


Vol 104, No 11 (2016)
- Year: 2016
- Articles: 14
- URL: https://ogarev-online.ru/0021-3640/issue/view/9707
Condensed Matter
Circular photogalvanic effect caused by the transitions between edge and 2D states in a 2D topological insulator
Abstract
The electron absorption and the edge photocurrent of a 2D topological insulator are studied for transitions between edge states to 2D states. The circular polarized light is found to produce the edge photocurrent, the direction of which is determined by light polarization and edge orientation. It is shown that the edge-state current is found to exceed the 2D current owing to the topological protection of the edge states.



Aharonov–Bohm oscillations caused by non-topological surface states in Dirac nanowires
Abstract
One intriguing fingerprint of surface states in topological insulators is the Aharonov–Bohm effect in magnetoconductivity of nanowires. We show that surface states in nanowires of Dirac materials (bismuth, bismuth antimony, and lead tin chalcogenides) being in non-topological phase, exhibit the same effect as amendment to magnetoconductivity of the bulk states. We consider a simple model of a cylindrical nanowire, which is described by the 3D Dirac equation with a general T-invariant boundary condition. The boundary condition is determined by a single phenomenological parameter whose sign defines topological-like and non-topological surface states. The non-topological surface states emerge outside the gap. In a longitudinal magnetic field B, they lead to Aharonov–Bohm amendment for the density of states and correspondingly for the conductivity of the nanowire. The phase of these magnetic oscillations increases with B from π to 2π.



Redistribution of a material at femtosecond laser ablation of a thin silver film
Abstract
Energy-dispersive X-ray microspectroscopy is used for the first time to quantitatively study the spatial displacement of the material of a 100-nm silver film irradiated by a single femtosecond laser pulse focused on a small spot in the diffraction limit. The silver mass distribution over radial cross sections is determined and matter balance is analyzed for the resulting radially symmetric submicron structures of a microcone with a nanospike with various heights and a through hole. Hydrodynamic processes and phase transitions inducing the melting of the film, motion of the melt, and its recrystallization within a focal spot are studied.



Superconducting properties of long TiN wires
Abstract
The low-temperature transport properties of titanium nitride wires with the width comparable with or much larger than the superconducting coherence length are studied experimentally. It is shown that the reduction of the width of wires does not affect the transport properties at the temperatures above the superconducting transition temperature and electron transport in this temperature range is determined by quantum contributions to the conductivity from weak localization and electron–electron interaction. It is established that the reduction of the width of wires does not change the superconducting transition temperature but completely suppresses the topological Berezinskii–Kosterlitz–Thouless transition. It is found that the threshold magnetic field increases with a decrease in the width of wires.



Aging effects in the nonequilibrium behavior of multilayer magnetic superstructures
Abstract
A numerical Monte Carlo study of the nonequilibrium behavior of multilayer magnetic superstructures consisting of alternating magnetic and nonmagnetic nanolayers is performed. The calculated two-time autocorrelation function and the staggered magnetization of the structure at its evolution starting from various initial states are analyzed. The analysis reveals aging effects characterized by a slowing down of the relaxation and correlation characteristics in the system with the waiting time. It is shown that, in contrast to bulk magnetic systems, the aging effects in magnetic superstructures arise not only near the ferromagnetic ordering temperature Tc in the films but also within a wide temperature range at T ≤ Tc.



Bose–Einstei condensation of dipolar excitons in a ring trap
Abstract
The temperature of Bose–Einstein condensation and the fraction of particles in a condensate for a system of spatially indirect dipole excitons in an electrostatic ring trap have been found. If only levels of the radial motion close to the bottom of the potential well of the trap are populated considerably, the oscillatory model of the single-particle spectrum is applicable. In this case, even the strong exciton–exciton interaction can be taken into account.



Miscellaneous
Energy gap in tunneling spectroscopy: Effect of the chemical potential shift
Abstract
We study the effect of a shift of the chemical potential level on the tunneling conductance spectra. In the systems with gapped energy spectra, significant chemical-potential dependent distortions of the differential tunneling conductance curves, dI/dV, arise in the gap region. An expression is derived for the correction of dI/dV, which in a number of cases is found to be large. The sign of the correction depends on the chemical potential level position with respect to the gap. The correction of associated with the dI/dV chemical potential shift has a nearly linear dependence on the tip-sample separation z and vanishes at z → 0.



Observation of subterahertz monochromatic transition radiation from a grating
Abstract
Transition radiation appearing when a charged particle crosses the interface between two media with different dielectric constants, e.g., a metal–vacuum interface, has been well studied in a wide spectral range. However, primarily, radiation from smooth interfaces has been studied. Transition radiation from conducting gratings (grating transition radiation) is experimentally studied and theoretically analyzed in this work. In this case, it is possible to obtain monochromatic radiation with a tunable frequency depending on the rotation angle of the grating with respect to the electron momentum. Coherent grating transition radiation can be efficiently used as a source of terahertz radiation based on the use of a compact electron accelerator with an energy below 10 MeV and a bunch duration of ≤1 ps.



Biophysics
Scroll-wave dynamics in the presence of ionic and conduction inhomogeneities in an anatomically realistic mathematical model for the pig heart
Abstract
Nonlinear waves of the reaction–diffusion (RD) type occur in many biophysical systems, including the heart, where they initiate cardiac contraction. Such waves can form vortices called scroll waves, which result in the onset of life-threatening cardiac arrhythmias. The dynamics of scroll waves is affected by the presence of inhomogeneities, which, in a very general way, can be of (i) ionic type; i.e., they affect the reaction part, or (ii) conduction type, i.e., they affect the diffusion part of an RD-equation. We demonstrate, for the first time, by using a state-of-the-art, anatomically realistic model of the pig heart, how differences in the geometrical and biophysical nature of such inhomogeneities can influence scroll-wave dynamics in different ways. Our study reveals that conduction-type inhomogeneities become increasingly important at small length scales, i.e., in the case of multiple, randomly distributed, obstacles in space at the cellular scale (0.2–0.4 mm). Such configurations can lead to scroll-wave break up. In contrast, ionic inhomogeneities affect scroll-wave dynamics significantly at large length scales, when these inhomogeneities are localized in space at the tissue level (5–10 mm). In such configurations, these inhomogeneities can attract scroll waves, by pinning them to the heterogeneity, or lead to scroll-wave breakup.



Fields, Particles, and Nuclei
Phonon–particle coupling effects in odd–even double mass differences of semi-magic nuclei
Abstract
A method is developed to consider the particle–phonon coupling (PC) effects in the calculation of the odd–even double mass differences (DMD) in semi-magic nuclei starting from the free NN potential. The PC correction δΣPC to the mass operator Σ is found in gL2-approximation, gL being the vertex of creating the L-phonon. The tadpole term of the operator δΣPC is taken into account. The method is based on a direct, without any use of the perturbation theory, solution of the Dyson equation with the mass operator Σ(ε) = Σ0 + δΣPC(ε) for finding the single-particle energies and Z-factors. In its turn, they are used as an input for finding different PC corrections to the DMD values. Results for a chain of even semi-magic nuclei 200−206Pb show that the inclusion of the PC corrections makes agreement with the experimental data significantly better.



Optics and Laser Physics
Light-induced atomic elevator in optical lattices
Abstract
It is shown how an atomic elevator that can elevate falling cold atoms in a vertical optical lattice can be created. The effect appears near resonance owing to the nonlinear interaction between the electronic and mechanical degrees of freedom of an atom, which is responsible for its random walk in rigid optical lattices without any modulation and additional action. Numerical experiments involving spontaneous emission demonstrate that random walk of atoms and light-induced atomic elevator can be observed in a real experiment.



Two-photon confocal microscopy as a tool for nonequilibrium charge-carrier lifetime tomography in semiconductor materials
Abstract
By the example of ZnSe crystals, the capabilities of two-photon confocal microscopy as a tool for obtaining “planar” maps of nonequilibrium charge-carrier lifetimes in semiconductor materials and for investigating other direct-gap semiconductors and semiconductor heterostructures are considered. It is shown that such maps with a depth step and an in-plane resolution of several microns can be obtained for distances from the surface up to 1 mm. This technique is used to visualize inhomogeneities in the crystals under study and to examine their structure and luminescence characteristics.



Scientific Summaries
Spin effects in edge transport in two-dimensional topological insulators
Abstract
Investigations of topological insulators, which are two- and three-dimensional systems with a gap in the bulk spectrum and topologically protected gapless edge states, are of considerable fundamental interest at present. The experiments confirming the presence of the edge states in two-dimensional systems with inverted bands and problems of determining the nature of such states in these experiments are reviewed. Special attention is focused on spin-sensitive experiments since the topological edge states have a nontrivial spin structure.



Erratum
Erratum to: “Scroll Wave dynamics in a model of the heterogeneous heart”


