Vol 117, No 5-6 (3) (2023)

After fixing the Maximal Abelian gauge in  lattice gluodynamics we decompose the nonabelian gauge field into the Abelian field created by Abelian monopoles and the modified nonabelian field with monopoles removed. We then calculate respective static potentials in the fundamental representation and show that the sum of these potentials approximates the nonabelian static potential with good precision at all distances considered. Comparison with other ways of decomposition is made.

The features of nonlinear propagation of high-intensity pulses in the short-wavelength infrared range in extended one-dimensional waveguide arrays with different spatial periods, formed in fused silica by laser writing, are studied. More than tenfold self-compression of femtosecond pulses up to a duration of several periods of the light field is experimentally observed.

The electron distribution over Landau levels is calculated in the regime of the quantum Hall effect at strong Coulomb interaction. For this purpose, a modified scheme of exact diagonalization with a significantly reduced basis of many-particle configurations has been developed, which makes it possible to adequately take into account the mixing of states in several Landau levels. The behavior of the electron distribution function over Landau levels is studied as a function of the filling factor and the Wigner–Seitz radius rs. It is shown that the Landau quantization at a fixed electron density significantly suppresses the smearing of the electron distribution function as compared to the case of zero magnetic field. For example, for rs < 1 and low filling factors, the quasiparticle contribution to the Migdal jump 1 − Z in the distribution function is an approximately linear function of ν and a quadratic function of rs. Simultaneously, as ν decreases, the tails of the distribution function become longer. The mechanism of rearrangement of the distribution function in the regime of the quantum Hall effect is described in terms of the generation of magnetoplasmon fluctuations involved in the structure of the ground state of the system.

The joint intercalation of Co and Fe atoms under a graphene buffer layer synthesized on a SiC(0001) single crystal has been studied. Intercalation has been performed by means of the alternating deposition of ultrathin Fe and Co metal films on the substrate heated to 450°C with the subsequent heating to 600°C in 15 min. It has been shown that Co and Fe atoms under these conditions are intercalated under graphene, forming compounds with silicon and with each other. The existence of a magnetic order in the system up to room temperature has been demonstrated using a superconducting quantum interferometer. A possible stoichiometry of the formed alloys has been analyzed using data on the shape and magnitude of hysteresis loops. In addition, it has been found that Fe and Co in the system exposed to the atmosphere are not oxidized. Thus, graphene protects the formed system. This study makes contribution to the investigation of graphene in contact with magnetic metals and promotes its application in spintronic and nanoelectronic devices.

The intensity of backscattering of near infrared laser radiation has been calculated for a multilayer biological tissue simulating the human head as a function of the distance between a source and a detector of radiation that are located on the head. The iterative solution of the Bethe–Salpeter equation has been represented as a series in scattering orders. A modification of the known Monte Carlo method for photon transport in multilayer tissues has been proposed to accelerate calculations. It has been shown that the resulting dependences of the backscattering intensity change significantly under the variation of the optical properties of the biological tissue, primarily in the case of penetration of blood to the cerebrospinal fluid layer. This can be used to develop optical methods for diagnosis of traumatic injuries of biological tissues.

Quantum-mechanical simulations of the nonlinear response of a one-dimensional quantum system with the energy structure close to that of the xenon atom to an ultraviolet femtosecond pulse with an intensity of 1–100 TW/cm2 reveal the dispersion of the cubic nonlinearity coefficient in the range of 266–400 nm and its intensity dependence. This excludes the description of the response of bound electrons as 
. The calculation of the polarization with this one-dimensional quantum model can be used to simulate the propagation of ultraviolet femtosecond radiation in a gas.

A theory of optical modes in an elliptical microcavity has been developed using Mathieu functions in elliptical coordinates. A key difference from the circular case is the splitting of doubly degenerate modes. Split optical modes have been numerically calculated and their symmetry has been determined. A method has been proposed to choose the parameters of a cavity for a certain wavelength. The difference between the energies of optical modes in the cavity with metallic walls and in the dielectric cavity is no more than ~20%. The dispersion relations of optical modes show the possibility of degeneracy of modes with different symmetries, which allows the spectral and polarization filtering of radiation of single-photon sources and the fabrication of sources of multiply entangled states.

Processes of multiple electron-impact ionization of ions in a plasma and a beam passing through the plasma have been considered. Using experimental data and theoretical calculations of the cross sections for n-electron ionization 
, the contribution from many-electron ionization rates 
 to the total ionization rate has been determined as a function of the electron temperature of the plasma T. It has been shown that the total contribution of many-electron ionization rates to the total ionization rate in ion beams passing through the plasma is determined by the relation between the velocity of an ion beam 
 and the thermal velocity of electrons in the plasma 
. Many-electron ionization rates 
 have been numerically calculated for W+ ions for electron temperatures of the plasma from 1 eV to 10 keV and velocities of the ion beam 
 = 0–30 a.u., where 1 a.u. ≈ 2.2 × 108 cm/s is the atomic unit of velocity.

Carbon nanowall films with different thicknesses have been obtained by chemical deposition from a gas phase in a dc discharge. The thermal conductivity of the resulting structures has been measured for the first time using the 3ω method in the temperature range of 280–310 K. It has been shown that the thermal conductivity of walls depends on their thickness. The thermal conductivity of 1-μm carbon nanowalls is 6.9 W m–1 K–1. The results obtained in this work are necessary to design electro-optical devices based on carbon nanowalls.

The radiation formation of interlayer bridges in bilayer graphene has been studied with the nonorthogonal tight binding model. It has been shown that most (~85%) of the formed bridges have a low thermal stability excluding their application in elements of graphene electronics working at room temperature. Three types of stable bridges with the annealing activation energies of 1.50, 1.52, and 2.44 eV have been revealed. Estimates by the Arrhenius formula have shown that these bridge types have macroscopic lifetime at room temperature. It has been found that the radiation formation of bridges in bilayer graphene significantly differs from a similar process in graphite.

The quantum cryptography technology allows key distribution in individual segments of a network in a point–point configuration; then, keys in individual segments are used to protect traffic between any nodes of the network, which are not connected directly by a quantum channel. Correspondingly, the problem of negotiation (distribution) of keys between separate segments of the network appears. In this work, the problem of the transmission of an independent key through trusted nodes of the quantum network, between which keys are provided as a result of quantum key distribution, is considered. Quantum keys are used to encrypt the transmitted key. The transmitted key can be encrypted by both the block cipher and the one-time pad. It has been shown that the complexity of search for the key transmitted through the network depends on the imperfection of the external key and quantum keys as well as on the imperfection of the block cipher, i.e., on the average probability of collisions in the block cipher. The complexity in the case of the encryption of the transmitted key by the one-time pad depends only on the imperfection of the transmitted key and encryption keys. Perfect keys keep the perfectness of the transmitted key. In the block cipher, the transmitted key is no longer perfect even with the perfect keys in the measure of difference of the block cipher from the one-time pad. It has also been shown that the larger the number of collisions of the block cipher, i.e., the smaller the number of ciphertexts covered by the block cipher, the smaller the number of search steps required to find the key.