Том 105, № 5 (2017)

The performance of dense wavelength division multiplexed (DWDM) soliton transmission system for returnto-zero (RZ) and non-return-to-zero (NRZ) modulation formats have been investigated. The main aim of this paper is to estimate and mitigate the four wave mixing (FWM) power by using in-line optical phase conjugator (OPC). The effect of FWM has been estimated using real fiber link having nonlinear and attenuation losses. The FWM power is strongly suppressed by introducing destructive interference between the first and second halves of in-line OPC. It has been indicated that RZ with OPC yields the better performance with FWM power suppression (more than 20 dBm in certain cases) with reasonable bit error rate and Q-factor.

We discuss the type of the general macroscopic parity-violating effects, when there is the current along the vortex, which is concentrated in the vortex core. We consider vortices in chiral superfluids with Weyl points. In the vortex core, the positions of the Weyl points form the skyrmion structure. We show that the mass current concentrated in such a core is provided by the spectral flow through the Weyl points according to the Adler–Bell–Jackiw equation for chiral anomaly.

A new efficient method is proposed for inducing magnetism on the surface of a topological insulator through the deposition of a thin film of an isostructural magnetic insulator whose atomic composition is maximally close to that of the topological material. Such a design prevents the formation of a strong interface potential between subsystems. As a result, the topological state freely penetrates into the magnetic region, where it interacts with the exchange field and gets significantly split at the Dirac point. It is shown that the application of this approach to thin films of a tetradymite-like topological insulator allows realizing the quantum anomalous Hall state with a band gap of several tens of meV.

A phenomenological model has been proposed for tunneling electron spin resonance (ESR) of an isolated surface spin situated in a scanning tunneling microscope (STM), which explains the dependence of features (local maxima) of the tunneling current on the radio-frequency (RF) electric field and on the position of the tip with respect to the spin. A crossover of the line shape of the resonance signals, whose nature in weak and strong pumping fields corresponds to Lorentzian and Fano resonances, respectively, has been interpreted. New ESR–STM effects that are linear and nonlinear in the RF field and are promising for developing the methods of controlling spin qubits have been predicted.

Tensile-strained germanium films in Ge/GeSn/Si/GeSnSi multilayer heterostructures grown by molecularbeam epitaxy on Si(001) substrates are investigated by Raman spectroscopy. Biaxial tensile strains in the films reach 1.5%, which exceeds values previously obtained for this system. Splitting of frequencies of long-wavelength optical phonons is experimentally observed; i.e., the shift of the frequency of the singlet induced by biaxial tensile strains is larger than the shift of the frequency of the doublet in agreement with calculations. The strain-induced shift of Raman scattering peaks from two-phonon scattering in germanium is also detected.

The possibility of producing polarized molecules of hydrogen isotopes by their spin separation in the inhomogeneous field of superconducting magnets has been demonstrated. This method proposed in our previous works has been implemented with a source of polarized atoms developed at the Budker Institute for Nuclear Physics. The measured flux of polarized molecules is compared with the simulation results. The possibility of developing a more intense source of polarized molecules is discussed.

Externally stimulated fluctuations of the size of a particle in an asymmetric environment result in its directional motion. This is demonstrated by considering the particle drift in a periodic symmetric channel, which arises due to fluctuations of the particle size. The emergence of the drift is caused by the time variation of the particle entropy, whereas fluctuations of the diffusion coefficient accompanying fluctuations of the size enhance the drift. The effect of the geometry of the channel and the amplitude and frequency of fluctuations on the drift velocity is studied by the Brownian dynamics method. A coarse-grained analytical description of the process is proposed whose predictions are in satisfactory agreement with the results of simulation.

A complete set of quasiparticle operators diagonalizing operators of the Coulomb and exchange interactions of copper and oxygen holes in cuprate high-temperature superconductors (HTSCs) is obtained. A scheme of energy bands in the regime of strong electron correlations is constructed. The effective operator for the singleband approximation is obtained with this scheme. It is found that the role of three-site correlations in hole HTSCs is negligibly small. This circumstance explains both the sharp increase in critical temperatures of hole HTSCs in comparison with electron-doped ones and the asymmetry between the spectra of collective spin excitations in these compounds.