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Vol 104, No 11 (2016)

Condensed Matter

Circular photogalvanic effect caused by the transitions between edge and 2D states in a 2D topological insulator

Magarill L.I., Entin M.V.

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.

JETP Letters. 2016;104(11):771-775
pages 771-775 views

Aharonov–Bohm oscillations caused by non-topological surface states in Dirac nanowires

Enaldiev V.V., Volkov V.A.

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.

JETP Letters. 2016;104(11):784-790
pages 784-790 views

Redistribution of a material at femtosecond laser ablation of a thin silver film

Danilov P.A., Zayarny D.A., Ionin A.A., Kudryashov S.I., Rudenko A.A., Kuchmizhak A.A., Vitrik O.B., Kulchin Y.N., Zhakhovsky V.V., Inogamov N.A.

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.

JETP Letters. 2016;104(11):759-765
pages 759-765 views

Superconducting properties of long TiN wires

Mironov A.Y., Postolova S.V., Nasimov D.A.

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.

JETP Letters. 2016;104(11):766-770
pages 766-770 views

Aging effects in the nonequilibrium behavior of multilayer magnetic superstructures

Prudnikov V.V., Prudnikov P.V., Purtov A.N., Mamonova M.V.

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 TTc.

JETP Letters. 2016;104(11):776-783
pages 776-783 views

Bose–Einstei condensation of dipolar excitons in a ring trap

Chaplik A.V.

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.

JETP Letters. 2016;104(11):791-795
pages 791-795 views

Miscellaneous

Energy gap in tunneling spectroscopy: Effect of the chemical potential shift

Fedotov N.I., Zaitsev-Zotov S.V.

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.

JETP Letters. 2016;104(11):800-805
pages 800-805 views

Observation of subterahertz monochromatic transition radiation from a grating

Potylitsyn A.P., Naumenko G.A., Sukhikh L.G., Aryshev A., Shevelev M., Terunuma N., Urakawa J.

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.

JETP Letters. 2016;104(11):806-810
pages 806-810 views

Biophysics

Scroll-wave dynamics in the presence of ionic and conduction inhomogeneities in an anatomically realistic mathematical model for the pig heart

Majumder R., Pandit R., Panfilov A.V.

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.

JETP Letters. 2016;104(11):796-799
pages 796-799 views

Fields, Particles, and Nuclei

Phonon–particle coupling effects in odd–even double mass differences of semi-magic nuclei

Saperstein E.E., Baldo M., Pankratov S.S., Tolokonnikov S.V.

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.

JETP Letters. 2016;104(11):743-748
pages 743-748 views

Optics and Laser Physics

Light-induced atomic elevator in optical lattices

Prants S.V.

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.

JETP Letters. 2016;104(11):749-753
pages 749-753 views

Two-photon confocal microscopy as a tool for nonequilibrium charge-carrier lifetime tomography in semiconductor materials

Kalinushkin V.P., Uvarov O.V.

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.

JETP Letters. 2016;104(11):754-758
pages 754-758 views

Scientific Summaries

Spin effects in edge transport in two-dimensional topological insulators

Kononov A.A., Deviatov E.V.

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.

JETP Letters. 2016;104(11):811-820
pages 811-820 views

Erratum

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

Konovalov P.V., Pravdin S.F., Solovyova O.E., Panfilov A.V.
JETP Letters. 2016;104(11):821-821
pages 821-821 views