Vol 118, No 5-6 (9) (2023)

The polarization properties of narrow spectral modes appearing in a Raman fiber laser with random distributed feedback due to Rayleigh backscattering near the lasing threshold have been studied experimentally. It has been shown that the modes have a high degree of polarization and that the polarization states of simultaneously generated modes are weakly correlated.

The dependence of the topology of the fermion excitation spectrum on the magnetic state of the system is analyzed taking into account the structure of the Te–Mn–Te trilayer in the Te–Bi–Te–Mn–Te–Bi–Te layer sequence of the MnBi₂Te₄ van der Waals single crystal, crystal field effects, spin–orbit coupling, and the covalent mixing of electronic states of Mn²⁺ ions with electronic states of Te^2– ions in the strong electron correlation regime. The Chern number in the ferromagnetic phase, which is due to the kinematic interaction between Hubbard fermions, is equal to 1; i.e., the topology of the band structure of the Te–Mn–Te trilayer is nontrivial. The Chern number in the paramagnetic phase is zero; i.e., the topology is trivial. The magnetic moments of Mn²⁺ ions for the constructed spin orbitals are perpendicular to the layers. The magnetic moments of Mn²⁺ ions in the nearest layers are antiferromagnetically ordered via the Anderson mechanism.

The PT-symmetric photoconductivity has been detected for the first time in microwave-irradiated heterostructures based on thick Hg_{1 − x}Cd_xTe films with the CdTe content x corresponding to the topological phase although the magnetic field symmetry (T symmetry) and the symmetry in the positions of potential contact pairs (P symmetry) are not conserved separately. The microwave photoconductivity in similar heterostructures based on the trivial Hg_{1 − x}Cd_xTe phase is both P- and T-symmetric.

In order to create neuromorphic computing systems (NCSs) capable of efficiently solving artificial intelligence problems, elements with short- and long-term memory effects are required. Memristors are promising candidates for the implementation of such elements since they demonstrate volatile and nonvolatile resistive switching (RS) modes. Of particular interest are structures that realize both RS modes in a single device. In this work, parylene-based nanocomposite memristors with MoO₃ nanoparticles have been studied in crossbar architecture, which is convenient for NCS implementation. For these structures, a reversible temperature-induced transition between volatile and nonvolatile RS modes was found if local, controlled via the compliance current, or external temperature is fine-tuned. In addition, the crossbar structures showed high endurance to cyclic RS, ability to retain states in nonvolatile mode and multilevel nature of RS. The obtained results open the possibility of using parylene-based crossbar structures in bioinspired NCSs.

We study a superlattice formed by tunnel-coupled identical antidots periodically situated in a two-dimensional topological insulator placed in a magnetic field. The superlattice spectrum can be controlled by gate electrodes or by changing the magnetic flux through the antidots. We demonstrate that a topologically protected qubit appears at the boundary between two regions with different fluxes. The qubit properties depend on the value of the flux jump on the boundary and can be controlled by the gate voltage. We derive the effective Hamiltonian of such a qubit and analyze the dependence of its properties on the main parameters of the superlattice: the tunnel coupling between antidots, and the probability of jumps with the spin flip.

We propose a system to produce multiple spin reversals of a polarized proton beam based on orbit-steerer dipoles already installed in the Nuclotron, a superconducting synchrotron at the Joint Institute for Nuclear Research, when the latter operates in the spin-transparency regime. The beam momentum of 3.54 GeV/c corresponds to the integer spin resonance γG=7">$\gamma G=7$. We report the results of numerical simulation of the proton spin dynamics pertinent to the acceleration up to γG=7">$\gamma G=7$, including the adiabatic capture of spins by navigators and the subsequent multiple spin flips. A feasibility of the pilot experiment to verify our approach with the current magnetic lattice of the Nuclotron is discussed. To preserve the beam polarization during the crossing of integer resonances we propose to employ intentional resonance-strength enhancements effected by controlled variations of the beam orbit during acceleration.

We study bound states in the continuum (BICs) in a Fabry–Pérot (FP) resonator within a quantum-mechanical waveguide. We show that besides typical FP BICs corresponding to a discrete set of cavity lengths, there is a pair of symmetric and antisymmetric twin BICs (TBICs) if isolated mirrors possess BIC themselves. In contrast to the FP BIC, the TBIC does not require the formation of standing waves of the FP resonance between the mirrors. Therefore, the energy and parameters of TBICs are almost independent of the length of the FP resonator, and their wavefunctions have an exponentially small amplitude between the mirrors. Results of the numerical simulation of the 2D quantum-mechanical waveguide with attractive potentials (“impurities”) playing the role of mirrors of an FP resonator are supported by the illustrative analytical model.

A brief review is given of the author’s recent achievements in classifying singular points of the Poynting vector patterns in electromagnetic fields of complex configuration. The deep connection between the topological structure of the force lines pattern and the law of energy conservation, the symmetry of the problem, and the dimension of the space has been unveiled.

The strong suppression of equilibrium magnetic tunneling in a graphene/hBN/graphene heterostructure caused by the Coulomb correlation gap in the tunneling density of states has been found. Comparison has shown that the suppression of the equilibrium tunneling conductivity G0">$G_0$ in a high magnetic field with a decrease in the temperature and the dependence of the observed gap width Δ on the filling factor of Landau levels ν are qualitatively similar to the respective results of similar experiments in GaAs heterostructures and has confirmed our hypothesis concerning the nature of the effect. However, the determined gap width Δ is much larger than those measured in all previous works in semiconductor heterostructures probably because the cyclotron energy in graphene is much higher than that in GaAs in the region of low Landau levels.

The ferromagnetic film in the electric film of a charged filament is studied theoretically. It has been shown that solitary magnetic inhomogeneities can be formed in this film in the presence of the inhomogeneous magnetoelectric interaction; their structure and nucleation conditions are determined by the sign of interacting charges. In particular, it has been established that the minimum magnitude of the linear charge density for the formation of an inhomogeneity in a positively charged filament is several times different from that for a negatively charged filament.

An ensemble of neutral excitations in a 1/3 Laughlin liquid is studied experimentally. It has been found that excitations induce a nonlinear optical response in the form of a quadratic dependence of the reflection signal on the pump power. The reported experimental results have shown that the observed effect is due to the contribution of the coherent anti-Stokes–Stokes scattering from the excited Laughlin liquid.