Nonlinear dispersion of stationary waves in collisionless plasmas

A nonlinear dispersion of a general stationary wave in collisionless plasma is obtained in a non-differential form from a single-particle oscillation-center Hamiltonian. For electrostatic oscillations in nonmagnetized plasma, considered as a paradigmatic example, the linear dielectric function is generalized, and the trapped particle contribution to the wave frequency shift $\Delta\omega$ is found analytically as a function of the wave amplitude $a$. Smooth distributions yield $\Delta\omega\sim a^{1/2}$, as usual. However, beam-like distributions of trapped electrons result in different power laws, or even a logarithmic nonlinearity, which are derived as asymptotic limits of the same dispersion relation

Adiabatic nonlinear waves with trapped particles: II. Wave dispersion

A general nonlinear dispersion relation is derived in a nondifferential form for an adiabatic sinusoidal Langmuir wave in collisionless plasma, allowing for an arbitrary distribution of trapped electrons. The linear dielectric function is generalized, and the nonlinear kinetic frequency shift $\omega_{\rm NL}$ is found analytically as a function of the wave amplitude $a$. Smooth distributions yield $\omega_{\rm NL} \propto \sqrt{a}$, as usual. However, beam-like distributions of trapped electrons result in different power laws, or even a logarithmic nonlinearity, which are derived as asymptotic limits of the same dispersion relation. Such beams are formed whenever the phase velocity changes, because the trapped distribution is in autoresonance and thus evolves differently from the passing distribution. Hence, even adiabatic $\omega_{\rm NL}(a)$ is generally nonlocal.Comment: submitted together with Papers I and II

Transition from anticipatory to lag synchronization via complete synchronization in time-delay systems

The existence of anticipatory, complete and lag synchronization in a single system having two different time-delays, that is feedback delay $\tau_1$ and coupling delay $\tau_2$, is identified. The transition from anticipatory to complete synchronization and from complete to lag synchronization as a function of coupling delay $\tau_2$ with suitable stability condition is discussed. The existence of anticipatory and lag synchronization is characterized both by the minimum of similarity function and the transition from on-off intermittency to periodic structure in laminar phase distribution.Comment: 14 Pages and 12 Figure

Dissipative cosmological solutions

The exact general solution to the Einstein equations in a homogeneous Universe with a full causal viscous fluid source for the bulk viscosity index $m=1/2$ is found. We have investigated the asymptotic stability of Friedmann and de Sitter solutions, the former is stable for $m\ge 1/2$ and the latter for $m\le 1/2$. The comparison with results of the truncated theory is made. For $m=1/2$, it was found that families of solutions with extrema no longer remain in the full case, and they are replaced by asymptotically Minkowski evolutions. These solutions are monotonic.Comment: 17 pages, LaTeX 2.09, 1 figure. To be published in Classical and Quantum Gravit

Experimental verification of PbBi2_{2}Te4_{4} as a 3D topological insulator

The first experimental evidence is presented of the topological insulator state in PbBi$_{2}$Te$_{4}$. A single surface Dirac cone is observed by angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. Topological invariants $\mathbb{Z}_2$ are calculated from the {\it ab initio} band structure to be 1; (111). The observed two-dimensional iso-energy contours in the bulk energy gap are found to be the largest among the known three-dimensional topological insulators. This opens a pathway to achieving a sufficiently large spin current density in future spintronic devices.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let

A Theory of Magnets with Competing Double Exchange and Superexchange Interactions

We study the competition between ferromagnetic double exchange (DE) and nearest-neighbour antiferromagnetic exchange in CMR materials. Towards this end, a single site mean field theory is proposed which emphasizes the hopping-mediated nature of the DE contribution. We find that the competition between these two exchange interactions leads to ferro- or antiferromagnetic order with incomplete saturation of the (sub)lattice magnetization. This conclusion is in contrast to previous results in the literature which find a canted spin arrangement under similar circumstances. We attribute this difference to the highly anisotropic exchange interactions used elsewhere. The associated experimental implications are discussed.Comment: 4 pages, Latex-Revtex, 3 PostScript figures. Please see report cond-mat/980523

Получение методом «горячей стенки» тонких пленок PbxSn1–xTe для создания ИК-фотоприемников

Alloys of lead and tin telluride (PbxSn1–xTe) are materials with good thermoelectric properties, as well as semiconductors that can be used as long-wave infrared detectors. Polycrystalline telluride of PbxSn1–xTe (0.05 £ x £ 0.80) alloys has been synthesized by direct fusion technique. Thin films of these materials have been obtained by the hot wall method depositing Сorning 7059 on glass substrates at Tsub = (200–350) oC and vacuum of about 10–5 Torr. The microstructure of the films has been investigated by XRD, SEM and EDX methods. The X-ray spectra of thin films have been in satisfactorily agreement with the spectra of the powder target and indicated the absence of binary phases. The films have shown a natural cubic crystalline structure. While increasing the lead content, the unit cell parameter of the crystal also increases. The established linear relationship between the unit cell parameter and the elemental composition corresponds to Vegard's law. The SEM analysis has shown that the films are polycrystalline, have a columnar structure, are tightly packed and have good mechanical adhesion. The grain size depends on the chemical composition and temperature of the substrate. The electrical measurements have shown that the grown films are non-degenerate semiconductors of p-type conductivity. The conductivity of the films was in the range of σ = (3 × 101)–(1 × 104) Ω–1×cm–1. An increase of lead concentration leads to a decrease in electrical conductivity. Hall mobility in the grown thin films increases in the range of changes in the lead content from ~10 to ~23 at. %, and decreases with a further increase to ~33 at. %. At the same time, the strongest dependence of the decrease in mobility on an increase in temperature increase is observed for films with a high lead content and is explained by the predominant scattering of charge carriers by vibrations of the crystal lattice. For a sample with an average lead concentration, an alternative effect of two scattering mechanisms is observed in the temperature dependence of the mobility: by impurity ions and by phonons.Сплавы теллурида свинца и олова (PbxSn1–xTe) являются материалами с хорошими термоэлектрическими свойствами, а также полупроводниками, которые можно применять в качестве длинноволновых инфракрасных детекторов. Методом прямого плавления синтезирован поликристаллический теллурид сплавов PbxSn1–xTe (0,05 £ x £ 0,80). Тонкие пленки этих материалов были получены методом «горячей стенки» осаждением на стеклянные подложки Corning 7059 при Tsub = (200–350) oC и вакууме около 10–5 Торр. Микроструктура пленок исследовалась методами XRD, SEM и EDX. Рентгеновские спектры тонких пленок удовлетворительно соответствовали спектрам порошковой мишени и указывали на отсутствие бинарных фаз. Пленки демонстрировали естественную кубическую кристаллическую структуру. С возрастанием содержания свинца увеличивается параметр элементарной ячейки кристаллов. Установленная линейная зависимость между параметром элементарной ячейки и элементным составом соответствует закону Вегарда. SEM-анализ показал, что пленки являются поликристаллическими, имеют столбчатую структуру, плотно упакованы и обладают хорошей механической адгезией. Размеры зерен зависят от химического состава и температуры подложки. Электрические измерения показали, что выращенные пленки – это невырожденные полупроводники р-типа проводимости. Проводимость пленок находилась в диапазоне σ = (3 × 101)–(1 × 104) Ом–1×см–1. Увеличение концентрации свинца приводит к снижению электропроводности. Холловская подвижность в выращенных тонких пленках в диапазоне изменения содержания свинца от ~10 до ~23 ат. % возрастает, а при дальнейшем увеличении до ~33 ат. % – падает. При этом наиболее сильная зависимость падения подвижности от роста температуры наблюдается для пленок с большим содержанием свинца и объясняется преобладающим рассеянием носителей заряда на колебаниях кристаллической решетки. Для образца со средней концентрацией свинца в температурной зависимости подвижности наблюдается альтернативное влияние двух механизмов рассеяния: на ионах примеси и на фононах. На рис. 2 приведены температурные зависимости электропроводности для исследуемых пленок. В соответствии с табл. 1 и рис. 2 увеличение концентрации атомов свинца приводит к уменьшению электропроводности