О научном журнале«Письма в "Журнал экспериментальной и теоретической физики"»
Журнал срочной публикации кратких сообщений о наиболее интересных результатах исследований ученых в области теоретической и экспериментальной физики. Письма в ЖЭТФ является двуязычным журналом, принимая и публикуя статьи на русском и на английском языках.
Архив научных статейиз журнала «Письма в "Журнал экспериментальной и теоретической физики"»
A STUDY OF NEUTRINO DECAY IN MAGNETIC FIELD WITH THE “WORLDLINE INSTANTON” APPROACH
SATUNIN P. — 2015 г.
We study the process of neutrino decay to electron and IF-boson in the external magnetic field using the semiclassical “worldline instanton” approach. Being interested only in the leading exponential factor, we make calculations in a toy model, treating all particles as scalars. This calculation determines the effective threshold energy of the reaction as a function of the magnetic field. Possible astrophysical applications are discussed. It is emphasized that the method is general and is applicable to a decay of an arbitrary neutral particle into charged ones in the external electromagnetic field.
ANISOTROPIC FLAT BANDS ON THE SURFACE OF MULTILAYER GRAPHENELIKE LATTICE
ZYUZIN V.A., ZYUZM A.A. — 2015 г.
The fermionic energy spectrum on the surface of the multilayer honeycomb lattice with rhombohedral stacking has topologically protected flat bands. It is shown that topological phase transition occurs in the anisotropic multilayer graphene-like structure with strongly anisotropic intra-layer coupling, at which two flat bands with opposite chirality merge into one and split, opening up a gap in the energy spectrum, depending on the anisotropy of the intralayer hopping. The dispersion of the flat bands of the multilayer is anisotropic and the density of states is more singular in the vicinity of the transition.
ANISOTROPIC SPIN DIFFUSION IN LIQUID 3HE CONFINED IN NAFEN
DMITRIEV V.V., MELNIKOVSKY L.A., SENIN A.A., SOLDATOV A.A., YUDIN A.N. — 2015 г.
We report results of spin diffusion measurements in normal phase of liquid 3He confined in nafen. Nafen is a new type of aerogel and it consists of Al 2O 3 strands which are nearly parallel to one another at macroscopic distances. We examine two samples of nafen with different porosities using spin echo techniques. Spin diffusion of 3He along and across the strands was measured. The aerogel alignment is clearly evident from observed spin diffusion anisotropy. A theory describing this effect is developed and compared with the experiment.
ANISOTROPY OF THE FISSION FRAGMENTS FROM NEUTRON-INDUCED FISSION IN INTERMEDIATE ENERGY RANGE 1-200 MEV
BARABANOV A.L., GAGARSKI A.M., SHCHERBAKOV O.A., VAISHNENE L.A., VOROBYEV A.S. — 2015 г.
Angular distributions of fission fragments from the neutron-induced fission of 232Th, 235U, and 238U have been measured in the energy range 1-200 MeV at the neutron time-of-flight (TOF) spectrometer GNEIS using position sensitive multiwire proportional counters as fission fragment detector. A short description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors.
ANOMALOUS HALL EFFECT IN MNSI: INTRINSIC TO EXTRINSIC CROSSOVER
DEMISHEV S.V., GLUSHKOV V.V., IVANOV V.YU., LOBANOVA I.I. — 2015 г.
Temperature dependences of low field Hall resistivity ph are used to separate anomalous (p H a) and normal (R HB) contributions to Hall effect in chiral magnet MnSi (T c ~ 29.1 K). It is found that the transition between paramagnetic (T > T c) and magnetically ordered (T < T c) phases is accompanied by the change in anomalous Hall resistivity from low temperature behavior governed by Berry phase effects (ρ a H = μ 0S 2ρ 2M, T < T), to high temperature regime dominated by skew scattering (ρ a H = μ 0S 1ρM, T > Tc). The crossover between the intrinsic (~ p 2) and extrinsic (~/o) contributions to anomalous Hall effect develops together with the noticeable increase of the charge carriers’ concentration estimated from the normal Hall coefficient (from n/n Mn(T > T c) ~ 0.94 to n/n Mn(T < T c) ~ 1.5, n Mn ~ 4.2 • 10 22 cm -3). The observed features may correspond to the dramatic change in Fermi surface topology induced by the onset of long range magnetic order in MnSi.
BOUNDARY CONDITIONS AND SURFACE STATE SPECTRA IN TOPOLOGICAL INSULATORS
ENALDIEV V.V., VOLKOV V.A., ZAGORODNEV I.V. — 2015 г.
We study surface states spectra in 2D topological insulators (TIs) based on HgTe/(Hg,Cd)Te quantum wells and 3D Bi2Se3-type compounds by constructing a class of feasible time-reversal invariant boundary conditions (BCs) for an effective kp-Hamiltonian and a tight-binding model of the topological insulators. The BCs contain some phenomenological parameters which implicitly depend on both bulk Hamiltonian parameters and crystal potential behavior near the crystal surface. Space symmetry reduces the number of the boundary parameters to four real parameters in the 2D case and three in the 3D case. We found that the boundary parameters may strongly affect not only an energy spectrum but even the very existence of these states inside the bulk gap near the Brillouin zone center. Nevertheless, we reveal in frames of the tight-binding model that when surface states do not exist in the bulk gap in the Brillouin zone center they cross the gap in other points of the Brillouin zone in agreement with the bulk-boundary correspondence.
CALCULATION OF QCD PARAMETERS BY USING THE JET RESOLUTION PARAMETER
SALEH-MOGHADDAM R., ZOMORRODIAN M.E. — 2015 г.
We describe the measurement of the coupling constant from both the dispersive and the shape function models. This parameter depends on the scale at which the QCD process occurs. We present distributions of the jet resolution parameter (Уз). This parameter is one observable among the event shape variables. Both models are divided into the perturbative as well as the non-perturbative regions. The average value of the strong coupling constant is α s = 0.11887 ± 0.03537 being consistent with world average. We will explain all these features in this paper.
CHAOS INDUCED BY COUPLING BETWEEN JOSEPHSON JUNCTIONS
AZEMTSA-DONFACK H., BOTHA A.E., SHUKRINOV YU.M. — 2015 г.
It is found that, in a stack of intrinsic Josephson junctions in layered high temperature superconductors under external electromagnetic radiation, the chaotic features are triggered by inter-junction coupling, i.e. the coupling between different junctions in the stack. While the radiation is well known to produce chaotic effects in the single junction, the effect of inter-junction coupling is fundamentally different and it can lead to the onset of chaos via a different route to that of the single junction. A precise numerical study of the phase dynamics of intrinsic Josephson junctions, as described by the CCJJ+DC model, is performed. We demonstrate the charging of superconducting layers, in a bias current interval corresponding to a Shapiro step subharmonic, due to the creation of a longitudinal plasma wave along the stack of junctions. With increase in radiation amplitude chaotic behavior sets in. The chaotic features of the coupled Josephson junctions are analyzed by calculations of the Lyapunov exponents. We compare results for a stack of junctions to the case of a single junction and prove that the observed chaos is induced by the coupling between the junctions. The use of Shapiro step subharmonics may allow longitudinal plasma waves to be excited at low radiation power.
CLASSICAL INTEGRABLE SYSTEMS AND KNIZHNIK- ZAMOLODCHIKOV-BERNARD EQUATIONS
AMINOV G., LEVIN A., OLSHANETSKY M., ZOTOV A. — 2015 г.
This paper is a short review of results obtained as part of The Russian Foundation for Basic Research project 12-02-00594. We mainly focus on interrelations between classical integrable systems, Painleve- Schlesinger equations and related algebraic structures such as classical and quantum R-matrices. The constructions are explained in terms of simplest examples.
COMPARATIVE RESULTS ON THE DEFLECTION OF POSITIVELY AND NEGATIVELY CHARGED PARTICLES BY MULTIPLE VOLUME REFLECTIONS IN A MULTI-STRIP SILICON DEFLECTOR
AFONIN A.G., ARDUINI G., BAGLI E., BANDIERA L., BARICORDI S., BOLOGNINI D., BUTCHER M., CAVOTO G., CERUTTI F., CHESNOKOV YU.A., CLAPS G., DABAGOV S., DALPIAZ P., DURUM A.A., FERGUSON W., FULCHER J., GALLUCCIO F., GARATTINI M., GAVRIKOV YU.A., GERMOGLI G., GILARDONI S., GUIDI V., HALL G., HAMPAI D., HASAN S., IACOANGELI F., IVANOV YU.M., KOVALENKO A.D., LAPINA L.P., LECHNER A., LOSITO R., LUDOVICI L., MAISHEEV V.A., MASI A., MAZZOLARI A., MEREGHETTI A., METRAL E., MIRARCHI D., MONTESANO S., MURTAS F., PESARESI M., PREST M., RAYMOND M., REDAELLI S., ROSSI R., SANDOMIRSKIY YU.E., SANTACESARIA R., SCANDALE W., SCHOOFS P., SMIRNOV G., TARATIN A.M., VALENTE P., VALLAZZA E., VINCENZI D., YANOVICH A.A. — 2015 г.
Bent silicon crystals in channeling mode are already used for beam extraction and collimation in particle accelerators. Volume reflection of beam particles is more efficient than beam channeling; however the mean deflection angle is rather small. An experiment on the deflection of a 400 GeV/с proton beam and a 150 GeV/с 7beam at CERN using a multi-strip silicon deflector in reflection mode is described. The mean deflection angle of beam particles has been considerably increased due to sequential volume reflections realized in the deflector. This gives possibility for a successful usage of the multi-strip deflectors for beam collimation in high energy accelerators.
CONDUCTANCE OSCILLATIONS AT THE INTERFACE BETWEEN A SUPERCONDUCTOR AND THE HELICAL EDGE CHANNEL IN A NARROW HGTE QUANTUM WELL
DEVIATOV E.V., DVORETSKY S.A., EGOROV S.V., KONONOV A., KVON Z.D., MIKHAILOV N.N., TITOVA N. — 2015 г.
We experimentally investigate electron transport through the interface between a superconductor and the edge of a two-dimensional electron system with band inversion. The interface is realized as a tunnel NbN side contact to a narrow 8 nm HgTe quantum well. It demonstrates a typical Andreev behavior with finite conductance within the superconducting gap. Surprisingly, the conductance is modulated by a number of equally-spaced oscillations. The oscillations are present only within the superconducting gap and at lowest, below IK, temperatures. The oscillations disappear completely in magnetic fields, normal to the twodimensional electron system plane. In contrast, the oscillations’ period is only weakly affected by the highest, up to 14 T, in-plane oriented magnetic fields. We interpret this behavior as the interference oscillations in a helical one-dimensional edge channel due to a proximity with a superconductor.
CONDUCTANCE THROUGH CHAINS OF GE/SI QUANTUM DOTS: CROSSOVER FROM ONE-DIMENSIONAL TO QUASI-ONEDIMENSIONAL HOPPING
DVURECHENSKII A.V., GALPERIN Y.M., SMAGINA ZH.V., STEPINA N.P., VALKOVSKII V.V. — 2015 г.
Parallel chains of germanium quantum dots were grown on a patterned silicon (100) substrate prepared by the combination of nanoimprint lithography and ion irradiation. Strong anisotropy of the conductance between the direction of the chains and the perpendicular one was observed; the current-voltage curves being essentially superlinear. At low bias voltage dependence of the conductance obeys the Arrhenius law indicating one-dimensional (ID) hopping. With increase of the bias this dependence crosses over to G ∝ exp[-(T 0/T )1/2] explained by a quasi-ID transport involving hopping between nearest neighboring chains.
CONFINEMENT OF INERTIAL PARTICLES IN VISCOUS BOUNDARY LAYER OF TURBULENT FLOW
BELAN S., CHERNYKH A., LEBEDEV V., VERGELES S. — 2015 г.
We examine space and momentum probability distribution of inertial particles when they are placed in the viscous boundary sublayer of a turbulent flow. We demonstrate that at varying elasticity of the particle collisions with the wall the confinement-deconfinement transition occurs: at β > β c the particles are blocked near the wall whereas at /3 > /3 C they gradually pass into bulk. Here /3 is elasticity coefficient and βc = exp(-π/√3).
CONTROLLING OF GOOS-HANCHEN SHIFT VIA BIEXCITON COHERENCE IN A QUANTUM DOT
ASADPOUR S.H., MAHMOUDI M., NASEHI R., SOLEIMANI H.R. — 2015 г.
Controlling of the Goos-Honchen (GH) shifts of the reflected and transmitted probe pulses through a cavity containing four-level GaAs/AlGaAs quantum dot with 15 periods of 17.5 nm GaAs wells and 25-nm Alo.3Gao.7As barriers is investigated. Under appropriate conditions, the probe absorption can be converted to the probe gain, therefore the controlling of negative and positive GH shift in the both reflected and transmitted probe beams can be occurred simultaneously. Our obtained results show that the group index of the probe beams could be negative or positive in both reflected and transmitted pulses. Therefore, simultaneous subluminal or superluminal light propagation in reflected and transmitted pulses can be achieved.
CORRELATIONS OF MUTUAL POSITIONS OF CHARGE DENSITY WAVES NODES IN SIDE-BY-SIDE PLACED INAS WIRES MEASURED WITH SCANNING GATE MICROSCOPY
HARDTDEGEN H., SCHAPERS TH., VOLK CH., WINDEN A., ZHUKOV A.A. — 2015 г.
We investigate the correlations of mutual positions of charge density waves nodes in side-by-side placed InAs nanowires in presence of a conductive atomic force microscope tip served as a mobile gate at helium temperatures. Scanning gate microscopy scans demonstrate mutual correlation of positions of charge density waves nodes of two wires. A general mutual shift of the nodes positions and “crystal lattice mismatch” defect were observed. These observations demonstrate the crucial role of Coulomb interaction in formation of charge density waves in InAs nanowires.
ELECTRON IMPACT IONIZATION OF TUNGSTEN IONS IN STATISTICAL MODEL
DEMURA A.V., KADOMTSEV M.B., LISITSA V.S., SHURYGIN V.A. — 2015 г.
The statistical model for calculations of the electron impact ionization cross sections of multielectron ions is developed for the first time. The model is based on the idea of collective excitations of atomic electrons with the local plasma frequency, while the Thomas-Fermi model is used for atomic electrons density distribution. The electron impact ionization cross sections and related ionization rates of tungsten ions from W + up to W 63+ are calculated and then compared with the vast collection of modern experimental and modeling results. The reasonable correspondence between experimental and theoretical data demonstrates the universal nature of statistical approach to the description of atomic processes in multielectron systems.
ELECTRON-CONFORMATIONAL TRANSFORMATIONS GOVERN THE TEMPERATURE DEPENDENCE OF THE CARDIAC RYANODINE RECEPTOR GATING
IAPAROV B.I., MARKHASIN V.S., MOSKVIN A.S., RYVKIN A.M., SOLOVYOVA O.E. — 2015 г.
Temperature influences many aspects of cardiac excitation-contraction coupling, in particular, hypothermia increases the open probability (P open) of cardiac sarcoplasmic reticulum (SR) Ca 2+-release channels (ryanodine-sensitive RyR channels) rising the SR Ca 2+ load in mammalian myocytes. However, to the best of our knowledge, no theoretical models are available for that effect. Traditional Markov chain models do not provide a reasonable molecular mechanistic insight on the origin of the temperature effects. Here in the paper we address a simple physically clear electron-conformational model to describe the RyR gating and argue that a synergetic effect of external thermal fluctuation forces (Gaussian-Markovian noise) and internal friction via the temperature stimulation/suppression of the open-close RyR tunneling probability can be considered as a main contributor to temperature effects on the RyR gating. Results of the computer modeling allowed us to successfully reproduce all the temperature effects observed for an isolated RyR gating in vitro under reducing the temperature: increase in P open and mean open time without any significant effect on mean closed time.
ELECTRONIC AND MAGNETIC PROPERTIES OF THE NEW IRON-BASED SUPERCONDUCTOR [LI 1-XFE XOH]FESE
NEKRASOV I.A., SADOVSKII M.V. — 2015 г.
We present the results of paramagnetic LDA band structure calculations: band dispersions, densities of states and Fermi surfaces, for the new iron based high-temperature superconductor LiOHFeSe. Main structural motif providing bands in the vicinity of the Fermi level is FeSe layer which is isostructural to the bulk FeSe prototype superconductor. The bands crossing the Fermi level and Fermi surfaces of the new compound are typical for other iron based superconductors. Experimentally it was shown that introduction of Fe ions into LiOH layer gives rise to ferromagnetic ordering of the Fe ions at Tc = 10 K. To study magnetic properties of [Li 0.8Fe 0.2OH]FeSe system we have performed LSD A calculations for √5 × √5 super lattice and found ferromagnetism within the Li 4Fe(OH) layer. To estimate the Curie temperature we obtained Fe-Fe exchange interaction parameters for Heisenberg model from our LSDA calculations, leading to theoretical value of Curie temperature 10.4 К in close agreement with experiment.
ELECTRONIC STRUCTURE OF NAFEAS SUPERCONDUCTOR: LDA+DMFT CALCULATIONS COMPARED WITH ARPES EXPERIMENT
NEKRASOV I.A., PAVLOV N.S., SADOVSKII M.V. — 2015 г.
We present the results of extended theoretical LDA+DMFT calculations for a new iron-pnictide high temperature superconductor NaFeAs compared with the recent high quality angle-resolved photoemission (ARPES) experiments on this system (see arXiv:1409.1537). The universal manifestation of correlation effects in iron-pnictides is narrowing of conducting bands near the Fermi level. Our calculations demonstrate that for NaFeAs the effective mass is renormalized on average by a factor of the order of 3, in good agreement with ARPES data. This is essentially due to correlation effects on Fe-3d orbitals only and no additional interactions with any kind of Boson modes, as suggested in the work mentioned, are necessary to describe the experiment. Also we show that ARPES data taken at about 160 eV beam energy most probably corresponds to k z = tt Brillouin zone boundary, while ARPES data measured at about 80 eV beam energy rather represents k z = 0. Contributions of different Fe-3d orbitals into spectral function map are also discussed.
EMERGENT PHYSICS ON MACH’S PRINCIPLE AND THE ROTATING VACUUM
JANNES G., VOLOVIK G.E. — 2015 г.
Mach’s principle applied to rotation can be correct if one takes into account the rotation of the quantum vacuum together with the Universe. Whether one can detect the rotation of the vacuum or not depends on its properties. If the vacuum is fully relativistic at all scales, Mach’s principle should work and one cannot distinguish the rotation: in the rotating Universe+vacuum, the co-rotating bucket will have a flat surface (not concave). However, if there are “quantum gravity” effects which violate Lorentz invariance at high energy, then the rotation will become observable. This is demonstrated by analogy in condensed-matter systems, which consist of two subsystems: superfluid background (analog of vacuum) and “relativistic” excitations (analog of matter). For the low-energy (long-wavelength) observer the rotation of the vacuum is not observable. In the rotating frame, the “relativistic” quasiparticles feel the background as a Minkowski vacuum, i.e. they do not feel the rotation. Mach’s idea of the relativity of rotational motion does indeed work for them. But rotation becomes observable by high-energy observers, who can see the quantum gravity effects.