научный журнал по физике Письма в "Журнал экспериментальной и теоретической физики" ISSN: 0370-274X

ИОНИН А.А., КУДРЯШОВ С.И., ЛЕДНЕВ В.А., МАКАРОВ С.В., ПЕРШИН С.М., САЛТУГАНОВ П.Н., СЕЛЕЗНЕВ Л.В., СИНИЦЫН Д.В. — 2015 г.

Эмиссия эрозионной плазмы обнаружена при электрических коллекторных и оптико-эмиссионных спектральных исследованиях продуктов одноимпульсной фемтосекундной лазерной абляции поверхности оптического качества различных материалов (меди, титана, кремния) существенно ниже пороговой плотности энергии для термической абляции этих материалов. Она сменяет преимущественно электронную эмиссию при меньших плотностях энергии. Появление эрозионной плазмы коррелирует с насыщением зависимостей от плотности энергии коэффициента отражения самих мощных возбуждающих фемтосекундных лазерных импульсов накачки, отвечая “замораживанию” параметров (плотности, температуры носителей) электронной подсистемы материалов в масштабе возбуждающего ультракороткого лазерного импульса при монотонно растущей плотности энергии накачки.

БЕЛЫХ С.Ф., ЛОЗОВАН А.А., ТОЛСТОГУЗОВ А.Б. — 2015 г.

Получены аналитические формулы для расчета энергетического спектра F +(E) атомных ионов и энергетической зависимости степени ионизации а +(Е) атомов, распыленных из металлов в режиме нелинейных каскадов столкновений. Сравнение зависимостей а + (Е) для линейного и нелинейного режимов распыления демонстрирует существенное различие механизмов, ответственных за формирование зарядового состава атомных ионов.

КОВАЛЕВ В.М., ЧАПЛИК А.В. — 2015 г.

Излагается теория эффекта увлечения экситонов поверхностной волной Релея при температурах выше температуры конденсации экситонного газа, а также при нулевой температуре, когда наиболее ярко проявляются эффекты бозе-эйнштейновской конденсации экситонного газа. При высоких температурах вычислена величина тока акустического увлечения в экситонном газе с учетом экситон-экситонного взаимодействия. Показано, что для типичных экспериментальных параметров ток увлечения (при заданной интенсивности поверхностной акустической волны - ПАВ) не зависит от частоты акустической волны, а взаимодействие экситонов приводит к экранированию возмущения, вызванного ПАВ, вследствие чего с ростом плотности экситонов ток уменьшается экспоненциально быстро. При низких температурах при наличии конденсата ток увлечения конденсатных частиц имеет резонансный характер при приближении скорости боголюбовских возбуждений к скорости акустической волны, а величина тока линейна по частоте ПАВ. Ток увлечения надконденсатных частиц имеет пороговый характер: надконденсатные частицы увлекаются волной при скорости акустической волны, превышающей скорость боголонов. Величина надконденсатного тока обратно пропорциональна частоте акустической волны.

АВЕРЬЯНОВ Е.М. — 2015 г.

Установлена связь эффективного показателя преломления n ∗ = √n1n2 двумерной поликристаллической пленки диэлектрика в области прозрачности с показателями преломления n1,2 кристаллитов при положении осей 1, 2 эллипсоидов рефракции кристаллитов в плоскости пленки. Эта связь и соотношение L∗ = (L1 + L2)/2 между компонентами тензоров Лорентца для пленки и кристаллитов подтверждены сравнением с данными эксперимента для пленок сопряженного полимера с одноосными доменами.

ЧАПЛИК А.В. — 2015 г.

Исследованы дисперсионные зависимости плазменных мод в двухслойной системе и в структуре с полевым электродом вне рамок квазистатического приближения. Показано, что существование слабозатухающей моды в режиме сильных столкновений обеспечивается высокой проводимостью 2D плазмы. Однако это условие не носит порогового характера, как в случае одиночного неэкранированного слоя. Экранирование полевым электродом существенно подавляет проявление эффектов запаздывания.

МАЛЯРЕНКО П.Н., ПОСПЕЛОВ Е.А., ПРУДНИКОВ В.В., ПРУДНИКОВ П.В. — 2015 г.

Осуществлено численное исследование методами Монте-Карло неравновесной критической эволюции структурно неупорядоченных анизотропных магнетиков из начального низкотемпературного состояния с приведенной намагниченностью m o = 1 для широкого спектра спиновых концентраций: р = 1.0, 0. 95, 0.8, 0.6, 0.5. Показано, что в таких системах пиннинг доменных стенок на дефектах структуры при старте из низкотемпературного состояния приводит к существенному изменению неравновесных эффектов “старения” и “памяти” по сравнению с “чистой” системой. В результате в долговременном режиме на временах t - t w≫ t w≫ 1 выявлено аномально сильное замедление корреляционных эффектов. Показано, что спадание автокорреляционной функции со временем в нарушение скейлинговой зависимости осуществляется по степенному закону критической релаксации намагниченности. В итоге предельное значение флуктуационно-диссипативного отношения Х ∞ для структурно неупорядоченных систем с р < 1 становится равным нулю, в то время как для “чистой” системы Х ∞ = 0.784(5). Выделен неравновесный критический этап “сверхстарения” с показателем μ = 2.30(6) для слабо неупорядоченных и μ= 2.80(7) для сильно неупорядоченных систем.

FEDOROV I.A., PARFENYEVA V.M., SARYCHEV A.K., TARTAKOVSKY G.T., VERGELES S.S. — 2014 г.

We address thermal and strength phenomena occurring in metal nanoparticles due to excitation of surface plasmons. The temperature of the nanoparticle is found as a function of the plasmon population, allowing for the Kapitza heat boundary resistance and temperature dependencies of the host dielectric heat conductivity and the metal electrical conductivity. The latter is shown to result in the positive thermal feedback which leads to appearance of the maximum possible number of plasmon quanta in the steady-state regime. In the pulsed regime the number of plasmon quanta is shown to be restricted from above also by the ponderomotive forces, which tend to deform the nanoparticle. Obtained results provide instruments for the heat and strength management in the plasmonic engineering.

ASKHADULLIN R.SH., DMITRIEV V.V., MARTYNOV P.N., OSIPOV A.A., SENIN A.A., YUDIN A.N. — 2014 г.

We present results of experiments in superfluid phases of 3He confined in aerogel which strands are nearly parallel to one another. High temperature superfluid phases of 3He in this aerogel (ESP1 and ESP2) are biaxial chiral phases and have polar distorted ABM order parameter which orbital part forms 2D Larkin-Imry-Ma state. We demonstrate that this state can be anisotropic if the aerogel is squeezed in direction transverse to the strands. Values of this anisotropy in ESP1 and ESP2 phases are different, what leads to different NMR properties.

CHUBOVA N.M., DEMISHEV S.V., DYADKIN V.A., GILMANOV M.I., GLUSHKOV V.V., GRIGORIEV S.V., LOBANOVA I.I., SAMARIN A.N., SAMARIN N.A., SEMENOV A.V., SLUCHANKO N.E. — 2014 г.

We report results of the high frequency (60 GHz) electron spin resonance (ESR) study of the quantum critical metallic system Mn1− x Fe x Si. The ESR is observed for the first time in the concentration range 0 < x < 0. 24 at temperatures up to 50 K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of W¨olfle and Abrahams, are observed at quantum critical points x ∗ ∼ 0. 11 and xc ∼ 0. 24.

KLOPOT YA., OGANESIAN A., TERYAEV O. — 2014 г.

A connection between the axial anomaly and the vector meson dominance model is revealed for the processes of pseudoscalar meson-photon transitions. The analytical continuation of the anomaly sum rules, which are exact QCD relations following follow from the dispersive representation of the axial anomaly, to the time- like region is performed. Using these sum rules, the transition form factors of π 0, η, and η ′ mesons in this region are calculated. A good agreement with the available experimental data is found.

ENTIN M.V., MAGARILL L.I. — 2014 г.

A strip of the 2D HgTe topological insulator is studied. The same-spin edge states in an ideal system propagate in opposite directions on different sides of the strip and do not mix by tunneling. Impurities, edge irregularities, and phonons produce transitions between the contrapropagating edge states on different edges. This backscattering determines the conductivity of an infinitely long strip. The conductivity at finite temperature is determined in the framework of the kinetic equation. It is found that the conductivity exponentially grows with the strip width. In the same approximation the non-local resistance coefficients of a 4-terminal strip are found.

RUBTSOV G.I., SOKOLOVA E.V. — 2014 г.

The Fermi Large Area Telescope (LAT) has observed more than a hundred of gamma-ray pulsars, about one third of which are radio-quiet, i.e. not detected at radio frequencies. The most of radio-loud pulsars are detected by Fermi LAT by using the radio timing models, while the radio-quiet ones are discovered in a blind search. The difference in the techniques introduces an observational selection bias and, consequently, the direct comparison of populations is complicated. In order to produce an unbiased sample, we perform a blind search of gamma-ray pulsations using Fermi-LAT data alone. No radio data or observations at optical or X-ray frequencies are involved in the search process. We produce a gamma-ray selected catalog of 25 non-recycled gamma-ray pulsars found in a blind search, including 16 radio-quiet and 9 radio-loud pulsars. This results in the direct measurement of the fraction of radio-quiet pulsars srq = 64 ± 10 %, which is in agreement with the existing estimates from the population modeling in the outer magnetosphere model. The Polar cap models are disfavored due to a lower expected fraction and the prediction of age dependence. The age, gamma-ray energy flux, spin-down luminosity and sky location distributions of the radio-loud and radio-quiet pulsars from the catalog do not demonstrate any statistically significant difference. The results indicate that the radio-quiet and radio-loud pulsars belong to one and the same population. The catalog shows no evidence for the radio beam evolution.

GOR’KOV L.P. — 2014 г.

We studied interactions between the coherent excitations on disconnected arcs along a “bare” Fermi surface (the so-called Fermi arcs FAs) seen by angle-resolved photo emission spectroscopy (ARPES) in several underdoped (UD) cuprates and incommensurate charge density wave (IC CDW) ordering at lowering of the temperature. The carriers on FAs scatter strongly on the short-wavelength potential of CDW. The large momentum transfer relates FAs with the electronic states lying deeply under the chemical potential thus involving into consideration the Fermi liquid interactions. At low temperatures IC CDW may fully destroy low lying excitations on the Fermi arcs, leaving electrons on the pocket at the Г-point as the only charged elementary excitations in the CDW phase in UD cuprates. The results infer competition between superconducting and CDW order parameters.

RUBTSOV G.I., TROITSKY S.V. — 2014 г.

Energetic gamma rays scatter on soft background radiation when propagating through the Universe, producing electron-positron pairs (A.I. Nikishov, Sov. Phys. JETP 14, 393 (1962)). Gamma rays with energies between 100 GeV and a few TeV interact mostly with infrared background photons whose amount is poorly known experimentally but safely constrained from below by account of the contribution of observed light from known galaxies (R. C. Keenan, A. J. Barger, L. L. Cowie, and W.-H. Wang, Astrophys. J. 723, 40 (2010); arXiv:1102.2428). The expected opacity of the intergalactic space limits the mean free path of TeV gamma rays to dozens of Megaparsecs. However, TeV photons from numerous more distant sources have been detected (S. P. Wakely and D. Horan, http://tevcat.uchicago.edu/). This might be interpreted, in each particular case, in terms of hardening of the emitted spectrum caused by presently unknown mechanisms at work in the sources (S. Archambault et al. (VERITAS and Fermi LAT Collaborations), Astrophys. J. 785, L16 (2014); arXiv: 1403.4308). Here we show that this interpretation is not supported by the analysis of the ensemble of all observed sources. In the frameworks of an infrared-background model with the lowest opacity (R. C. Gilmore, R. S. Somerville, J. R. Primack, and A. Dominguez, Mon. Not. Roy. Astron. Soc. 422, 3189 (2012); arXiv:1104.0671), we reconstruct the emitted spectra of distant blazars and find that upward spectral breaks appear precisely at those energies where absorption effects are essential. Since these energies are very different for similar sources located at various distances, we conclude that the breaks are artefacts of the incorrect account of absorption and, therefore, the opacity of the Universe for gamma rays is overestimated even in the most conservative model. This implies that some novel physical or astrophysical phenomena should affect long-distance propagation of gamma rays. A scenario in which a part of energetic photons is converted to an inert new particle in the vicinity of the source and reconverts back close to the observer (M. Simet, D. Hooper, and P. Serpico, Phys. Rev. D 77, 063001 (2008); arXiv:0712.2825; M. Fairbairn, T. Rashba, and S. Troitsky, Phys. Rev. D 84, 125019 (2011); arXiv:0901.4085) does not contradict to our results. This new axion-like particle appears in several extensions of the Standard Model of particle physics (J. Jaeckel and A. Ringwald, Ann. Rev. Nucl. Part. Sci. 60, 405 (2010); arXiv: 1002.0329) and may constitute the dark matter (P. Arias et al., JCAP 1206, 013 (2012); arXiv:1201.5902)

ALEKSEEV P.A., CLEMENTYEV E.S., GRIBANOV A.V., HERMANN R.P., KLOBES B., KOZLENKO D.P., MENUSHENKOV A.P., NEMKOVSKI K.S., PANTALEI C., YAROSLAVTSEV A.A. — 2014 г.

Experimental results of the X-ray absorption spectroscopy, Mofibauer spectroscopy (isomer shift) and neutron diffraction are presented for the series of EuCu 2(Si xGe 1-x) 2 polycrystalline samples (0

ABRAMKIN D.S., GUTAKOVSKII A.K., PUTYATO M.A., SHAMIRZAEV T.S., SHAMIRZAEV V.T. — 2014 г.

Band alignment of heterostructures with pseudomorphic GaSb 1−xP x/GaP self-assembled quantum dots (SAQDs) lying on wetting layer was studied. Coexistence of type-I and type-II band alignment was found within the same heterostructure. Wetting layer has band alignment of type-I with the lowest electronic state belonging to the X XY valley of GaSb 1−xP x conduction band, in contrast to SAQDs, which have band alignment of type-II, independently of the ternary alloy composition x. It is shown that type-I - type-II transition is a result of GaP matrix deformation around the SAQD.

DENG H.X., NAUMENKO G.A., POTYLITSYN A.P., SHKITOV D.A., ZHANG J.B. — 2014 г.

In the paper the results of measurements of the coherent diffraction radiation yield generated by femtosecond electron beam are presented. It is shown that the simulated and experimental data agreed quite well. The coherent diffraction radiation can be considered as a real candidate to develop a source of radiation in far-infrared and terahertz range.

FIORE R., NIKOLAEV N.N., ZOLLER V.R. — 2014 г.

We show that a growth of the proton-proton total cross section with energy can be entirely attributed to the purely perturbative mechanism. The infrared regularization at rather short distances R c ~ 0.3 fm allows to extend the BFKL technique from deep inelastic to hadron-hadron scattering. With the account of the absorption corrections our results are in agreement with the LHC data on a pp t.

ALLOUL H., GILMUTDINOV I.F., MUKHAMEDSHIN I.R., SALOSIN M.A. — 2014 г.

Single crystals of sodium cobaltates Na xCoO 2 with x ~ 0.8 were grown by the floating zone technique. Using electrochemical Na de-intercalation method we reduced the sodium content in the as-grown crystals down to pure phase with 22 K Neel temperature and x ~ 0.77.The 59 Co NMR study in the paramagnetic state of the Tn = 22 K phase permitted us to evidence that at least 6 Co sites are differentiated. They could be separated by their magnetic behaviour into three types: a single site with cobalt close to non-magnetic Co 3+, two sites with the most magnetic cobalts in the system, and the remaining three sites displaying an intermediate behaviour. This unusual magnetic differentiation calls for more detailed NMR experiments on our well characterized samples.

AKHUNZYANOV R.R., SHEVCHENKO O.YU. — 2014 г.

The formulas directly connecting parton distribution functions (PDFs) at the leading (LO) and next to leading (NLO) QCD orders are applied with respect to both unpolarized and polarized valence PDFs. It is shown that the connection formulas allow without any restriction on the allowed QQ range for the analyzed data to produce improved LO results on valence PDFs, which strongly differ from the standard parametriza-tions on these quantities, and which could be obtained within the standard approach only by using the data produced at very high Q [1] values (that is hardly possible in reality).