卷 117, 编号 7-8 (4) (2023)

We consider 1D quantum scattering problem for a Hamiltonian with symmetries. We show that the proper treatment of symmetries in the spirit of homological algebra leads to new objects, generalizing the well-known T- and K-matrices. Homological treatment implies that old objects and new ones are to be combined in a differential. This differential arises from homotopy transfer of induced interaction and symmetries on solutions of free equations of motion. Therefore, old and new objects satisfy remarkable quadratic equations. We construct an explicit example in SUSY QM on a circle demonstrating nontriviality of the above relation.

Modern methods of nanophotonics allow creating miniature devices that change the direction of light propagation, modulate the phase front, and control the outcoming state of the polarization. One of the promising areas of research is the development of flat optics elements based on planar analogues of metamaterials—dielectric metasurfaces, which are two-dimensional arrays of subwavelength nanoparticles with a high refractive index and low absorption coefficient. However, the resonances of such nanoscatterers have usually a low quality factor. Symmetry breaking of particle can lead to the excitation of a high-Q quasi-bound states in the continuum. In this work, we numerically study infrared metasurfaces that support such resonances and are formed by dimers of germanium nanocuboids. The possibility of focusing radiation to a point and line by 300‑nm-thick spherical and cylindrical metalenses is shown.

Nonlinear resonances in alkali metal vapor, which are detected by the magneto-optical rotation of the linear polarization of light, are actively used in quantum magnetometry to fabricate atomic magnetometers. The magneto-optical rotation in most such sensors is due to magnetic birefringence, and rotation angles usually do not exceed tens of milliradians. In this work, an experiment where magneto-optical resonances of linear polarization rotation of a probe wave are due to strong dichroism induced in a medium by a counterpropagating pump wave has been proposed. Both waves are in resonance with the Fg = 2 → Fe = 1 optical transition in the 87Rb D1 line (λ ≈ 795 nm). Experiments have been carried out with a 2-cm-long cylindrical cell filled with a buffer gas, and the maximum rotation angle is ≈390 mrad (22°) at a width of resonance of about 300 nT. The results show that the configuration proposed for the observation of magneto-optical rotation is promising for the fabrication of compact high-sensitivity atomic magnetometers.

The convective motion of water in a small cylindrical container, where the bottom and walls are heated and maintained at a constant temperature and heat is removed from the top surface, has been studied numerically. The no-slip condition is specified at the water–air interface to simulate the effect of a thin absorption film. A temperature wave, which rotates in parallel to the surface at an angular velocity of (0.06 ± 0.02) rad/s, has been detected for the first time in this system. This wave is high-mode, has a frequency of about 0.1 Hz, and is observed in very narrow ranges of the dimensions of the container and temperatures.

In this work the formation of modulated structures in chiral liquid crystals is studied. For different chiral nematics that at low temperature form the usual (with twist in one direction) cholesteric phase, we found that at high temperature in the vicinity of the phase transition into isotropic liquid a universal sequence of structural transformations is observed. Planar cholesteric transforms at short helical pitch into the three-dimensional phases with cubic symmetry (Blue Phases), in two-dimensional structure at intermediate helical pitch and in one-dimensional structure in the plane of the sample at large pitch. The structures possess periodic orientational and translational order on scales much larger than molecular scale. Optical measurements were made on ordered structures obtained near the transition temperature to the isotropic phase. Possible reasons of formation of the structures are discussed on the basis of existing experimental data and theoretical considerations.

The influence of an intense electron beam on a nonstoichiometric oxide HfOx (х@) layer of a TaN/HfOx/Ni memristor on its electrophysical properties is studied. It is found that the crystalline h-Hf, m‑HfO2, o-HfO2, and t-HfO2 phases are formed in the HfOx film under this impact. It is established that memristors demonstrate resistive switching at certain electron fluence values. At the same time, such memristors have resistive switching voltages several times lower than those of unirradiated memristors. In addition, they exhibit a multiple decrease in the spread of resistive switching voltages, as well as resistances in low- and high-resistance states. The current–voltage curves of the obtained memristors indicate that the charge transport in them is described by the space-charge-limited current mechanism.

The cross section for the neutron-induced fission of 238U nuclei has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, in the neutron energy range of 0.3–500 MeV. Fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The cross section for 238U(n, f) fission has been measured with respect to the cross section for 235U(n,  f) fission, which is an accepted international standard. Data on the energy dependence of the anisotropy of the angular distribution of fragments of neutron-induced 238U nuclei are also presented. The data obtained have been compared to previous experiments carried out using both similar and significantly different methods.

Photons have zero rest mass and always travel at the speed of light in a vacuum, but have no dipole moment. Atoms and molecules, which may have a constant or variable dipole moment, have mass and therefore cannot move at or above the speed of light. As a result, the radiation from such systems moving at the velocity of light was not considered. However, it is possible to create many artificial objects (light spots, effective charges, current pulses, etc.) that can travel at the speed of light and even exceed it. In this case, they become a source of electromagnetic radiation. In this work, the radiation of a solitary polarization pulse that travels at the speed of light and has a variable or constant amplitude is discussed. It is shown that if the amplitude does not change, then such an object does not radiate outward; i.e., the field emitted by it remains completely localized inside the moving polarization pulse. If the amplitude changes over time, then it begins to radiate backwards. In this case, unipolar pulses of an unusual shape, such as a rectangular one, can be obtained.

By employing a combined method of density functional theory and dynamical mean-field theory (DFT + DMFT) we study the spectral properties and local moment formation in the normal state of a Co-based superconductor CuCo2S4. The obtained quasiparticle mass enhancement 
 is smaller than that in iron-based parent compounds indicating weak correlations in the Co 
 states. We show that the mass enhancement is accompanied by an insignificant renormalization and shift of the bands in the vicinity of the Fermi level. This subtle modification is sufficient to induce a substantial transformation of one of the Fermi surface sheets and occurs due to the presence of shallow Fermi surface pockets in the electronic structure of CuCo2S4. The calculated local and fluctuating moments are smaller than those in iron-based superconductors questioning the importance of spin fluctuations for understanding the pairing mechanism of CuCo2S4.

The electrostatic interaction between nanoparticles caused by the overlapping of double electric layers and the van der Waals interaction caused by quantum and thermodynamic fluctuations of electromagnetic fields are considered. The linearized Poisson–Boltzmann equation for particles with a fixed electric potential on their surface is used in the case of the electrostatic interaction. An exact solution of the problem has been obtained both for identical particles and for particles with strongly different sizes. The screening of static fluctuations and the retardation of electromagnetic fields for the dispersion part of the van der Waals interaction have been taken into account. The total interaction energy of two particles has been calculated for ion concentrations in an electrolyte from 10–6 to 10–2 mol/L and sizes of nanoparticles from 1 to 103 nm. It has been found that the van der Waals force exceeds the screened electrostatic repulsive force at high concentrations of the electrolyte from 10–3 to 10–2 mol/L at both small and large interparticle distances.

We study the structure of the superconducting order parameter in underdoped NaFe1 – xCoxAs pnictides with Tc ≈ 19–21 K related to the 111 family. Using incoherent multiple Andreev reflection effect spectroscopy of planar break junctions, we directly determine the magnitudes of the two microscopic superconducting order parameters: the small superconducting gap ΔS(0), and possible edges of the large gap ΔL(0) having an anisotropy in the 
 plane at T ≪ Tc, the corresponding characteristic ratios, as well as their temperature dependences. Additionally, we detect features of the tunneling spectra in NaFe1 – xCoxAs at 
, those irrelative to superconducting state, and discuss their origin.

The influence of the size of dislocation loops on sublattice ferrimagnetism in graphene is studied. It is shown that graphene and the underlying gold layer with Au/Co dislocation loops of various sizes are characterized by ferrimagnetic ordering within atomic layers. Additional gold adatoms under graphene enhance the induced Rashba spin–orbit coupling in graphene but do not destroy the ferrimagnetic order in graphene. Since gold clusters can remain during the intercalation of gold on the surface of graphene and under graphene, the number and size of clusters after intercalation can be controlled to enhance the induced Rashba interaction and to obtain a topological phase in graphene.