influence of random potential fluctuations on the probability of optical recombination of the defect is suppressed (random potential superscreening). Filling the Laughlin liquid with single-spin excitations (spin-magnetogravitons) does not affect this observation.

The ground and excited states of A- and B-excitons in monolayers of MoSe2 and WSe2 were studied by optical reflectance spectroscopy in a wide range of temperatures up to room temperature. It has been shown that excited states are observed in the spectrum even at room temperature. Depending on the selected parameters of the heterostructure, the B-exciton line may be comparable in intensity to the A-exciton line.

It was discovered that in metallic films with periodic holes (the size of the square hole was half the period) the effect of a giant enhancement of the intensity of inelastic light scattering is observed, and the enhancement coefficient depends significantly on the thickness of the metal (silver). It is shown that when the thickness of the silver film changes in the range from 5 nm to 140 nm, strong oscillations of the enhancement coefficient are observed, and the amplitude of the oscillations can be more than an order of magnitude. The observed oscillations are explained in terms of the resonant excitation of standing plasmon-polariton waves in metal films, which dispersion varies significantly with variation of the metal thickness.

Several variants of gold nanoparticles were proposed for the detection of formazan formed because of enzymatic reduction of the MTT reagent by E. coli enzymes. It is shown that gold nanostars coated with a micellar stabilizer are the most promising SERS-substrate for the detection of formazan in biological mixtures, reducing the required titer of bacteria by at least an order of magnitude.

Different approaches for creating an enhancing surface based on a track-etched polyethylene terephthalate membrane are studied. The stability of the covering and the potential for the usage of the obtained substrates were evaluated on the example of the aptasensor for the determination of the influenza A virus.

Theoretical study is performed of a quasi-two-dimensional exciton-polariton system localized in a circular microcavity mesa under the conditions of resonant photoexcitation. It is predicted that in a case when several size-quantized sublevels are excited, a series of transitions occurs from stationary to self-oscillatory and further to chaotic states. The transition from stationary states to oscillations is accompanied by a lowering of the rotational symmetry down to a discrete one, whereas in the chaotic region the spatial symmetry disappears completely. In a spinor system, analogous phenomena result in polarization chaos.

Experimental studies of Raman scattering spectra in single crystals of topological magnetic insulators MnBi2Te4 have been performed in a wide temperature range. The influence of spin-phonon interaction on the studied spectra at temperatures below the antiferromagnetic phase transition temperature is discussed.

The temperature dependence of Raman scattering is investigated in nanowires of a dilute magnetic semiconductor Ge0.99Mn0.01. It was found that with increasing temperature, a red shift (“softening”) of the optical LO-phonon line occurs at T ≈ 25 K. The observed behaviour correlates with the data of the electron paramagnetic resonance of mobile charge carriers and indicates a strong interaction of holes with the phonon and magnetic subsystems.

The surface perturbation in a viscous, stratified liquid is investigated in a two-dimensional setting. Expressions for the dynamics of periodic surface motion and the fine-scale structure of currents are derived. Distributions of the wave and ligament components of the density, density gradients, and pressure are constructed. A fine structure accompanying the wave component of the flow is identified in physically measurable variables.

In Euler’s work Principia motus fluidorum, the continuity equation for a fluid is derived using high-order terms of smallness that contain the quadratic and cubic invariants of the strain rate tensor. From Maxwell’s system of electrodynamics equations, the wave equation for the electric field strength is derived taking into account the quadratic and cubic invariants. These invariants describe the generation of electric field intensity waves.