WorldWideScience

Sample records for high-angle phonon scattered

  1. Phonon scattering in graphite

    International Nuclear Information System (INIS)

    Wagner, P.

    1976-04-01

    Effects on graphite thermal conductivities due to controlled alterations of the graphite structure by impurity addition, porosity, and neutron irradiation are shown to be consistent with the phonon-scattering formulation 1/l = Σ/sub i equals 1/sup/n/ 1/l/sub i/. Observed temperature effects on these doped and irradiated graphites are also explained by this mechanism

  2. Towards weighing individual atoms by high-angle scattering of electrons

    Energy Technology Data Exchange (ETDEWEB)

    Argentero, G.; Mangler, C.; Kotakoski, J.; Eder, F.R.; Meyer, J.C., E-mail: Jannik.Meyer@univie.ac.at

    2015-04-15

    We consider theoretically the energy loss of electrons scattered to high angles when assuming that the primary beam can be limited to a single atom. We discuss the possibility of identifying the isotopes of light elements and of extracting information about phonons in this signal. The energy loss is related to the mass of the much heavier nucleus, and is spread out due to atomic vibrations. Importantly, while the width of the broadening is much larger than the energy separation of isotopes, only the shift in the peak positions must be detected if the beam is limited to a single atom. We conclude that the experimental case will be challenging but is not excluded by the physical principles as far as considered here. Moreover, the initial experiments demonstrate that the separation of gold and carbon based on a signal that is related to their mass, rather than their atomic number. - Highlights: • We explore how energy loss spectroscopy could be used to obtain information about the mass, rather than the charge, of atoms. • The dose and precision that would be needed to distinguish between the two isotopes of carbon, C12 and C13, is estimated. • Signal broadening due to phonons is included in the calculation. • Initial experiments show the separation between gold and carbon based on their mass rather than charge.

  3. Phonon scattering in metallic glasses

    International Nuclear Information System (INIS)

    Black, J.L.

    1979-01-01

    The purpose of this article is to review some recent theoretical and experimental developments in the study of metallic glasses at temperatures near or below 1K. In this temperature regime, it appears that practically all glasses, whether metallic or insulating, behave in a similar fashion. The fact that such similarities occur, despite substantial structural differences between metallic and insulating glasses, constitutes a major theoretical challenge. This challenge, however, is not directly addressed in what follows. Instead, the evidence for universal behavior and the theory which is necessary to understand this evidence are emphasized. It turns out that most of this evidence involves a comparison of phonon scattering in metallic glasses with its counterpart in insulating glasses

  4. Phonon lineshapes in atom-surface scattering

    Energy Technology Data Exchange (ETDEWEB)

    MartInez-Casado, R [Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ (United Kingdom); Sanz, A S; Miret-Artes, S [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones CientIficas, Serrano 123, E-28006 Madrid (Spain)

    2010-08-04

    Phonon lineshapes in atom-surface scattering are obtained from a simple stochastic model based on the so-called Caldeira-Leggett Hamiltonian. In this single-bath model, the excited phonon resulting from a creation or annihilation event is coupled to a thermal bath consisting of an infinite number of harmonic oscillators, namely the bath phonons. The diagonalization of the corresponding Hamiltonian leads to a renormalization of the phonon frequencies in terms of the phonon friction or damping coefficient. Moreover, when there are adsorbates on the surface, this single-bath model can be extended to a two-bath model accounting for the effect induced by the adsorbates on the phonon lineshapes as well as their corresponding lineshapes.

  5. Scattering of phonons by dislocations

    International Nuclear Information System (INIS)

    Anderson, A.C.

    1979-01-01

    By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The most basic questions are still debated in the literature. It therefore is pointless to attempt a quantitative comparison between an extensive accumulation of experimental data on the one hand, and the numerous theoretical models on the other. Instead, this chapter will attempt to glean a few qualitative conclusions from the existing experimental data. These results will then be compared with two general models which incorporate, in a qualitative manner, most of the proposed theories of the phonon-dislocation interaction. Until very recently, measurement of thermal conductivity was the only means available to probe the interaction between phonons and defects at phonon frequencies above the standard ultrasonic range of approx. = 10 9 Hz. The introductory paragraphs provide a brief review of the thermal-conductivity technique and the problems which are encountered in practice. There is also a brief presentation of the theoretical models and the complications that may occur in more realistic situations

  6. Phonon scattering by isotopic impurities

    International Nuclear Information System (INIS)

    Dacol, D.K.

    1974-06-01

    The effects upon vibrations of a perfect crystal lattice due to the replacement of some of its atoms by isotopes of these atoms are studied. The approach consists in considering the isotopic impurities as scattering centres for the quanta of the elastic waves the objective is to obtain the scattering amplitudes. These amplitudes are obtained through a canonical transformation method which was introduced by Chevalier and Rideau in the study of the Wentzel's model in quantum field theory

  7. "Phonon" scattering beyond perturbation theory

    Science.gov (United States)

    Qiu, WuJie; Ke, XueZhi; Xi, LiLi; Wu, LiHua; Yang, Jiong; Zhang, WenQing

    2016-02-01

    Searching and designing materials with intrinsically low lattice thermal conductivity (LTC) have attracted extensive consideration in thermoelectrics and thermal management community. The concept of part-crystalline part-liquid state, or even part-crystalline part-amorphous state, has recently been proposed to describe the exotic structure of materials with chemical- bond hierarchy, in which a set of atoms is weakly bonded to the rest species while the other sublattices retain relatively strong rigidity. The whole system inherently manifests the coexistence of rigid crystalline sublattices and fluctuating noncrystalline substructures. Representative materials in the unusual state can be classified into two categories, i.e., caged and non-caged ones. LTCs in both systems deviate from the traditional T -1 relationship ( T, the absolute temperature), which can hardly be described by small-parameter-based perturbation approaches. Beyond the classical perturbation theory, an extra rattling-like scattering should be considered to interpret the liquid-like and sublattice-amorphization-induced heat transport. Such a kind of compounds could be promising high-performance thermoelectric materials, due to the extremely low LTCs. Other physical properties for these part-crystalline substances should also exhibit certain novelty and deserve further exploration.

  8. Theory of Raman scattering in coupled electron-phonon systems

    Science.gov (United States)

    Itai, K.

    1992-01-01

    The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.

  9. Phonon Scattering and Confinement in Crystalline Films

    Science.gov (United States)

    Parrish, Kevin D.

    The operating temperature of energy conversion and electronic devices affects their efficiency and efficacy. In many devices, however, the reference values of the thermal properties of the materials used are no longer applicable due to processing techniques performed. This leads to challenges in thermal management and thermal engineering that demand accurate predictive tools and high fidelity measurements. The thermal conductivity of strained, nanostructured, and ultra-thin dielectrics are predicted computationally using solutions to the Boltzmann transport equation. Experimental measurements of thermal diffusivity are performed using transient grating spectroscopy. The thermal conductivities of argon, modeled using the Lennard-Jones potential, and silicon, modeled using density functional theory, are predicted under compressive and tensile strain from lattice dynamics calculations. The thermal conductivity of silicon is found to be invariant with compression, a result that is in disagreement with previous computational efforts. This difference is attributed to the more accurate force constants calculated from density functional theory. The invariance is found to be a result of competing effects of increased phonon group velocities and decreased phonon lifetimes, demonstrating how the anharmonic contribution of the atomic potential can scale differently than the harmonic contribution. Using three Monte Carlo techniques, the phonon-boundary scattering and the subsequent thermal conductivity reduction are predicted for nanoporous silicon thin films. The Monte Carlo techniques used are free path sampling, isotropic ray-tracing, and a new technique, modal ray-tracing. The thermal conductivity predictions from all three techniques are observed to be comparable to previous experimental measurements on nanoporous silicon films. The phonon mean free paths predicted from isotropic ray-tracing, however, are unphysical as compared to those predicted by free path sampling

  10. Light scattering by surface phonons in crystals

    International Nuclear Information System (INIS)

    Albuquerque, E.L. de

    1981-01-01

    A theory of inelastic light scattering by surface acoustic phonons in homogeneous crystals is presented. The Green functions are determined by the use of a classical linear response method and used to evaluate the Brillouin cross section. The acoustic modes are found from solutions to the acoustical-wave equation and boundary conditions appropriated. Two light-scattering mechanisms, namely the surface corrugation and bulk elasto-optic effect are analyzed by deriving optical fields which satisfy both the acousto-optically driven wave equation and the electromagnetic boundary conditions. No restrictions are imposed concerning the angle of incidence of the light. Some representative computed Brillouin lineshapes are also presented and their features discussed. (Author) [pt

  11. Light scattering by surface phonons in crystals

    International Nuclear Information System (INIS)

    Albuquerque, D.L.

    1980-01-01

    Theory of inelastic light scattering by surface acoustic phonons homogeneous crystals is presented. The Green functions are determined by the use of a classical linear response method and used to evaluate the Brillouin cross section. The acoustic modes are found from solutions to the acoustical-wave equation and boundary conditions appropriated. Two light-scattering mechanisms, amely the surface corrugation and bulk elasto-optic effect are analyzed by deriving optical fields which satisfy both the acousto-optically driven wave equation and the electromagnetic boundary conditions. No restrictions are imposed concerning the angle of incidence of the light. Some representative computed Brillouin ineshapes are also presented and their features discussed. (author) [pt

  12. Magnon and phonon thermometry with inelastic light scattering

    Science.gov (United States)

    Olsson, Kevin S.; An, Kyongmo; Li, Xiaoqin

    2018-04-01

    Spin caloritronics investigates the interplay between the transport of spin and heat. In the spin Seebeck effect, a thermal gradient across a magnetic material generates a spin current. A temperature difference between the energy carriers of the spin and lattice subsystems, namely the magnons and phonons, is necessary for such thermal nonequilibrium generation of spin current. Inelastic light scattering is a powerful method that can resolve the individual temperatures of magnons and phonons. In this review, we discuss the thermometry capabilities of inelastic light scattering for measuring optical and acoustic phonons, as well as magnons. A scattering spectrum offers three temperature sensitive parameters: frequency shift, linewidth, and integrated intensity. We discuss the temperatures measured via each of these parameters for both phonon and magnons. Finally, we discuss inelastic light scattering experiments that have examined the magnon and phonon temperatures in thermal nonequilibrium which are particularly relevant to spin caloritronic phenomena.

  13. Normal processes of phonon-phonon scattering and thermal conductivity of germanium crystals with isotopic disorder

    CERN Document Server

    Kuleev, I G

    2001-01-01

    The effect of normal processes of the phonon-phonon scattering on the thermal conductivity of the germanium crystals with various isotopic disorder degrees is considered. The phonon pulse redistribution in the normal scattering processes both inside each oscillatory branch (the Simons mechanism) and between various phonon oscillatory branches (the Herring mechanism) is accounted for. The contributions of the longitudinal and cross-sectional phonons drift motion into the thermal conductivity are analyzed. It is shown that the pulse redistribution in the Herring relaxation mechanism leads to essential suppression of the longitudinal phonons drift motion in the isotopically pure germanium crystals. The calculations results of thermal conductivity for the Herring relaxation mechanism agree well with experimental data on the germanium crystals with various isotopic disorder degrees

  14. Quasiparticle-phonon coupling in inelastic proton scattering

    International Nuclear Information System (INIS)

    Weissbach, B.

    1980-01-01

    Multistep-processes in inelastic proton scattering from 89 Y are analyzed by using CCBA and DWBA on a quasiparticle phonon nuclear structure model. Indirect excitations caused by quasiparticle phonon coupling effects are found to be very important for the transition strengths and the shape of angular distributions. Core excitations are dominant for the higher order steps of the reaction. (author)

  15. One-phonon scattering of ultra cold neutrons in copper

    International Nuclear Information System (INIS)

    Holas, A.

    1977-01-01

    Experiments with ultra cold neutrons (UCN) showed that their lifetime in a closed vessel is much smaller than expected. In order to explain this phenomenon, many different mechanisms leading to heating of UCN were proposed, among other things one-phonon coherent inelastic scattering (with phonon absorption). This paper shows quantitatively the contribution of this process to the total heating of UCN

  16. On the interplay between phonon-boundary scattering and phonon-point-defect scattering in SiGe thin films

    Science.gov (United States)

    Iskandar, A.; Abou-Khalil, A.; Kazan, M.; Kassem, W.; Volz, S.

    2015-03-01

    This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a single-crystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film.

  17. Long-Wavelength Phonon Scattering in Nonpolar Semiconductors

    DEFF Research Database (Denmark)

    Lawætz, Peter

    1969-01-01

    The long-wavelength acoustic- and optical-phonon scattering of carriers in nonpolar semiconductors is considered from a general point of view. The deformation-potential approximation is defined and it is shown that long-range electrostatic forces give a nontrivial correction to the scattering...... of the very-short-range nature of interactions in a covalent semiconductor....

  18. Flexural-Phonon Scattering Induced by Electrostatic Gating in Graphene

    DEFF Research Database (Denmark)

    Gunst, Tue; Kaasbjerg, Kristen; Brandbyge, Mads

    2017-01-01

    Graphene has an extremely high carrier mobility partly due to its planar mirror symmetry inhibiting scattering by the highly occupied acoustic flexural phonons. Electrostatic gating of a graphene device can break the planar mirror symmetry, yielding a coupling mechanism to the flexural phonons......-limiting factor, and show how the carrier density and temperature scaling of the mobility depends on the electrostatic environment. Our findings may explain the high deformation potential for in-plane acoustic phonons extracted from experiments and, furthermore, suggest a direct relation between device symmetry...

  19. Phonon scattering in graphene over substrate steps

    DEFF Research Database (Denmark)

    Sevincli, Haldun; Brandbyge, Mads

    2014-01-01

    We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance...

  20. Theory of the Influence of Phonon-Phonon and Electron-Phonon Interactions on the Scattering of Neutrons by Crystals

    International Nuclear Information System (INIS)

    Kokkedee, J.J.J.

    1963-01-01

    As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0 o K) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest

  1. Electron-phonon interaction and scattering in Si and Ge: Implications for phonon engineering

    International Nuclear Information System (INIS)

    Tandon, Nandan; Albrecht, J. D.; Ram-Mohan, L. R.

    2015-01-01

    We report ab-initio results for electron-phonon (e-ph) coupling and display the existence of a large variation in the coupling parameter as a function of electron and phonon dispersion. This variation is observed for all phonon modes in Si and Ge, and we show this for representative cases where the initial electron states are at the band gap edges. Using these e-ph matrix elements, which include all possible phonon modes and electron bands within a relevant energy range, we evaluate the imaginary part of the electron self-energy in order to obtain the associated scattering rates. The temperature dependence is seen through calculations of the scattering rates at 0 K and 300 K. The results provide a basis for understanding the impacts of phonon scattering vs. orientation and geometry in the design of devices, and in analysis of transport phenomena. This provides an additional tool for engineering the transfer of energy from carriers to the lattice

  2. High-angle scattering events strongly affect light collection in clinically relevant measurement geometries for light transport through tissue

    International Nuclear Information System (INIS)

    Canpolat, M.; Mourant, J.R.

    2000-01-01

    Measurement of light transport in tissue has the potential to be an inexpensive and practical tool for non-invasive tissue diagnosis in medical applications because it can provide information on both morphological and biochemical properties. To capitalize on the potential of light transport as a diagnostic tool, an understanding of what information can be gleaned from light transport measurements is needed. We present data concerning the sensitivity of light transport measurements, made in clinically relevant geometries, to scattering properties. The intensity of the backscattered light at small source-detector separations is shown to be sensitive to the phase function, and furthermore the collected light intensity is found to be correlated with the amount of high-angle scattering in the medium. (author)

  3. Phonon scattering in graphene over substrate steps

    International Nuclear Information System (INIS)

    Sevinçli, H.; Brandbyge, M.

    2014-01-01

    We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights.

  4. Mapping momentum-dependent electron-phonon coupling and nonequilibrium phonon dynamics with ultrafast electron diffuse scattering

    Science.gov (United States)

    Stern, Mark J.; René de Cotret, Laurent P.; Otto, Martin R.; Chatelain, Robert P.; Boisvert, Jean-Philippe; Sutton, Mark; Siwick, Bradley J.

    2018-04-01

    Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the K -point TO phonon of A1' symmetry (K -A1' ) and along the entire TO branch between Γ -K , not only to the Γ -E2 g phonon. We also determine that the subsequent phonon relaxation of these strongly coupled optical phonons involve three stages: decay via several identifiable channels to TA and LA phonons (1 -2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30 -40 ps) and interband relaxation of the TA/LA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems has a strong influence on emergent properties.

  5. Neutron scattering on equilibrium and nonequilibrium phonons, excitons and polaritons

    International Nuclear Information System (INIS)

    Broude, V.L.; Sheka, E.F.

    1978-01-01

    A number of problems of solid-state physics representing interest for neutron spectroscopy of future is considered. The development of the neutron inelastic scattering spectroscopy (neutron spectroscopy of equilibrium phonons) is discussed with application to nuclear dynamics of crystals in the thermodynamic equilibrium. The results of high-flux neutron source experiments on molecular crystals are presented. The advantages of neutron inelastic scattering over optical spectroscopy are discussed. The spectroscopy of quasi-equilibrium and non-equilibrium quasi-particles is discussed. In particular, the neutron scattering on polaritons, excitons in thermal equilibrium and production of light-excitons are considered. The problem of the possibility of such experiments is elucidated

  6. Uncertainty in the inelastic resonant scattering assisted by phonons

    International Nuclear Information System (INIS)

    Garcia, N.; Garcia-Sanz, J.; Solana, J.

    1977-01-01

    We have analyzed the inelastic minima observed in new results of He atoms scattered from LiF(001) surfaces. This is done considering bound state resonance processes assisted by phonons. The analysis presents large uncertainties. In the range of uncertainty, we find two ''possible'' bands associated with the vibrations of F - and Li + , respectively. Many more experimental data are necessary to confirm the existence of these processes

  7. Four-phonon scattering significantly reduces intrinsic thermal conductivity of solids

    Science.gov (United States)

    Feng, Tianli; Lindsay, Lucas; Ruan, Xiulin

    2017-10-01

    For decades, the three-phonon scattering process has been considered to govern thermal transport in solids, while the role of higher-order four-phonon scattering has been persistently unclear and so ignored. However, recent quantitative calculations of three-phonon scattering have often shown a significant overestimation of thermal conductivity as compared to experimental values. In this Rapid Communication we show that four-phonon scattering is generally important in solids and can remedy such discrepancies. For silicon and diamond, the predicted thermal conductivity is reduced by 30% at 1000 K after including four-phonon scattering, bringing predictions in excellent agreement with measurements. For the projected ultrahigh-thermal conductivity material, zinc-blende BAs, a competitor of diamond as a heat sink material, four-phonon scattering is found to be strikingly strong as three-phonon processes have an extremely limited phase space for scattering. The four-phonon scattering reduces the predicted thermal conductivity from 2200 to 1400 W/m K at room temperature. The reduction at 1000 K is 60%. We also find that optical phonon scattering rates are largely affected, being important in applications such as phonon bottlenecks in equilibrating electronic excitations. Recognizing that four-phonon scattering is expensive to calculate, in the end we provide some guidelines on how to quickly assess the significance of four-phonon scattering, based on energy surface anharmonicity and the scattering phase space. Our work clears the decades-long fundamental question of the significance of higher-order scattering, and points out ways to improve thermoelectrics, thermal barrier coatings, nuclear materials, and radiative heat transfer.

  8. A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale

    Energy Technology Data Exchange (ETDEWEB)

    Bong, Victor N-S; Wong, Basil T. [Swinburne Sarawak Research Centre for Sustainable Technologies, Faculty of Engineering, Computing & Science, Swinburne University of Technology Sarawak Campus, 93350 Kuching, Sarawak (Malaysia)

    2015-08-28

    Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering.

  9. A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale

    International Nuclear Information System (INIS)

    Bong, Victor N-S; Wong, Basil T.

    2015-01-01

    Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering

  10. Phonon scattering in quasi-one-dimensional structure

    Energy Technology Data Exchange (ETDEWEB)

    Bourahla, B., E-mail: bourahla_boualem@yahoo.f [Laboratoire de Physique et Chimie Quantique, Universite de Tizi Ouzou, BP 17 RP 15000 (Algeria); Laboratoire de Physique de l' etat Condense, UMR 6087, Universite du Maine, 72085 Le Mans (France); Nafa, O. [Laboratoire de Physique et Chimie Quantique, Universite de Tizi Ouzou, BP 17 RP 15000 (Algeria); Tigrine, R. [Laboratoire de Physique et Chimie Quantique, Universite de Tizi Ouzou, BP 17 RP 15000 (Algeria); Laboratoire de Physique de l' etat Condense, UMR 6087, Universite du Maine, 72085 Le Mans (France)

    2011-02-15

    We introduce a model to study a symmetric nanocontact, whereby its mechanical properties can be analyzed via the vibration spectra. The model system consists of two groups of triple semi-infinite atomic chains joined by atoms in between. The matching method theoretical approach is used to calculate the coherent reflection and transmission scattering probabilities, the characteristic vibration Green functions and densities of states (DOS), for the vibration components of the individual atomic sites that constitute a complete representation of the nanocontact domain boundaries. The nanocontact observables are numerically calculated for different cases of elastic hardening and softening, to investigate how the local dynamics can respond to changes in the microscopic environment on the nanocontact domain. The analysis of the vibration spectra and the DOS demonstrate the fluctuations, related to Fano resonances, due to the coherent coupling between traveling phonons and the localized vibration modes in the nanocontact domain.

  11. Electron–phonon interaction and scattering in phosphorene

    Science.gov (United States)

    Fan, Xiaolin; Zhao, Guojun; Wang, Shudong

    2018-04-01

    The electron–phonon scattering of phosphorene is investigated via performing first-principles calculations. Our results reveal that the scattering rates are negligible at the valence band maximum (VBM) and conduction band minimum, but they are much larger away from the band edges. The scattering rates increase with the rising temperature. The relaxation times run up to ~850 fs around the VBM at 1 K, and they will decrease with the increasing temperature. In addition, we find that the mean free paths (MFPs) are anisotropic. The MFPs along the armchair direction are two times larger than that along the zigzag direction near the band edges. According to our results, we predict that the extraction of hot holes is best achieved along the armchair direction in phosphorene with a 65 nm range at 1 K. The best extraction range of hot electrons is less than 30 nm along the armchair direction at 1 K. On the other hand, the extraction range of hot holes and hot electrons will decrease to 15 nm along both directions in phosphorene at 300 K.

  12. RAMAN SCATTERING BY ACOUSTIC PHONONS AND STRUCTURAL PROPERTIES OF FIBONACCI, THUE-MORSE AND RANDOM SUPERLATTICES

    OpenAIRE

    Merlin , R.; Bajema , K.; Nagle , J.; Ploog , K.

    1987-01-01

    We report structural studies of incommensurate and random GaAs-AlAs superlattices using Raman scattering by acoustic phonons. Properties of the structure factor of Fibonacci and Thue-Morse superlattices are discussed in some detail.

  13. Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

    International Nuclear Information System (INIS)

    Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

    2015-01-01

    Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons

  14. Phonon dispersion relation in zircon, ZrSiO4 using inelastic neutron scattering at a pulsed neutron source

    International Nuclear Information System (INIS)

    Mittal, R.; Chaplot, S.L.; Parthasarathy, R.; Bull, M.J.; Harris, M.J.

    2000-01-01

    The coherent inelastic neutron scattering technique is used for the measurements of phonon dispersion relation in a geophysically important mineral zircon using PRISMA spectrometer as ISIS, UK. Lattice dynamical calculations of the phonon dispersion relation are carried out using a shell model. The one-phonon structure factors are calculated for selecting the Bragg points for the measurements and assignment of phonons to different branches. The calculations are in good agreement with the measured phonon dispersion relation. (author)

  15. One phonon resonant Raman scattering in semiconductor quantum wires: Magnetic field effect

    Energy Technology Data Exchange (ETDEWEB)

    Betancourt-Riera, Re., E-mail: rbriera@posgrado.cifus.uson.mx [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonor, (Mexico); Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico); Betancourt-Riera, Ri. [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonora (Mexico); Nieto Jalil, J.M. [Tecnologico de Monterrey-Campus Sonora Norte, Bulevar Enrique Mazon Lopez No. 965, C.P. 83000, Hermosillo, Sonora (Mexico); Riera, R. [Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico)

    2013-02-01

    We have developed a theory of one phonon resonant Raman scattering in a semiconductor quantum wire of cylindrical geometry in the presence of an external magnetic field distribution, parallel to the cylinder axis. The effect of the magnetic field in the electron and hole states, and in the Raman scattering efficiency, is determinate. We consider the electron-phonon interaction using a Froehlich-type Hamiltonian, deduced for the case of complete confinement phonon modes by Comas and his collaborators. We also assume T=0 K, a single parabolic conduction and valence bands. The spectra are discussed for different magnetic field values and the selection rules for the processes are also studied.

  16. Towards phonon photonics: scattering-type near-field optical microscopy reveals phonon-enhanced near-field interaction

    International Nuclear Information System (INIS)

    Hillenbrand, Rainer

    2004-01-01

    Diffraction limits the spatial resolution in classical microscopy or the dimensions of optical circuits to about half the illumination wavelength. Scanning near-field microscopy can overcome this limitation by exploiting the evanescent near fields existing close to any illuminated object. We use a scattering-type near-field optical microscope (s-SNOM) that uses the illuminated metal tip of an atomic force microscope (AFM) to act as scattering near-field probe. The presented images are direct evidence that the s-SNOM enables optical imaging at a spatial resolution on a 10 nm scale, independent of the wavelength used (λ=633 nm and 10 μm). Operating the microscope at specific mid-infrared frequencies we found a tip-induced phonon-polariton resonance on flat polar crystals such as SiC and Si 3 N 4 . Being a spectral fingerprint of any polar material such phonon-enhanced near-field interaction has enormous applicability in nondestructive, material-specific infrared microscopy at nanoscale resolution. The potential of s-SNOM to study eigenfields of surface polaritons in nanostructures opens the door to the development of phonon photonics--a proposed infrared nanotechnology that uses localized or propagating surface phonon polaritons for probing, manipulating and guiding infrared light in nanoscale devices, analogous to plasmon photonics

  17. Experimental determination of the berilium phonon spectra using inelastic neutro scattering

    International Nuclear Information System (INIS)

    Sirota, N.N.; Bulat, I.A.

    1976-01-01

    A study has been made of in elastic scattering of cold neutrons with energies between 0.0022 and 0.00523 eV by polycrystalline beryllium and restoration of its phonon spectrum. The specimen studied is a block of polycrystalline beryllium. In the case of beryllium the averaging of coherent effects upon scattering on a thick specimen takes place as a result of multiple internal Bragg-type reflections of neutrons which undergo inelastic scattering with absorption of phonons. The thickness of the spheric averaging layer for Esub(6) = 0.00523 eV is almost equal to the maximum dimension of the Brillouin band. The phonon spectrum of beryllium for three mean energies used of incident neutrons has been demonstrated. The phonon spectrum of beryllium, measured for the first time, is of interest for quantitative calculations of a number of its physical properties

  18. Low-Field Mobility and Galvanomagnetic Properties of Holes in Germanium with Phonon Scattering

    DEFF Research Database (Denmark)

    Lawætz, Peter

    1968-01-01

    acoustic scattering, no overall consistency is found between available galvanomagnetic data and deformation potentials derived directly from experiments on strained Ge. The discrepancies may be ascribed to ionized-impurity scattering, but at higher temperatures where optical phonon scattering is operative......A theoretical calculation of the low-field galvanomagnetic properties of holes in Ge has been carried out incorporating all relevant details of the band structure. The scattering is limited to acoustic and optical phonons and is described by the deformation potentials a, b, d, and d0. For pure......, the deviations are still appreciable. We are led to conclude that the deformation-potential theory of phonon scattering needs reconsideration, and a nontrivial correction is pointed out....

  19. Phononic thermal conductivity in silicene: the role of vacancy defects and boundary scattering

    Science.gov (United States)

    Barati, M.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.

    2018-04-01

    We calculate the thermal conductivity of free-standing silicene using the phonon Boltzmann transport equation within the relaxation time approximation. In this calculation, we investigate the effects of sample size and different scattering mechanisms such as phonon–phonon, phonon-boundary, phonon-isotope and phonon-vacancy defect. We obtain some similar results to earlier works using a different model and provide a more detailed analysis of the phonon conduction behavior and various mode contributions. We show that the dominant contribution to the thermal conductivity of silicene, which originates from the in-plane acoustic branches, is about 70% at room temperature and this contribution becomes larger by considering vacancy defects. Our results indicate that while the thermal conductivity of silicene is significantly suppressed by the vacancy defects, the effect of isotopes on the phononic transport is small. Our calculations demonstrate that by removing only one of every 400 silicon atoms, a substantial reduction of about 58% in thermal conductivity is achieved. Furthermore, we find that the phonon-boundary scattering is important in defectless and small-size silicene samples, especially at low temperatures.

  20. Elastic scattering by hot electrons and apparent lifetime of longitudinal optical phonons in gallium nitride

    Energy Technology Data Exchange (ETDEWEB)

    Khurgin, Jacob B., E-mail: jakek@jhu.edu [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Bajaj, Sanyam; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2015-12-28

    Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results.

  1. Phonons in Solid Hydrogen and Deuterium Studied by Inelastic Coherent Neutron Scattering

    DEFF Research Database (Denmark)

    Nielsen, Mourits

    1973-01-01

    Phonon dispersion relations have been measured by coherent neutron scattering in solid para-hydrogen and ortho-deuterium. The phonon energies are found to be nearly equal in the two solids, the highest energy in each case lying close to 10 meV. The pressure and temperature dependence of the phonon...... energies have been measured in ortho-deuterium and the lattice change determined by neutron diffraction. When a pressure of 275 bar is applied, the phonon energies are increased by about 10%, and heating the crystal to near the melting point decreases them by about 7%. The densities of states, the specific...... heats, and the Debye temperatures have been deduced and found to be in agreement with the published experimental results. The Debye temperatures are 118 K for hydrogen and 114 K for deuterium. For hydrogen the Debye-Waller factor has been measured by incoherent neutron scattering and it corresponds...

  2. An unusually strong resonant phonon scattering by 3-d impurities in II-VI semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lonchakov, A.T.; Sokolov, V.I.; Gruzdev, N.B. [Institute of Metal Physics, Russian Academy of Sciences, Ural Branch, S. Kovalevskaya Str. 18, 620219 Ekaterinburg (Russian Federation)

    2004-11-01

    Low temperature phonon heat conductivity was measured for ZnSe and ZnS crystals, doped with 3-d impurities. A strong resonance-like phonon scattering by 3-d ions with orbitally degenerate ground state was observed. The Jahn-Teller effect is proposed as the reason of the strong resonance-like behaviour of heat conductivity. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Temperature dependence of Raman scattering by optical phonons in ZnTe

    International Nuclear Information System (INIS)

    Simmonds, P.E.; Martin, A.D.

    1987-01-01

    Measurements of the temperature dependence of Raman scattering by optical phonons between temperatures 5 K and 293 K in the II-VI semiconductor ZnTe are reported. Typical Raman spectra for ZnTe at different temperatures are shown and values of the measured LO and TO phonon Raman shifts and linewidths are given for T = 5, 77, and 293 K. The measured linewidth of the LO Raman line as a function of temperature is plotted and compared with model predictions based on various three- and four-phonon processes

  4. One phonon resonant Raman scattering in free-standing quantum wires

    International Nuclear Information System (INIS)

    Zhao, Xiang-Fu; Liu, Cui-Hong

    2007-01-01

    The scattering intensity (SI) of a free-standing cylindrical semiconductor quantum wire for an electron resonant Raman scattering (ERRS) process associated with bulk longitudinal optical (LO) phonon modes and surface optical (SO) phonon modes is calculated separately for T=0 K. The Frohlich interaction is considered to illustrate the theory for GaAs and CdS systems. Electron states are confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Numerical results and a discussion are also presented for various radii of the cylindrical

  5. Phonon scattering and thermal conductance properties in two coupled graphene nanoribbons modulated with bridge atoms

    International Nuclear Information System (INIS)

    Tan, Shi-Hua; Tang, Li-Ming; Chen, Ke-Qiu

    2014-01-01

    The phonon scattering and thermal conductance properties have been studied in two coupled graphene nanoribbons connected by different bridge atoms by using density functional theory in combination with non-equilibrium Green's function approach. The results show that a wide range of thermal conductance tuning can be realized by changing the chemical bond strength and atom mass of the bridge atoms. It is found that the chemical bond strength (bridge atom mass) plays the main role in phonon scattering at low (high) temperature. A simple equation is presented to describe the relationship among the thermal conductance, bridge atom, and temperature.

  6. One- and two-phonon mixed-symmetry states in 94Mo in high-resolution electron and proton scattering

    International Nuclear Information System (INIS)

    Fujita, H.; Botha, N.T.; Burda, O.; Carter, J.; Fearick, R.W.; Foertsch, S.V.; Fransen, C.; Kuhar, M.; Lenhardt, A.; Neumann-Cosel, P. von; Neveling, R.; Pietralla, N.; Ponomarev, V.Yu.; Richter, A.; Scholten, O.; Sideras-Haddad, E.; Smit, F.D.; Wambach, J.

    2007-01-01

    High-resolution inelastic electron scattering experiments at the S-DALINAC and proton scattering experiments at iThemba LABS permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2 + states of the nucleus 94 Mo. The combined analysis reveals the one-phonon content of the mixed-symmetry state and its isovector character suggested by microscopic calculations. The purity of two-phonon 2 + states is extracted

  7. Phonon populations by nanosecond-pulsed Raman scattering in Si

    International Nuclear Information System (INIS)

    Compaan, A.; Lee, M.C.; Trott, G.J.

    1985-01-01

    Since the first time-resolved Raman studies of phonon populations under pulsed-laser-annealing conditions, a number of cw Raman studies have been performed which provide a much improved basis for interpreting the pulsed Raman data. Here we present new pulsed Raman results and interpret them with reference to temperature-dependent resonance effects, high-carrier-density effects, phonon anharmonicity, and laser-induced strain effects. The pulsed Raman data: Stokes to anti-Stokes ratios, shift and shape of the first-order peak, and second-order spectra: indicate the existence of a phase in which the Raman signal disappears followed by a rapidly cooling solid which begins within 300 K of the 1685 K normal melting temperature of Si. We identify a major difficulty in pulsed Raman studies in Si to be the decrease in Raman intensity at high temperatures

  8. Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices.

    Science.gov (United States)

    Ravichandran, Jayakanth; Yadav, Ajay K; Cheaito, Ramez; Rossen, Pim B; Soukiassian, Arsen; Suresha, S J; Duda, John C; Foley, Brian M; Lee, Che-Hui; Zhu, Ye; Lichtenberger, Arthur W; Moore, Joel E; Muller, David A; Schlom, Darrell G; Hopkins, Patrick E; Majumdar, Arun; Ramesh, Ramamoorthy; Zurbuchen, Mark A

    2014-02-01

    Elementary particles such as electrons or photons are frequent subjects of wave-nature-driven investigations, unlike collective excitations such as phonons. The demonstration of wave-particle crossover, in terms of macroscopic properties, is crucial to the understanding and application of the wave behaviour of matter. We present an unambiguous demonstration of the theoretically predicted crossover from diffuse (particle-like) to specular (wave-like) phonon scattering in epitaxial oxide superlattices, manifested by a minimum in lattice thermal conductivity as a function of interface density. We do so by synthesizing superlattices of electrically insulating perovskite oxides and systematically varying the interface density, with unit-cell precision, using two different epitaxial-growth techniques. These observations open up opportunities for studies on the wave nature of phonons, particularly phonon interference effects, using oxide superlattices as model systems, with extensive applications in thermoelectrics and thermal management.

  9. Semiclassical multi-phonon theory for atom-surface scattering: Application to the Cu(111) system.

    Science.gov (United States)

    Daon, Shauli; Pollak, Eli

    2015-05-07

    The semiclassical perturbation theory of Hubbard and Miller [J. Chem. Phys. 80, 5827 (1984)] is further developed to include the full multi-phonon transitions in atom-surface scattering. A practically applicable expression is developed for the angular scattering distribution by utilising a discretized bath of oscillators, instead of the continuum limit. At sufficiently low surface temperature good agreement is found between the present multi-phonon theory and the previous one-, and two-phonon theory derived in the continuum limit in our previous study [Daon, Pollak, and Miret-Artés, J. Chem. Phys. 137, 201103 (2012)]. The theory is applied to the measured angular distributions of Ne, Ar, and Kr scattered from a Cu(111) surface. We find that the present multi-phonon theory substantially improves the agreement between experiment and theory, especially at the higher surface temperatures. This provides evidence for the importance of multi-phonon transitions in determining the angular distribution as the surface temperature is increased.

  10. A bond-order theory on the phonon scattering by vacancies in two-dimensional materials.

    Science.gov (United States)

    Xie, Guofeng; Shen, Yulu; Wei, Xiaolin; Yang, Liwen; Xiao, Huaping; Zhong, Jianxin; Zhang, Gang

    2014-05-28

    We theoretically investigate the phonon scattering by vacancies, including the impacts of missing mass and linkages (τ(V)(-1)) and the variation of the force constant of bonds associated with vacancies (τ(A)(-1)) by the bond-order-length-strength correlation mechanism. We find that in bulk crystals, the phonon scattering rate due to change of force constant τ(A)(-1) is about three orders of magnitude lower than that due to missing mass and linkages τ(V)(-1). In contrast to the negligible τ(A)(-1) in bulk materials, τ(A)(-1) in two-dimensional materials can be 3-10 folds larger than τ(V)(-1). Incorporating this phonon scattering mechanism to the Boltzmann transport equation derives that the thermal conductivity of vacancy defective graphene is severely reduced even for very low vacancy density. High-frequency phonon contribution to thermal conductivity reduces substantially. Our findings are helpful not only to understand the severe suppression of thermal conductivity by vacancies, but also to manipulate thermal conductivity in two-dimensional materials by phononic engineering.

  11. Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2.

    Science.gov (United States)

    Ma, J; Delaire, O; May, A F; Carlton, C E; McGuire, M A; VanBebber, L H; Abernathy, D L; Ehlers, G; Hong, Tao; Huq, A; Tian, Wei; Keppens, V M; Shao-Horn, Y; Sales, B C

    2013-06-01

    Materials with very low thermal conductivity are of great interest for both thermoelectric and optical phase-change applications. Synthetic nanostructuring is most promising for suppressing thermal conductivity through phonon scattering, but challenges remain in producing bulk samples. In crystalline AgSbTe2 we show that a spontaneously forming nanostructure leads to a suppression of thermal conductivity to a glass-like level. Our mapping of the phonon mean free paths provides a novel bottom-up microscopic account of thermal conductivity and also reveals intrinsic anisotropies associated with the nanostructure. Ground-state degeneracy in AgSbTe2 leads to the natural formation of nanoscale domains with different orderings on the cation sublattice, and correlated atomic displacements, which efficiently scatter phonons. This mechanism is general and suggests a new avenue for the nanoscale engineering of materials to achieve low thermal conductivities for efficient thermoelectric converters and phase-change memory devices.

  12. Anharmonic phonon-phonon scattering modeling of three-dimensional atomistic transport: An efficient quantum treatment

    Science.gov (United States)

    Lee, Y.; Bescond, M.; Logoteta, D.; Cavassilas, N.; Lannoo, M.; Luisier, M.

    2018-05-01

    We propose an efficient method to quantum mechanically treat anharmonic interactions in the atomistic nonequilibrium Green's function simulation of phonon transport. We demonstrate that the so-called lowest-order approximation, implemented through a rescaling technique and analytically continued by means of the Padé approximants, can be used to accurately model third-order anharmonic effects. Although the paper focuses on a specific self-energy, the method is applicable to a very wide class of physical interactions. We apply this approach to the simulation of anharmonic phonon transport in realistic Si and Ge nanowires with uniform or discontinuous cross sections. The effect of increasing the temperature above 300 K is also investigated. In all the considered cases, we are able to obtain a good agreement with the routinely adopted self-consistent Born approximation, at a remarkably lower computational cost. In the more complicated case of high temperatures (≫300 K), we find that the first-order Richardson extrapolation applied to the sequence of the Padé approximants N -1 /N results in a significant acceleration of the convergence.

  13. Resonant intersubband polariton-LO phonon scattering in an optically pumped polaritonic device

    Science.gov (United States)

    Manceau, J.-M.; Tran, N.-L.; Biasiol, G.; Laurent, T.; Sagnes, I.; Beaudoin, G.; De Liberato, S.; Carusotto, I.; Colombelli, R.

    2018-05-01

    We report experimental evidence of longitudinal optical (LO) phonon-intersubband polariton scattering processes under resonant injection of light. The scattering process is resonant with both the initial (upper polariton) and final (lower polariton) states and is induced by the interaction of confined electrons with longitudinal optical phonons. The system is optically pumped with a mid-IR laser tuned between 1094 cm-1 and 1134 cm-1 (λ = 9.14 μm and λ = 8.82 μm). The demonstration is provided for both GaAs/AlGaAs and InGaAs/AlInAs doped quantum well systems whose intersubband plasmon lies at a wavelength of ≈10 μm. In addition to elucidating the microscopic mechanism of the polariton-phonon scattering, it is found to differ substantially from the standard single particle electron-LO phonon scattering mechanism, and this work constitutes an important step towards the hopefully forthcoming demonstration of an intersubband polariton laser.

  14. Electrical resistivity due to electron-phonon scattering in thin gadolinium films

    International Nuclear Information System (INIS)

    Urbaniak-Kucharczyk, A.

    1988-01-01

    The contribution to the electrical resistivity due to the electron-phonon scattering for the special case of h.c.p. structure is derived. The numerical results obtained for the case of polycrystalline gadolinum films show the resistivity dependence on the film thickness and the surface properties. (author)

  15. Modeling inelastic phonon scattering in atomic- and molecular-wire junctions

    DEFF Research Database (Denmark)

    Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads

    2005-01-01

    Computationally inexpensive approximations describing electron-phonon scattering in molecular-scale conductors are derived from the nonequilibrium Green's function method. The accuracy is demonstrated with a first-principles calculation on an atomic gold wire. Quantitative agreement between the f...

  16. Electron mobility variance in the presence of an electric field: Electron-phonon field-induced tunnel scattering

    International Nuclear Information System (INIS)

    Melkonyan, S.V.

    2012-01-01

    The problem of electron mobility variance is discussed. It is established that in equilibrium semiconductors the mobility variance is infinite. It is revealed that the cause of the mobility variance infinity is the threshold of phonon emission. The electron-phonon interaction theory in the presence of an electric field is developed. A new mechanism of electron scattering, called electron-phonon field-induced tunnel (FIT) scattering, is observed. The effect of the electron-phonon FIT scattering is explained in terms of penetration of the electron wave function into the semiconductor band gap in the presence of an electric field. New and more general expressions for the electron-non-polar optical phonon scattering probability and relaxation time are obtained. The results show that FIT transitions have principle meaning for the mobility fluctuation theory: mobility variance becomes finite.

  17. LA phonons scattering of surface electrons in Bi2Se3

    International Nuclear Information System (INIS)

    Huang, Lang-Tao; Zhu, Bang-Fen

    2013-01-01

    Within the Boltzmann equation formalism we evaluate the transport relaxation time of Dirac surface states (SSs) in the typical topological insulator(TI) Bi 2 Se 3 due to the phonon scattering. We find that although the back-scattering of the SSs in TIs is strictly forbidden, the in-plane scattering between SSs in 3-dimensional TIs is allowed, maximum around the right-angle scattering. Thus the topological property of the SSs only reduces the scattering rate to its one half approximately. Besides, the larger LA deformation potential and lower sound velocity of Bi 2 Se 3 enhance the scattering rate significantly. Compared with the Dirac electrons in graphene, we find the scattering rate of SSs in Bi 2 Se 3 are two orders of magnitudes larger, which agree with the recent transport experiments

  18. LA phonons scattering of surface electrons in Bi{sub 2}Se{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lang-Tao [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Zhu, Bang-Fen [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China and Institute of Advanced Study, Tsinghua University, Beijing 100084 (China)

    2013-12-04

    Within the Boltzmann equation formalism we evaluate the transport relaxation time of Dirac surface states (SSs) in the typical topological insulator(TI) Bi{sub 2}Se{sub 3} due to the phonon scattering. We find that although the back-scattering of the SSs in TIs is strictly forbidden, the in-plane scattering between SSs in 3-dimensional TIs is allowed, maximum around the right-angle scattering. Thus the topological property of the SSs only reduces the scattering rate to its one half approximately. Besides, the larger LA deformation potential and lower sound velocity of Bi{sub 2}Se{sub 3} enhance the scattering rate significantly. Compared with the Dirac electrons in graphene, we find the scattering rate of SSs in Bi{sub 2}Se{sub 3} are two orders of magnitudes larger, which agree with the recent transport experiments.

  19. Electron-longitudinal-acoustic-phonon scattering in double-quantum-dot based quantum gates

    International Nuclear Information System (INIS)

    Zhao Peiji; Woolard, Dwight L.

    2008-01-01

    We propose a nanostructure design which can significantly suppress longitudinal-acoustic-phonon-electron scattering in double-quantum-dot based quantum gates for quantum computing. The calculated relaxation rates vs. bias voltage exhibit a double-peak feature with a minimum approaching 10 5 s -1 . In this matter, the energy conservation law prohibits scattering contributions from phonons with large momenta; furthermore, increasing the barrier height between the double quantum dots reduces coupling strength between the dots. Hence, the joint action of the energy conservation law and the decoupling greatly reduces the scattering rates. The degrading effects of temperatures can be reduced simply by increasing the height of the barrier between the dots

  20. Theory of phonon inelastic atom--surface scattering. I. Quantum mechanical treatment of collision dynamics

    International Nuclear Information System (INIS)

    Choi, B.H.; Poe, R.T.

    1985-01-01

    We present a systematic formulation of the atom--surface scattering dynamics which includes the vibrational states of the atoms in the solid (phonons). The properties of the total scattering wave function of the system, a representation of the interaction potential matrix, and the characteristics of the independent physical solutions are all derived from the translational invariance of the full Hamiltonian. The scattering equations in the integral forms as well as the related Green functions were also obtained. The configurational representations of the Green functions, in particular, are quite different from those of the conventional scattering theory where the collision partners are spatially localized. Various versions of the integral expression of scattering, transition, and reactance matrices were also obtained. They are useful for introducing approximation schemes. From the present formulation, some specific theoretical schemes which are more realistic compared to those that have been employed so far and at the same time capable of yielding effective ab initio computation are derived in the following paper. The time reversal invariance and the microscopic reversibility of the atom--surface scattering were discussed. The relations between the in and outgoing scattering wave functions which are satisfied in the atom--surface system and important in the transition matrix methods were presented. The phonon annihilation and creation, and the adsorption and desorption of the atom are related through the time reversal invariance, and thus the microscopic reversibility can be tested by the experiment

  1. Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene.

    Science.gov (United States)

    Shang, Jingzhi; Yu, Ting; Lin, Jianyi; Gurzadyan, Gagik G

    2011-04-26

    Ultrafast quasiparticle dynamics in graphene grown by chemical vapor deposition (CVD) has been studied by UV pump/white-light probe spectroscopy. Transient differential transmission spectra of monolayer graphene are observed in the visible probe range (400-650 nm). Kinetics of the quasiparticle (i.e., low-energy single-particle excitation with renormalized energy due to electron-electron Coulomb, electron-optical phonon (e-op), and optical phonon-acoustic phonon (op-ap) interactions) was monitored with 50 fs resolution. Extending the probe range to near-infrared, we find the evolution of quasiparticle relaxation channels from monoexponential e-op scattering to double exponential decay due to e-op and op-ap scattering. Moreover, quasiparticle lifetimes of mono- and randomly stacked graphene films are obtained for the probe photon energies continuously from 1.9 to 2.3 eV. Dependence of quasiparticle decay rate on the probe energy is linear for 10-layer stacked graphene films. This is due to the dominant e-op intervalley scattering and the linear density of states in the probed electronic band. A dimensionless coupling constant W is derived, which characterizes the scattering strength of quasiparticles by lattice points in graphene.

  2. Phononic thermal resistance due to a finite periodic array of nano-scatterers

    Energy Technology Data Exchange (ETDEWEB)

    Trang Nghiêm, T. T.; Chapuis, Pierre-Olivier [Univ. Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, F-69621 Villeurbanne (France)

    2016-07-28

    The wave property of phonons is employed to explore the thermal transport across a finite periodic array of nano-scatterers such as circular and triangular holes. As thermal phonons are generated in all directions, we study their transmission through a single array for both normal and oblique incidences, using a linear dispersionless time-dependent acoustic frame in a two-dimensional system. Roughness effects can be directly considered within the computations without relying on approximate analytical formulae. Analysis by spatio-temporal Fourier transform allows us to observe the diffraction effects and the conversion of polarization. Frequency-dependent energy transmission coefficients are computed for symmetric and asymmetric objects that are both subject to reciprocity. We demonstrate that the phononic array acts as an efficient thermal barrier by applying the theory of thermal boundary (Kapitza) resistances to arrays of smooth scattering holes in silicon for an exemplifying periodicity of 10 nm in the 5–100 K temperature range. It is observed that the associated thermal conductance has the same temperature dependence as that without phononic filtering.

  3. Two-dimensional phononic crystals with time-varying properties: a multiple scattering analysis

    International Nuclear Information System (INIS)

    Wright, D W; Cobbold, R S C

    2010-01-01

    Multiple scattering theory is a versatile two- and three-dimensional method for characterizing the acoustic wave transmission through many scatterers. It provides analytical solutions to wave propagation in scattering structures, and its computational complexity grows logarithmically with the number of scatterers. In this paper we show how the 2D method can be adapted to include the effects of time-varying material parameters. Specifically, a new T-matrix is defined to include the effects of frequency modulation that occurs in time-varying phononic crystals. Solutions were verified against finite difference time domain (FDTD) simulations and showed excellent agreement. This new method enables fast characterization of time-varying phononic crystals without the need to resort to lengthy FDTD simulations. Also, the method of combining T-matrices to form the T-supermatrix remains unchanged provided that the new matrix definitions are used. The method is quite compatible with existing implementations of multiple scattering theory and could be readily extended to three-dimensional multiple scattering theory

  4. Inelastic neutron scattering studies of the phonon spectra of Chevrel-phase superconductors

    International Nuclear Information System (INIS)

    Bader, S.D.; Sinha, S.K.; Shelton, R.N.

    1976-01-01

    Phonon spectra are obtained using inelastic neutron scattering by polycrystals of the Chevrel-phase superconductors SnMo 6 S 8 , PbMo 6 S 8 , Mo 6 Se 8 , and Pb 1 . 2 Mo 6 Se 8 . Modes associated primarily with Sn (or Pb) atomic displacements are clearly identified. Acoustic softening on cooling is noted for SnMo 6 S 8 . Anharmonicity and the superconductivity are discussed utilizing the molecular-crystal concept

  5. The broad Brillouin doublet and CP of KTaO3, second sound vs. Two-phonon difference scattering

    International Nuclear Information System (INIS)

    Farhi, E.; Tagantsev, A.K.; Hehlen, B.; Courtens, E.; Boatner, L.A.

    1999-01-01

    Complete text of publication follows. Low-T Brillouin spectra of the incipient ferroelectric KTaO 3 exhibit a broad central peak (CP) (1), and some additional broad Brillouin doublet (BD) (2), that can both relate to phonon-density fluctuations (3). Starting from extensive new high resolution neutron scattering measurements in pure crystals, low lying phonon sheets were modelled in the central part of Brillouin zone. Such a parameterisation was then used in order to analyse those up-mentioned unusual features in teens of two-phonon mechanisms (4). Numerical evaluations show that transverse acoustic (TA) phonons whose normal damping is faster than the BD frequency (Γ DB > ω DB ) may produce hydrodynamic second sound (propagation of heat). Moreover, two-phonon difference scattering from low damping thermal TA phonons ((Γ DB DB ) can contribute to the spectra with either a sharp or a broader BD, depending on the phonon group velocity and phonon-sheet anisotropy. The position of the doublet is consistent with both mechanisms, but comparing the computed anisotropies with experimental Brillouin and neutron scattering data, one favours the second process. (author)

  6. Screening-induced surface polar optical phonon scattering in dual-gated graphene field effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Bo, E-mail: hubo2011@semi.ac.cn

    2015-03-15

    The effect of surface polar optical phonons (SOs) from the dielectric layers on electron mobility in dual-gated graphene field effect transistors (GFETs) is studied theoretically. By taking into account SO scattering of electron as a main scattering mechanism, the electron mobility is calculated by the iterative solution of Boltzmann transport equation. In treating scattering with the SO modes, the dynamic dielectric screening is included and compared to the static dielectric screening and the dielectric screening in the static limit. It is found that the dynamic dielectric screening effect plays an important role in the range of low net carrier density. More importantly, in-plane acoustic phonon scattering and charged impurity scattering are also included in the total mobility for SiO{sub 2}-supported GFETs with various high-κ top-gate dielectric layers considered. The calculated total mobility results suggest both Al{sub 2}O{sub 3} and AlN are the promising candidate dielectric layers for the enhancement in room temperature mobility of graphene in the future.

  7. Impact of optical phonon scattering on inversion channel mobility in 4H-SiC trenched MOSFETs

    Science.gov (United States)

    Kutsuki, Katsuhiro; Kawaji, Sachiko; Watanabe, Yukihiko; Onishi, Toru; Fujiwara, Hirokazu; Yamamoto, Kensaku; Yamamoto, Toshimasa

    2017-04-01

    Temperature characteristics of the channel mobility were investigated for 4H-SiC trenched MOSFETs in the range from 30 to 200 °C. The conventional model of channel mobility limited by carrier scattering is based on Si-MOSFETs and shows a greatly different channel mobility from the experimental value, especially at high temperatures. On the other hand, our improved mobility model taking into account optical phonon scattering yielded results in excellent agreement with experimental results. Moreover, the major factors limiting the channel mobility were found to be Coulomb scattering in a low effective field (<0.7 MV/cm) and optical phonon scattering in a high effective field.

  8. Neutron scattering for investigation into the connection between phonons and diffusion in metallic systems

    International Nuclear Information System (INIS)

    Herzig, C.

    1995-01-01

    For examining the connection between the diffusion systematics and the lattice dynamics of the body-centered cubic metals, the temperature dependence of the self-diffusion (radiotracer technique) and the phonon dispersion (neutron scattering) have been measured in selected systems. In continuation of previous studies, the goal of the examinations reported was to put the earlier developed phonon-related diffusion model on a broader experimental basis, in order to perform verifying analyses. The phonon dispersion of the group 5 metal Nb has been measured up to high temperatures. In contrast to the values measured for the group 4 (β-Zr) and group 6 (Cr) metals, the dispersion in Nb revealed an only very weak temperature dependence. The exceptional case of the bcc β-Tl has been examined by measuring the diffusion and the dispersion in the β-T 83 In 17 alloy. Significant deviations from the conditions in the bcc transition metals have been found. Self-diffusion has been measured for the first time in Ba and β-Sc. Their diffusion systematics correlate with electron configuration. The influence of the d-electron concentration on the diffusion systematics has been measured in Ti-Mo and Hf-Nb alloys, the results backing the predictions of the phonon-related diffusion model. (orig.) [de

  9. The Van der Waals-force-induced phononic band gap and resonant scattering in two-nanosphere aggregate

    International Nuclear Information System (INIS)

    Wu Jiuhui; Zhang Siwen; Zhou Kejiang

    2012-01-01

    A physical mechanism of phononic band gap and resonant nanoacoustic scattering in an aggregate of two elastic nanospheres is presented in this paper. By considering the Van der Waals (VdW) force between two nanospheres illuminated by nanoacoustic wave, phononic band gap and frequency shift at the lower frequency side, and largely enhanced nanoacoustic scattering at the other frequency range have been found through calculating the form function of the acoustic scattering from the nanosystem. This VdW-force-induced band gap is different from the known mechanisms of Bragg scattering and local resonances for periodic media. It is shown that when the separation distance between two nanospheres is decreasing from 20 to 1 nm, due to the increasing VdW force, the nanoacoustic scattering is much heightened by two order of magnitude, and meanwhile the frequency shift and phononic band gap at the low frequencies are both widened. These results could provide potential applications of nanoacoustic devices.

  10. Monte Carlo Calculation of Thermal Neutron Inelastic Scattering Cross Section Uncertainties by Sampling Perturbed Phonon Spectra

    Science.gov (United States)

    Holmes, Jesse Curtis

    Nuclear data libraries provide fundamental reaction information required by nuclear system simulation codes. The inclusion of data covariances in these libraries allows the user to assess uncertainties in system response parameters as a function of uncertainties in the nuclear data. Formats and procedures are currently established for representing covariances for various types of reaction data in ENDF libraries. This covariance data is typically generated utilizing experimental measurements and empirical models, consistent with the method of parent data production. However, ENDF File 7 thermal neutron scattering library data is, by convention, produced theoretically through fundamental scattering physics model calculations. Currently, there is no published covariance data for ENDF File 7 thermal libraries. Furthermore, no accepted methodology exists for quantifying or representing uncertainty information associated with this thermal library data. The quality of thermal neutron inelastic scattering cross section data can be of high importance in reactor analysis and criticality safety applications. These cross sections depend on the material's structure and dynamics. The double-differential scattering law, S(alpha, beta), tabulated in ENDF File 7 libraries contains this information. For crystalline solids, S(alpha, beta) is primarily a function of the material's phonon density of states (DOS). Published ENDF File 7 libraries are commonly produced by calculation and processing codes, such as the LEAPR module of NJOY, which utilize the phonon DOS as the fundamental input for inelastic scattering calculations to directly output an S(alpha, beta) matrix. To determine covariances for the S(alpha, beta) data generated by this process, information about uncertainties in the DOS is required. The phonon DOS may be viewed as a probability density function of atomic vibrational energy states that exist in a material. Probable variation in the shape of this spectrum may be

  11. Study of Phonon Dispersion Relations in Cuprous Oxide by Inelastic Neutron Scattering

    DEFF Research Database (Denmark)

    Beg, M. M.; Shapiro, S. M.

    1976-01-01

    Phonon dispersion relations in Cu2O have been studied at 20°C using inelastic neutron scattering. Seven acoustic branches and twelve optical branches have been studied in detail in the three symmetry directions [00ζ], [ζζ0], and [ζζζ] of the cubic lattice. Four of the six zone-center phonons have...... been observed and the assignments and energies are confirmed as Γ25=87±2 cm-1, Γ12′=105±3 cm-1, Γ15=146±1 cm-1, and Γ2′≈347 cm-1. The dispersion relations agree only qualitatively with the rigid-ion-model calculations. It is suggested that more detailed calculations may be performed in the light...

  12. Thermal phonon scattering in silicon doped with Li, P and Li-O; influence of the electronic structure of the impurities

    International Nuclear Information System (INIS)

    Fortier, Dominique.

    1976-07-01

    Besides the three phonon scattering mechanisms generally considered in insulators, i.e. boundary effect, isotopic scattering and phonon-phonon interaction, the electron-phonon scattering mechanism was studied with special reference to the scattering of thermal phonons by donor impurities in silicon. In order to demonstrate clearly the effect of the electronic structure of the impurity on this scattering, three donor centres were investigated: Li, Li-O and P. On the basis of the calculated relaxation times it was possible from theoretical analysis to account for the main results and to explain why the Li centre scatters thermal phonons more efficiently than Li-O and P centres in the isolated impurity range [fr

  13. Enhanced creation of dispersive monolayer phonons in Xe/Pt(111) by inelastic helium atom scattering at low energies

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, Ludwig Walter

    2007-01-01

    Conditions likely to lead to enhanced inelastic atomic scattering that creates shear horizontal (SH) and longitudinal acoustic (LA) monolayer phonons are identified, specifically examining the inelastic scattering of He-4 atoms by a monolayer solid of Xe/Pt(111) at incident energies of 2-25 meV. ...

  14. Influence of screening on longitudinal-optical phonon scattering in quantum cascade lasers

    International Nuclear Information System (INIS)

    Ezhov, Ivan; Jirauschek, Christian

    2016-01-01

    We theoretically investigate the influence of screening on electron-longitudinal optical phonon scattering in quantum cascade lasers. By employing ensemble Monte Carlo simulations, an advanced screening model based on the random-phase approximation is compared to the more elementary Thomas-Fermi and Debye models. For mid-infrared structures, and to a lesser extent also for terahertz designs, the inclusion of screening is shown to affect the simulated current and optical output power. Furthermore, it is demonstrated that by using the electron temperature rather than the lattice temperature, the Debye model can be significantly improved

  15. The role of phonon scattering in the indistinguishability of photons emitted from semiconductor cavity QED systems

    DEFF Research Database (Denmark)

    Nielsen, Per Kær; Gregersen, Niels; Mørk, Jesper

    2013-01-01

    A solid-state single-photon source emitting indistinguishable photons on-demand is an essential component of linear optics quantum computing schemes. However, the emitter will inevitably interact with the solid-state environment causing decoherence and loss of indistinguishability. In this paper......, we present a comprehensive theoretical treatment of the influence of phonon scattering on the coherence properties of single photons emitted from semiconductor quantum dots. We model decoherence using a full microscopic theory and compare with standard Markovian approximations employing Lindblad...

  16. Simulation of long-wave phonon ({lambda}> b) scattering at geometric imperfections in nanowires by FDTD method

    Energy Technology Data Exchange (ETDEWEB)

    Salamatov, E.I. [Physico-Technical Institute, UrB RAS, 132 Kirov Street, Izhevsk (Russian Federation)

    2012-01-15

    Elementary acts of acoustic phonon scattering in nanowires are studied numerically by the FDTD method. The points of bifurcation of the main waveguide are considered as defects. The particularities of the reflection/transmission coefficient of phonons of different polarizations are studied as a function of the frequency and geometrical parameters of the problem. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Phonon linewidth due to electron-phonon interactions with strong forward scattering in FeSe thin films on oxide substrates

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yan [Univ. of Tennessee, Knoxville, TN (United States); Rademaker, Louk [Univ. of California, Santa Barbara, CA (United States); Dagotto, Elbio R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Johnston, Steven [Univ. of Tennessee, Knoxville, TN (United States)

    2017-08-18

    Here, the discovery of an enhanced superconducting transition temperature Tc in monolayers of FeSe grown on several oxide substrates has opened a new route to high-Tc superconductivity through interface engineering. One proposal for the origin of the observed enhancement is an electronphonon (e-ph) interaction across the interface that peaked at small momentum transfers. In this paper, we examine the implications of such a coupling on the phononic properties of the system. We show that a strong forward scattering leads to a sizable broadening of phonon lineshape, which may result in charge instabilities at long-wavelengths. However, we further find that the inclusion of Coulombic screening significantly reduces the phonon broadening. Our results show that one might not expect anomalously broad phonon linewidths in the FeSe interface systems, despite the fact that the e-ph interaction has a strong peak in the forward scattering (small \\bfq ) direction.

  18. Phonon and magnon scattering of Bi{sub 2}Fe{sub 4}O{sub 9} ceramic

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Poorva, E-mail: vdinesh33@rediffmail.com, E-mail: vdinesh33@rediffmail.com; Kumar, Ashwini, E-mail: vdinesh33@rediffmail.com, E-mail: vdinesh33@rediffmail.com; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com, E-mail: vdinesh33@rediffmail.com [School of Physics, Vigyan Bhawan, Devi Ahilya University, Khandwa Road Campus, Indore-452001 (India)

    2014-04-24

    We report the phonon structure of Bi{sub 2}Fe{sub 4}O{sub 9} ceramics as synthesized by solid-state reaction route. Rietveld refined X-ray diffraction patterns confirmed the formation of single-phase perovskite structure and all the peaks of Bi{sub 2}Fe{sub 4}O{sub 9} perfectly indexed to the orthorhombic (space group Pbam). Raman scattering measurements identifies 12A{sub g}+1B{sub 2g}+1B{sub 3g} Raman active optical phonon modes. Apart from phonon scattering, mode at 470 cm{sup −1} is observed which is due to magnon scattering. The P-E loop infers paraelectric nature of Bi{sub 2}Fe{sub 4}O{sub 9}.

  19. Role of thermal two-phonon scattering for impurity dynamics in a low-dimensional Bose-Einstein condensate

    Science.gov (United States)

    Lausch, Tobias; Widera, Artur; Fleischhauer, Michael

    2018-03-01

    We numerically study the relaxation dynamics of a single, heavy impurity atom interacting with a finite one- or two-dimensional, ultracold Bose gas. While there is a clear separation of time scales between processes resulting from single- and two-phonon scattering in three spatial dimensions, the thermalization in lower dimensions is dominated by two-phonon processes. This is due to infrared divergences in the corresponding scattering rates in the thermodynamic limit, which are a manifestation of the Mermin-Wagner-Hohenberg theorem. This makes it necessary to include second-order phonon scattering above a crossover temperature T2ph . T2ph scales inversely with the system size and is much smaller than currently experimentally accessible.

  20. Bulk phonon scattering in perturbed quasi-3D multichannel crystallographic waveguide.

    Science.gov (United States)

    Rabia, M S

    2008-11-19

    In the present paper, we concentrate on the influence of local defects on scattering properties of elastic waves in perturbed crystalline quasi-three-dimensional nanostructures in the harmonic approximation. Our model consists of three infinite atomic planes, assimilated into a perfect waveguide in which different distributions of scatterers (or defects) are inserted in the bulk. We have investigated phonon transmission and conductance for three bulk defect configurations. The numerical treatment of the problem, based on the Landauer approach, resorts to the matching method initially employed for the study of surface localized phonons and resonances. We present a detailed study of the defect-induced fluctuations in the transmission spectra. These fluctuations can be related to Fano resonances and Fabry-Pérot oscillations. The first is due to the coupling between localized defect states and the perfect waveguide propagating modes whereas the latter results from the interference between incidental and reflected waves. Numerical results reveal the intimate relation between transmission spectra and localized impurity states and provide a basis for the understanding of conductance spectroscopy experiments in disordered mesoscopic systems.

  1. Bulk phonon scattering in perturbed quasi-3D multichannel crystallographic waveguide

    Energy Technology Data Exchange (ETDEWEB)

    Rabia, M S [Laboratoire de Mecanique des Structures et Energetique, Departement de Genie Mecanique, Faculte du Genie de la Construction, Universite M. Mammeri, Tizi-Ouzou 15000 (Algeria)], E-mail: m2msr@yahoo.fr

    2008-11-19

    In the present paper, we concentrate on the influence of local defects on scattering properties of elastic waves in perturbed crystalline quasi-three-dimensional nanostructures in the harmonic approximation. Our model consists of three infinite atomic planes, assimilated into a perfect waveguide in which different distributions of scatterers (or defects) are inserted in the bulk. We have investigated phonon transmission and conductance for three bulk defect configurations. The numerical treatment of the problem, based on the Landauer approach, resorts to the matching method initially employed for the study of surface localized phonons and resonances. We present a detailed study of the defect-induced fluctuations in the transmission spectra. These fluctuations can be related to Fano resonances and Fabry-Perot oscillations. The first is due to the coupling between localized defect states and the perfect waveguide propagating modes whereas the latter results from the interference between incidental and reflected waves. Numerical results reveal the intimate relation between transmission spectra and localized impurity states and provide a basis for the understanding of conductance spectroscopy experiments in disordered mesoscopic systems.

  2. Plasmon-enhanced phonon and ionized impurity scattering in doped silicon

    International Nuclear Information System (INIS)

    Chen, Ming-Jer; Hsieh, Shang-Hsun; Chen, Chuan-Li

    2015-01-01

    Historically, two microscopic electron scattering calculation methods have been used to fit macroscopic electron mobility data in n-type silicon. The first method was performed using a static system that included long-range electron-plasmon scattering; however, the well-known Born approximation fails in this case when dealing with electron-impurity scattering. In the second method, sophisticated numerical simulations were developed around plasmon-excited potential fluctuations and successfully reproduced the mobility data at room temperature. In this paper, we propose a third method as an alternative to the first method. First, using a fluctuating system, which was characterized on the basis of our recently experimentally extracted plasmon-excited potential fluctuations, the microscopic calculations reveal enhanced short-range scattering of electrons by phonons and ionized impurities due to increased electron temperature and increased screening length, respectively. The increased hot electron population makes the Born approximation hold, which eases the overall calculation task substantially. Then, we return to the static system while incorporating plasmon-enhanced impurity scattering. The resulting macroscopic electron mobility shows fairly good agreement with data over wide ranges of temperatures (200–400 K) and doping concentrations (10 15 –10 20  cm −3 ). Application of the proposed method to strained silicon is also demonstrated

  3. Exciton Scattering approach for conjugated macromolecules: from electronic spectra to electron-phonon coupling

    Science.gov (United States)

    Tretiak, Sergei

    2014-03-01

    The exciton scattering (ES) technique is a multiscale approach developed for efficient calculations of excited-state electronic structure and optical spectra in low-dimensional conjugated macromolecules. Within the ES method, the electronic excitations in the molecular structure are attributed to standing waves representing quantum quasi-particles (excitons), which reside on the graph. The exciton propagation on the linear segments is characterized by the exciton dispersion, whereas the exciton scattering on the branching centers is determined by the energy-dependent scattering matrices. Using these ES energetic parameters, the excitation energies are then found by solving a set of generalized ``particle in a box'' problems on the graph that represents the molecule. All parameters can be extracted from quantum-chemical computations of small molecular fragments and tabulated in the ES library for further applications. Subsequently, spectroscopic modeling for any macrostructure within considered molecular family could be performed with negligible numerical effort. The exciton scattering properties of molecular vertices can be further described by tight-binding or equivalently lattice models. The on-site energies and hopping constants are obtained from the exciton dispersion and scattering matrices. Such tight-binding model approach is particularly useful to describe the exciton-phonon coupling, energetic disorder and incoherent energy transfer in large branched conjugated molecules. Overall the ES applications accurately reproduce the optical spectra compared to the reference quantum chemistry results, and make possible to predict spectra of complex macromolecules, where conventional electronic structure calculations are unfeasible.

  4. Interfacial phonon scattering and transmission loss in >1 μm thick silicon-on-insulator thin films

    Science.gov (United States)

    Jiang, Puqing; Lindsay, Lucas; Huang, Xi; Koh, Yee Kan

    2018-05-01

    Scattering of phonons at boundaries of a crystal (grains, surfaces, or solid/solid interfaces) is characterized by the phonon wavelength, the angle of incidence, and the interface roughness, as historically evaluated using a specularity parameter p formulated by Ziman [Electrons and Phonons (Clarendon Press, Oxford, 1960)]. This parameter was initially defined to determine the probability of a phonon specularly reflecting or diffusely scattering from the rough surface of a material. The validity of Ziman's theory as extended to solid/solid interfaces has not been previously validated. To better understand the interfacial scattering of phonons and to test the validity of Ziman's theory, we precisely measured the in-plane thermal conductivity of a series of Si films in silicon-on-insulator (SOI) wafers by time-domain thermoreflectance (TDTR) for a Si film thickness range of 1-10 μm and a temperature range of 100-300 K. The Si /SiO2 interface roughness was determined to be 0.11 ±0.04 nm using transmission electron microscopy (TEM). Furthermore, we compared our in-plane thermal conductivity measurements to theoretical calculations that combine first-principles phonon transport with Ziman's theory. Calculations using Ziman's specularity parameter significantly overestimate values from the TDTR measurements. We attribute this discrepancy to phonon transmission through the solid/solid interface into the substrate, which is not accounted for by Ziman's theory for surfaces. The phonons that are specularly transmitted into an amorphous layer will be sufficiently randomized by the time they come back to the crystalline Si layer, the effect of which is practically equivalent to a diffuse reflection at the interface. We derive a simple expression for the specularity parameter at solid/amorphous interfaces and achieve good agreement between calculations and measurement values.

  5. Electron nonelastic scattering by confined and interface polar optical phonons in a modulation-doped AlGaAs/GaAs/AlGaAs quantum well

    CERN Document Server

    Pozela, K

    2001-01-01

    The calculations of electron scattering rates by polar optical (PO) phonons in an AlGaAs/GaAs/AlGaAs quantum well (QW) with a different width and doping level are performed. The electron-PO-phonon scattering mechanisms which are responsible for the alternate dependence of electron mobility on a QW width, as well as for the decrease of conductivity in the QW with increasing electron concentration are determined. It is shown that the degeneration of electron gas decreases the electron scattering rate by PO-phonon emission and increases the scattering rate by phonon absorption. The competition between the decrease of the intrasubband scattering and the increase of the intersubband scattering by PO-phonon absorption is responsible for the alternate changes of the mobility with a QW width

  6. Direct measurements of surface scattering in Si nanosheets using a microscale phonon spectrometer: implications for Casimir-limit predicted by Ziman theory.

    Science.gov (United States)

    Hertzberg, Jared B; Aksit, Mahmut; Otelaja, Obafemi O; Stewart, Derek A; Robinson, Richard D

    2014-02-12

    Thermal transport in nanostructures is strongly affected by phonon-surface interactions, which are expected to depend on the phonon's wavelength and the surface roughness. Here we fabricate silicon nanosheets, measure their surface roughness (∼ 1 nm) using atomic force microscopy (AFM), and assess the phonon scattering rate in the sheets with a novel technique: a microscale phonon spectrometer. The spectrometer employs superconducting tunnel junctions (STJs) to produce and detect controllable nonthermal distributions of phonons from ∼ 90 to ∼ 870 GHz. This technique offers spectral resolution nearly 10 times better than a thermal conductance measurement. We compare measured phonon transmission rates to rates predicted by a Monte Carlo model of phonon trajectories, assuming that these trajectories are dominated by phonon-surface interactions and using the Ziman theory to predict phonon-surface scattering rates based on surface topology. Whereas theory predicts a diffuse surface scattering probability of less than 40%, our measurements are consistent with a 100% probability. Our nanosheets therefore exhibit the so-called "Casimir limit" at a much lower frequency than expected if the phonon scattering rates follow the Ziman theory for a 1 nm surface roughness. Such a result holds implications for thermal management in nanoscale electronics and the design of nanostructured thermoelectrics.

  7. Band structures in a two-dimensional phononic crystal with rotational multiple scatterers

    Science.gov (United States)

    Song, Ailing; Wang, Xiaopeng; Chen, Tianning; Wan, Lele

    2017-03-01

    In this paper, the acoustic wave propagation in a two-dimensional phononic crystal composed of rotational multiple scatterers is investigated. The dispersion relationships, the transmission spectra and the acoustic modes are calculated by using finite element method. In contrast to the system composed of square tubes, there exist a low-frequency resonant bandgap and two wide Bragg bandgaps in the proposed structure, and the transmission spectra coincide with band structures. Specially, the first bandgap is based on locally resonant mechanism, and the simulation results agree well with the results of electrical circuit analogy. Additionally, increasing the rotation angle can remarkably influence the band structures due to the transfer of sound pressure between the internal and external cavities in low-order modes, and the redistribution of sound pressure in high-order modes. Wider bandgaps are obtained in arrays composed of finite unit cells with different rotation angles. The analysis results provide a good reference for tuning and obtaining wide bandgaps, and hence exploring the potential applications of the proposed phononic crystal in low-frequency noise insulation.

  8. Terahertz lasers and amplifiers based on resonant optical phonon scattering to achieve population inversion

    Science.gov (United States)

    Williams, Benjamin S. (Inventor); Hu, Qing (Inventor)

    2009-01-01

    The present invention provides quantum cascade lasers and amplifier that operate in a frequency range of about 1 Terahertz to about 10 Terahertz. In one aspect, a quantum cascade laser of the invention includes a semiconductor heterostructure that provides a plurality of lasing modules connected in series. Each lasing module includes a plurality of quantum well structure that collectively generate at least an upper lasing state, a lower lasing state, and a relaxation state such that the upper and the lower lasing states are separated by an energy corresponding to an optical frequency in a range of about 1 to about 10 Terahertz. The lower lasing state is selectively depopulated via resonant LO-phonon scattering of electrons into the relaxation state.

  9. Electron-phonon scattering in indium from r.f. size effect measurements

    International Nuclear Information System (INIS)

    Hoff, A.B.M.

    1977-01-01

    The anisotropy of the electron-phonon collison frequency on the second and third zone Fermi surfaces of indium has been determined from the temperature dependence of radiofrequency size effect (R.F.S.E.) line amplitudes. The orbitally-averaged scattering rates turn out to vary with temperature T according to a T 3 -dependence over the entire Fermi surface, except for orbits on the hole surface close to the (100) and (001) symmetry planes. The anomalous temperatue dependences found in the experiments could be attributed to the special circumstances under which the R.F.S.E. was observed. The influences of both the scattering effectiveness and the multiple turns of the electrons on the observed temperature dependence are discussed extensively. For a large number of extreme orbits on the second and third zone Fermi surfaces, the average scattering rates were measured. In order to obtain a functional expression for the local collision frequency over the entire Fermi surface, an inversion technique was used. As a result, it was found that the anisotropy of the collision frequency over the second zone surface is quite high (1:20) whereas the anisotropy over the third zone surface is rather small (<20%). Further, the variation of the scattering rate round the [111]-point on the hole surface could be confirmed by the results of limiting point measurements. The experimental scattering rates at several points on the Fermi surface were compared with theoretical values obtained from a simple two-OPW model calculation. The calculated anisotropy agrees roughly with the experimental one, although locally the actual values can differ by a factor of 2 or more

  10. System of equations of the quasiparticle-phonon nuclear model with allowance for phonon scattering at finite temperature

    International Nuclear Information System (INIS)

    Dang, N.D.

    1986-01-01

    The discovery of giant resonances in reactions of nuclei with heavy ions and in deep inelastic processes has stimulated interest in the study of the properties of highly excited nuclei. By taking into account exactly the population numbers of the single-phonon levels, the authors obtain a system of equations describing the interaction with the configurations in even-even spherical nuclei at a finite temperature. The Pauli principle is taken into account for the two-phonon components of the wave function of the excited states in accordance with an approximate procedure. The new diagrams associated with the introduction of the temperature are analyzed, and a comparison is made with the diagrams of nuclear field theory and the results of the theory of finite Fermi systems

  11. Surface defects characterization in a quantum wire by coherent phonons scattering

    Energy Technology Data Exchange (ETDEWEB)

    Rabia, M. S. [Laboratoire de Mécanique des Structures et Energétique, Faculté du Génie de la Construction, Université. Mammeri de Tizi-Ouzou, BP 17 RP Hasnaoua II, Tizi-Ouzou 15000, Algérie m2msr@yahoo.fr (Algeria)

    2015-03-30

    The influence of surface defects on the scattering properties of elastic waves in a quasi-planar crystallographic waveguide is studied in the harmonic approximation using the matching method formalism. The structural model is based on three infinite atomic chains forming a perfect lattice surmounted by an atomic surface defect. Following the Landauer approach, we solve directly the Newton dynamical equation with scattering boundary conditions and taking into account the next nearest neighbour’s interaction. A detailed study of the defect-induced fluctuations in the transmission spectra is presented for different adatom masses. As in the electronic case, the presence of localized defect-induced states leads to Fano-like resonances. In the language of mechanical vibrations, these are called continuum resonances. Numerical results reveal the intimate relation between transmission spectra and localized defect states and provide a basis for the understanding of conductance spectroscopy experiments in disordered mesoscopic systems. The results could be useful for the design of phononic devices.

  12. Surface defects characterization in a quantum wire by coherent phonons scattering

    International Nuclear Information System (INIS)

    Rabia, M. S.

    2015-01-01

    The influence of surface defects on the scattering properties of elastic waves in a quasi-planar crystallographic waveguide is studied in the harmonic approximation using the matching method formalism. The structural model is based on three infinite atomic chains forming a perfect lattice surmounted by an atomic surface defect. Following the Landauer approach, we solve directly the Newton dynamical equation with scattering boundary conditions and taking into account the next nearest neighbour’s interaction. A detailed study of the defect-induced fluctuations in the transmission spectra is presented for different adatom masses. As in the electronic case, the presence of localized defect-induced states leads to Fano-like resonances. In the language of mechanical vibrations, these are called continuum resonances. Numerical results reveal the intimate relation between transmission spectra and localized defect states and provide a basis for the understanding of conductance spectroscopy experiments in disordered mesoscopic systems. The results could be useful for the design of phononic devices

  13. Inelastic Neutron Scattering Measurements of Phonon Dispersion Relations in Andalusite and Sillimanite, Al2SiO5

    International Nuclear Information System (INIS)

    Goel, P.

    2001-01-01

    This paper reports inelastic neutron scattering (INS) measurements of the phonon dispersion relations of the aluminum silicate minerals andalusite and sillimanite, Al 2 SiO 5 . The single crystal INS measurements were undertaken using the Triple-axis-spectrometer at the Dhruva reactor, Trombay for andalusite and at the Oak Ridge National Laboratory, USA for sillimanite. The phonon dispersion relations (upto 50 mev) along various high symmetry directions have been measured and have been analyzed on the basis of lattice dynamics shell model calculations. The calculated structure factors based on the model calculations were used as guides for planning these single crystal measurements and were used to identify regions in reciprocal space with large cross-sections. The calculated structure factors have been very useful in the planning, execution and analysis of the experimental data. The calculated phonon dispersion relations are found to be in good agreement with the measured data

  14. Probing electronic phase transitions with phonons via inelastic neutron scattering: superconductivity in borocarbides, charge and magnetic order in manganites

    Energy Technology Data Exchange (ETDEWEB)

    Weber, F.

    2007-11-02

    The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi{sub 2}B{sub 2}C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T{sub c}, for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2{delta}(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}. At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T{sub C}. The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO{sub 6} octahedra, which are introduced in this compound by the Jahn-Teller active Mn{sup 3+} ions. We observed strong renormalizations of the phonon frequencies and clear peaks of

  15. Probing electronic phase transitions with phonons via inelastic neutron scattering: superconductivity in borocarbides, charge and magnetic order in manganites

    International Nuclear Information System (INIS)

    Weber, F.

    2007-01-01

    The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi 2 B 2 C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T c , for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2Δ(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La 2-2x Sr 1+2x Mn 2 O 7 . At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T C . The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO 6 octahedra, which are introduced in this compound by the Jahn-Teller active Mn 3+ ions. We observed strong renormalizations of the phonon frequencies and clear peaks of the intrinsic phonon linewidth near the order

  16. Resonant A1 phonon and four-magnon Raman scattering in hexagonal HoMnO3 thin film

    International Nuclear Information System (INIS)

    Chen Xiangbai; Thi Minh Hien, Nguyen; Yang, In-Sang; Lee, D; Jang, S-Y; Noh, T W

    2010-01-01

    We present the results of resonant Raman scattering of the A 1 phonon at 680 cm -1 and of the four-magnon at 760 cm -1 in hexagonal HoMnO 3 thin film. We find that the A 1 phonon at 680 cm -1 shows a strong resonance effect near the on-site Mn d-d transition at ∼1.7 eV. Our Raman results show that the four-magnon scattering can be selectively excited with red lasers of 647 nm (1.92 eV) and 671 nm (1.85 eV), but are not detectable with green lasers of 532 nm (2.33 eV), indicating that the four-magnon scattering in hexagonal HoMnO 3 has an extremely strong resonance effect also near the on-site Mn d-d transition at ∼1.7 eV. Furthermore, through the analyses of our study of the resonant four-magnon Raman scattering and earlier studies of the resonant two-magnon Raman scattering, we propose a simple general model for all resonant magnon scattering. Our simple general model predicts a simple method for the investigation of the spin-flipping/spin-wave in magnetic materials, which would have significant impacts on the applications of spintronic devices.

  17. Optical phonon scattering on electronic mobility in Al2O3/AlGaN/AlN/GaN heterostructures

    Science.gov (United States)

    Zhou, X. J.; Qu, Y.; Ban, S. L.; Wang, Z. P.

    2017-12-01

    Considering the built-in electric fields and the two-mode property of transverse optical phonons in AlGaN material, the electronic eigen-energies and wave functions are obtained by solving Schrödinger equation with the finite difference method. The dispersion relations and potentials of the optical phonons are given by the transfer matrix method. The mobility of the two dimensional electron gas influenced by the optical phonons in Al2O3/AlGaN/AlN/GaN heterostructures is investigated based on the theory of Lei-Ting force balance equation. It is found that the scattering from the half-space phonons is the main factor affecting the electronic mobility, and the influence of the other phonons can be ignored. The results show that the mobility decreases with increasing the thicknesses of Al2O3 and AlN layers, but there is no definite relationship between the mobility and the thickness of AlGaN barrier. The mobility is obviously reduced by increasing Al component in AlGaN crystal to show that the effect of ternary mixed crystals is important. It is also found that the mobility increases first and then decreases as the increment of the fixed charges, but decreases always with increasing temperature. The heterostructures constructed here can be good candidates as metal-oxide-semiconductor high-electron-mobility-transistors since they have higher electronic mobility due to the influence from interface phonons weakened by the AlN interlayer.

  18. Surface phonons

    CERN Document Server

    Wette, Frederik

    1991-01-01

    In recent years substantial progress has been made in the detection of surface phonons owing to considerable improvements in inelastic rare gas scattering tech­ niques and electron energy loss spectroscopy. With these methods it has become possible to measure surface vibrations in a wide energy range for all wave vectors in the two-dimensional Brillouin zone and thus to deduce the complete surface phonon dispersion curves. Inelastic atomic beam scattering and electron energy loss spectroscopy have started to play a role in the study of surface phonons similar to the one played by inelastic neutron scattering in the investigation of bulk phonons in the last thirty years. Detailed comparison between experimen­ tal results and theoretical studies of inelastic surface scattering and of surface phonons has now become feasible. It is therefore possible to test and to improve the details of interaction models which have been worked out theoretically in the last few decades. At this point we felt that a concise, co...

  19. Raman Scattering Study of the Soft Phonon Mode in the Hexagonal Ferroelectric Crystal KNiCl 3

    Science.gov (United States)

    Machida, Ken-ichi; Kato, Tetsuya; Chao, Peng; Iio, Katsunori

    1997-10-01

    Raman spectra of some phonon modes of the hexagonal ferroelectriccrystal KNiCl3are obtained in the temperature range between 290 K and 590 K, which includes the structural phase transition point T2(=561 K) at which previous measurements of dielectric constant and spontaneouspolarization as a function of temperature had shown that KNiCl3 undergoes a transition between polar phases II and III. An optical birefringence measurement carried outas a complement to the present Raman scattering revealed that this transition is of second order. Towards this transition point, the totally symmetric phonon mode with the lowest frequency observed in the room-temperature phasewas found to soften with increasing temperature.The present results provide new information on the phase-transitionmechanism and the space groups of thehigher (II)- and lower (III)-symmetric phases around T2.

  20. Influence of nanoinclusions on scattering of holes and phonons and transport coefficients in BixSb1−xTe3 bulk nanostructures

    International Nuclear Information System (INIS)

    Bulat, Lev P.; Osvenskii, Vladimir B.; Parkhomenko, Yurii N.; Pshenay-Severin, Dmitry A.

    2012-01-01

    One of the possible ways to increase the thermoelectric figure of merit is the use of bulk nanostructured materials fabricated by melt spinning with subsequent hot pressing or spark plasma sintering. Among a variety of nanostructure types these materials contain regions of initial solid solution with nanometer sized inclusions of different compositions. In the present work the scattering of holes and phonons on nanoinclusions in such p-Bi x Sb 1−x Te 3 based materials is considered. The change of transport coefficients due to this scattering mechanism is theoretically estimated. The estimations showed that the reduction of lattice thermal conductivity (about 12–13%) for nanoinclusions of Bi 2 Te 3 –Sb 2 Te 3 solid solution with different compositions is much greater than the change in power factor. Therefore the corresponding increase of the thermoelectric figure of merit for this case is determined mainly by phonon scattering. Also it is shown that the results of estimations depend on phonon spectrum approximation, e.g. in the case of sine-shaped instead of linear phonon spectrum the estimations give two times higher thermal conductivity reduction. - Graphical abstract: Relative phonon thermal conductivity κ ph change (black line) due to nanoinclusion scattering versus nanoinclusion radius a, and relative thermoelectric power factor change (red line) due to nanoinclusion scattering versus chemical potential μ at nanoinclusion size a=1.5 nm and U 0 =−0.146 eV. Highlights: ► p-Bi x Sb 1−x Te 3 solid solutions with nanosized inclusions were considered. ► Selective hole scattering can increase power factor at high carrier concentrations. ► Lattice thermal conductivity estimations depend on phonon spectrum approximation. ► Phonon scattering can reduce lattice thermal conductivity by about 12–13%. ► The latter factor mainly determines the increase of thermoelectric efficiency.

  1. Observation of soft phonon mode in TbFe3(BO3)4 by inelastic neutron scattering

    Science.gov (United States)

    Pavlovskiy, M. S.; Shaykhutdinov, K. A.; Wu, L. S.; Ehlers, G.; Temerov, V. L.; Gudim, I. A.; Shinkorenko, A. S.; Podlesnyak, A.

    2018-02-01

    The phonon dispersion in terbium iron borate TbFe3(BO3)4 has been measured by inelastic neutron scattering in a temperature range 180

  2. Investigation of the dispersion of phonon modes in CdI2 single crystals by a method of inelastic scattering of thermal neutrons

    International Nuclear Information System (INIS)

    Piroga, S.A.

    2001-01-01

    Experimental observation using a method of inelastic scattering of thermal neutrons the longitudinal phonons in the G-Z, G-X and G-L directions in CdI 2 singe crystal has been obtained. The phonon subsystem observed in the case of CdI 2 single crystals is two dimensional. This is because of the fact that interlayer interactions are weak in compare to intra layer interactions

  3. Thermal transport across solid-solid interfaces enhanced by pre-interface isotope-phonon scattering

    Science.gov (United States)

    Lee, Eungkyu; Luo, Tengfei

    2018-01-01

    Thermal transport across solid interfaces can play critical roles in the thermal management of electronics. In this letter, we use non-equilibrium molecular dynamics simulations to investigate the isotope effect on the thermal transport across SiC/GaN interfaces. It is found that engineered isotopes (e.g., 10% 15N or 71Ga) in the GaN layer can increase the interfacial thermal conductance compared to the isotopically pure case by as much as 23%. Different isotope doping features, such as the isotope concentration, skin depth of the isotope region, and its distance from the interface, are investigated, and all of them lead to increases in thermal conductance. Studies of spectral temperatures of phonon modes indicate that interfacial thermal transport due to low-frequency phonons (transport. This work may provide insights into interfacial thermal transport and useful guidance to practical material design.

  4. Theory of the Influence of Phonon-Phonon and Electron-Phonon Interactions on the Scattering of Neutrons by Crystals; Theorie de l'influence des interactions phonon-phonon et electron-phonon sur la diffusion des neutrons par des cristaux; Teoriya vliyaniya vzaimodejstvij fonon-fonon iehlvktron-fonon na rasseyanie nejtronov kristalla-; Teoria de la influencia de las interacciones fonon-fonon y electron-fonon en la dispersion de neutrones por cristales

    Energy Technology Data Exchange (ETDEWEB)

    Kokkedee, J J.J. [Institute for Theoretical Physics of the University of Utrecht (Netherlands)

    1963-01-15

    As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0{sup o}K) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest

  5. Specific features of slow neutron coherent scattering by crystals with substitution impurities and selection rules for the mass operator of phonons

    International Nuclear Information System (INIS)

    Dzyub, I.P.; Kochmarskij, V.Z.

    1978-01-01

    The specific features of coherent slow-neutron scattering in the neighbourhood of the quasilocal oscillation (QLO) frequency are investigated. By means of the calculation for a simple cubic crystal containing substitutional impurities it is demonstrated that the dispersion curves are discontinuous in the QLO frequency range. This dispersion curve discontinuity is associated with one-phonon peak in the neighbourhood of the QLO frequency. The results of neutron scattering experiments on Crsub(1-x)Wsub(x) and Cusub(1-x)Ausub(x) solutions are then considered from this standpoint. Selection rules for the phonon mass operator are established which allow to determine the symmetry of QLO which contribute to the broadening and shift of one-phonon peaks in the directions of high symmetry, depending on the transfer neutron-momentum orientation with respect to the principal axes of a crystal

  6. Influence of spatial and temporal coherences on atomic resolution high angle annular dark field imaging

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, Andreas, E-mail: andreas.beyer@physik.uni-marburg.de; Belz, Jürgen; Knaub, Nikolai; Jandieri, Kakhaber; Volz, Kerstin

    2016-10-15

    Aberration-corrected (scanning) transmission electron microscopy ((S)TEM) has become a widely used technique when information on the chemical composition is sought on an atomic scale. To extract the desired information, complementary simulations of the scattering process are inevitable. Often the partial spatial and temporal coherences are neglected in the simulations, although they can have a huge influence on the high resolution images. With the example of binary gallium phosphide (GaP) we elucidate the influence of the source size and shape as well as the chromatic aberration on the high angle annular dark field (HAADF) intensity. We achieve a very good quantitative agreement between the frozen phonon simulation and experiment for different sample thicknesses when a Lorentzian source distribution is assumed and the effect of the chromatic aberration is considered. Additionally the influence of amorphous layers introduced by the preparation of the TEM samples is discussed. Taking into account these parameters, the intensity in the whole unit cell of GaP, i.e. at the positions of the different atomic columns and in the region between them, is described correctly. With the knowledge of the decisive parameters, the determination of the chemical composition of more complex, multinary materials becomes feasible. - Highlights: • Atomic resolution high angle annular dark field images of gallium phosphide are compared quantitatively with simulated ones. • The influence of partial spatial and temporal coherence on the HAADF-intensity is investigated. • The influence of amorphous layers introduced by the sample preparation is simulated.

  7. Rode's iterative calculation of surface optical phonon scattering limited electron mobility in N-polar GaN devices

    International Nuclear Information System (INIS)

    Ghosh, Krishnendu; Singisetti, Uttam

    2015-01-01

    N-polar GaN channel mobility is important for high frequency device applications. Here, we report theoretical calculations on the surface optical (SO) phonon scattering rate of two-dimensional electron gas (2DEG) in N-polar GaN quantum well channels with high-k dielectrics. Rode's iterative calculation is used to predict the scattering rate and mobility. Coupling of the GaN plasmon modes with the SO modes is taken into account and dynamic screening is employed under linear polarization response. The effect of SO phonons on 2DEG mobility was found to be small at >5 nm channel thickness. However, the SO mobility in 3 nm N-polar GaN channels with HfO 2 and ZrO 2 high-k dielectrics is low and limits the total mobility. The SO scattering for SiN dielectric on GaN was found to be negligible due to its high SO phonon energy. Using Al 2 O 3 , the SO phonon scattering does not affect mobility significantly only except the case when the channel is too thin with a low 2DEG density

  8. Well-width dependence of exciton-phonon scattering in InxGa1 - xAs/GaAs single quantum wells

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang Werner; Hvam, Jørn Märcher

    1999-01-01

    The temperature and density dependencies of the exciton dephasing time in In0.18Ga0.82As/GaAs single quantum wells with different thicknesses have been measured by degenerate four-wave mixing; The exciton-phonon scattering contribution to the dephasing is isolated by extrapolating the dephasing r...

  9. Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low-k Films: A Surface Brillouin Scattering Study

    Science.gov (United States)

    Zizka, J.; King, S.; Every, A.; Sooryakumar, R.

    2018-04-01

    To reduce the RC (resistance-capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low-k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low-k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson's ratio, and Young's modulus of these porous low-k SiOC:H films (˜ 25-250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

  10. Manipulation of Phonons with Phononic Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Leseman, Zayd Chad [Univ. of New Mexico, Albuquerque, NM (United States)

    2015-07-09

    There were three research goals associated with this project. First, was to experimentally demonstrate phonon spectrum control at THz frequencies using Phononic Crystals (PnCs), i.e. demonstrate coherent phonon scattering with PnCs. Second, was to experimentally demonstrate analog PnC circuitry components at GHz frequencies. The final research goal was to gain a fundamental understanding of phonon interaction using computational methods. As a result of this work, 7 journal papers have been published, 1 patent awarded, 14 conference presentations given, 4 conference publications, and 2 poster presentations given.

  11. Phonons in models for icosahedral quasicrystals: low frequency behaviour an inelastic scattering properties

    International Nuclear Information System (INIS)

    Los, J.; Janssen, T.; Gaehler, F.

    1993-01-01

    A detailed study of the low frequency behaviour of the phonon spectrum for 3-dimensional tiling models of icosahedral quasicrystals is presented, in commensurate approximations with up to 10336 atoms per unit cell. The scaling behaviour of the lowest phonon branches shows that the widths of the gaps relative to the bandwidths vanish in the low frequency limit. The density of states at low frequencies is calculated by Brillouin zone integration, using either local linear or local quadratic interpolation of the branch surface. For perfect approximants it appears that there is a deviation from the normal ω 2 -behaviour already at relatively low frequencies, in the form of pseudogaps. Also randomized approximants are considered, and it turns out that the pseudogaps in the density of states are flattened by randomization. When approaching the quasiperiodic limit, the dispersion of the acoustic branches becomes more and more isotropic, and the two transversal sound velocities tend to the same value. The dynamical structure factor is determined for several approximants, and it is shown that the linearity and the isotropy of the dispersion are extended far beyond the range of the acoustic branches inside the Brillouin zone. A sharply peaked response is observed at low frequencies, and broadening at higher frequencies. To obtain these results, an efficient algorithm based on Lanczos tridiagonalisation is used. (orig.)

  12. Phonon renormalization in LaCoO{sub 3} by inelastic neutron and X-ray scattering

    Energy Technology Data Exchange (ETDEWEB)

    Kauth, Maximilian; Weber, Frank [Institut fuer Festkoerperphysik, Karlsruher Institut fuer Technologie (Germany); Castellan, John-Paul [Institut fuer Festkoerperphysik, Karlsruher Institut fuer Technologie (Germany); Laboratoire Leon Brillouin, CEA Saclay (France)

    2016-07-01

    LaCoO{sub 3} exhibits two broad magnetic-electric transitions, a diamagnetic to paramagnetic spin-state transition at T{sub SS} ∼ 100 K and a metal-insulator transition at T{sub MI} ∼ 500 K. The spin transitions on heating are proposed to be as follows: from a homogeneous LS state to a mixed Low-Spin/High-Spin (LS/HS) state with strong spin-charge fluctuations at T=T{sub SS} and, subsequently, into a homogeneous HS state at T=T{sub MI}. The lattice participates in the state mixture by expansion of CoO{sub 6} octahedra around the HS sites, while the ones around LS sites have a reduced size. The originally proposed static order [2] has not been observed experimentally and, hence, the ordering is expected to be dynamic and short-ranged. We investigated the lattice dynamical properties of LaCoO{sub 3} using inelastic neutron scattering. Based on detailed ab-initio lattice dynamical calculations (performed in our institute), we aim for a comprehensive understanding of lattice dynamics in LaCoO{sub 3}. The above discussed crossovers and spin state order should be reflected in the lattice degrees of freedom via quasi elastic scattering and phonon renormalization effects.

  13. Optimizing phonon scattering by tuning surface-interdiffusion-driven intermixing to break the random-alloy limit of thermal conductivity

    Science.gov (United States)

    Yang, Xiaolong; Li, Wu

    2018-01-01

    We investigate the evolution of the cross-plane thermal conductivity κ of superlattices (SLs) as interfaces change from perfectly abrupt to totally intermixed, by using nonequilibrium molecular dynamics simulations in combination with the spectral heat current calculations. We highlight the role of surface-interdiffusion-driven intermixing by calculating the κ of SLs with changing interface roughness, whose tuning allows for κ values much lower than the "alloy limit" and the abrupt interface limit in same cases. The interplay between alloy and interface scattering in different frequency ranges provides a physical basis to predict a minimum of thermal conductivity. More specifically, we also explore how the interface roughness affects the thermal conductivities for SL materials with a broad span of atomic mass and bond strength. In particular, we find that (i) only when the "spacer" thickness of SLs increases up to a critical value, κ of rough SLs can break the corresponding "alloy limit," since SLs with different "spacer" thickness have different characteristic length of phonon transport, which is influenced by surface-interdiffusion-driven intermixing to different extend. (ii) Whether κ changes monotonically with interface roughness strongly depends on the period length and intrinsic behavior of phonon transport for SL materials. Especially, for the SL with large period length, there exists an optimal interface roughness that can minimize the thermal conductivity. (iii) Surface-interdiffusion-driven intermixing is more effective in achieving a low κ below the alloy limit for SL materials with large mass mismatch than with small one. (iv) It is possible for SL materials with large lattice mismatch (i.e., bond strength) to design an ideally abrupt interface structure with κ much below the alloy limit. These results have clear implications for optimization of thermal transport for heat management and for the development of thermoelectric materials.

  14. Spin-phonon coupling in rod-shaped half-metallic CrO sub 2 ultrafine particles: a magnetic Raman scattering study

    CERN Document Server

    Yu, T; Sun, W X; Lin, J Y; Ding, J

    2003-01-01

    Half-metallic CrO sub 2 powder compact with rod-shaped nanoparticles was studied by micro-Raman scattering in the presence of an external magnetic field at room temperature (300 K). In the low-field region (H <= 250 mT), the frequency and intensity of the E sub g mode, an internal phonon mode of CrO sub 2 , increase dramatically with increase in the magnetic field, while the corresponding linewidth decreases. The above parameters become constant when the CrO sub 2 powder enters the saturation state at higher magnetic field. The pronounced anomalies of the Raman phonon parameters under a low magnetic field are attributed to the spin-phonon coupling enhanced by the magnetic ordering, which is induced by the external magnetic field. (letter to the editor)

  15. Phonon spectra in the parent superconducting iron-tuned telluride F e1 +xTe from inelastic neutron scattering and ab initio calculations

    Science.gov (United States)

    Zbiri, Mohamed; Viennois, Romain

    2017-10-01

    We report inelastic neutron scattering measurements of phonon spectra in the parent superconductor iron-tuned chalcogenide F e1 +xTe for two different x contents (x ≤0.11 ) using neutron time-of-flight technique. Thermal neutron spectroscopy allowed the collection of the low-temperature Stokes spectra over an extended Q range at 2, 40, and 120 K, hence covering both the magnetic monoclinic and the paramagnetic tetragonal phases, whereas cold neutrons allowed the measurement of high-resolution anti-Stokes spectra at 140, 220, and 300 K, thus covering the tetragonal phase. Our results evidence a spin-phonon coupling behavior towards the observed noticeable temperature-dependent change of the Stokes spectra across the transition temperatures. On the other hand, the anti-Stokes spectra reveal a pronounced hardening of the low-energy, acoustic region of the phonon spectrum upon heating, indicating a strong anharmonicity and a subtle dependence of phonons on structural evolution within the tetragonal phase. Experimental results are accompanied by ab initio calculations of phonon spectra of the tetragonal stoichiometric phase for a comparison with the high-resolution anti-Stokes spectra. Calculations included different density functional methods. Spin polarization and van der Waals interaction were either considered or neglected, individually or concomitantly, in order to study their respective effect on lattice dynamics description. Our results suggest that including van der Waals interaction has only a slight effect on phonon dynamics; however, phonon spectra are better described when spin polarization is included in a cooperative way with van der Waals interactions.

  16. Hot phonon generation by split-off hole band electrons in AlxGa1-xAs alloys investigated by picosecond Raman scattering

    International Nuclear Information System (INIS)

    Jacob, J.M.; Kim, D.S.; Zhou, J.F.; Song, J.J.

    1992-01-01

    The initial generation of hot LO phonons by the relaxation of hot carriers in GaAs and Al x Ga 1-x As alloy semiconductors is studied. Within the initial 2ps of photoexcitation, only those electrons originating from the split-off hole bands are found to generate a significant number of I-valley hot phonons when photon energies of 2.33eV are used. A picosecond Raman scattering technique is used to determine the hot phonon occupation number in a series of MBE grown Al x Ga 1-x As samples with 0≤x≤0.39. The Stokes and anti-Stokes lines were measured for both GaAs-like and AlAs-like LO phonon modes to determine their occupation numbers. The authors observe a rapid decrease in the phonon occupation numbers as the aluminum concentration increases beyond x = 0.2. This rapid decrease is explained by considering only those electrons photoexcited from the split-off hole band. Almost all of the electrons originating from the heavy and light-hole bands are shown to quickly transfer and remain in the X and L valleys without generating significant numbers of hot LO phonons during the initial 2ps and at a carrier density of 10 17 cm -3 . A model based upon the instantaneous thermalization of hot electrons photoexcited from the split-off hole bands is used to fit the data. They have obtained very good agreement between experiment and theory. This work provides a clear understanding to the relaxation of Γ valley hot electrons by the generation of hot phonons on subpicosecond and picosecond time scales, which has long standing implications to previous time resolved Raman experiments

  17. A Neutron Scattering Study of Phonons in Per-Deuterated S-Triazine

    DEFF Research Database (Denmark)

    Doue, M. T.; Heilmann, I. U.; Kjems, Jørgen

    1983-01-01

    The lattice dynamics of a fully-deuterated single crystal of s-triazine is investigated using the technique of coherent inelastic neutron scattering. Detailed measurements of the temperature dependence of the dispersion of the soft acoustic mode associated with the ferroelastic phase transition...

  18. Enhanced light scattering of the forbidden longitudinal optical phonon mode studied by micro-Raman spectroscopy on single InN nanowires

    International Nuclear Information System (INIS)

    Schaefer-Nolte, E O; Stoica, T; Gotschke, T; Limbach, F A; Gruetzmacher, D; Calarco, R; Sutter, E; Sutter, P

    2010-01-01

    In the literature, there are controversies on the interpretation of the appearance in InN Raman spectra of a strong scattering peak in the energy region of the unscreened longitudinal optical (LO) phonons, although a shift caused by the phonon-plasmon interaction is expected for the high conductance observed in this material. Most measurements on light scattering are performed on ensembles of InN nanowires (NWs). However, it is important to investigate the behavior of individual nanowires and here we report on micro-Raman measurements on single nanowires. When changing the polarization direction of the incident light from parallel to perpendicular to the wire, the expected reduction of the Raman scattering was observed for transversal optical (TO) and E 2 phonon scattering modes, while a strong symmetry-forbidden LO mode was observed independently on the laser polarization direction. Single Mg- and Si-doped crystalline InN nanowires were also investigated. Magnesium doping results in a sharpening of the Raman peaks, while silicon doping leads to an asymmetric broadening of the LO peak. The results can be explained based on the influence of the high electron concentration with a strong contribution of the surface accumulation layer and the associated internal electric field.

  19. Enhanced Light Scattering of the Forbidden longitudinal Optical Phonon Mode Studied by Micro-Raman Spectroscopy on Single InN nanowires

    International Nuclear Information System (INIS)

    Sutter, E.; Schafer-Nolte, E.O.; Stoica, T.; Gotschke, T.; Limbach, F.A.; Sutter, P.; Grutzmacher, D.; Calarco, R.

    2010-01-01

    In the literature, there are controversies on the interpretation of the appearance in InN Raman spectra of a strong scattering peak in the energy region of the unscreened longitudinal optical (LO) phonons, although a shift caused by the phonon-plasmon interaction is expected for the high conductance observed in this material. Most measurements on light scattering are performed on ensembles of InN nanowires (NWs). However, it is important to investigate the behavior of individual nanowires and here we report on micro-Raman measurements on single nanowires. When changing the polarization direction of the incident light from parallel to perpendicular to the wire, the expected reduction of the Raman scattering was observed for transversal optical (TO) and E2 phonon scattering modes, while a strong symmetry-forbidden LO mode was observed independently on the laser polarization direction. Single Mg- and Si-doped crystalline InN nanowires were also investigated. Magnesium doping results in a sharpening of the Raman peaks, while silicon doping leads to an asymmetric broadening of the LO peak. The results can be explained based on the influence of the high electron concentration with a strong contribution of the surface accumulation layer and the associated internal electric field.

  20. Enhanced light scattering of the forbidden longitudinal optical phonon mode studied by micro-Raman spectroscopy on single InN nanowires.

    Science.gov (United States)

    Schäfer-Nolte, E O; Stoica, T; Gotschke, T; Limbach, F A; Sutter, E; Sutter, P; Grützmacher, D; Calarco, R

    2010-08-06

    In the literature, there are controversies on the interpretation of the appearance in InN Raman spectra of a strong scattering peak in the energy region of the unscreened longitudinal optical (LO) phonons, although a shift caused by the phonon-plasmon interaction is expected for the high conductance observed in this material. Most measurements on light scattering are performed on ensembles of InN nanowires (NWs). However, it is important to investigate the behavior of individual nanowires and here we report on micro-Raman measurements on single nanowires. When changing the polarization direction of the incident light from parallel to perpendicular to the wire, the expected reduction of the Raman scattering was observed for transversal optical (TO) and E(2) phonon scattering modes, while a strong symmetry-forbidden LO mode was observed independently on the laser polarization direction. Single Mg- and Si-doped crystalline InN nanowires were also investigated. Magnesium doping results in a sharpening of the Raman peaks, while silicon doping leads to an asymmetric broadening of the LO peak. The results can be explained based on the influence of the high electron concentration with a strong contribution of the surface accumulation layer and the associated internal electric field.

  1. Hypersonic phononic crystals.

    Science.gov (United States)

    Gorishnyy, T; Ullal, C K; Maldovan, M; Fytas, G; Thomas, E L

    2005-03-25

    In this Letter we propose the use of hypersonic phononic crystals to control the emission and propagation of high frequency phonons. We report the fabrication of high quality, single crystalline hypersonic crystals using interference lithography and show that direct measurement of their phononic band structure is possible with Brillouin light scattering. Numerical calculations are employed to explain the nature of the observed propagation modes. This work lays the foundation for experimental studies of hypersonic crystals and, more generally, phonon-dependent processes in nanostructures.

  2. Raman scattering study of phonons in Bi-based superconductor thin films

    International Nuclear Information System (INIS)

    Mejia-Garcia, C.; Diaz-Valdes, E.; Contreras-Puente, G.; Lopez-Lopez, J.L.; Jergel, M.; Morales, A.

    2004-01-01

    Raman spectra were obtained from samples of Bi-Pb-Sr-Ca-Cu-O (BPSCCO) thin films after varying several growth parameters, such as covering material, annealing time (t R ), annealing temperature (T R ), and nominal lead content (x). Thin films with the nominal composition Bi 1.4 Pb x Sr 2 Ca 2 Cu 3 O δ were grown on MgO substrates by a spray pyrolysis technique, followed by a solid state reaction. The results of Raman scattering measurements at room temperature show a series of vibrational optical modes within the range 300-900 cm -1 . The assignment of these modes was made by involving mainly the 2212 and 2223 phases and was confirmed by both X-ray diffraction and resistance in dependence of the temperature (R-T) measurements as well

  3. Interfacial electron and phonon scattering processes in high-powered nanoscale applications.

    Energy Technology Data Exchange (ETDEWEB)

    Hopkins, Patrick E.

    2011-10-01

    The overarching goal of this Truman LDRD project was to explore mechanisms of thermal transport at interfaces of nanomaterials, specifically linking the thermal conductivity and thermal boundary conductance to the structures and geometries of interfaces and boundaries. Deposition, fabrication, and post possessing procedures of nanocomposites and devices can give rise to interatomic mixing around interfaces of materials leading to stresses and imperfections that could affect heat transfer. An understanding of the physics of energy carrier scattering processes and their response to interfacial disorder will elucidate the potentials of applying these novel materials to next-generation high powered nanodevices and energy conversion applications. An additional goal of this project was to use the knowledge gained from linking interfacial structure to thermal transport in order to develop avenues to control, or 'tune' the thermal transport in nanosystems.

  4. Surface phonon modes of the NaI(001) crystal surface by inelastic He atom scattering

    International Nuclear Information System (INIS)

    Brug, W.P.; Chern, G.; Duan, J.; Safron, S.A.; Skofronick, J.G.; Benedek, G.

    1990-01-01

    The present theoretical treatment of the surface dynamics of ionic insulators employs the shell model with parameters obtained from bulk materials. The approach has been generally very successful in comparisons with experiment. However, most of the experimental surface dynamics work has been on the low-mass alkali halides with very little effort on higher energy modes or on the heavier alkali halides, where effects from relaxation might be important. The work of this paper explores these latter two conditions. Inelastic scattering of He atoms from the left-angle 110 right-angle NaI(001) surface has been used to obtain the acoustic S 1 Rayleigh mode, the S 6 longitudinal mode, and the S 8 crossing mode, however, no gap S 4 optical mode was seen. The results compare favorably with reported theoretical models employing both slab calculations and the Green's function method thus indicating that bulk parameters and the shell model go a long way in explaining most of the observations

  5. Phonon engineering for nanostructures.

    Energy Technology Data Exchange (ETDEWEB)

    Aubry, Sylvie (Stanford University); Friedmann, Thomas Aquinas; Sullivan, John Patrick; Peebles, Diane Elaine; Hurley, David H. (Idaho National Laboratory); Shinde, Subhash L.; Piekos, Edward Stanley; Emerson, John Allen

    2010-01-01

    Understanding the physics of phonon transport at small length scales is increasingly important for basic research in nanoelectronics, optoelectronics, nanomechanics, and thermoelectrics. We conducted several studies to develop an understanding of phonon behavior in very small structures. This report describes the modeling, experimental, and fabrication activities used to explore phonon transport across and along material interfaces and through nanopatterned structures. Toward the understanding of phonon transport across interfaces, we computed the Kapitza conductance for {Sigma}29(001) and {Sigma}3(111) interfaces in silicon, fabricated the interfaces in single-crystal silicon substrates, and used picosecond laser pulses to image the thermal waves crossing the interfaces. Toward the understanding of phonon transport along interfaces, we designed and fabricated a unique differential test structure that can measure the proportion of specular to diffuse thermal phonon scattering from silicon surfaces. Phonon-scale simulation of the test ligaments, as well as continuum scale modeling of the complete experiment, confirmed its sensitivity to surface scattering. To further our understanding of phonon transport through nanostructures, we fabricated microscale-patterned structures in diamond thin films.

  6. Flexural phonon limited phonon drag thermopower in bilayer graphene

    Science.gov (United States)

    Ansari, Mohd Meenhaz; Ashraf, SSZ

    2018-05-01

    We investigate the phonon drag thermopower from flexural phonons as a function of electron temperature and carrier concentration in the Bloch-Gruneisen regime in non-strained bilayer graphene using Boltzmann transport equation approach. The flexural phonons are expected to be the major source of intrinsic scattering mechanism in unstrained bilayer graphene due to their large density. The flexural phonon modes dispersion relation is quadratic so these low energy flexural phonons abound at room temperature and as a result deform the bilayer graphene sheet in the out of plane direction and affects the transport properties. We also produce analytical result for phonon-drag thermopower from flexural phonons and find that phonon-drag thermopower depicts T2 dependence on temperature and n-1 on carrier concentration.

  7. Phonon dispersion in vanadium

    International Nuclear Information System (INIS)

    Ivanov, A.S.; Rumiantsev, A.Yu.

    1999-01-01

    Complete text of publication follows. Phonon dispersion curves in Vanadium metal are investigated by neutron inelastic scattering using three-axis spectrometers. Due to extremely low coherent scattering amplitude of neutrons in natural isotope mixture of vanadium the phonon frequencies could be determined in the energy range below about 15 meV. Several phonon groups were measured with the polarised neutron scattering set-up. It is demonstrated that the intensity of coherent inelastic scattering observed in the non-spin-flip channel vanishes in the spin-flip channel. The phonon density of states is measured on a single crystal keeping the momentum transfer equal to a vector of reciprocal lattice where the coherent inelastic scattering is suppressed. Phonon dispersion curves in vanadium, as measured by neutron and earlier by X-ray scattering, are described in frames of a charge-fluctuation model involving monopolar and dipolar degrees of freedom. The model parameters are compared for different transition metals with body-centred cubic-structure. (author)

  8. Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO3 substrates

    Science.gov (United States)

    Wang, Y.; Nakatsukasa, K.; Rademaker, L.; Berlijn, T.; Johnston, S.

    2016-05-01

    Mono- and multilayer FeSe thin films grown on SrTiO3 and BiTiO3 substrates exhibit a greatly enhanced superconductivity over that found in bulk FeSe. A number of proposals have been advanced for the mechanism of this enhancement. One possibility is the introduction of a cross-interface electron-phonon (e-ph) interaction between the FeSe electrons and oxygen phonons in the substrates that is peaked in the forward scattering (small {q}) direction due to the two-dimensional nature of the interface system. Motivated by this, we explore the consequences of such an interaction on the superconducting state and electronic structure of a two-dimensional system using Migdal-Eliashberg (ME) theory. This interaction produces not only deviations from the expectations of conventional phonon-mediated pairing but also replica structures in the spectral function and density of states, as probed by angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and quasiparticle interference imaging. We also discuss the applicability of ME theory for a situation where the e-ph interaction is peaked at small momentum transfer and in the FeSe/STO system.

  9. Resonant surface-enhanced Raman scattering by optical phonons in a monolayer of CdSe nanocrystals on Au nanocluster arrays

    Energy Technology Data Exchange (ETDEWEB)

    Milekhin, Alexander G., E-mail: milekhin@isp.nsc.ru [A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentjeva, 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov str. 2, 630090 Novosibirsk (Russian Federation); Sveshnikova, Larisa L.; Duda, Tatyana A. [A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentjeva, 13, 630090 Novosibirsk (Russian Federation); Rodyakina, Ekaterina E. [A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentjeva, 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov str. 2, 630090 Novosibirsk (Russian Federation); Dzhagan, Volodymyr M. [Semiconductor Physics, Technische Universität Chemnitz, D-09107 Chemnitz (Germany); Sheremet, Evgeniya [Solid Surfaces Analysis, Technische Universität Chemnitz, D-09107 Chemnitz (Germany); Gordan, Ovidiu D. [Semiconductor Physics, Technische Universität Chemnitz, D-09107 Chemnitz (Germany); Himcinschi, Cameliu [Institut für Theoretische Physik, TU Bergakademie Freiberg, 09596 Freiberg (Germany); Latyshev, Alexander V. [A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentjeva, 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov str. 2, 630090 Novosibirsk (Russian Federation); Zahn, Dietrich R.T. [Semiconductor Physics, Technische Universität Chemnitz, D-09107 Chemnitz (Germany)

    2016-05-01

    Highlights: • Regular Au nanocluster and dimer arrays as well as single Au dimers are fabricated. • Resonant SERS by monolayers of CdSe nanocrystals deposited on the Au nanostructures is observed. • LO energy change for CdSe NCs on different single Au dimers indicates SERS by single or a few NCs. - Abstract: Here we present the results on an investigation of resonant Stokes and anti- Stokes surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on arrays of Au nanoclusters using the Langmuir–Blodgett technology. The thickness of deposited NCs, determined by transmission and scanning electron microscopy, amounts to approximately 1 monolayer. Special attention is paid to the determination of the localized surface plasmon resonance (LSPR) energy in the arrays of Au nanoclusters as a function of the nanocluster size by means of micro-ellipsometry. SERS by optical phonons in CdSe NCs shows a significant enhancement factor with a maximal value of 2 × 10{sup 3} which depends resonantly on the Au nanocluster size and thus on the LSPR energy. The deposition of CdSe NCs on the arrays of Au nanocluster dimers enabled us to study the polarization dependence of SERS. It was found that a maximal SERS signal is observed for the light polarization along the dimer axis. Finally, SERS by optical phonons was observed for CdSe NCs deposited on the structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates quasi-single NC Raman spectra being obtained.

  10. Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in (Na ,Bi ) Ti O3-x BaTi O3 single crystals near the morphotropic phase boundary

    Science.gov (United States)

    Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang; Viehland, Dwight; Winn, Barry; Ren, Yang; Li, Xiaobing; Luo, Haosu; Delaire, Olivier

    2017-11-01

    Neutron and x-ray scattering measurements were performed on (N a1 /2B i1 /2 ) Ti O3-x at %BaTi O3 (NBT-x BT ) single crystals (x =4 , 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the Γ points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. In samples with compositions closest to the MPB, our inelastic neutron scattering investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and Γ points, respectively. These critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.

  11. Electron-confined LO-phonon scattering in GaAs-Al0.45Ga0.55As ...

    Indian Academy of Sciences (India)

    resonance [17] – at high field where a longitudinal-optical (LO) phonon mediates a transition ..... This competition is controlled through the factor. Γ = γLLw ... [3] L Eaves, F W Sheard and G A T Toombs, Band structure engineering in semicon-.

  12. Supra-ballistic phonons

    International Nuclear Information System (INIS)

    Russell, F.M.

    1989-05-01

    Energetic particles moving with a solid, either from nuclear reactions or externally injected, deposit energy by inelastic scattering processes which eventually appears as thermal energy. If the transfer of energy occurs in a crystalline solid then it is possible to couple some of the energy directly to the nuclei forming the lattice by generating phonons. In this paper the transfer of energy from a compound excited nucleus to the lattice is examined by introducing a virtual particle Π. It is shown that by including a Π in the nuclear reaction a substantial amount of energy can be coupled directly to the lattice. In the lattice this particle behaves as a spatially localized phonon of high energy, the so-called supra-ballistic phonon. By multiple inelastic scattering the supra-ballistic phonon eventually thermalizes. Because both the virtual particle Π and the equivalent supra-ballistic phonon have no charge or spin and can only exist within a lattice it is difficult to detect other than by its decay into thermal phonons. The possibility of a Π removing excess energy from a compound nucleus formed by the cold fusion of deuterium is examined. (Author)

  13. A Monte Carlo Sampling Technique for Multi-phonon Processes

    Energy Technology Data Exchange (ETDEWEB)

    Hoegberg, Thure

    1961-12-15

    A sampling technique for selecting scattering angle and energy gain in Monte Carlo calculations of neutron thermalization is described. It is supposed that the scattering is separated into processes involving different numbers of phonons. The number of phonons involved is first determined. Scattering angle and energy gain are then chosen by using special properties of the multi-phonon term.

  14. Excitation strengths and transition radii differences of one-phonon quadrupole excitations from electron scattering on {sup 92,94}Zr and {sup 94}Mo

    Energy Technology Data Exchange (ETDEWEB)

    Sheikh Obeid, Abdulrahman

    2014-11-01

    In the framework of this thesis electron scattering experiments on low-energy excitations of {sup 92}Zr and {sup 94}Zr were performed at the S-DALINAC in a momentum transfer range q=0.3-0.6 fm{sup -1}. The nature of one-phonon symmetric and mixed-symmetric 2{sup +} and 3{sup -} states of {sup 92}Zr was investigated by comparison with predictions of the quasi-particle phonon model (QPM). Theoretical (e,e') cross sections have been calculated within the distorted wave Born approximation (DWBA) to account for Coulomb distortion effects. The reduced strengths of the one-quadrupole phonon states and the one-octupole phonon state have been extracted. The similarity of the momentum-transfer dependence of the form factors between the 2{sup +} states supports the one-phonon nature of the 2{sup +}{sub 2} state of {sup 92}Zr. A new method based on the Plane Wave Born Approximation (PWBA) for a model-independent determination of the ratio of the E2 transition strengths of fully symmetric (FSS) and mixed-symmetry (MSS) one-phonon excitations of heavy vibrational nuclei is introduced. Due to the sensitivity of electron scattering to charge distributions, the charge transition-radii difference can be determined. The basic assumptions (independence from the ratio of Coulomb corrections and from absolute values of transition radii) are tested within the Tassie model, which makes no specific assumptions about the structure of the states other than collectivity. It is shown that a PWBA analysis of the form factors, which usually fails for heavy nuclei, can nevertheless be applied in a relative analysis. This is a new promising approach to determine the ground state transition strength of the 2{sup +} MSS of vibrational nuclei with a precision limited only by the experimental information about the B(E2;2{sup +}{sub 1}→0{sup +}{sub 1}) strength. The PWBA approach furthermore provides information about differences of the proton transition radii of the respective states

  15. Multiphonon resonant Raman scattering in the semimagnetic semiconductor Cd1-xMnxTe: Froehlich and deformation potential exciton-phonon interaction

    International Nuclear Information System (INIS)

    Riera, R; Rosas, R; Marin, J L; Bergues, J M; Campoy, G

    2003-01-01

    A theory describing multiphonon resonant Raman scattering (MPRRS) processes in wide-gap diluted magnetic semiconductors is presented, with Cd 1-x Mn x Te as an example. The incident radiation frequency ω l is taken above the fundamental absorption region. The photoexcited electron and hole make real transitions through the LO phonon, when one considers Froehlich (F) and deformation potential (DP) interactions. The strong exchange interaction, typical of these materials, leads to a large spin splitting of the exciton states in the magnetic field. Neglecting Landau quantization, this Zeeman splitting gives rise to the formation of eight bands (two conduction and six valence ones) and ten different exciton states according to the polarization of the incident light. Explicit expressions for the MPRRS intensity of second and third order, the indirect creation and annihilation probabilities, the exciton lifetime, and the probabilities of transition between different exciton states and different types of exciton as a function of ω l and the external magnetic field are presented. The selection rules for all hot exciton transitions via exciton-photon interaction and F and DP exciton-phonon interactions are investigated. The exciton energies, as a function of B, the Mn concentration x, and the temperature T, are compared to a theoretical expression. Graphics for creation and annihilation probabilities, lifetime, and Raman intensity of second and third order are discussed

  16. Detecting the phonon spin in magnon-phonon conversion experiments

    Science.gov (United States)

    Holanda, J.; Maior, D. S.; Azevedo, A.; Rezende, S. M.

    2018-05-01

    Recent advances in the emerging field of magnon spintronics have stimulated renewed interest in phenomena involving the interaction between spin waves, the collective excitations of spins in magnetic materials that quantize as magnons, and the elastic waves that arise from excitations in the crystal lattice, which quantize as phonons. In magnetic insulators, owing to the magnetostrictive properties of materials, spin waves can become strongly coupled to elastic waves, forming magnetoelastic waves—a hybridized magnon-phonon excitation. While several aspects of this interaction have been subject to recent scrutiny, it remains unclear whether or not phonons can carry spin. Here we report experiments on a film of the ferrimagnetic insulator yttrium iron garnet under a non-uniform magnetic field demonstrating the conversion of coherent magnons generated by a microwave field into phonons that have spin. While it is well established that photons in circularly polarized light carry a spin, the spin of phonons has had little attention in the literature. By means of wavevector-resolved Brillouin light-scattering measurements, we show that the magnon-phonon conversion occurs with constant energy and varying linear momentum, and that the light scattered by the phonons is circularly polarized, thus demonstrating that the phonons have spin.

  17. Role of phonon scattering by elastic strain field in thermoelectric Sr1−xYxTiO3−δ

    KAUST Repository

    Bhattacharya, S.

    2014-06-12

    Perovskite-type SrTiO3-δ ceramics are multifunctional materials with significant potential as n-type thermoelectric (TE) materials. The electronic and thermal transport properties of spark plasma sintered polycrystalline Sr1-xYxTiO3-δ (x=0.05, 0.075, 0.1) ceramics are systematically investigated from (15-800) K. The Sr0.9Y0.1TiO3-δ simultaneously exhibits a large Seebeck coefficient, α>-80μV/K and moderately high electrical resistivity, ρ∼0.8mΩ-cm at a carrier concentration of ∼1021cm-3 at 300K resulting in a high TE power factor defined herein as (α2σT)∼0.84W/m-K at 760K. Despite the similar atomic masses of Sr (87.6g/mol) and Y (88.9g/mol), the lattice thermal conductivity (κL) of Sr1-xY xTiO3-δ is significantly reduced with increased Y-doping, owing to the smaller ionic radii of Y3+ (∼1.23Å, coordination number 12) compared to Sr2+ (∼1.44Å, coordination number 12) ions. In order to understand the thermal conductivity reduction mechanism, the κL in the Sr1-xY xTiO3-δ series are phenomenologically modeled with a modified Callaway\\'s equation from 30-600K. Phonon scattering by elastic strain field due to ionic radii mismatch is found to be the prominent scattering mechanism in reducing κL of these materials. In addition, the effect of Y-doping on the elastic moduli of Sr1-xY xTiO3-δ (x=0, 0.1) is investigated using resonant ultrasound spectroscopy, which exhibits an anomaly in x=0.1 in the temperature range 300-600K. As a result, the phonon mean free path is found to be further reduced in the Sr0.9Y0.1TiO3-δ compared to that of SrTiO3-δ, resulting in a considerably low thermal conductivity κ∼2.7W/m-K at 760K. Finally, we report a thermoelectric figure of merit (ZT)∼0.3 at 760K in the Sr0.9Y 0.1TiO3-δ, the highest ZT value reported in the Y-doped SrTiO3 ceramics thus far. © 2014 AIP Publishing LLC.

  18. Role of phonon scattering by elastic strain field in thermoelectric Sr1−xYxTiO3−δ

    KAUST Repository

    Bhattacharya, S.; Mehdizadeh Dehkordi, A.; Tennakoon, S.; Adebisi, R.; Gladden, J. R.; Darroudi, T.; Alshareef, Husam N.; Tritt, T. M.

    2014-01-01

    Perovskite-type SrTiO3-δ ceramics are multifunctional materials with significant potential as n-type thermoelectric (TE) materials. The electronic and thermal transport properties of spark plasma sintered polycrystalline Sr1-xYxTiO3-δ (x=0.05, 0.075, 0.1) ceramics are systematically investigated from (15-800) K. The Sr0.9Y0.1TiO3-δ simultaneously exhibits a large Seebeck coefficient, α>-80μV/K and moderately high electrical resistivity, ρ∼0.8mΩ-cm at a carrier concentration of ∼1021cm-3 at 300K resulting in a high TE power factor defined herein as (α2σT)∼0.84W/m-K at 760K. Despite the similar atomic masses of Sr (87.6g/mol) and Y (88.9g/mol), the lattice thermal conductivity (κL) of Sr1-xY xTiO3-δ is significantly reduced with increased Y-doping, owing to the smaller ionic radii of Y3+ (∼1.23Å, coordination number 12) compared to Sr2+ (∼1.44Å, coordination number 12) ions. In order to understand the thermal conductivity reduction mechanism, the κL in the Sr1-xY xTiO3-δ series are phenomenologically modeled with a modified Callaway's equation from 30-600K. Phonon scattering by elastic strain field due to ionic radii mismatch is found to be the prominent scattering mechanism in reducing κL of these materials. In addition, the effect of Y-doping on the elastic moduli of Sr1-xY xTiO3-δ (x=0, 0.1) is investigated using resonant ultrasound spectroscopy, which exhibits an anomaly in x=0.1 in the temperature range 300-600K. As a result, the phonon mean free path is found to be further reduced in the Sr0.9Y0.1TiO3-δ compared to that of SrTiO3-δ, resulting in a considerably low thermal conductivity κ∼2.7W/m-K at 760K. Finally, we report a thermoelectric figure of merit (ZT)∼0.3 at 760K in the Sr0.9Y 0.1TiO3-δ, the highest ZT value reported in the Y-doped SrTiO3 ceramics thus far. © 2014 AIP Publishing LLC.

  19. Preface: Phonons 2007

    Science.gov (United States)

    Perrin, Bernard

    2007-06-01

    logo.jpg" ALT="Conference logo"/> The conference PHONONS 2007 was held 15-20 July 2007 in the Conservatoire National des Arts et Métiers (CNAM) Paris, France. CNAM is a college of higher technology for training students in the application of science to industry, founded by Henri Grégoire in 1794. This was the 12th International Conference on Phonon Scattering in Condensed Matter. This international conference series, held every 3 years, started in France at Sainte-Maxime in 1972. It was then followed by meetings at Nottingham (1975), Providence (1979), Stuttgart (1983), Urbana-Champaign (1986), Heidelberg (1989), Ithaca (1992), Sapporo (1995), Lancaster (1998), Dartmouth (2001) and St Petersburg (2004). PHONONS 2007 was attended by 346 delegates from 37 different countries as follows: France 120, Japan 45, Germany 25, USA 25, Russia 21, Italy 13, Poland 9, UK 9, Canada 7, The Netherlands 7, Finland 6, Spain 6, Taiwan 6, Greece 4, India 4, Israel 4, Ukraine 4, Serbia 3, South Africa 3, Argentina 2, Belgium 2, China 2, Iran 2, Korea 2, Romania 2, Switzerland 2, and one each from Belarus, Bosnia-Herzegovina, Brazil, Bulgaria, Egypt, Estonia, Mexico, Moldova, Morocco, Saudi Arabia, Turkey. There were 5 plenary lectures, 14 invited talks and 84 oral contributions; 225 posters were presented during three poster sessions. The first plenary lecture was given by H J Maris who presented fascinating movies featuring the motion of a single electron in liquid helium. Robert Blick gave us a review on the new possibilities afforded by nanotechnology to design nano-electomechanical systems (NEMS) and the way to use them to study elementary and fundamental processes. The growing interest for phonon transport studies in nanostructured materials was demonstrated by Arun Majumdar. Andrey Akimov described how ultrafast acoustic solitons can monitor the optical properties of quantum wells. Finally, Maurice Chapellier told us how phonons can help tracking dark matter. These 328

  20. Measurement of surface phonon dispersion relations for LiF, NaF, and KCl through energy-analysed inelastic scattering of a helium atomic beam

    International Nuclear Information System (INIS)

    Doak, R.B.

    1981-01-01

    A crystal surface terminates abruptly one dimension of lattice periodicity, constituting a lattice defect with concomitant localized modes of vibration, termed surface phonons. Such surface phonons have previously been investigated in the long wavelength, non-dispersive regime. The present work reports the first observation of surface phonons in the short wavelength, dispersive range. The data allow for the first time a surface phonon dispersion curve to be plotted completely from origin to edge of the surface Brillouin zone. Measurements were made of phonons along the (anti GAMMA anti M) and (anti GAMMA anti X) azimuths of the LiF(001) surface and along the azimuth of NaF(001) and KC1(001) surfaces. The results are in substantial agreement with theoretical predictions, although for LiF the measured Rayleigh dispersion curve at M lies appreciably below the theoretical value, possibly reflecting the effects of surface relaxation. (orig.)

  1. Electron-phonon coupling in one dimension

    International Nuclear Information System (INIS)

    Apostol, M.; Baldea, I.

    1981-08-01

    The Ward identity is derived for the electron-phonon coupling in one dimension and the spectrum of elementary excitations is calculated by assuming that the Fermi distribution is not strongly distorted by interaction. The electron-phonon vertex is renormalized in the case of the forward scattering and Migdal's theorem is discussed. A model is proposed for the giant Kohn anomaly. The dip in the phonon spectrum is obtained and found to be in agreement with the experimental data for KCP. (author)

  2. Features of the non-collinear one-phonon anomalous light scattering controlled by elastic waves with elevated linear losses: potentials for multi-frequency parallel spectrum analysis of radio-wave signals.

    Science.gov (United States)

    Shcherbakov, Alexandre S; Arellanes, Adan Omar

    2017-12-01

    During subsequent development of the recently proposed multi-frequency parallel spectrometer for precise spectrum analysis of wideband radio-wave signals, we study potentials of new acousto-optical cells exploiting selected crystalline materials at the limits of their capabilities. Characterizing these wide-aperture cells is non-trivial due to new features inherent in the chosen regime of an advanced non-collinear one-phonon anomalous light scattering by elastic waves with significantly elevated acoustic losses. These features can be observed simpler in uniaxial, tetragonal, and trigonal crystals possessing linear acoustic attenuation. We demonstrate that formerly studied additional degree of freedom, revealed initially for multi-phonon regimes of acousto-optical interaction, can be identified within the one-phonon geometry as well and exploited for designing new cells. We clarify the role of varying the central acoustic frequency and acoustic attenuation using the identified degree of freedom. Therewith, we are strongly restricted by a linear regime of acousto-optical interaction to avoid the origin of multi-phonon processes within carrying out a multi-frequency parallel spectrum analysis of radio-wave signals. Proof-of-principle experiments confirm the developed approaches and illustrate their applicability to innovative technique for an advanced spectrum analysis of wideband radio-wave signals with the improved resolution in an extended frequency range.

  3. Characterization of nanometer-thick polycrystalline silicon with phonon-boundary scattering enhanced thermoelectric properties and its application in infrared sensors.

    Science.gov (United States)

    Zhou, Huchuan; Kropelnicki, Piotr; Lee, Chengkuo

    2015-01-14

    Although significantly reducing the thermal conductivity of silicon nanowires has been reported, it remains a challenge to integrate silicon nanowires with structure materials and electrodes in the complementary metal-oxide-semiconductor (CMOS) process. In this paper, we investigated the thermal conductivity of nanometer-thick polycrystalline silicon (poly-Si) theoretically and experimentally. By leveraging the phonon-boundary scattering, the thermal conductivity of 52 nm thick poly-Si was measured as low as around 12 W mK(-1) which is only about 10% of the value of bulk single crystalline silicon. The ZT of n-doped and p-doped 52 nm thick poly-Si was measured as 0.067 and 0.024, respectively, while most previously reported data had values of about 0.02 and 0.01 for a poly-Si layer with a thickness of 0.5 μm and above. Thermopile infrared sensors comprising 128 pairs of thermocouples made of either n-doped or p-doped nanometer-thick poly-Si strips in a series connected by an aluminium (Al) metal interconnect layer are fabricated using microelectromechanical system (MEMS) technology. The measured vacuum specific detectivity (D*) of the n-doped and p-doped thermopile infrared (IR) sensors are 3.00 × 10(8) and 1.83 × 10(8) cm Hz(1/2) W(-1) for sensors of 52 nm thick poly-Si, and 5.75 × 10(7) and 3.95 × 10(7) cm Hz(1/2) W(-1) for sensors of 300 nm thick poly-Si, respectively. The outstanding thermoelectric properties indicate our approach is promising for diverse applications using ultrathin poly-Si technology.

  4. Optical pumping of hot phonons in GaAs

    International Nuclear Information System (INIS)

    Collins, C.L.; Yu, P.Y.

    1982-01-01

    Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated

  5. Frictional drag between quantum wells mediated by phonon exchange

    DEFF Research Database (Denmark)

    Bønsager, M.C.; Flensberg, Karsten; Hu, Ben Yu-Kuang

    1998-01-01

    We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either...

  6. Phonon manipulation with phononic crystals.

    Energy Technology Data Exchange (ETDEWEB)

    Kim Bongsang; Hopkins, Patrick Edward; Leseman, Zayd C.; Goettler, Drew F.; Su, Mehmet F. (University of New Mexico, Albuquerque, NM); El-Kady, Ihab Fathy; Reinke, Charles M.; Olsson, Roy H., III

    2012-01-01

    In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power

  7. Squeezed Phonons: Modulating Quantum Fluctuations of Atomic Displacements.

    Science.gov (United States)

    Hu, Xuedong; Nori, Franco

    1997-03-01

    We have studied phonon squeezed states and also put forward several proposals for their generation(On phonon parametric process, X. Hu and F. Nori, Phys. Rev. Lett. 76), 2294 (1996); on polariton mechanism, X. Hu and F. Nori, Phys. Rev. B 53, 2419 (1996); on second-order Raman scattering, X. Hu and F. Nori, preprint.. Here, we compare the relative merits and limitations of these approaches, including several factors that will limit the amount of phonon squeezing. In particular, we investigate the effect of the initial thermal states on the phonon modes. Using a model for the phonon density matrix, we also study the mixing of the phonon squeezed states with thermal states, which describes the decay of the phonon coherence. Finally, we calculate the maximum possible squeezing from a phonon parametric process limited by phonon decay.

  8. Phonon Squeezing by Raman Scattering.

    Science.gov (United States)

    Nori, Franco; Hu, Xuedong

    1997-03-01

    We have studied quantum fluctuation properties of a crystal lattice, and proposed several mechanisms to achieve this goal(X. Hu and F. Nori, Phys. Rev. Lett. 76, 2294 (1996); Phys. Rev. B 53, 2419 (1996); preprint.).

  9. Polarization dependent behavior of CdS around the first and second LO-phonon modes

    International Nuclear Information System (INIS)

    Frausto-Reyes, C.; Molina-Contreras, J.R.; Lopez-Alvarez, Y.F.; Medel-Ruiz, C.I.; Perez Ladron de Guevara, H.; Ortiz-Morales, M.

    2010-01-01

    The present work report studies on resonant Raman experimental line shape for CdS around the first and second LO-phonon modes. The application of our method to the study of LO-phonon modes of CdS suggests that the scattered intensity is dominated by the surface and dependent on polarization. Results showed that the Raman spectra for CdS, roughly fall into three groups: a broad line-wing with apparent maxima around 194 cm -1 in the range of 140 and 240 cm -1 which can be ascribed to overtone scattering from acoustic phonons; a band near the 1LO phonon mode which can be attributed to a combination of one-phonon scattering and peak acoustic phonon and finally, a band near the 2LO phonon mode which can be attributed to a combination of two-phonon scattering and peak acoustic phonon.

  10. Holographic Phonons

    Science.gov (United States)

    Alberte, Lasma; Ammon, Martin; Jiménez-Alba, Amadeo; Baggioli, Matteo; Pujolàs, Oriol

    2018-04-01

    We present a class of holographic massive gravity models that realize a spontaneous breaking of translational symmetry—they exhibit transverse phonon modes whose speed relates to the elastic shear modulus according to elasticity theory. Massive gravity theories thus emerge as versatile and convenient theories to model generic types of translational symmetry breaking: explicit, spontaneous, and a mixture of both. The nature of the breaking is encoded in the radial dependence of the graviton mass. As an application of the model, we compute the temperature dependence of the shear modulus and find that it features a glasslike melting transition.

  11. Ballistic phonon transport in holey silicon.

    Science.gov (United States)

    Lee, Jaeho; Lim, Jongwoo; Yang, Peidong

    2015-05-13

    When the size of semiconductors is smaller than the phonon mean free path, phonons can carry heat with no internal scattering. Ballistic phonon transport has received attention for both theoretical and practical aspects because Fourier's law of heat conduction breaks down and the heat dissipation in nanoscale transistors becomes unpredictable in the ballistic regime. While recent experiments demonstrate room-temperature evidence of ballistic phonon transport in various nanomaterials, the thermal conductivity data for silicon in the length scale of 10-100 nm is still not available due to experimental challenges. Here we show ballistic phonon transport prevails in the cross-plane direction of holey silicon from 35 to 200 nm. The thermal conductivity scales linearly with the length (thickness) even though the lateral dimension (neck) is as narrow as 20 nm. We assess the impact of long-wavelength phonons and predict a transition from ballistic to diffusive regime using scaling models. Our results support strong persistence of long-wavelength phonons in nanostructures and are useful for controlling phonon transport for thermoelectrics and potential phononic applications.

  12. Lifetime of the phonons in the PLT ceramic

    Energy Technology Data Exchange (ETDEWEB)

    Barba-Ortega, J., E-mail: jjbarba@unal.edu.co; Joya, M. R., E-mail: mrinconj@unal.edu.co [Departamento de Física, Universidad Nacional de Colombia, carrera 30 # 45-03, Bogotá 1149 (Colombia); Londoño, F. A., E-mail: flondono@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, Calle 67 #53-108 Of.6-105, Medellin (Colombia)

    2014-11-05

    The lifetimes at higher temperatures on lanthanum-modified lead titanate (PLT) are mainly due to the anharmonic decay of optical phonons into low-energy phonons. The temperature-independent contributions from inherent crystal defects and from boundary scattering become comparable to the phonon scattering contribution at lower temperatures. The thermal interaction is large at higher temperatures which decreases the phonon mean free path, and so the decay lifetime decreases as the temperature of the system is increased. This leads to the increased line width at higher temperatures. We made an estimate of the lifetimes for different concentrations and temperatures in PLT.

  13. Mutual interactions of phonons, rotons, and gravity

    Science.gov (United States)

    Nicolis, Alberto; Penco, Riccardo

    2018-04-01

    We introduce an effective point-particle action for generic particles living in a zero-temperature superfluid. This action describes the motion of the particles in the medium at equilibrium as well as their couplings to sound waves and generic fluid flows. While we place the emphasis on elementary excitations such as phonons and rotons, our formalism applies also to macroscopic objects such as vortex rings and rigid bodies interacting with long-wavelength fluid modes. Within our approach, we reproduce phonon decay and phonon-phonon scattering as predicted using a purely field-theoretic description of phonons. We also correct classic results by Landau and Khalatnikov on roton-phonon scattering. Finally, we discuss how phonons and rotons couple to gravity, and show that the former tend to float while the latter tend to sink but with rather peculiar trajectories. Our formalism can be easily extended to include (general) relativistic effects and couplings to additional matter fields. As such, it can be relevant in contexts as diverse as neutron star physics and light dark matter detection.

  14. Phonon excitations in multicomponent amorphous solids

    International Nuclear Information System (INIS)

    Vakarchuk, I.A.; Migal', V.M.; Tkachuk, V.M.

    1988-01-01

    The method of two-time temperature-dependent Green's functions is used to investigate phonon excitations in multicomponent amorphous solids. The equation obtained for the energy spectrum of the phonon excitations takes into account the damping associated with scattering of phonons by structure fluctuations. The quasicrystal approximation is considered, and as an example explicit expressions are obtained for the case of a two-component amorphous solid for the frequencies of the acoustical and optical modes and for the longitudinal and transverse velocities of sound. The damping is investigated

  15. Nonlinear electron-phonon heat exchange

    International Nuclear Information System (INIS)

    Woods, L.M.; Mahan, G.D.

    1998-01-01

    A calculation of the energy exchange between phonons and electrons is done for a metal at very low temperatures. We consider the energy exchange due to two-phonon processes. Second-order processes are expected to be important at temperatures less than 1 K. We include two different second-order processes: (i) the Compton-like scattering of phonons, and (ii) the electron-dual-phonon scattering from the second-order electron-phonon interaction. It is found that the Compton-like process contains a singular energy denominator. The singularity is removed by introducing quasiparticle damping. For pure metals we find that the energy exchange depends upon the lifetime of the electrons and it is proportional to the temperature of the lattice as T L 8 . The same calculation is performed for the electron-dual-phonon scattering and it is found that the temperature dependence is T L 9 . The results can be applied to quantum dot refrigerators. copyright 1998 The American Physical Society

  16. Specularity of longitudinal acoustic phonons at rough surfaces

    Science.gov (United States)

    Gelda, Dhruv; Ghossoub, Marc G.; Valavala, Krishna; Ma, Jun; Rajagopal, Manjunath C.; Sinha, Sanjiv

    2018-01-01

    The specularity of phonons at crystal surfaces is of direct importance to thermal transport in nanostructures and to dissipation in nanomechanical resonators. Wave scattering theory provides a framework for estimating wavelength-dependent specularity, but experimental validation remains elusive. Widely available thermal conductivity data presents poor validation since the involvement of the infinitude of phonon wavelengths in thermal transport presents an underconstrained test for specularity theory. Here, we report phonon specularity by measuring the lifetimes of individual coherent longitudinal acoustic phonon modes excited in ultrathin (36-205 nm) suspended silicon membranes at room temperature over the frequency range ˜20 -118 GHz. Phonon surface scattering dominates intrinsic Akhiezer damping at frequencies ≳60 GHz, enabling measurements of phonon boundary scattering time over wavelengths ˜72 -140 nm . We obtain detailed statistics of the surface roughness at the top and bottom surfaces of membranes using HRTEM imaging. We find that the specularity of the excited modes are in good agreement with solutions of wave scattering only when the TEM statistics are corrected for projection errors. The often-cited Ziman formula for phonon specularity also appears in good agreement with the data, contradicting previous results. This work helps to advance the fundamental understanding of phonon scattering at the surfaces of nanostructures.

  17. High angle of attack aerodynamics subsonic, transonic, and supersonic flows

    CERN Document Server

    Rom, Josef

    1992-01-01

    The aerodynamics of aircraft at high angles of attack is a subject which is being pursued diligently, because the modern agile fighter aircraft and many of the current generation of missiles must perform well at very high incidence, near and beyond stall. However, a comprehensive presentation of the methods and results applicable to the studies of the complex aerodynamics at high angle of attack has not been covered in monographs or textbooks. This book is not the usual textbook in that it goes beyond just presenting the basic theoretical and experimental know-how, since it contains reference material to practical calculation methods and technical and experimental results which can be useful to the practicing aerospace engineers and scientists. It can certainly be used as a text and reference book for graduate courses on subjects related to high angles of attack aerodynamics and for topics related to three-dimensional separation in viscous flow courses. In addition, the book is addressed to the aerodynamicist...

  18. Acoustic phonon dispersion of CoSi2

    International Nuclear Information System (INIS)

    Weiss, L.; Rumyantsev, A.Yu.; Ivanov, A.S.

    1985-01-01

    The acoustical phonon dispersion curves of CoSi 2 are measured at room temperature along the main symmetry directions by means of coherent one-phonon scattering of thermal neutrons. The dispersion curves are compared with those of Ge, Si, and the fluorite structure types as CaF 2 and UO 2 . From the slope of the phonon dispersion curves at the GAMMA-point the elastic constants have been obtained

  19. Computational modeling of geometry dependent phonon transport in silicon nanostructures

    Science.gov (United States)

    Cheney, Drew A.

    Recent experiments have demonstrated that thermal properties of semiconductor nanostructures depend on nanostructure boundary geometry. Phonons are quantized mechanical vibrations that are the dominant carrier of heat in semiconductor materials and their aggregate behavior determine a nanostructure's thermal performance. Phonon-geometry scattering processes as well as waveguiding effects which result from coherent phonon interference are responsible for the shape dependence of thermal transport in these systems. Nanoscale phonon-geometry interactions provide a mechanism by which nanostructure geometry may be used to create materials with targeted thermal properties. However, the ability to manipulate material thermal properties via controlling nanostructure geometry is contingent upon first obtaining increased theoretical understanding of fundamental geometry induced phonon scattering processes and having robust analytical and computational models capable of exploring the nanostructure design space, simulating the phonon scattering events, and linking the behavior of individual phonon modes to overall thermal behavior. The overall goal of this research is to predict and analyze the effect of nanostructure geometry on thermal transport. To this end, a harmonic lattice-dynamics based atomistic computational modeling tool was created to calculate phonon spectra and modal phonon transmission coefficients in geometrically irregular nanostructures. The computational tool is used to evaluate the accuracy and regimes of applicability of alternative computational techniques based upon continuum elastic wave theory. The model is also used to investigate phonon transmission and thermal conductance in diameter modulated silicon nanowires. Motivated by the complexity of the transmission results, a simplified model based upon long wavelength beam theory was derived and helps explain geometry induced phonon scattering of low frequency nanowire phonon modes.

  20. Phonon dispersion curves for CsCN

    International Nuclear Information System (INIS)

    Gaur, N.K.; Singh, Preeti; Rini, E.G.; Galgale, Jyostna; Singh, R.K.

    2004-01-01

    The motivation for the present work was gained from the recent publication on phonon dispersion curves (PDCs) of CsCN from the neutron scattering technique. We have applied the extended three-body force shell model (ETSM) by incorporating the effect of coupling between the translation modes and the orientation of cyanide molecules for the description of phonon dispersion curves of CsCN between the temperatures 195 and 295 K. Our results on PDCs in symmetric direction are in good agreement with the experimental data measured with inelastic neutron scattering technique. (author)

  1. Electron-phonon contribution to the phonon and excited electron (hole) linewidths in bulk Pd

    International Nuclear Information System (INIS)

    Sklyadneva, I Yu; Leonardo, A; Echenique, P M; Eremeev, S V; Chulkov, E V

    2006-01-01

    We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function α 2 F(ω), e-ph coupling constant λ, and the contribution to the lifetime broadening, Γ e-ph , show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T 1 in the Σ direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface

  2. SCATTER

    International Nuclear Information System (INIS)

    Broome, J.

    1965-11-01

    The programme SCATTER is a KDF9 programme in the Egtran dialect of Fortran to generate normalized angular distributions for elastically scattered neutrons from data input as the coefficients of a Legendre polynomial series, or from differential cross-section data. Also, differential cross-section data may be analysed to produce Legendre polynomial coefficients. Output on cards punched in the format of the U.K. A. E. A. Nuclear Data Library is optional. (author)

  3. Phonon broadening in high entropy alloys

    Science.gov (United States)

    Körmann, Fritz; Ikeda, Yuji; Grabowski, Blazej; Sluiter, Marcel H. F.

    2017-09-01

    Refractory high entropy alloys feature outstanding properties making them a promising materials class for next-generation high-temperature applications. At high temperatures, materials properties are strongly affected by lattice vibrations (phonons). Phonons critically influence thermal stability, thermodynamic and elastic properties, as well as thermal conductivity. In contrast to perfect crystals and ordered alloys, the inherently present mass and force constant fluctuations in multi-component random alloys (high entropy alloys) can induce significant phonon scattering and broadening. Despite their importance, phonon scattering and broadening have so far only scarcely been investigated for high entropy alloys. We tackle this challenge from a theoretical perspective and employ ab initio calculations to systematically study the impact of force constant and mass fluctuations on the phonon spectral functions of 12 body-centered cubic random alloys, from binaries up to 5-component high entropy alloys, addressing the key question of how chemical complexity impacts phonons. We find that it is crucial to include both mass and force constant fluctuations. If one or the other is neglected, qualitatively wrong results can be obtained such as artificial phonon band gaps. We analyze how the results obtained for the phonons translate into thermodynamically integrated quantities, specifically the vibrational entropy. Changes in the vibrational entropy with increasing the number of elements can be as large as changes in the configurational entropy and are thus important for phase stability considerations. The set of studied alloys includes MoTa, MoTaNb, MoTaNbW, MoTaNbWV, VW, VWNb, VWTa, VWNbTa, VTaNbTi, VWNbTaTi, HfZrNb, HfMoTaTiZr.

  4. Observation of chiral phonons

    KAUST Repository

    Zhu, Hanyu; Yi, Jun; Li, Ming-yang; Xiao, Jun; Zhang, Lifa; Yang, Chih-Wen; Kaindl, Robert A.; Li, Lain-Jong; Wang, Yuan; Zhang, Xiang

    2018-01-01

    Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

  5. Observation of chiral phonons

    KAUST Repository

    Zhu, Hanyu

    2018-02-01

    Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

  6. Microscopic theory of phonon-induced effects on semiconductor quantum dot decay dynamics in cavity QED

    DEFF Research Database (Denmark)

    Nielsen, Per Kær; Nielsen, Torben Roland; Lodahl, P.

    2012-01-01

    of the physics and emphasize the important role played by the effective phonon density, describing the availability of phonons for scattering, in quantum dot decay dynamics. Based on the analytical expressions, we present the parameter regimes where phonon effects are expected to be important. Also, we include...

  7. Phonon localization transition in relaxor ferroelectric PZN-5%PT

    International Nuclear Information System (INIS)

    Manley, Michael E.; Christianson, Andrew D.; Abernathy, Douglas L.; Sahul, Raffi

    2017-01-01

    Relaxor ferroelectric behavior occurs in many disordered ferroelectric materials but is not well understood at the atomic level. Recent experiments and theoretical arguments indicate that Anderson localization of phonons instigates relaxor behavior by driving the formation of polar nanoregions (PNRs). Here, we use inelastic neutron scattering to observe phonon localization in relaxor ferroelectric PZN-5%PT (0.95[Pb(Zn 1/3 Nb 2/3 )O 3 ]–0.05PbTiO 3 ) and detect additional features of the localization process. In the lead, up to phonon localization on cooling, the local resonant modes that drive phonon localization increase in number. The increase in resonant scattering centers is attributed to a known increase in the number of locally off centered Pb atoms on cooling. The transition to phonon localization occurs when these random scattering centers increase to a concentration where the Ioffe-Regel criterion is satisfied for localizing the phonon. Finally, we also model the effects of damped mode coupling on the observed phonons and phonon localization structure.

  8. Phonon dispersion relations for caesium thiocyanate

    International Nuclear Information System (INIS)

    Irving, M.A.; Smith, T.F.; Elcombe, M.M.

    1984-01-01

    Room temperature phonon dispersion relations for frequencies below 2 THz have been measured, along the three orthorhombic axes and selected diagonal directions by neutron inelastic scattering, for caesium thiocyanate. These curves, which represent 13 acoustic modes and 11 optic modes of vibration, do not agree with the dispersion behaviour calculated from the rigid-ion model developed by Ti and Ra to describe their Raman scattering observations

  9. Quantum non-demolition phonon counter with a hybrid optomechnical system

    Science.gov (United States)

    Song, Qiao; Zhang, KeYe; Dong, Ying; Zhang, WeiPing

    2018-05-01

    A phonon counting scheme based on the control of polaritons in an optomechanical system is proposed. This approach permits us to measure the number of phonons in a quantum non-demolition (QND) manner for arbitrary modes not limited by the frequency matching condition as in usual photon-phonon scattering detections. The performance on phonon number transfer and quantum state transfer of the counter are analyzed and simulated numerically by taking into account all relevant sources of noise.

  10. Microstructure-Induced Phonon Focusing Effects and Opportunities for Improved Material Quantification (Postprint)

    Science.gov (United States)

    2012-02-01

    phonon interactions with electrons , electron -hole pairs, defects, super- lattices, and interfaces [1-4]. As pointed out by Hauser et. al. [3], and...phonon-phonon and electron - phonon scattering processes placed limits on the methods applicability. More recently, the advantages of using lower...texture effects. In particular, the elongated grains result in colonies that are largely cigar -shaped or cylindrical in their form, where elastic

  11. Probing phonons in plutonium

    International Nuclear Information System (INIS)

    Wong, Joe; Krisch, M.; Farber, D.; Occelli, F.; Schwartz, A.; Chiang, T.C.; Wall, M.; Boro, C.; Xu, Ruqing

    2010-01-01

    Plutonium (Pu) is well known to have complex and unique physico-chemical properties. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state: α → β → γ → (delta) → (delta)(prime) → (var e psilon) → liquid. Unalloyed Pu melts at a relatively low temperature ∼640 C to yield a higher density liquid than that of the solid from which it melts, (Figure 1). Detailed understanding of the properties of plutonium and plutonium-based alloys is critical for the safe handling, utilization, and long-term storage of these important, but highly toxic materials. However, both technical and and safety issues have made experimental observations extremely difficult. Phonon dispersion curves (PDCs) are key experimenta l data to the understanding of the basic properties of Pu materials such as: force constants, sound velocities, elastic constants, thermodynamics, phase stability, electron-phonon coupling, structural relaxation, etc. However, phonon dispersion curves (PDCs) in plutonium (Pu) and its alloys have defied measurement for the past few decades since the discovery of this element in 1941. This is due to a combination of the high thermal-neutron absorption cross section of plutonium and the inability to grow the large single crystals (with dimensions of a few millimeters) necessary for inelastic neutron scattering. Theoretical simulations of the Pu PDC continue to be hampered by the lack of suitable inter -atomic potentials. Thus, until recently the PDCs for Pu and its alloys have remained unknown experimentally and theoretically. The experimental limitations have recently been overcome by using a tightly focused undulator x-ray micro-beam scattered from single -grain domains in polycrystalline specimens. This experimental approach has been applied successfully to map the complete PDCs of an fcc d-Pu-Ga alloy using the high resolution inelastic x-ray scattering (HRIXS

  12. Thermal transport in phononic crystals: The role of zone folding effect

    Science.gov (United States)

    Dechaumphai, Edward; Chen, Renkun

    2012-04-01

    Recent experiments [Yu et al., Nature Nanotech 5, 718 (2010); Tang et al., Nano Lett. 10, 4279 (2010); Hopkins etal., Nano Lett. 11, 107(2011)] on silicon based nanoscale phononic crystals demonstrated substantially reduced thermal conductivity compared to bulk Si, which cannot be explained by incoherent phonon boundary scattering within the Boltzmann Transport Equation (BTE). In this paper, partial coherent treatment of phonons, where phonons are regarded as either wave or particles depending on their frequencies, was considered. Phonons with mean free path smaller than the characteristic size of phononic crystals are treated as particles and the transport in this regime is modeled by BTE with phonon boundary scattering taken into account. On the other hand, phonons with mean free path longer than the characteristic size are treated as waves. In this regime, phonon dispersion relations are computed using the Finite Difference Time Domain (FDTD) method and are found to be modified due to the zone folding effect. The new phonon spectra are then used to compute phonon group velocity and density of states for thermal conductivity modeling. Our partial coherent model agrees well with the recent experimental results on in-plane thermal conductivity of phononic crystals. Our study highlights the importance of zone folding effect on thermal transport in phononic crystals.

  13. Phonon thermal transport through tilt grain boundaries in strontium titanate

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Zexi; Chen, Xiang; Yang, Shengfeng; Xiong, Liming; Chen, Youping [Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States); Deng, Bowen; Chernatynskiy, Aleksandr [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)

    2014-08-21

    In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO{sub 3}. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO{sub 3} contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.

  14. Phonon thermal transport through tilt grain boundaries in strontium titanate

    International Nuclear Information System (INIS)

    Zheng, Zexi; Chen, Xiang; Yang, Shengfeng; Xiong, Liming; Chen, Youping; Deng, Bowen; Chernatynskiy, Aleksandr

    2014-01-01

    In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO 3 . Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO 3 contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies

  15. Damped soft phonons and diffuse scattering in 40%Pb(Mg1/3Nb2/3)O3-60%PbTiO3

    International Nuclear Information System (INIS)

    Stock, C.; Ellis, D.; Swainson, I. P.; Xu, Guangyong; Hiraka, H.; Shirane, G.; Zhong, Z.; Luo, H.; Zhao, X.; Viehland, D.; Birgeneau, R. J.

    2006-01-01

    Using neutron elastic and inelastic scattering and high-energy x-ray diffraction, we present a comparison of 40% Pb(Mg 1/3 Nb 2/3 )O 3 -60% PbTiO 3 (PMN-60PT) with pure Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and PbTiO 3 (PT). We measure the structural properties of PMN-60PT to be identical to pure PT, however, the lattice dynamics are exactly that previously found in relaxors PMN and Pb(Zn 1/3 Nb 2/3 )O 3 (PZN). PMN-60PT displays a well-defined macroscopic structural transition from a cubic to tetragonal unit cell at 550 K. The diffuse scattering is shown to be weak indicating that the structural distortion is long-range in PMN-60PT and short-range polar correlations (polar nanoregions) are not present. Even though polar nanoregions are absent, the soft optic mode is short-lived for wave vectors near the zone center. Therefore PMN-60PT displays the same waterfall effect as prototypical relaxors PMN and PZN. We conclude that it is random fields resulting from the intrinsic chemical disorder which is the reason for the broad transverse optic mode observed in PMN and PMN-60PT near the zone center and not due to the formation of short-ranged polar correlations. Through our comparison of PMN, PMN-60PT, and pure PT, we interpret the dynamic and static properties of the PMN-xPT system in terms of a random field model in which the cubic anisotropy term dominates with increasing doping of PbTiO 3

  16. Two-phonon bound states in imperfect crystals

    International Nuclear Information System (INIS)

    Behera, S.N.; Samsur, Sk.

    1980-01-01

    The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of Gasub(1-c)Alsub(c)P and Gesub(1-c)Sisub(c) are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak, observed in structural phase transitions, is conjectured. (author)

  17. Electrons and Phonons in Semiconductor Multilayers

    Science.gov (United States)

    Ridley, B. K.

    1996-11-01

    This book provides a detailed description of the quantum confinement of electrons and phonons in semiconductor wells, superlattices and quantum wires, and shows how this affects their mutual interactions. It discusses the transition from microscopic to continuum models, emphasizing the use of quasi-continuum theory to describe the confinement of optical phonons and electrons. The hybridization of optical phonons and their interactions with electrons are treated, as are other electron scattering mechanisms. The book concludes with an account of the electron distribution function in three-, two- and one-dimensional systems, in the presence of electrical or optical excitation. This text will be of great use to graduate students and researchers investigating low-dimensional semiconductor structures, as well as to those developing new devices based on these systems.

  18. Quantitative atomic resolution mapping using high-angle annular dark field scanning transmission electron microscopy

    International Nuclear Information System (INIS)

    Van Aert, S.; Verbeeck, J.; Erni, R.; Bals, S.; Luysberg, M.; Dyck, D. Van; Tendeloo, G. Van

    2009-01-01

    A model-based method is proposed to relatively quantify the chemical composition of atomic columns using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images. The method is based on a quantification of the total intensity of the scattered electrons for the individual atomic columns using statistical parameter estimation theory. In order to apply this theory, a model is required describing the image contrast of the HAADF STEM images. Therefore, a simple, effective incoherent model has been assumed which takes the probe intensity profile into account. The scattered intensities can then be estimated by fitting this model to an experimental HAADF STEM image. These estimates are used as a performance measure to distinguish between different atomic column types and to identify the nature of unknown columns with good accuracy and precision using statistical hypothesis testing. The reliability of the method is supported by means of simulated HAADF STEM images as well as a combination of experimental images and electron energy-loss spectra. It is experimentally shown that statistically meaningful information on the composition of individual columns can be obtained even if the difference in averaged atomic number Z is only 3. Using this method, quantitative mapping at atomic resolution using HAADF STEM images only has become possible without the need of simultaneously recorded electron energy loss spectra.

  19. Phonon dynamics of graphene on metals

    Science.gov (United States)

    Taleb, Amjad Al; Farías, Daniel

    2016-03-01

    The study of surface phonon dispersion curves is motivated by the quest for a detailed understanding of the forces between the atoms at the surface and in the bulk. In the case of graphene, additional motivation comes from the fact that thermal conductivity is dominated by contributions from acoustic phonons, while optical phonon properties are essential to understand Raman spectra. In this article, we review recent progress made in the experimental determination of phonon dispersion curves of graphene grown on several single-crystal metal surfaces. The two main experimental techniques usually employed are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS). The different dispersion branches provide a detailed insight into the graphene-substrate interaction. Softening of optical modes and signatures of the substrate‧s Rayleigh wave are observed for strong graphene-substrate interactions, while acoustic phonon modes resemble those of free-standing graphene for weakly interacting systems. The latter allows determining the bending rigidity and the graphene-substrate coupling strength. A comparison between theory and experiment is discussed for several illustrative examples. Perspectives for future experiments are discussed.

  20. Phonon mechanism of mobility equilibrium fluctuation and properties of 1/f-noise

    International Nuclear Information System (INIS)

    Melkonyan, S.V.; Aroutiounian, V.M.; Gasparyan, F.V.; Asriyan, H.V.

    2006-01-01

    The main mechanisms of the generation of the equilibrium fluctuations of the electron mobility in homogeneous and non-degenerate semiconductors are studied. It is proven that the mobility fluctuations are related to energy fluctuations and are conditioned by random non-elastic scattering and generation-recombination processes. In particular, it is shown that the mobility fluctuations come into existence as a result of random electron-phonon and phonon-phonon scattering processes. The case of acoustic phonon-phonon scattering is considered in detail. The spectral density of the electron lattice mobility fluctuations is calculated on the base of a new phonon mechanism. It is shown that the noise spectrum over a broad frequency range has a 1/f form. The theoretical results for many samples agree with experimental data

  1. Phonon squeezed states: quantum noise reduction in solids

    Science.gov (United States)

    Hu, Xuedong; Nori, Franco

    1999-03-01

    This article discusses quantum fluctuation properties of a crystal lattice, and in particular, phonon squeezed states. Squeezed states of phonons allow a reduction in the quantum fluctuations of the atomic displacements to below the zero-point quantum noise level of coherent phonon states. Here we discuss our studies of both continuous-wave and impulsive second-order Raman scattering mechanisms. The later approach was used to experimentally suppress (by one part in a million) fluctuations in phonons. We calculate the expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, as well as the effects of the phonon squeezed states on macroscopically measurable quantities, such as changes in the dielectric constant. These results are compared with recent experiments. Further information, including preprints and animations, are available in http://www-personal.engin.umich.edu/∼nori/squeezed.html.

  2. Electron-phonon interaction on an Al(001) surface

    International Nuclear Information System (INIS)

    Sklyadneva, I Yu; Chulkov, E V; Echenique, P M

    2008-01-01

    We report an ab initio study of the electron-phonon (e-ph) interaction and its contribution to the lifetime broadening of excited hole (electron) surface states on Al(001). The calculations based on density-functional theory were carried out using a linear response approach in the plane-wave pseudopotential representation. The obtained results show that both the electron-phonon coupling and the linewidth experience a weak variation with the energy and momentum position of a hole (electron) surface state in the energy band. An analysis of different contributions to the e-ph coupling reveals that bulk phonon modes turn out to be more involved in the scattering processes of excited electrons and holes than surface phonon modes. It is also shown that the role of the e-ph coupling in the broadening of the Rayleigh surface phonon mode is insignificant compared to anharmonic effects

  3. Vacuum phonon tunneling.

    Science.gov (United States)

    Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

    2010-10-15

    Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

  4. Theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena

    Science.gov (United States)

    Jin, Yongmei M.; Wang, Yu U.; Ren, Yang

    2015-12-01

    Pre-martensitic phenomena, also called martensite precursor effects, have been known for decades while yet remain outstanding issues. This paper addresses pre-martensitic phenomena from new theoretical and experimental perspectives. A statistical mechanics-based Grüneisen-type phonon theory is developed. On the basis of deformation-dependent incompletely softened low-energy phonons, the theory predicts a lattice instability and pre-martensitic transition into elastic-phonon domains via 'phonon spinodal decomposition.' The phase transition lifts phonon degeneracy in cubic crystal and has a nature of phonon pseudo-Jahn-Teller lattice instability. The theory and notion of phonon domains consistently explain the ubiquitous pre-martensitic anomalies as natural consequences of incomplete phonon softening. The phonon domains are characterised by broken dynamic symmetry of lattice vibrations and deform through internal phonon relaxation in response to stress (a particular case of Le Chatelier's principle), leading to previously unexplored new domain phenomenon. Experimental evidence of phonon domains is obtained by in situ three-dimensional phonon diffuse scattering and Bragg reflection using high-energy synchrotron X-ray single-crystal diffraction, which observes exotic domain phenomenon fundamentally different from usual ferroelastic domain switching phenomenon. In light of the theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena, currently existing alternative opinions on martensitic precursor phenomena are revisited.

  5. Renormalisation of Nonequilibrium Phonons Under Strong Perturbative Influences.

    Science.gov (United States)

    Mehta, Sushrut Madhukar

    Effects of strong perturbative influences, namely the presence of a narrow distribution of acoustic phonons, and the presence of an electron plasma, on the dynamics of nonequilibrium, near zone center, longitudinal optical phonons in GaP have been investigated in two separate experiments. The study of the effects of the interaction between the LO phonons and a heavily populated, narrow distribution of acoustic phonons lead to the observation of a new optically driven nonequilibrium phonon state. Time Resolved Coherent Antistokes Raman Scattering (TR-CARS), with picosecond resolution, was used to investigate the new mode. In order to achieve high occupation numbers in the acoustic branch, the picosecond laser pulses used were amplified up to 1.0 GW/cm^2 peak power per laser beam. An important characteristic property of the new state which differentiates it from the well known LO phonon state is the fact that rather than having the single decay rate observed under thermal equilibrium, the new state has two decay rates. Moreover, these two decay rates depend strongly on the distribution of the acoustic phonon occupation number. The coupling of the LO phonons with an electron plasma, on the other hand, was investigated by measurements of the shape of the Raman scattered line associated with the phonon-plasmon coupled mode. The plasma was generated by thermal excitation of carriers in doped samples. It was possible to study a large variety of plasma excitations by controlling the concentration of the dopant and the ambient temperature. A complete, self consistant model based on standard dielectric response theory is presented, and applied to the measurements of the phonon-plasmon coupled mode. It is possible to recover, via this model, the effective coupled mode damping rate, the plasma damping rate, and the plasma frequency as functions of ambient temperature, or the carrier concentration.

  6. Beryllium phonon spectrum from cold neutron measurements

    International Nuclear Information System (INIS)

    Bulat, I.A.

    1979-01-01

    The inelastic coherent scattering of neutrons with the initial energy E 0 =4.65 MeV on the spectrometer according to the time of flight is studied in polycrystalline beryllium. The measurements are made for the scattering angles THETA=15, 30, 45, 60, 75 and 90 deg at 293 K. The phonon spectrum of beryllium, i-e. g(w) is reestablished from the experimental data. The data obtained are compared with the data of model calculations. It is pointed out that the phonon spectrum of beryllium has a bit excessive state density in the energy range from 10 to 30 MeV. It is caused by the insufficient statistical accuracy of the experiment at low energy transfer

  7. Birefringent phononic structures

    Directory of Open Access Journals (Sweden)

    I. E. Psarobas

    2014-12-01

    Full Text Available Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.

  8. Broadband sound blocking in phononic crystals with rotationally symmetric inclusions.

    Science.gov (United States)

    Lee, Joong Seok; Yoo, Sungmin; Ahn, Young Kwan; Kim, Yoon Young

    2015-09-01

    This paper investigates the feasibility of broadband sound blocking with rotationally symmetric extensible inclusions introduced in phononic crystals. By varying the size of four equally shaped inclusions gradually, the phononic crystal experiences remarkable changes in its band-stop properties, such as shifting/widening of multiple Bragg bandgaps and evolution to resonance gaps. Necessary extensions of the inclusions to block sound effectively can be determined for given incident frequencies by evaluating power transmission characteristics. By arraying finite dissimilar unit cells, the resulting phononic crystal exhibits broadband sound blocking from combinational effects of multiple Bragg scattering and local resonances even with small-numbered cells.

  9. Soft phonon anomalies in relaxor ferroelectrics

    International Nuclear Information System (INIS)

    Shirane, Gen; Gehring, Peter M.

    2001-01-01

    A review is given of the phonon anomalies, which have been termed waterfalls', that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions. (author)

  10. Soft phonon anomalies in relaxor ferroelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Shirane, Gen [Department of Physics, Brookhaven National Laboratory, Upton, New York (United States); Gehring, Peter M. [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland (United States)

    2001-03-01

    A review is given of the phonon anomalies, which have been termed waterfalls', that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions. (author)

  11. Four-phonon processes in the thermal conductivity of GaSb

    International Nuclear Information System (INIS)

    Aliev, M.I.; Arasly, D.G.; Guseinov, R.E.

    1978-01-01

    Phonon thermal conductivity of GaSb in the 300-700 K temperature range is studied by the light pulsed heating which is aimed at estimation of contributions of different polarized branches of acoustic oscillations into lattice thermal conductivity. The role of optico-acoustic interactions and multiphonon processes in phonon-phonon scattering at high temperatures is discussed. It is shown that the X thermal conductivity caused by the current carriers is negligibly small, and the Xsub(ph) phonon conductivity changes depending on temperature according to the Xsub(ph) approximately Tsup(-1.4) law. While calculating Xsub(ph) according to the Holland model taking into account phonon scattering on point defects the phonon thermal conductivity is given as a sum of contributions from longitudinal and transverse low-frequency Xsub(th1) and high-frequency Xsub(th2) acoustic phonons. It is established that at T>500 K Xsub(ph) is caused only by high-frequency transverse phonons and to explain the observed Xsub(ph) dependence on temperature it is necessary to introduce four-phonon process along with the three-phonon processes into intraphonon scattering

  12. Interaction Between Electrons, Magnons and Phonons in Nickel. RCN Report

    International Nuclear Information System (INIS)

    Frikkee, E.

    1971-02-01

    By means of inelastic neutron scattering, a localized electron excitation was observed in Ni and (4% Fe). The excitation interacts with magnons and phonons, and is assumed to correspond with transitions between the nearly-degenerate electronstates Δ 6 ↑ and Δ 7 ↑ near X, which are situated just below the Fermi level.Selection rules for electron-phonon and electronmagnon scattering are determined by means of group theory. It is found that in particular the transverse (Δ 5 ) phonons in the [100] direction are perturbed. The observed neutron-electron scattering turns out to be an indirect process, which is only possible due to the interaction between the (Δ 6 , Δ 7 ) electrons and the lattice. The basic mechanism for the observed effects is the electron spin-orbit coupling, which establishes the interaction between the electron spin system and the lattice. (author)

  13. Phonon dispersion curves of fcc La

    International Nuclear Information System (INIS)

    Stassis, C.; Loong, C.; Zarestky, J.

    1982-01-01

    Large single crystals of fcc La were grown in situ and were used to study the lattice dynamics of this phase of La by coherent inelastic neutron scattering. The phonon dispersion curves have been measured along the [xi00], [xixi0], [xixixi], and [0xi1] symmetry directions at 660 and 1100 K. The T[xixixi] branch exhibits anomalous dispersion for xi>0.25 and, in addition, close to the zone boundary, the phonon frequencies of this branch decrease with decreasing temperature. This soft-mode behavior may be related to the #betta→α# transformation in La, an assumption supported by recent band-theoretical calculations of the generalized susceptibility of fcc La. At X the frequencies of the L[xi00] branch are considerably lower than those of the corresponding branch of #betta#-Ce; a similar but not as pronounced effect is observed for the frequencies of the L[xixixi] branch close to the point L. Since the calculated generalized susceptibility of fcc La exhibits strong peaks at X and L, these anomalies may be due to the renormalization of the phonon frequencies by virtual fbold-arrow-left-rightd transitions to the unoccupied 4f level in La. The data were used to evaluate the elastic constants, the phonon density of states, and the lattice specific heat at constant pressure C/sub P//sup

  14. Search for the 3-phonon state of 40Ca

    International Nuclear Information System (INIS)

    Fallot, M.

    2002-09-01

    We study collective vibrational states of the nucleus: giant resonances and multiphonon states. It has been shown that multiphonon states, which are built with several superimposed giant resonances, can be excited in inelastic heavy ion scattering near the grazing angle. No three photon states have been observed until now. An experiment has been performed at GANIL, aiming at the observation of the 3-phonon state built with the giant quadrupole resonance (GQR) in 40 Ca, with the reaction 40 Ca + 40 Ca at 50 A.Me.V. The ejectile was identified in the SPEG spectrometer. Light charged particles were detected in 240 CsI scintillators of the INDRA 4π array. The analysis confirms the previous results about the GQR and the 2-phonon state in 40 Ca. For the first time, we have measured an important direct decay branch of the GQR by alpha particles. Applying the so-called 'missing energy method' to events containing three protons measured in coincidence with the ejectile, we observe a direct decay branch revealing the presence of a 3-phonon state in the excitation energy region expected for the triple GQR. Dynamical processes are also studied in the inelastic channel, emphasizing a recently discovered mechanism named towing-mode. We observe for the first time the towing-mode of alpha particles. The energies of multiphonon states in 40 Ca and 208 Pb have been computed microscopically including some anharmonicities via boson mapping methods. The basis of the calculation has been extended to the 3-phonon states. Our results show large anharmonicities (several MeV), due to the coupling of 3-phonon states to 2-phonon states. The extension of the basis to 4-phonon states has been performed for the first time. The inclusion of the 4 phonon states in the calculation did not affect the previous observations concerning the 2-phonon states. Preliminary results on the anharmonicities of the 3-phonon states are presented. (author)

  15. Phonon superradiance and phonon laser effect in nanomagnets.

    Science.gov (United States)

    Chudnovsky, E M; Garanin, D A

    2004-12-17

    We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.

  16. Direct observation of magnon-phonon coupling in yttrium iron garnet

    Science.gov (United States)

    Man, Haoran; Shi, Zhong; Xu, Guangyong; Xu, Yadong; Chen, Xi; Sullivan, Sean; Zhou, Jianshi; Xia, Ke; Shi, Jing; Dai, Pengcheng

    2017-09-01

    The magnetic insulator yttrium iron garnet (YIG) with a ferrimagnetic transition temperature of ˜560 K has been widely used in microwave and spintronic devices. Anomalous features in spin Seeback effect (SSE) voltages have been observed in Pt/YIG and attributed to magnon-phonon coupling. Here, we use inelastic neutron scattering to map out low-energy spin waves and acoustic phonons of YIG at 100 K as a function of increasing magnetic field. By comparing the zero and 9.1 T data, we find that instead of splitting and opening up gaps at the spin wave and acoustic phonon dispersion intersecting points, magnon-phonon coupling in YIG enhances the hybridized scattering intensity. These results are different from expectations of conventional spin-lattice coupling, calling for different paradigms to understand the scattering process of magnon-phonon interactions and the resulting magnon polarons.

  17. Observation of magnon-phonon interaction at short wavelengths

    International Nuclear Information System (INIS)

    Dolling, G.; Cowley, R.A.

    1966-01-01

    Measurements have been made of the magnon and phonon dispersion relations in uranium dioxide at 9 o K. These measurements provide evidence of a strong interaction between the magnon and phonon excitations and enable a value to be deduced for the coupling constant. The interaction of long-wavelength magnons in ferromagnetic materials has been studied previously with ultrasonic techniques; however, inelastic scattering of slow neutrons enables both the magnon and phonon dispersion relations to be determined for short wavelengths. In those magnetic materials which have been studied by earlier workers, the magnons and phonons either interacted with one another very weakly or else their frequencies were very different. The results could then be understood without introducing any magnon-phonon interaction. In this note we report measurements of both the magnon and the phonon spectra of antiferromagnetic uranium dioxide, which lead to a magnon-phonon coupling constant of 9.6 ± 1.6 o K. Since the Neel temperature is 30.8 o K, this coupling constant is of a similar magnitude to the direct magnetic interactions. (author)

  18. Modelling of AlAs/GaAs interfacial structures using high-angle annular dark field (HAADF) image simulations.

    Science.gov (United States)

    Robb, Paul D; Finnie, Michael; Craven, Alan J

    2012-07-01

    High angle annular dark field (HAADF) image simulations were performed on a series of AlAs/GaAs interfacial models using the frozen-phonon multislice method. Three general types of models were considered-perfect, vicinal/sawtooth and diffusion. These were chosen to demonstrate how HAADF image measurements are influenced by different interfacial structures in the technologically important III-V semiconductor system. For each model, interfacial sharpness was calculated as a function of depth and compared to aberration-corrected HAADF experiments of two types of AlAs/GaAs interfaces. The results show that the sharpness measured from HAADF imaging changes in a complicated manner with thickness for complex interfacial structures. For vicinal structures, it was revealed that the type of material that the probe projects through first of all has a significant effect on the measured sharpness. An increase in the vicinal angle was also shown to generate a wider interface in the random step model. The Moison diffusion model produced an increase in the interface width with depth which closely matched the experimental results of the AlAs-on-GaAs interface. In contrast, the interface width decreased as a function of depth in the linear diffusion model. Only in the case of the perfect model was it possible to ascertain the underlying structure directly from HAADF image analysis. Copyright © 2012 Elsevier B.V. All rights reserved.

  19. Freeform Phononic Waveguides

    Directory of Open Access Journals (Sweden)

    Georgios Gkantzounis

    2017-11-01

    Full Text Available We employ a recently introduced class of artificial structurally-disordered phononic structures that exhibit large and robust elastic frequency band gaps for efficient phonon guiding. Phononic crystals are periodic structures that prohibit the propagation of elastic waves through destructive interference and exhibit large band gaps and ballistic propagation of elastic waves in the permitted frequency ranges. In contrast, random-structured materials do not exhibit band gaps and favour localization or diffusive propagation. Here, we use structures with correlated disorder constructed from the so-called stealthy hyperuniform disordered point patterns, which can smoothly vary from completely random to periodic (full order by adjusting a single parameter. Such amorphous-like structures exhibit large band gaps (comparable to the periodic ones, both ballistic-like and diffusive propagation of elastic waves, and a large number of localized modes near the band edges. The presence of large elastic band gaps allows the creation of waveguides in hyperuniform materials, and we analyse various waveguide architectures displaying nearly 100% transmission in the GHz regime. Such phononic-circuit architectures are expected to have a direct impact on integrated micro-electro-mechanical filters and modulators for wireless communications and acousto-optical sensing applications.

  20. Phonon self-energy corrections to non-zero wavevector phonon modes in single-layer graphene

    Science.gov (United States)

    Araujo, Paulo; Mafra, Daniela; Sato, Kentaro; Saito, Richiiro; Kong, Jing; Dresselhaus, Mildred

    2012-02-01

    Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q = 0) wave-vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene (1LG) in the frequency range from 2350 to 2750 cm-1, which shows the G* and the G'-band features originating from a double-resonant Raman process with q 0. The observed phonon renormalization effects are different from what is observed for the zone-center q = 0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with non-zero wave-vectors (q 0) in 1LG in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q = 0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G* Raman feature at 2450 cm-1 to include the iTO+LA combination modes with q 0 and the 2iTO overtone modes with q = 0, showing both to be associated with wave-vectors near the high symmetry point K in the Brillouin zone.

  1. Phonon Self-Energy Corrections to Nonzero Wave-Vector Phonon Modes in Single-Layer Graphene

    Science.gov (United States)

    Araujo, P. T.; Mafra, D. L.; Sato, K.; Saito, R.; Kong, J.; Dresselhaus, M. S.

    2012-07-01

    Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q=0) wave vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene originating from a double-resonant Raman process with q≠0. The observed phonon renormalization effects are different from what is observed for the zone-center q=0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with nonzero wave vectors (q≠0) in single-layer graphene in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q=0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G⋆ Raman feature at 2450cm-1 to include the iTO+LA combination modes with q≠0 and also the 2iTO overtone modes with q=0, showing both to be associated with wave vectors near the high symmetry point K in the Brillouin zone.

  2. Anomalous dispersion of optical phonons in La2-xSrxCuO4 at low temperatures

    International Nuclear Information System (INIS)

    Bishoyi, K.C.; Rout, G.C.; Behera, S.N.

    2001-01-01

    Inelastic neutron scattering measurements of cuprate system show that a discontinuity in dispersion develops in the middle of the highest energy of optical phonon at low temperatures. We present here a microscopic theory to explain the phonon anomaly in doped cuprate system in normal state. Anti-ferromagnetism due to copper moments is introduced in the electronic Hamiltonian. Phonon coupling to the hybridisation between conduction electrons of the system and the doped f-electrons is incorporated. The phonon self energy due to electron-phonon interaction, which involves the electronic density response function, is evaluated explicitly by Zubarev's Green's function technique in finite temperature and small wave vector limit. The temperature dependence of phonon frequency and the anomalous phonon dispersion are calculated numerically and studied by varying the position of the f-level (ε f ), the effective electron-phonon coupling strength (g), staggered field (h), and the hybridisation parameter (V). (author)

  3. Phonon heat transport through periodically stubbed waveguides

    International Nuclear Information System (INIS)

    Li Wenxia; Chen Keqiu

    2006-01-01

    We investigate the acoustic phonon band structure, transmission spectrum and thermal conductance in a periodically stubbed waveguide structure by use of the transfer matrix method and the scattering matrix method. We find that the existence of stop-frequencies or dips in the transmission spectrum, which corresponds to the stop bands or gaps in the acoustic band structure. The dependence of the stop band width and the dip width on the stub height is also demonstrated. We also find that the universal quantum thermal conductance can be clearly observed and the thermal conductance increases monotonically with increasing temperature. Our results show that the acoustic phonon band structure, transmission spectrum and thermal conductance can be artificially controlled by adjusting the height of the stub

  4. Electron-optical phonon coupling in superconductors

    International Nuclear Information System (INIS)

    Rietschel, H.

    1975-01-01

    The role of the optical phonons in superconductivity is investigated in the case of compounds with different atomic masses Msub(k). It is shown that the electron mass enhancement factor lambda is independent of Msub(k) if the force constant matrix is mass independent. However, when using lambda to calculate Tsub(c), it must be decomposed into its acoustical and optical contributions, which depend separately on Msub(k). Interference scattering from a light and a heavy mass is studied and its contributions to lambda within the free electron approximation. Numerical results are presented for a rocksalt structure crystal with nearest and next nearest neighbour coupling. These results indicate that the optical phonon contributions to lambda may substantially increase Tsub(c). (orig.) [de

  5. Phonon properties of americium phosphide

    Energy Technology Data Exchange (ETDEWEB)

    Arya, B. S., E-mail: bsarya13@yahoo.com [Department of Physics, Govt. Narmada P G College, Hoshangabad -461001 (India); Aynyas, Mahendra [Department of Physics, C. S. A. Govt. P. G. College Sehore-46601 (India); Sanyal, S. P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

    2016-05-23

    Phonon properties of AmP have been studied by using breathing shell models (BSM) which includes breathing motion of electrons of the Am atoms due to f-d hybridization. The phonon dispersion curves, specific heat calculated from present model. The calculated phonon dispersion curves of AmP are presented follow the same trend as observed in uranium phosphide. We discuss the significance of this approach in predicting the phonon dispersion curves of these compounds and examine the role of electron-phonon interaction.

  6. Quantum Theory of Conditional Phonon States in a Dual-Pumped Raman Optical Frequency Comb

    Science.gov (United States)

    Mondloch, Erin

    In this work, we theoretically and numerically investigate nonclassical phonon states created in the collective vibration of a Raman medium by the generation of a dual-pumped Raman optical frequency comb in an optical cavity. This frequency comb is generated by cascaded Raman scattering driven by two phase-locked pump lasers that are separated in frequency by three times the Raman phonon frequency. We characterize the variety of conditioned phonon states that are created when the number of photons in all optical frequency modes except the pump modes are measured. Almost all of these conditioned phonon states are extremely well approximated as three-phonon-squeezed states or Schrodinger-cat states, depending on the outcomes of the photon number measurements. We show how the combinations of first-, second-, and third-order Raman scattering that correspond to each set of measured photon numbers determine the fidelity of the conditioned phonon state with model three-phonon-squeezed states and Schrodinger-cat states. All of the conditioned phonon states demonstrate preferential growth of the phonon mode along three directions in phase space. That is, there are three preferred phase values that the phonon state takes on as a result of Raman scattering. We show that the combination of Raman processes that produces a given set of measured photon numbers always produces phonons in multiples of three. In the quantum number-state representation, these multiples of three are responsible for the threefold phase-space symmetry seen in the conditioned phonon states. With a semiclassical model, we show how this three-phase preference can also be understood in light of phase correlations that are known to spontaneously arise in single-pumped Raman frequency combs. Additionally, our semiclassical model predicts that the optical modes also grow preferentially along three phases, suggesting that the dual-pumped Raman optical frequency comb is partially phase-stabilized.

  7. Phonon operators for deformed nuclei

    International Nuclear Information System (INIS)

    Solov'ev, V.G.

    1982-01-01

    The mathematical formalism with the phonon operators independent of the signature of the angular momentum projection turns out to be inadequate for describing excited states of deformed nuclei. New phonon operators are introduced which depend on the signature of the angular momentum projection on the symmetry axis of a deformed nucleus. It is shown that the calculations with the new phonons take correctly into account the Pauli principle in two-phonon components of wave functions. The results obtained differ from those given by the phonons independent of the signature of the angular momentum projection. The new phonons must be used in deformed nuclei at taking systematically the Pauli principle into account and in calculations involving wave functions of excited states having components with more than one-phonon operator

  8. Phononic crystals fundamentals and applications

    CERN Document Server

    Adibi, Ali

    2016-01-01

    This book provides an in-depth analysis as well as an overview of phononic crystals. This book discusses numerous techniques for the analysis of phononic crystals and covers, among other material, sonic and ultrasonic structures, hypersonic planar structures and their characterization, and novel applications of phononic crystals. This is an ideal book for those working with micro and nanotechnology, MEMS (microelectromechanical systems), and acoustic devices. This book also: Presents an introduction to the fundamentals and properties of phononic crystals Covers simulation techniques for the analysis of phononic crystals Discusses sonic and ultrasonic, hypersonic and planar, and three-dimensional phononic crystal structures Illustrates how phononic crystal structures are being deployed in communication systems and sensing systems.

  9. Photon control of phonons in mixed crystal quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ingale, Alka

    2003-12-15

    Coherent phonon oscillations in solids can be excited impulsively by a single femtosecond laser pulse whose duration is shorter than a phonon period. In the impulsive stimulated Raman scattering (ISRS) experiment, scattering of probe is monitored as a function of time with respect to pump to generate time domain spectra of coherent phonons. In this paper, we present one such study of CdSe{sub 0.68}Te{sub 0.32} (d{approx}80 A) quantum dots in glass matrix, i.e semiconductor-doped glass (SDG) RG780 from Schott, USA and the experiment was performed at Prof. Merlin's laboratory at the University of Michigan, USA. Here, we present first report of selectively driving only CdSe-like modes in these mixed crystal quantum dots using photon control with two pump beams.

  10. Phonon-induced anomalous Raman spectra in undoped high-Tc cuprates

    International Nuclear Information System (INIS)

    Lee, J.D.; Min, B.I.

    1997-01-01

    In order to describe a shoulder peak structure near 4J in the magnon Raman spectra of undoped high-T c cuprates, we have explored the phonon contribution to the Raman spectra. Incorporating the magnon-phonon Hamiltonian in the spin-wave theory, we have evaluated the two-magnon Raman spectral function originating from the lowest-order magnon-phonon-magnon scattering. It is found that phonons induce a shoulder peak near 4J besides the dominant two-magnon peak near 3J, in agreement with experiments. (orig.)

  11. Characterization and Control of Vortex Breakdown over a Delta Wing at High Angles of Attack

    National Research Council Canada - National Science Library

    Mitchell, Anthony

    2000-01-01

    .... The goal of this research is the control of leading-edge vortex breakdown by open-loop, along-the-core blowing near the apex of a delta wing to improve lift and maneuverability at high angles of attack...

  12. Development of an engineering level prediction method for high angle of attack aerodynamics

    Science.gov (United States)

    Reisenthel, Patrick H.; Rodman, Laura C.; Nixon, David

    1993-01-01

    The present work is concerned with predicting the unsteady flow considered to be the cause of the structural failure of twin vertical tail aircraft. An engineering tool has been produced for high angle of attack aerodynamics using the simplest physical models. The main innovation behind this work is its emphasis on the modeling of two key aspects of the dominant physics associated with high angle-of-attack airflows, namely unsteady separation and vortex breakdown.

  13. Phonon dispersions in graphene sheet and single-walled carbon ...

    Indian Academy of Sciences (India)

    Abstract. In the present research paper, phonons in graphene sheet have been calculated by con- structing a dynamical matrix using the force constants derived from the second-generation reactive empirical bond order potential by Brenner and co-workers. Our results are comparable to inelastic. X-ray scattering as well as ...

  14. Phonons, defects and optical damage in crystalline acetanilide

    Science.gov (United States)

    Kosic, Thomas J.; Hill, Jeffrey R.; Dlott, Dana D.

    1986-04-01

    Intense picosecond pulses cause accumulated optical damage in acetanilide crystals at low temperature. Catastrophic damage to the irradiated volume occurs after an incubation period where defects accumulate. The optical damage is monitored with subanosecond time resolution. The generation of defects is studied with damage-detected picosecond spectroscopy. The accumulation of defects is studied by time-resolved coherent Raman scattering, which is used to measure optical phonon scattering from the accumulating defects.

  15. Raman selection rule of surface optical phonon in ZnS nanobelts

    KAUST Repository

    Ho, Chih-Hsiang; Varadhan, Purushothaman; Wang, Hsin-Hua; Chen, Cheng-Ying; Fang, Xiaosheng; He, Jr-Hau

    2016-01-01

    We report Raman scattering results of high-quality wurtzite ZnS nanobelts (NBs) grown by chemical vapor deposition. In Raman spectrum, the ensembles of ZnS NBs exhibit first order phonon modes at 274 cm-1 and 350 cm-1, corresponding to A1/E1 transverse optical and A1/E1 longitudinal optical phonons, in addition with strong surface optical (SO) phonon mode at 329 cm-1. The existence of SO band is confirmed by its shift with different surrounding dielectric media. Polarization dependent Raman spectrum was performed on a single ZnS NB and for the first time SO phonon band has been detected on a single nanobelt. Different selection rules of SO phonon modeshown from their corresponding E1/A1 phonon modeswere attributed to the anisotropic translational symmetry breaking on the NB surface.

  16. Raman selection rule of surface optical phonon in ZnS nanobelts

    KAUST Repository

    Ho, Chih-Hsiang

    2016-02-18

    We report Raman scattering results of high-quality wurtzite ZnS nanobelts (NBs) grown by chemical vapor deposition. In Raman spectrum, the ensembles of ZnS NBs exhibit first order phonon modes at 274 cm-1 and 350 cm-1, corresponding to A1/E1 transverse optical and A1/E1 longitudinal optical phonons, in addition with strong surface optical (SO) phonon mode at 329 cm-1. The existence of SO band is confirmed by its shift with different surrounding dielectric media. Polarization dependent Raman spectrum was performed on a single ZnS NB and for the first time SO phonon band has been detected on a single nanobelt. Different selection rules of SO phonon modeshown from their corresponding E1/A1 phonon modeswere attributed to the anisotropic translational symmetry breaking on the NB surface.

  17. A study of some temperature effects on the phonons in aluminium by use of cold neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Larsson, K E; Dahlborg, U; Holmryd, S

    1960-04-15

    Using the cold neutron scattering technique about 300 phonons have been determined in a single aluminium crystal at room temperature to define 10 pairs of dispersion curves, Investigations have been made of the variation of frequencies, phonon line widths and multi-phonon spectra in the temperature range 293 < T < 932 K. For a particular direction in the crystal lattice it is shown that the frequencies vary about 15 % over this temperature range The line widths are of such a magnitude that the derived phonon mean free paths vary from about 5 phonon wave lengths at 600 K to about 1.5 phonon wave lengths at 930 K. The observed multiphonon spectra are found to agree with calculated differential cross sections in the incoherent approximation.

  18. Electron - polar acoustical phonon interactions in nitride based diluted magnetic semiconductor quantum well via hot electron magnetotransport

    International Nuclear Information System (INIS)

    Pandya, Ankur; Shinde, Satyam; Jha, Prafulla K.

    2015-01-01

    In this paper the hot electron transport properties like carrier energy and momentum scattering rates and electron energy loss rates are calculated via interactions of electrons with polar acoustical phonons for Mn doped BN quantum well in BN nanosheets via piezoelectric scattering and deformation potential mechanisms at low temperatures with high electric field. Electron energy loss rate increases with the electric field. It is observed that at low temperatures and for low electric field the phonon absorption is taking place whereas, for sufficient large electric field, phonon emission takes place. Under the piezoelectric (polar acoustical phonon) scattering mechanism, the carrier scattering rate decreases with the reduction of electric field at low temperatures wherein, the scattering rate variation with electric field is limited by a specific temperature beyond which there is no any impact of electric field on such scattering

  19. Tri-component phononic crystals for underwater anechoic coatings

    International Nuclear Information System (INIS)

    Zhao, Honggang; Liu, Yaozong; Wen, Jihong; Yu, Dianlong; Wen, Xisen

    2007-01-01

    Localized resonance in phononic crystal, composed of three-dimensional arrays of composite units, has been discovered recently. The composite unit is a high-density sphere coated by soft silicon rubber. In this Letter, the absorptive properties induced by the localized resonance are systemically investigated. The mode conversions during the Mie scattering of a single coated lead sphere in unbounded epoxy are analyzed by referring the elements of the scattering matrix. Then the anechoic properties of a slab containing a plane of such composite scatterers are investigated with the multiple-scattering method by accounting the effects of the multiple scattering and the viscous dissipation. The results show that the longitudinal to transverse mode conversion nearby the locally resonant region is an effective way to enhance the anechoic performance of the finite slab of phononic crystal. Then, the influences of the viscoelasticity of the silicon rubber and the coating thickness on the acoustic properties of the finite slab are investigated for anechoic optimization. Finally, we synthetically consider the destructive scattering in the finite slab of phononic crystal and the backing, and design an anechoic slab composed of bi-layer coated spheres. The results show that the most of the incident energy is absorbed at the desired frequency band

  20. Phononic crystals of spherical particles: A tight binding approach

    Energy Technology Data Exchange (ETDEWEB)

    Mattarelli, M., E-mail: maurizio.mattarelli@fisica.unipg.it [NiPS Laboratory, Dipartimento di Fisica, Università di Perugia, Via Pascoli, 06100 Perugia (Italy); Secchi, M. [CMM - Fondazione Bruno Kessler, Via Sommarive 18, 38123 Trento (Italy); Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123 Trento (Italy); Montagna, M. [Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123 Trento (Italy)

    2013-11-07

    The vibrational dynamics of a fcc phononic crystal of spheres is studied and compared with that of a single free sphere, modelled either by a continuous homogeneous medium or by a finite cluster of atoms. For weak interaction among the spheres, the vibrational dynamics of the phononic crystal is described by shallow bands, with low degree of dispersion, corresponding to the acoustic spheroidal and torsional modes of the single sphere. The phonon displacements are therefore related to the vibrations of a sphere, as the electron wave functions in a crystal are related to the atomic wave functions in a tight binding model. Important dispersion is found for the two lowest phonon bands, which correspond to zero frequency free translation and rotation of a free sphere. Brillouin scattering spectra are calculated at some values of the exchanged wavevectors of the light, and compared with those of a single sphere. With weak interaction between particles, given the high acoustic impedance mismatch in dry systems, the density of phonon states consist of sharp bands separated by large gaps, which can be well accounted for by a single particle model. Based on the width of the frequency gaps, tunable with the particle size, and on the small number of dispersive acoustic phonons, such systems may provide excellent materials for application as sound or heat filters.

  1. Reduction of thermal conductivity in phononic nanomesh structures

    KAUST Repository

    Yu, Jen-Kan

    2010-07-25

    Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications1,2 and in the cooling of integrated circuits3. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity. © 2010 Macmillan Publishers Limited. All rights reserved.

  2. Reduction of thermal conductivity in phononic nanomesh structures.

    Science.gov (United States)

    Yu, Jen-Kan; Mitrovic, Slobodan; Tham, Douglas; Varghese, Joseph; Heath, James R

    2010-10-01

    Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications and in the cooling of integrated circuits. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity.

  3. Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

    International Nuclear Information System (INIS)

    Giri, Ashutosh; Hopkins, Patrick E.

    2015-01-01

    Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot be accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states

  4. Phonon operators in deformed nuclei

    International Nuclear Information System (INIS)

    Soloviev, V.G.

    1981-01-01

    For the description of the excited states in deformed nuclei new phonon operators are introduced, which depend on the sign of the angular momentum projection onto the symmetry axis of a deformed nucleus. In the calculations with new phonons the Pauli principle is correctly taken into account in the two-phonon components of the wave functions. There is a difference in comparison with the calculation with phonons independent of the sign of the angular momentum projection. The new phonons should be used in deformed nuclei if the Pauli principle is consistently taken into account and in the calculations with the excited state wave functions having the components with more than one phonon operator [ru

  5. First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene

    International Nuclear Information System (INIS)

    Gu, Xiaokun; Yang, Ronggui

    2015-01-01

    There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ∼10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides

  6. Phonons: Theory and experiments II. Volume 2

    International Nuclear Information System (INIS)

    Bruesch, P.

    1986-01-01

    The present second volume titled as ''Phonons: Theory and Experiments II'', contains, a thorough study of experimental techniques and the interpretation of experimental results. This three-volume set tries to bridge the gap between theory and experiment, and is addressed to those working in both camps in the vast field of dynamical properties of solids. Topics presented in the second volume include; infrared-, Raman and Brillouin spectroscopy, interaction of X-rays with phonons, and inelastic neutron scattering. In addition an account is given of some other techniques, including ultrasonic methods, inelastic electron tunneling spectroscopy, point contact spectroscopy, and spectroscopy of surface phonons, thin films and adsorbates. Both experimental aspects and theoretical concepts necessary for the interpretation of experimental data are discussed. An attempt is made to present the descriptive as well as the analytical aspects of the topics. Simple models are often used to illustrate the basic concepts and more than 100 figures are included to illustrate both theoretical and experimental results. Many chapters contain a number of problems with hints and results giving additional information

  7. Flight test of the X-29A at high angle of attack: Flight dynamics and controls

    Science.gov (United States)

    Bauer, Jeffrey E.; Clarke, Robert; Burken, John J.

    1995-01-01

    The NASA Dryden Flight Research Center has flight tested two X-29A aircraft at low and high angles of attack. The high-angle-of-attack tests evaluate the feasibility of integrated X-29A technologies. More specific objectives focus on evaluating the high-angle-of-attack flying qualities, defining multiaxis controllability limits, and determining the maximum pitch-pointing capability. A pilot-selectable gain system allows examination of tradeoffs in airplane stability and maneuverability. Basic fighter maneuvers provide qualitative evaluation. Bank angle captures permit qualitative data analysis. This paper discusses the design goals and approach for high-angle-of-attack control laws and provides results from the envelope expansion and handling qualities testing at intermediate angles of attack. Comparisons of the flight test results to the predictions are made where appropriate. The pitch rate command structure of the longitudinal control system is shown to be a valid design for high-angle-of-attack control laws. Flight test results show that wing rock amplitude was overpredicted and aileron and rudder effectiveness were underpredicted. Flight tests show the X-29A airplane to be a good aircraft up to 40 deg angle of attack.

  8. Thermal neutron inelastic scattering and it's application to the material science

    International Nuclear Information System (INIS)

    Li Zhuqi

    1986-01-01

    A brief description of the elementary scattering theory of the interaction between the thermal neutrons and the condensed matter is given and the characteristics related to the experimental method of the thermal neutrons inelastic scattering is described. Expressions of the phonons dispersion, density of the phonon state and the self-diffusion coefficient at the some conditions are also introduced. Some examples of describing diagram of the phonon dispersion, density of the phonons state and selfdiffusion coefficient measured by different authors are given

  9. Intrinsic to extrinsic phonon lifetime transition in a GaAs-AlAs superlattice.

    Science.gov (United States)

    Hofmann, F; Garg, J; Maznev, A A; Jandl, A; Bulsara, M; Fitzgerald, E A; Chen, G; Nelson, K A

    2013-07-24

    We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 and 640 GHz, in a 14 nm GaAs/2 nm AlAs superlattice structure. By comparing measurements at 296 and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon-phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320 GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with intrinsic and extrinsic scattering rates in the superlattice obtained from first-principles lattice dynamics calculations. The calculated room-temperature intrinsic lifetime of longitudinal phonons at 320 GHz is in agreement with the experimentally measured value of 0.9 ns. The model correctly predicts the transition from predominantly intrinsic to predominantly extrinsic scattering; however the predicted transition occurs at higher frequencies. Our analysis indicates that the 'interfacial atomic disorder' model is not entirely adequate and that the observed frequency dependence of the extrinsic scattering rate is likely to be determined by a finite correlation length of interface roughness.

  10. Phonon-induced optical superlattice.

    Science.gov (United States)

    de Lima, M M; Hey, R; Santos, P V; Cantarero, A

    2005-04-01

    We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments.

  11. Tunable Topological Phononic Crystals

    KAUST Repository

    Chen, Zeguo; Wu, Ying

    2016-01-01

    Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.

  12. Tunable Topological Phononic Crystals

    KAUST Repository

    Chen, Zeguo

    2016-05-27

    Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.

  13. Quasiparticle-phonon nuclear model

    International Nuclear Information System (INIS)

    Soloviev, V.G.

    1977-01-01

    The general assumptions of the quasiparticle-phonon model of complex nuclei are given. The choice of the model hamiltonian as an average field and residual forces is discussed. The phonon description and quasiparticle-phonon interaction are presented. The system of basic equations and their approximate solutions are obtained. The approximation is chosen so as to obtain the most correct description of few-quasiparticle components rather than of the whole wave function. The method of strenght functions is presented, which plays a decisive role in practical realization of the quasiparticle-phonon model for the description of some properties of complex nuclei. The range of applicability of the quasiparticle-phonon nuclear model is determined as few-quasiparticle components of the wave functions at low, intermediate and high excitation energies averaged in a certain energy interval

  14. Anharmonic phonons and magnons in BiFeO3

    Energy Technology Data Exchange (ETDEWEB)

    Delaire, Olivier A [ORNL; Ma, Jie [ORNL; Stone, Matthew B [ORNL; Huq, Ashfia [ORNL; Gout, Delphine J [ORNL; Brown, Craig [National Institute of Standards and Technology (NIST); Wang, Kefeng [Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing; Ren, Zhifeng [Boston College, Chestnut Hill

    2012-01-01

    The phonon density of states (DOS) and magnetic excitation spectrum of polycrystalline BiFeO3 were measured for temperatures 200 < T < 750K , using inelastic neutron scattering (INS). Our results indicate that the magnetic spectrum of BiFeO3 closely resembles that of similar Fe perovskites, such as LaFeO3, despite the cycloid modulation in BiFeO3. We do not find any evidence for a spin gap. A strong T-dependence of the phonon DOS was found, with a marked broadening of the whole spectrum, providing evidence of strong anharmonicity. This anharmonicity is corroborated by large amplitude motions of Bi and O ions observed with neutron diffraction. These results highlight the importance of spin-phonon coupling in this material.

  15. Phonon Density of States and Heat Capacity of La3-xTe4

    International Nuclear Information System (INIS)

    Delaire, Olivier A.; May, Andrew F.; McGuire, Michael A.; Porter, Wallace D.; Lucas, Matthew S.; Stone, Matthew B.; Abernathy, Douglas L.; Snyder, G.J.

    2009-01-01

    The phonon density of states (DOS) of La 3-x Te 4 compounds (x=0.0, 0.18, 0.32) was measured at 300, 520, and 780 K, using inelastic neutron scattering. A significant stiffening of the phonon DOS, and a large broadening of features were observed upon introduction of vacancies on La sites (increasing x). Heat capacity measurements were performed at temperatures ∼1.85 ≤ T ≤ 1200 K and were analyzed to quantify the contributions of phonons and electrons. The Debye temperature and the electronic coefficient of heat capacity determined from these measurements are consistent with the neutron scattering results, and with previously reported first-principles calculations. Our results indicate that La vacancies in La 3-x Te 4 strongly scatter phonons, and this source of scattering appears to be independent of temperature. The stiffening of the phonon DOS induced by the introduction of vacancies is explained in terms of the electronic structure and the change in bonding. The temperature dependence of the phonon DOS is captured satisfactorily by the quasiharmonic approximation.

  16. Designing Phononic Crystals with Wide and Robust Band Gaps

    Science.gov (United States)

    Jia, Zian; Chen, Yanyu; Yang, Haoxiang; Wang, Lifeng

    2018-04-01

    Phononic crystals (PnCs) engineered to manipulate and control the propagation of mechanical waves have enabled the design of a range of novel devices, such as waveguides, frequency modulators, and acoustic cloaks, for which wide and robust phononic band gaps are highly preferable. While numerous PnCs have been designed in recent decades, to the best of our knowledge, PnCs that possess simultaneous wide and robust band gaps (to randomness and deformations) have not yet been reported. Here, we demonstrate that by combining the band-gap formation mechanisms of Bragg scattering and local resonances (the latter one is dominating), PnCs with wide and robust phononic band gaps can be established. The robustness of the phononic band gaps are then discussed from two aspects: robustness to geometric randomness (manufacture defects) and robustness to deformations (mechanical stimuli). Analytical formulations further predict the optimal design parameters, and an uncertainty analysis quantifies the randomness effect of each designing parameter. Moreover, we show that the deformation robustness originates from a local resonance-dominant mechanism together with the suppression of structural instability. Importantly, the proposed PnCs require only a small number of layers of elements (three unit cells) to obtain broad, robust, and strong attenuation bands, which offer great potential in designing flexible and deformable phononic devices.

  17. Toward single electron resolution phonon mediated ionization detectors

    Energy Technology Data Exchange (ETDEWEB)

    Mirabolfathi, Nader, E-mail: mirabolfathi@physics.tamu.edu [Department of Physics and Astronomy, Texas A& M University (United States); Harris, H. Rusty; Mahapatra, Rupak; Sundqvist, Kyle; Jastram, Andrew [Department of Physics and Astronomy, Texas A& M University (United States); Serfass, Bruno; Faiez, Dana; Sadoulet, Bernard [Department of Physics, University of California at Berkeley (United States)

    2017-05-21

    Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14 eV{sub ee}. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5 GeV/c{sup 2} but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7 eV{sub ee} for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of ∼2.8 eV{sub ee}. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

  18. Designing Phononic Crystals with Wide and Robust Band Gaps

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yanyu [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jia, Zian [State University of New York at Stony Brook; Yang, Haoxiang [State University of New York at Stony Brook; Wang, Lifeng [State University of New York at Stony Brook

    2018-04-16

    Phononic crystals (PnCs) engineered to manipulate and control the propagation of mechanical waves have enabled the design of a range of novel devices, such as waveguides, frequency modulators, and acoustic cloaks, for which wide and robust phononic band gaps are highly preferable. While numerous PnCs have been designed in recent decades, to the best of our knowledge, PnCs that possess simultaneous wide and robust band gaps (to randomness and deformations) have not yet been reported. Here, we demonstrate that by combining the band-gap formation mechanisms of Bragg scattering and local resonances (the latter one is dominating), PnCs with wide and robust phononic band gaps can be established. The robustness of the phononic band gaps are then discussed from two aspects: robustness to geometric randomness (manufacture defects) and robustness to deformations (mechanical stimuli). Analytical formulations further predict the optimal design parameters, and an uncertainty analysis quantifies the randomness effect of each designing parameter. Moreover, we show that the deformation robustness originates from a local resonance-dominant mechanism together with the suppression of structural instability. Importantly, the proposed PnCs require only a small number of layers of elements (three unit cells) to obtain broad, robust, and strong attenuation bands, which offer great potential in designing flexible and deformable phononic devices.

  19. Interaction between confined phonons and photons in periodic silicon resonators

    Science.gov (United States)

    Iskandar, A.; Gwiazda, A.; Younes, J.; Kazan, M.; Bruyant, A.; Tabbal, M.; Lerondel, G.

    2018-03-01

    In this paper, we demonstrate that phonons and photons of different momenta can be confined and interact with each other within the same nanostructure. The interaction between confined phonons and confined photons in silicon resonator arrays is observed by means of Raman scattering. The Raman spectra from large arrays of dielectric silicon resonators exhibited Raman enhancement accompanied with a downshift and broadening. The analysis of the Raman intensity and line shape using finite-difference time-domain simulations and a spatial correlation model demonstrated an interaction between photons confined in the resonators and phonons confined in highly defective regions prompted by the structuring process. It was shown that the Raman enhancement is due to collective lattice resonance inducing field confinement in the resonators, while the spectra downshift and broadening are signatures of the relaxation of the phonon wave vector due to phonon confinement in defective regions located in the surface layer of the Si resonators. We found that as the resonators increase in height and their shape becomes cylindrical, the amplitude of their coherent oscillation increases and hence their ability to confine the incoming electric field increases.

  20. Semi-Dirac points in phononic crystals

    KAUST Repository

    Zhang, Xiujuan

    2014-01-01

    A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. It was originally discovered in electron systems, in which the associated quasi-particles are massless along one direction, like those in graphene, but effective-mass-like along the other. It was reported that a semi-Dirac point is associated with the topological phase transition between a semi-metallic phase and a band insulator. Very recently, the classical analogy of a semi-Dirac cone has been reported in an electromagnetic system. Here, we demonstrate that, by accidental degeneracy, two-dimensional phononic crystals consisting of square arrays of elliptical cylinders embedded in water are also able to produce the particular dispersion relation of a semi-Dirac cone in the center of the Brillouin zone. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. If the scatterers are made of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso-frequency surface of the phononic crystal, in which an open hyperbola is changed into a closed ellipse. This topological transition results in drastic change in wave manipulation. On the other hand, the theory also reveals that the phononic crystal is a double-zero-index material along the x-direction and photonic-band-edge material along the perpendicular direction (y-direction). If the scatterers are made of steel, in which the acoustic wave velocity is higher than that in water, the effective medium description fails, even though the semi-Dirac dispersion relation looks similar to that in the previous case. Therefore different wave transport behavior is expected. The semi-Dirac points in phononic crystals described in

  1. Spacetime representation of topological phononics

    Science.gov (United States)

    Deymier, Pierre A.; Runge, Keith; Lucas, Pierre; Vasseur, Jérôme O.

    2018-05-01

    Non-conventional topology of elastic waves arises from breaking symmetry of phononic structures either intrinsically through internal resonances or extrinsically via application of external stimuli. We develop a spacetime representation based on twistor theory of an intrinsic topological elastic structure composed of a harmonic chain attached to a rigid substrate. Elastic waves in this structure obey the Klein–Gordon and Dirac equations and possesses spinorial character. We demonstrate the mapping between straight line trajectories of these elastic waves in spacetime and the twistor complex space. The twistor representation of these Dirac phonons is related to their topological and fermion-like properties. The second topological phononic structure is an extrinsic structure composed of a one-dimensional elastic medium subjected to a moving superlattice. We report an analogy between the elastic behavior of this time-dependent superlattice, the scalar quantum field theory and general relativity of two types of exotic particle excitations, namely temporal Dirac phonons and temporal ghost (tachyonic) phonons. These phonons live on separate sides of a two-dimensional frequency space and are delimited by ghost lines reminiscent of the conventional light cone. Both phonon types exhibit spinorial amplitudes that can be measured by mapping the particle behavior to the band structure of elastic waves.

  2. Strong electron-phonon interaction in the high-Tc superconductors: Evidence from the infrared

    International Nuclear Information System (INIS)

    Timusk, T.; Porter, C.D.; Tanner, D.B.

    1991-01-01

    We show that low-frequency structure in the infrared reflectance of the high-temperature superconductor YBa 2 Cu 3 O 7 results from the electron-phonon interaction. Characteristic antiresonant line shapes are seen in the phonon region of the spectrum and the frequency-dependent scattering rate of the mid-infrared electronic continuum has peaks at 150 cm -1 (19 meV) and at 360 cm -1 (45 meV) in good agreement with phonon density-of-states peaks in neutron time-of-flight spectra that develop in superconducting samples. The interaction between the phonons and the charge carriers can be understood in terms of a charged-phonon model

  3. Signature of electron-phonon interaction in high temperature superconductors

    Directory of Open Access Journals (Sweden)

    Vinod Ashokan

    2011-09-01

    Full Text Available The theory of thermal conductivity of high temperature superconductors (HTS based on electron and phonon line width (life times formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high Tc superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.

  4. Lumped model for rotational modes in phononic crystals

    KAUST Repository

    Peng, Pai

    2012-10-16

    We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in determining the band structure, and reproduces the dispersion relations in a certain range. The model increases the possibilities of manipulating wave propagation in phononic crystals. In particular, expressions derived from the model for eigenfrequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.

  5. Lumped model for rotational modes in phononic crystals

    KAUST Repository

    Peng, Pai; Mei, Jun; Wu, Ying

    2012-01-01

    We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in determining the band structure, and reproduces the dispersion relations in a certain range. The model increases the possibilities of manipulating wave propagation in phononic crystals. In particular, expressions derived from the model for eigenfrequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.

  6. Intrinsic to extrinsic phonon lifetime transition in a GaAs–AlAs superlattice

    International Nuclear Information System (INIS)

    Hofmann, F; Garg, J; Chen, G; Maznev, A A; Nelson, K A; Jandl, A; Bulsara, M; Fitzgerald, E A

    2013-01-01

    We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 and 640 GHz, in a 14 nm GaAs/2 nm AlAs superlattice structure. By comparing measurements at 296 and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon–phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320 GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with intrinsic and extrinsic scattering rates in the superlattice obtained from first-principles lattice dynamics calculations. The calculated room-temperature intrinsic lifetime of longitudinal phonons at 320 GHz is in agreement with the experimentally measured value of 0.9 ns. The model correctly predicts the transition from predominantly intrinsic to predominantly extrinsic scattering; however the predicted transition occurs at higher frequencies. Our analysis indicates that the ‘interfacial atomic disorder’ model is not entirely adequate and that the observed frequency dependence of the extrinsic scattering rate is likely to be determined by a finite correlation length of interface roughness. (paper)

  7. Density of phonon states in the light-harvesting complex II of green plants

    CERN Document Server

    Pieper, J K; Irrgang, K D; Renger, G

    2002-01-01

    In photosynthetic antenna complexes, the coupling of electronic transitions to low-frequency vibrations of the protein matrix (phonons) plays an essential role in light absorption and ultra-fast excitation energy transfer (EET). The model calculations presented here indicate that inelastic neutron scattering experiments provide invaluable information on the phonon density of states for light-harvesting complex II, which may permit a consistent interpretation of contradictory results from high-resolution optical spectroscopy. (orig.)

  8. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

    Energy Technology Data Exchange (ETDEWEB)

    Mike L. Laue

    1997-05-30

    The distal fan margin in the northeast portion of the Yowlumne field contains significant reserves but is not economical to develop using vertical wells. Numerous interbedded shales and deteriorating rock properties limit producibility. In addition, extreme depths (13,000 ft) present a challenging environment for hydraulic fracturing and artificial lift. Lastly, a mature waterflood increases risk because of the uncertainty with size and location of flood fronts. This project attempts to demonstrate the effectiveness of exploiting the distal fan margin of this slope-basin clastic reservoir through the use of a high-angle well completed with multiple hydraulic-fracture treatments. The combination of a high-angle (or horizontal) well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. The equivalent production rate and reserves of three vertical wells are anticipated at one-half to two-thirds the cost.

  9. Robust, nonlinear, high angle-of-attack control design for a supermaneuverable vehicle

    Science.gov (United States)

    Adams, Richard J.

    1993-01-01

    High angle-of-attack flight control laws are developed for a supermaneuverable fighter aircraft. The methods of dynamic inversion and structured singular value synthesis are combined into an approach which addresses both the nonlinearity and robustness problems of flight at extreme operating conditions. The primary purpose of the dynamic inversion control elements is to linearize the vehicle response across the flight envelope. Structured singular value synthesis is used to design a dynamic controller which provides robust tracking to pilot commands. The resulting control system achieves desired flying qualities and guarantees a large margin of robustness to uncertainties for high angle-of-attack flight conditions. The results of linear simulation and structured singular value stability analysis are presented to demonstrate satisfaction of the design criteria. High fidelity nonlinear simulation results show that the combined dynamics inversion/structured singular value synthesis control law achieves a high level of performance in a realistic environment.

  10. Pitch control margin at high angle of attack - Quantitative requirements (flight test correlation with simulation predictions)

    Science.gov (United States)

    Lackey, J.; Hadfield, C.

    1992-01-01

    Recent mishaps and incidents on Class IV aircraft have shown a need for establishing quantitative longitudinal high angle of attack (AOA) pitch control margin design guidelines for future aircraft. NASA Langley Research Center has conducted a series of simulation tests to define these design guidelines. Flight test results have confirmed the simulation studies in that pilot rating of high AOA nose-down recoveries were based on the short-term response interval in the forms of pitch acceleration and rate.

  11. High angle grain boundaries as sources or sinks for point defects

    Energy Technology Data Exchange (ETDEWEB)

    Balluffi, R.W.

    1979-09-01

    A secondary grain boundary dislocation climb model for high angle grain boundaries as sources/sinks for point defects is described in the light of recent advances in our knowledge of grain boundary structure. Experimental results are reviewed and are then compared with the expected behavior of the proposed model. Reasonably good consistency is found at the level of our present understanding of the subject. However, several gaps in our present knowledge still exist, and these are identified and discussed briefly.

  12. Collective hypersonic excitations in strongly multiple scattering colloids.

    Science.gov (United States)

    Still, T; Gantzounis, G; Kiefer, D; Hellmann, G; Sainidou, R; Fytas, G; Stefanou, N

    2011-04-29

    Unprecedented low-dispersion high-frequency acoustic excitations are observed in dense suspensions of elastically hard colloids. The experimental phononic band structure for SiO(2) particles with different sizes and volume fractions is well represented by rigorous full-elastodynamic multiple-scattering calculations. The slow phonons, which do not relate to particle resonances, are localized in the surrounding liquid medium and stem from coherent multiple scattering that becomes strong in the close-packing regime. Such rich phonon-matter interactions in nanostructures, being still unexplored, can open new opportunities in phononics.

  13. The determination of the acoustical phonon dispersion branches of CePd3 by inelastic neutron diffraction

    International Nuclear Information System (INIS)

    Severing, A.

    1985-07-01

    The result of this thesis is, that the phonon dispersion of CePd 3 , measured by inelastic neutron scattering, does not show any phonon softening effects due to valence fluctuations as it is observed in the phonon dispersion spectra of TmSe, SmS under pressure and SMsub(.75)Ysub(.25)S in dependence of the temperature. Even at low temperature no softening effects could be detected in comparison to the room temperature data. However we see indications for the existence of intermediate valence induced electron-phonon couplings in the linewidth of the longitudinal acoustic phonon in -direction with reduced wavevector xi=0.2. This phonon seems to be broadened at 135 K. If this broadening is a real intermediate valence effect, this effects manifest themselves much weaker in CePd 3 than in the substances with NaCl-structure. The question whether such couplings realy exist can only be answered by further measurements. (orig.)

  14. Density of phonon states on NiO polycrystal

    International Nuclear Information System (INIS)

    Bulat, I.A.; Makovetskij, G.I.; Pashkovskij, Yu.L.; Semencheva, O.P.; Smolik, Ch.K.

    1984-01-01

    The density of phonon states g(epsilon) of nickel monoxide polycrystal was investigated by the method of inelastic scattering of cold neutrons with E 0 =4.43 MeV initial energy E 0 =4.43 MeV on the time-of-flight spectrometer at T=293 K. The obtained data are compared with existing results of calculations on the base of the simple shell model and the model, taking into account the deformation of bond angles

  15. Coherent heat transport in 2D phononic crystals with acoustic impedance mismatch

    International Nuclear Information System (INIS)

    Arantes, A; Anjos, V

    2016-01-01

    In this work we have calculated the cumulative thermal conductivities of micro-phononic crystals formed by different combinations of inclusions and matrices at a sub-Kelvin temperature regime. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation for inhomogeneous media with the plane wave expansion method. The thermal conductivity was calculated from Boltzmann transport theory highlighting the role of the low-frequency thermal phonons and neglecting phonon–phonon scattering. A purely coherent thermal transport regime was assumed throughout the structures. Our findings show that the cumulative thermal conductivity drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity due to a flattening of the phonon dispersion relation, the extinction of phonon modes in the density of states or due to the presence of complete band gaps. According to the contrast between the inclusions and the matrices, three types of two dimensional phononic crystals were considered: carbon/epoxy, carbon/polyethylene and tungsten/silicon, which correspond respectively to a moderate, strong and very strong mismatch in the mechanical properties of these materials. (paper)

  16. Current & Heat Transport in Graphene Nanoribbons: Role of Non-Equilibrium Phonons

    Science.gov (United States)

    Pennington, Gary; Finkenstadt, Daniel

    2010-03-01

    The conducting channel of a graphitic nanoscale device is expected to experience a larger degree of thermal isolation when compared to traditional inversion channels of electronic devices. This leads to enhanced non-equilibrium phonon populations which are likely to adversely affect the mobility of graphene-based nanoribbons due to enhanced phonon scattering. Recent reports indicating the importance of carrier scattering with substrate surface polar optical phonons in carbon nanotubes^1 and graphene^2,3 show that this mechanism may allow enhanced heat removal from the nanoribbon channel. To investigate the effects of hot phonon populations on current and heat conduction, we solve the graphene nanoribbon multiband Boltzmann transport equation. Monte Carlo transport techniques are used since phonon populations may be tracked and updated temporally.^4 The electronic structure is solved using the NRL Tight-Binding method,^5 where carriers are scattered by confined acoustic, optical, edge and substrate polar optical phonons. [1] S. V. Rotkin et al., Nano Lett. 9, 1850 (2009). [2] J. H. Chen, C. Jang, S. Xiao, M. Ishigami and M. S. Fuhrer, Nature Nanotech. 3, 206 (2008). [3] V. Perebeinos and P. Avouris, arXiv:0910.4665v1 [cond-mat.mes-hall] (2009). [4] P. Lugli et al., Appl. Phys. Lett. 50, 1251 (1987). [5] D. Finkenstadt, G. Pennington & M.J. Mehl, Phys. Rev. B 76, 121405(R) (2007).

  17. Phonon density of states and anharmonicity of UO2

    Science.gov (United States)

    Pang, Judy W. L.; Chernatynskiy, Aleksandr; Larson, Bennett C.; Buyers, William J. L.; Abernathy, Douglas L.; McClellan, Kenneth J.; Phillpot, Simon R.

    2014-03-01

    Phonon density of states (PDOS) measurements have been performed on polycrystalline UO2 at 295 and 1200 K using time-of-flight inelastic neutron scattering to investigate the impact of anharmonicity on the vibrational spectra and to benchmark ab initio PDOS simulations performed on this strongly correlated Mott insulator. Time-of-flight PDOS measurements include anharmonic linewidth broadening, inherently, and the factor of ˜7 enhancement of the oxygen spectrum relative to the uranium component by the increased neutron sensitivity to the oxygen-dominated optical phonon modes. The first-principles simulations of quasiharmonic PDOS spectra were neutron weighted and anharmonicity was introduced in an approximate way by convolution with wave-vector-weighted averages over our previously measured phonon linewidths for UO2, which are provided in numerical form. Comparisons between the PDOS measurements and the simulations show reasonable agreement overall, but they also reveal important areas of disagreement for both high and low temperatures. The discrepancies stem largely from a ˜10 meV compression in the overall bandwidth (energy range) of the oxygen-dominated optical phonons in the simulations. A similar linewidth-convoluted comparison performed with the PDOS spectrum of Dolling et al. obtained by shell-model fitting to their historical phonon dispersion measurements shows excellent agreement with the time-of-flight PDOS measurements reported here. In contrast, we show by comparisons of spectra in linewidth-convoluted form that recent first-principles simulations for UO2 fail to account for the PDOS spectrum determined from the measurements of Dolling et al. These results demonstrate PDOS measurements to be stringent tests for ab inito simulations of phonon physics in UO2 and they indicate further the need for advances in theory to address the lattice dynamics of UO2.

  18. Experimental Study of Electron and Phonon Dynamics in Nanoscale Materials by Ultrafast Laser Time-Domain Spectroscopy

    Science.gov (United States)

    Shen, Xiaohan

    With the rapid advances in the development of nanotechnology, nowadays, the sizes of elementary unit, i.e. transistor, of micro- and nanoelectronic devices are well deep into nanoscale. For the pursuit of cheaper and faster nanoscale electronic devices, the size of transistors keeps scaling down. As the miniaturization of the nanoelectronic devices, the electrical resistivity increases dramatically, resulting rapid growth in the heat generation. The heat generation and limited thermal dissipation in nanoscale materials have become a critical problem in the development of the next generation nanoelectronic devices. Copper (Cu) is widely used conducting material in nanoelectronic devices, and the electron-phonon scattering is the dominant contributor to the resistivity in Cu nanowires at room temperature. Meanwhile, phonons are the main carriers of heat in insulators, intrinsic and lightly doped semiconductors. The thermal transport is an ensemble of phonon transport, which strongly depends on the phonon frequency. In addition, the phonon transport in nanoscale materials can behave fundamentally different than in bulk materials, because of the spatial confinement. However, the size effect on electron-phonon scattering and frequency dependent phonon transport in nanoscale materials remain largely unexplored, due to the lack of suitable experimental techniques. This thesis is mainly focusing on the study of carrier dynamics and acoustic phonon transport in nanoscale materials. The weak photothermal interaction in Cu makes thermoreflectance measurement difficult, we rather measured the reflectivity change of Cu induced by absorption variation. We have developed a method to separately measure the processes of electron-electron scattering and electron-phonon scattering in epitaxial Cu films by monitoring the transient reflectivity signal using the resonant probe with particular wavelengths. The enhancement on electron-phonon scattering in epitaxial Cu films with thickness

  19. Electron hopping and optic phonons in Eu3S4

    International Nuclear Information System (INIS)

    Guentherodt, G.

    1981-01-01

    Raman scattering on single crystals of Eu 3 S 4 does not show the allowed q=o phonon modes in the cubic phase and exhibits no new modes in the distorted low temperature phase (T 2- ions. This mode does not show any anomaly near the charge order -disorder phase transition Tsub(t)=186 K. Temperature tunable spin fluctuations associated with the temperature activated Eu 2+ → Eu 3+ electron hopping are detected in the scattering intensity, superimposed on the usual thermal spin disorder. (author)

  20. Creation of high-energy phonons by four-phonon processes in anisotropic phonon system of He II

    International Nuclear Information System (INIS)

    Adamenko, I.N.; Nemchenko, K.E.; Slipko, V.A.; Kitsenko, Yu.A.; Wyatt, A.F.G.

    2007-01-01

    The problem of the creation of high-energy phonons (h-phonons) by a pulse of low-energy phonons (I-phonons) moving from a heater to a detector in superfluid helium, is solved. The rate of h-phonon creation is obtained and it is shown that created h-phonons occupy a much smaller solid angle in momentum space, than the I-phonons. Analytical expression for the creation rate of h-phonon, along the symmetry axis of a pulse, are derived. It allows us to get useful approximate analytical expressions for creation rate of h-phonons. The time dependences of the parameters which describe the I-phonon pulse are obtained. This shows that half of the initial energy of I-phonon pulse can be transferred into h-phonons. The results of the calculations are compared with experimental data and we show that this theory explains a number of experimental results. The value of the momentum, which separates the I- and h-phonon subsystems, is found

  1. Enhancing of optic phonon contribution in hydrodynamic phonon transport

    Science.gov (United States)

    de Tomas, C.; Cantarero, A.; Lopeandia, A. F.; Alvarez, F. X.

    2015-10-01

    In the framework of the kinetic-collective model of phonon heat transport, we analyze how each range of the phonon frequency spectrum contributes to the total thermal conductivity both in the macro and the nanoscale. For this purpose, we use two case study samples: naturally occurring bulk silicon and a 115 nm of diameter silicon nanowire. We show that the contribution of high-energy phonons (optic branches) is non-negligible only when N-collisions are strongly present. This contribution increases when the effective size of the sample decreases, and it is found to be up to a 10% at room temperature for the 115 nm nanowire, corroborating preliminar ab-initio predictions.

  2. Phonon anomalies and electron-phonon coupling of metal surfaces and thin films; Phononenanomalien und Elektron-Phonon-Kopplung an Metalloberflaechen und duennen Schichten

    Energy Technology Data Exchange (ETDEWEB)

    Flach, B.

    2000-01-01

    This thesis has two topics: One is the investigation of an adsorbate induced phonon anomaly on W(110) and Mo{sub 1-x}Re{sub x}(110) (x = 5, 15, 25%) with inelastic helium atom scattering (HAS). The other one is the study of the growth, morphology and dynamics of ultra-thin lithium films deposited on W(110). In 1992 a giant phonon anomaly was found by J. Luedecke on the hydrogen saturated W(110) and Mo(110) surfaces. The anomaly consists of a deep and sharp indentation in the phonon dispersion curves in which the phonon energy nearly drops to zero ({omega}{sub 1}). In addition, a small and broad dip in the surface Rayleigh mode is observed ({omega}{sub 2}). The anomaly appears in the anti {gamma}-H- as well as in the anti {gamma}-S-direction of the surface Brillouin zone (SBZ). Since its first discovery, numerous other experimental and theoretical studies have followed. In the present work the effects is reinvestigated and experimental parameters, such as the crystal temperature and the incident energy, were changed in order to study their influence on the anomalous phonon behavior. In the case of H/Mo(110) the substrate was changed as well by alloying with small amounts of rhenium. In the present experiments a strong crystal temperature dependence of the {omega}{sub 2}-branch was found which leads to lower energies at the 'dip' for smaller temperatures, while the {omega}{sub 1}-anomaly remains unchanged. Such behavior agrees well with the picture that the {omega}{sub 2}-branch is due to a Kohn anomaly. (orig.)

  3. Phonon dispersion in the ferromagnetic shape memory alloy Ni2MnGa studied by neutron spectroscopy

    International Nuclear Information System (INIS)

    Vorderwisch, P.; Shapiro, S.M.

    2006-01-01

    Neutron spectroscopy is an ideal technique to study the structure and dynamics of crystals. For the ferromagnetic shape memory alloy Ni 2 MnGa, all previously obtained information from inelastic neutron scattering experiments is restricted to the phonon dispersion in the austenitic (fcc) phase of alloys with different compositions. For the (tetragonally distorted) martensitic phase recent inelastic neutron scattering data are presented. These new data were taken on a single crystal with stoichiometric composition. A single-variant martensitic phase of the sample has been obtained by the application of magnetic fields in horizontal or vertical direction with respect to the scattering plane used in the experiments. The measured phonon-dispersion curves are compared with recently published ab initio (zero-temperature) phonon-dispersion calculations. The anomalous phonon behavior observed in both, the austenitic and martensitic phase is discussed

  4. Magnus effects at high angles of attack and critical Reynolds numbers

    Science.gov (United States)

    Seginer, A.; Ringel, M.

    1983-01-01

    The Magnus force and moment experienced by a yawed, spinning cylinder were studied experimentally in low speed and subsonic flows at high angles of attack and critical Reynolds numbers. Flow-field visualization aided in describing a flow model that divides the Magnus phenomenon into a subcritical region, where reverse Magnus loads are experienced, and a supercritical region where these loads are not encountered. The roles of the spin rate, angle of attack, and crossflow Reynolds number in determining the boundaries of the subcritical region and the variations of the Magnus loads were studied.

  5. The Electron-Phonon Interaction in Strongly Correlated Systems

    International Nuclear Information System (INIS)

    Castellani, C.; Grilli, M.

    1995-01-01

    We analyze the effect of strong electron-electron repulsion on the electron-phonon interaction from a Fermi-liquid point of view and show that the electron-electron interaction is responsible for vertex corrections, which generically lead to a strong suppression of the electron-phonon coupling in the v F q/ω >>1 region, while such effect is not present when v F q/ω F is the Fermi velocity and q and ω are the transferred momentum and frequency respectively. In particular the e-ph scattering is suppressed in transport properties which are dominated by low-energy-high-momentum processes. On the other hand, analyzing the stability criterion for the compressibility, which involves the effective interactions in the dynamical limit, we show that a sizable electron-phonon interaction can push the system towards a phase-separation instability. Finally a detailed analysis of these ideas is carried out using a slave-boson approach for the infinite-U three-band Hubbard model in the presence of a coupling between the local hole density and a dispersionless optical phonon. (author)

  6. Optical phonons in PbTe/CdTe multilayer heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Novikova, N. N.; Yakovlev, V. A. [Russian Academy of Sciences, Institute for Spectroscopy (Russian Federation); Kucherenko, I. V., E-mail: kucheren@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Karczewski, G. [Polish Academy of Sciences, Institute of Physics (Poland); Aleshchenko, Yu. A.; Muratov, A. V.; Zavaritskaya, T. N.; Melnik, N. N. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    2015-05-15

    The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

  7. Hyperbolic phonon polaritons in hexagonal boron nitride (Conference Presentation)

    Science.gov (United States)

    Dai, Siyuan; Ma, Qiong; Fei, Zhe; Liu, Mengkun; Goldflam, Michael D.; Andersen, Trond; Garnett, William; Regan, Will; Wagner, Martin; McLeod, Alexander S.; Rodin, Alexandr; Zhu, Shou-En; Watanabe, Kenji; Taniguchi, T.; Dominguez, Gerado; Thiemens, Mark; Castro Neto, Antonio H.; Janssen, Guido C. A. M.; Zettl, Alex; Keilmann, Fritz; Jarillo-Herrero, Pablo; Fogler, Michael M.; Basov, Dmitri N.

    2016-09-01

    Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. While hyperbolic responses are normally achieved with metamaterials, hexagonal boron nitride (hBN) naturally possesses this property due to the anisotropic phonons in the mid-infrared. Using scattering-type scanning near-field optical microscopy, we studied polaritonic phenomena in hBN. We performed infrared nano-imaging of highly confined and low-loss hyperbolic phonon polaritons in hBN. The polariton wavelength was shown to be governed by the hBN thickness according to a linear law persisting down to few atomic layers [1]. Additionally, we carried out the modification of hyperbolic response in meta-structures comprised of a mononlayer graphene deposited on hBN [2]. Electrostatic gating of the top graphene layer allows for the modification of wavelength and intensity of hyperbolic phonon polaritons in bulk hBN. The physics of the modification originates from the plasmon-phonon coupling in the hyperbolic medium. Furthermore, we demonstrated the "hyperlens" for subdiffractional focusing and imaging using a slab of hBN [3]. References [1] S. Dai et al., Science, 343, 1125 (2014). [2] S. Dai et al., Nature Nanotechnology, 10, 682 (2015). [3] S. Dai et al., Nature Communications, 6, 6963 (2015).

  8. Isotopic effects on phonon anharmonicity in layered van der Waals crystals: Isotopically pure hexagonal boron nitride

    Science.gov (United States)

    Cuscó, Ramon; Artús, Luis; Edgar, James H.; Liu, Song; Cassabois, Guillaume; Gil, Bernard

    2018-04-01

    Hexagonal boron nitride (h -BN) is a layered crystal that is attracting a great deal of attention as a promising material for nanophotonic applications. The strong optical anisotropy of this crystal is key to exploit polaritonic modes for manipulating light-matter interactions in 2D materials. h -BN has also great potential for solid-state neutron detection and neutron imaging devices, given the exceptionally high thermal neutron capture cross section of the boron-10 isotope. A good knowledge of phonons in layered crystals is essential for harnessing long-lived phonon-polariton modes for nanophotonic applications and may prove valuable for developing solid-state 10BN neutron detectors with improved device architectures and higher detection efficiencies. Although phonons in graphene and isoelectronic materials with a similar hexagonal layer structure have been studied, the effect of isotopic substitution on the phonons of such lamellar compounds has not been addressed yet. Here we present a Raman scattering study of the in-plane high-energy Raman active mode on isotopically enriched single-crystal h -BN. Phonon frequency and lifetime are measured in the 80-600-K temperature range for 10B-enriched, 11B-enriched, and natural composition high quality crystals. Their temperature dependence is explained in the light of perturbation theory calculations of the phonon self-energy. The effects of crystal anisotropy, isotopic disorder, and anharmonic phonon-decay channels are investigated in detail. The isotopic-induced changes in the phonon density of states are shown to enhance three-phonon anharmonic decay channels in 10B-enriched crystals, opening the possibility of isotope tuning of the anharmonic phonon decay processes.

  9. Detecting phonon blockade with photons

    International Nuclear Information System (INIS)

    Didier, Nicolas; Pugnetti, Stefano; Fazio, Rosario; Blanter, Yaroslav M.

    2011-01-01

    Measuring the quantum dynamics of a mechanical system, when few phonons are involved, remains a challenge. We show that a superconducting microwave resonator linearly coupled to the mechanical mode constitutes a very powerful probe for this scope. This new coupling can be much stronger than the usual radiation pressure interaction by adjusting a gate voltage. We focus on the detection of phonon blockade, showing that it can be observed by measuring the statistics of the light in the cavity. The underlying reason is the formation of an entangled state between the two resonators. Our scheme realizes a phonotonic Josephson junction, giving rise to coherent oscillations between phonons and photons as well as a self-trapping regime for a coupling smaller than a critical value. The transition from the self-trapping to the oscillating regime is also induced dynamically by dissipation.

  10. Optimizing phonon space in the phonon-coupling model

    Science.gov (United States)

    Tselyaev, V.; Lyutorovich, N.; Speth, J.; Reinhard, P.-G.

    2017-08-01

    We present a new scheme to select the most relevant phonons in the phonon-coupling model, named here the time-blocking approximation (TBA). The new criterion, based on the phonon-nucleon coupling strengths rather than on B (E L ) values, is more selective and thus produces much smaller phonon spaces in the TBA. This is beneficial in two respects: first, it curbs the computational cost, and second, it reduces the danger of double counting in the expansion basis of the TBA. We use here the TBA in a form where the coupling strength is regularized to keep the given Hartree-Fock ground state stable. The scheme is implemented in a random-phase approximation and TBA code based on the Skyrme energy functional. We first explore carefully the cutoff dependence with the new criterion and can work out a natural (optimal) cutoff parameter. Then we use the freshly developed and tested scheme for a survey of giant resonances and low-lying collective states in six doubly magic nuclei looking also at the dependence of the results when varying the Skyrme parametrization.

  11. Overview of Appalachian Basin high-angle and horizontal air and mud drilling

    International Nuclear Information System (INIS)

    Yost, A.B. III; Javins, B.H.

    1991-01-01

    The United States Department of Energy's Morgantown Energy Technology Center has been investigating the potential of using high angle and horizontal drilling technology to improve gas production from low permeability reservoirs for more than 20 years. A chronology of 45 high angle and horizontal wells have been identified to show the date, type well, type build curve, location, formation and the type of application. The historical well drilling events that have taken place since the first well are discussed to evaluate the progress in developing the technology. Detailed discussion about how the drilling technology developed in the Appalachian Basin for directional drilling and completion was provided. A discussion of the types of applications for high and horizontal drilling in the Appalachian Basin were identified. A summary of four jointly funded DOE/Industry horizontal wells were discussed to illustrate how the air horizontal drilling technology developed and learning curves for drilling cost and feet per day were provided to illustrate the improvement in the technology and equipment reliability

  12. Unsteady aerodynamic modeling at high angles of attack using support vector machines

    Directory of Open Access Journals (Sweden)

    Wang Qing

    2015-06-01

    Full Text Available Accurate aerodynamic models are the basis of flight simulation and control law design. Mathematically modeling unsteady aerodynamics at high angles of attack bears great difficulties in model structure determination and parameter estimation due to little understanding of the flow mechanism. Support vector machines (SVMs based on statistical learning theory provide a novel tool for nonlinear system modeling. The work presented here examines the feasibility of applying SVMs to high angle-of-attack unsteady aerodynamic modeling field. Mainly, after a review of SVMs, several issues associated with unsteady aerodynamic modeling by use of SVMs are discussed in detail, such as selection of input variables, selection of output variables and determination of SVM parameters. The least squares SVM (LS-SVM models are set up from certain dynamic wind tunnel test data of a delta wing and an aircraft configuration, and then used to predict the aerodynamic responses in other tests. The predictions are in good agreement with the test data, which indicates the satisfying learning and generalization performance of LS-SVMs.

  13. Simulation of flow around a slender body at high angles of attack

    Directory of Open Access Journals (Sweden)

    Obeid Osama

    2017-01-01

    Full Text Available LES of the flow around an ogive-cylinder body at high angles of attack were carried out to investigate the possibility of the development of asymmetric wake-vortex without the introduction of artificial perturbations. The study investigated the effect of grid resolution and scheme bias on the solution. The numerical solution was found to be sensitive to the bias in the numerical scheme. The simulation was carried for angles of attack α = 30°, 40°, 50°, 55°, and 60°. The simulation at α = 30° − 40° produced symmetric wake-vortex. At α = 50°, the wake-vortex is also symmetric but with vortex separation. At α = 60°, the wake-vortex becomes asymmetric. At 60°, the wake-vortex is highly asymmetric with vortex separation and breakdown. It was concluded that asymmetric flow around slender bodies at high angles of attack can be simulated in the absence geometrical or flow perturbations.

  14. Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene.

    Science.gov (United States)

    Araujo, Paulo T; Mafra, Daniela L; Sato, Kentaro; Saito, Riichiro; Kong, Jing; Dresselhaus, Mildred S

    2012-01-01

    In this letter, we present a step towards understanding the bilayer graphene (2LG) interlayer (IL)-related phonon combination modes and overtones as well as their phonon self-energy renormalizations by using both gate-modulated and laser-energy dependent inelastic scattering spectroscopy. We show that although the IL interactions are weak, their respective phonon renormalization response is significant. Particularly special, the IL interactions are mediated by Van der Waals forces and are fundamental for understanding low-energy phenomena such as transport and infrared optics. Our approach opens up a new route to understanding fundamental properties of IL interactions which can be extended to any graphene-like material, such as MoS₂, WSe₂, oxides and hydroxides. Furthermore, we report a previously elusive crossing between IL-related phonon combination modes in 2LG, which might have important technological applications.

  15. Local symmetry breaking and spin–phonon coupling in SmCrO3 orthochromite

    International Nuclear Information System (INIS)

    El Amrani, M.; Zaghrioui, M.; Ta Phuoc, V.; Gervais, F.; Massa, Néstor E.

    2014-01-01

    Raman scattering and infrared reflectivity performed on polycrystalline SmCrO 3 support strong influence of the antiferromagnetic order on phonon modes. Both measurements show softening of some modes below T N . Such a behavior is explained by spin–phonon coupling in this compound. Furthermore, temperature dependence of the infrared spectra has demonstrated important changes compared to the Raman spectra, suggesting strong structural modifications due to the cation displacements rather to those of the oxygen ions. Our results reveal that polar distortions originating in local symmetry breaking, i.e. local non-centrosymmetry, resulting in Cr off-centring. - Highlights: • We investigated Raman and infrared phonon modes of SmCrO 3 versus temperature. • Results reveal strong influence of the antiferromagnetic order on phonon modes. • Temperature dependence of the infrared spectra shows strong structural modifications suggesting local symmetry breaking

  16. Local symmetry breaking and spin–phonon coupling in SmCrO{sub 3} orthochromite

    Energy Technology Data Exchange (ETDEWEB)

    El Amrani, M. [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Zaghrioui, M., E-mail: zaghrioui@univ-tours.fr [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Ta Phuoc, V.; Gervais, F. [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Massa, Néstor E. [Laboratorio Nacional de Investigacion y Servicios en Espectroscopia Optica-Centro CEQUINOR, Universidad Nacional de La Plata, C. C. 962, 1900 La Plata (Argentina)

    2014-06-01

    Raman scattering and infrared reflectivity performed on polycrystalline SmCrO{sub 3} support strong influence of the antiferromagnetic order on phonon modes. Both measurements show softening of some modes below T{sub N}. Such a behavior is explained by spin–phonon coupling in this compound. Furthermore, temperature dependence of the infrared spectra has demonstrated important changes compared to the Raman spectra, suggesting strong structural modifications due to the cation displacements rather to those of the oxygen ions. Our results reveal that polar distortions originating in local symmetry breaking, i.e. local non-centrosymmetry, resulting in Cr off-centring. - Highlights: • We investigated Raman and infrared phonon modes of SmCrO{sub 3} versus temperature. • Results reveal strong influence of the antiferromagnetic order on phonon modes. • Temperature dependence of the infrared spectra shows strong structural modifications suggesting local symmetry breaking.

  17. Lattice Waves, Spin Waves, and Neutron Scattering

    Science.gov (United States)

    Brockhouse, Bertram N.

    1962-03-01

    Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)

  18. Thermal Transport and Phonon Hydrodynamics in Strontium Titanate

    Science.gov (United States)

    Martelli, Valentina; Jiménez, Julio Larrea; Continentino, Mucio; Baggio-Saitovitch, Elisa; Behnia, Kamran

    2018-03-01

    We present a study of thermal conductivity, κ , in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow. In undoped SrTiO3 , κ evolves faster than cubic with temperature below its peak and in a narrow temperature window. Such behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones. The effect disappears in the presence of dopants. In SrTi1 -xNbx O3 , a significant reduction in lattice thermal conductivity starts below the temperature at which the average inter-dopant distance and the thermal wavelength of acoustic phonons become comparable. In the high-temperature regime, thermal diffusivity becomes proportional to the inverse of temperature, with a prefactor set by sound velocity and Planckian time (τp=(ℏ/kBT ) ).

  19. Sound and heat revolutions in phononics

    Science.gov (United States)

    Maldovan, Martin

    2013-11-01

    The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics.

  20. Bifurcation analysis and stability design for aircraft longitudinal motion with high angle of attack

    Directory of Open Access Journals (Sweden)

    Xin Qi

    2015-02-01

    Full Text Available Bifurcation analysis and stability design for aircraft longitudinal motion are investigated when the nonlinearity in flight dynamics takes place severely at high angle of attack regime. To predict the special nonlinear flight phenomena, bifurcation theory and continuation method are employed to systematically analyze the nonlinear motions. With the refinement of the flight dynamics for F-8 Crusader longitudinal motion, a framework is derived to identify the stationary bifurcation and dynamic bifurcation for high-dimensional system. Case study shows that the F-8 longitudinal motion undergoes saddle node bifurcation, Hopf bifurcation, Zero-Hopf bifurcation and branch point bifurcation under certain conditions. Moreover, the Hopf bifurcation renders series of multiple frequency pitch oscillation phenomena, which deteriorate the flight control stability severely. To relieve the adverse effects of these phenomena, a stabilization control based on gain scheduling and polynomial fitting for F-8 longitudinal motion is presented to enlarge the flight envelope. Simulation results validate the effectiveness of the proposed scheme.

  1. Simulating Effects of High Angle of Attack on Turbofan Engine Performance

    Science.gov (United States)

    Liu, Yuan; Claus, Russell W.; Litt, Jonathan S.; Guo, Ten-Huei

    2013-01-01

    A method of investigating the effects of high angle of attack (AOA) flight on turbofan engine performance is presented. The methodology involves combining a suite of diverse simulation tools. Three-dimensional, steady-state computational fluid dynamics (CFD) software is used to model the change in performance of a commercial aircraft-type inlet and fan geometry due to various levels of AOA. Parallel compressor theory is then applied to assimilate the CFD data with a zero-dimensional, nonlinear, dynamic turbofan engine model. The combined model shows that high AOA operation degrades fan performance and, thus, negatively impacts compressor stability margins and engine thrust. In addition, the engine response to high AOA conditions is shown to be highly dependent upon the type of control system employed.

  2. A holographic perspective on phonons and pseudo-phonons

    Energy Technology Data Exchange (ETDEWEB)

    Amoretti, Andrea [Institute of Theoretical Physics and Astrophysics, University of Würzburg,97074 Würzburg (Germany); Physique Théorique et Mathématique and International Solvay Institutes,Université Libre de Bruxelles,C.P. 231, 1050 Brussels (Belgium); Areán, Daniel [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, D-80805, Munich (Germany); Argurio, Riccardo [Physique Théorique et Mathématique and International Solvay Institutes,Université Libre de Bruxelles,C.P. 231, 1050 Brussels (Belgium); Musso, Daniele [Departamento de Física de Partículas, Universidade de Santiago de Compostelaand Instituto Galego de Física de Altas Enerxías (IGFAE),E-15782, Santiago de Compostela (Spain); Zayas, Leopoldo A. Pando [Michigan Center for Theoretical Physics, Department of Physics, University of Michigan,Ann Arbor, MI 48109 (United States)

    2017-05-10

    We analyze the concomitant spontaneous breaking of translation and conformal symmetries by introducing in a CFT a complex scalar operator that acquires a spatially dependent expectation value. The model, inspired by the holographic Q-lattice, provides a privileged setup to study the emergence of phonons from a spontaneous translational symmetry breaking in a conformal field theory and offers valuable hints for the treatment of phonons in QFT at large. We first analyze the Ward identity structure by means of standard QFT techniques, considering both spontaneous and explicit symmetry breaking. Next, by implementing holographic renormalization, we show that the same set of Ward identities holds in the holographic Q-lattice. Eventually, relying on the holographic and QFT results, we study the correlators realizing the symmetry breaking pattern and how they encode information about the low-energy spectrum.

  3. Light Scattering Spectroscopies of Semiconductor Nanocrystals (Quantum Dots)

    International Nuclear Information System (INIS)

    Yu, Peter Y; Gardner, Grat; Nozaki, Shinji; Berbezier, Isabelle

    2006-01-01

    We review the study of nanocrystals or quantum dots using inelastic light scattering spectroscopies. In particular recent calculations of the phonon density of states and low frequency Raman spectra in Ge nanocrystals are presented for comparison with experimental results

  4. Büttiker probes for dissipative phonon quantum transport in semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Miao, K., E-mail: kmiao@purdue.edu; Charles, J.; Klimeck, G. [School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Network for Computational Nanotechnology, Purdue University, West Lafayette, Indiana 47907 (United States); Sadasivam, S.; Fisher, T. S. [School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); Kubis, T. [Network for Computational Nanotechnology, Purdue University, West Lafayette, Indiana 47907 (United States)

    2016-03-14

    Theoretical prediction of phonon transport in modern semiconductor nanodevices requires atomic resolution of device features and quantum transport models covering coherent and incoherent effects. The nonequilibrium Green's function method is known to serve this purpose well but is numerically expensive in simulating incoherent scattering processes. This work extends the efficient Büttiker probe approach widely used in electron transport to phonons and considers salient implications of the method. Different scattering mechanisms such as impurity, boundary, and Umklapp scattering are included, and the method is shown to reproduce the experimental thermal conductivity of bulk Si and Ge over a wide temperature range. Temperature jumps at the lead/device interface are captured in the quasi-ballistic transport regime consistent with results from the Boltzmann transport equation. Results of this method in Si/Ge heterojunctions illustrate the impact of atomic relaxation on the thermal interface conductance and the importance of inelastic scattering to activate high-energy channels for phonon transport. The resultant phonon transport model is capable of predicting the thermal performance in the heterostructure efficiently.

  5. Büttiker probes for dissipative phonon quantum transport in semiconductor nanostructures

    International Nuclear Information System (INIS)

    Miao, K.; Charles, J.; Klimeck, G.; Sadasivam, S.; Fisher, T. S.; Kubis, T.

    2016-01-01

    Theoretical prediction of phonon transport in modern semiconductor nanodevices requires atomic resolution of device features and quantum transport models covering coherent and incoherent effects. The nonequilibrium Green's function method is known to serve this purpose well but is numerically expensive in simulating incoherent scattering processes. This work extends the efficient Büttiker probe approach widely used in electron transport to phonons and considers salient implications of the method. Different scattering mechanisms such as impurity, boundary, and Umklapp scattering are included, and the method is shown to reproduce the experimental thermal conductivity of bulk Si and Ge over a wide temperature range. Temperature jumps at the lead/device interface are captured in the quasi-ballistic transport regime consistent with results from the Boltzmann transport equation. Results of this method in Si/Ge heterojunctions illustrate the impact of atomic relaxation on the thermal interface conductance and the importance of inelastic scattering to activate high-energy channels for phonon transport. The resultant phonon transport model is capable of predicting the thermal performance in the heterostructure efficiently.

  6. Büttiker probes for dissipative phonon quantum transport in semiconductor nanostructures

    Science.gov (United States)

    Miao, K.; Sadasivam, S.; Charles, J.; Klimeck, G.; Fisher, T. S.; Kubis, T.

    2016-03-01

    Theoretical prediction of phonon transport in modern semiconductor nanodevices requires atomic resolution of device features and quantum transport models covering coherent and incoherent effects. The nonequilibrium Green's function method is known to serve this purpose well but is numerically expensive in simulating incoherent scattering processes. This work extends the efficient Büttiker probe approach widely used in electron transport to phonons and considers salient implications of the method. Different scattering mechanisms such as impurity, boundary, and Umklapp scattering are included, and the method is shown to reproduce the experimental thermal conductivity of bulk Si and Ge over a wide temperature range. Temperature jumps at the lead/device interface are captured in the quasi-ballistic transport regime consistent with results from the Boltzmann transport equation. Results of this method in Si/Ge heterojunctions illustrate the impact of atomic relaxation on the thermal interface conductance and the importance of inelastic scattering to activate high-energy channels for phonon transport. The resultant phonon transport model is capable of predicting the thermal performance in the heterostructure efficiently.

  7. Phonon conductivity and relaxation rate in solids with disturbances by the Green function method

    International Nuclear Information System (INIS)

    Singh, M.

    1980-09-01

    In this present article we have established an expression for the temperature dependence of the lattice thermal conductivity of solids with harmonic disturbances. The relaxation rate for scattering of phonons with point defect is also derived. We will apply the Kubo-correlation function formalism for the thermal conductivity, and the double time temperature dependent Green function technique for the evaluation of correlation functions

  8. Phonon-affected steady-state transport through molecular quantum dots

    Czech Academy of Sciences Publication Activity Database

    Koch, T.; Fehske, H.; Loos, Jan

    T151, č. 1 (2012), 1-10 ISSN 0031-8949 Institutional research plan: CEZ:AV0Z10100521 Keywords : the ory of electron ic transport * scattering mechanisms * polarons and electron -phonon interactions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.032, year: 2012

  9. Thermal conductivity of electron-doped CaMnO3 perovskites: Local lattice distortions and optical phonon thermal excitation

    International Nuclear Information System (INIS)

    Wang Yang; Sui Yu; Wang Xianjie; Su Wenhui; Liu Xiaoyang; Fan, Hong Jin

    2010-01-01

    The thermal transport properties of a series of electron-doped CaMnO 3 perovskites have been investigated. Throughout the temperature range 5-300 K, phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible. The short phonon mean free paths in this system result in the relatively low thermal conductivities. The strong phonon scatterings stem from the A-site mismatch and bond-length fluctuations induced by local distortions of MnO 6 octahedra. The thermal conductivity in the magnetically ordered state is enhanced as a result of the decrease in spin-phonon scattering. The results also indicate that above the magnetic ordering temperature, observable thermal excitation of optical phonons occurs. The contribution of optical phonons to thermal conductivity becomes non-negligible and is proposed to play an important role in the glass-like thermal transport behavior (i.e. positive temperature dependence of the thermal conductivity) in the paramagnetic state. These features can be understood in terms of an expression of thermal conductivity that includes both acoustic and optical phonon terms.

  10. Phonons in fcc binary alloys

    International Nuclear Information System (INIS)

    Sharma, Amita; Rathore, R.P.S.

    1992-01-01

    Born-Mayer potential has been modified to account for the unpaired (three body) forces among the common nearest neighbours of the ordered binary fcc alloys i.e. Ni 3 Fe 7 , Ni 5 Fe 5 and Ni 75 Fe 25 . The three body potential is added to the two body form of Morse to formalize the total interaction potential. Measured inverse ionic compressibility, cohesive energy, lattice constant and one measured phonon frequency are used to evaluate the defining parameters of the potential. The potential seeks to bring about the binding among 140 and 132 atoms though pair wise (two body) and non-pair wise (three body) forces respectively. The phonon-dispersion relations obtained by solving the secular equation are compared with the experimental findings on the aforesaid alloys. (author). 19 refs., 3 figs

  11. Engineering dissipation with phononic spectral hole burning

    Science.gov (United States)

    Behunin, R. O.; Kharel, P.; Renninger, W. H.; Rakich, P. T.

    2017-03-01

    Optomechanics, nano-electromechanics, and integrated photonics have brought about a renaissance in phononic device physics and technology. Central to this advance are devices and materials supporting ultra-long-lived photonic and phononic excitations that enable novel regimes of classical and quantum dynamics based on tailorable photon-phonon coupling. Silica-based devices have been at the forefront of such innovations for their ability to support optical excitations persisting for nearly 1 billion cycles, and for their low optical nonlinearity. While acoustic phonon modes can persist for a similar number of cycles in crystalline solids at cryogenic temperatures, it has not been possible to achieve such performance in silica, as silica becomes acoustically opaque at low temperatures. We demonstrate that these intrinsic forms of phonon dissipation are greatly reduced (by >90%) by nonlinear saturation using continuous drive fields of disparate frequencies. The result is a form of steady-state phononic spectral hole burning that produces a wideband transparency window with optically generated phonon fields of modest (nW) powers. We developed a simple model that explains both dissipative and dispersive changes produced by phononic saturation. Our studies, conducted in a microscale device, represent an important step towards engineerable phonon dynamics on demand and the use of glasses as low-loss phononic media.

  12. Raman scattering by the E{sub 2h} and A{sub 1}(LO) phonons of In{sub x}Ga{sub 1-x}N epilayers (0.25 < x < 0.75) grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Oliva, R.; Ibanez, J.; Cusco, R.; Artus, L. [Institut Jaume Almera, Consell Superior d' Investigacions Cientifiques (CSIC), Lluis Sole i Sabaris s.n, 08028 Barcelona, Catalonia (Spain); Kudrawiec, R. [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Serafinczuk, J. [Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw (Poland); Martinez, O.; Jimenez, J. [Departamento de Fisica de la Materia Condensada, Cristalografia, y Mineralogia, Universidad de Valladolid, 47011 Valladolid (Spain); Henini, M. [Nottingham Nanotechnology and Nanoscience Centre, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Boney, C.; Bensaoula, A. [Department of Physics, University of Houston, 4800 Calhoun, Houston, Texas 77004 (United States)

    2012-03-15

    We use Raman scattering to investigate the composition behavior of the E{sub 2h} and A{sub 1}(LO) phonons of In{sub x}Ga{sub 1-x}N and to evaluate the role of lateral compositional fluctuations and in-depth strain/composition gradients on the frequency of the A{sub 1}(LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A{sub 1}(LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A{sub 1}(LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E{sub 2h} frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E{sub 2h} peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A{sub 1}(LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material.

  13. Heat transport in two-dimensional materials by directly solving the phonon Boltzmann equation under Callaway's dual relaxation model

    Science.gov (United States)

    Guo, Yangyu; Wang, Moran

    2017-10-01

    The single mode relaxation time approximation has been demonstrated to greatly underestimate the lattice thermal conductivity of two-dimensional materials due to the collective effect of phonon normal scattering. Callaway's dual relaxation model represents a good approximation to the otherwise ab initio solution of the phonon Boltzmann equation. In this work we develop a discrete-ordinate-method (DOM) scheme for the numerical solution of the phonon Boltzmann equation under Callaway's model. Heat transport in a graphene ribbon with different geometries is modeled by our scheme, which produces results quite consistent with the available molecular dynamics, Monte Carlo simulations, and experimental measurements. Callaway's lattice thermal conductivity model with empirical boundary scattering rates is examined and shown to overestimate or underestimate the direct DOM solution. The length convergence of the lattice thermal conductivity of a rectangular graphene ribbon is explored and found to depend appreciably on the ribbon width, with a semiquantitative correlation provided between the convergence length and the width. Finally, we predict the existence of a phonon Knudsen minimum in a graphene ribbon only at a low system temperature and isotope concentration so that the average normal scattering rate is two orders of magnitude stronger than the intrinsic resistive one. The present work will promote not only the methodology for the solution of the phonon Boltzmann equation but also the theoretical modeling and experimental detection of hydrodynamic phonon transport in two-dimensional materials.

  14. Vibrational spectroscopy of superconducting MgB2 by neutron inelastic scattering

    International Nuclear Information System (INIS)

    Muranaka, Takahiro

    2001-01-01

    Neutron inelastic scattering measurements have been performed on superconducting MgB 2 above and below T c . The temperature dependence of the generalized phonon density-of-states showed clear anomalous behaviour near 24 meV in the acoustic phonon region, which may be interpreted as evidence of a substantial contribution to the total electron-phonon coupling strength deriving from these phonons. Weaker evidence for a corresponding response in the high-energy B bond stretching phonons was also encountered. (author)

  15. A Neutron Scattering Study of Lattice Dynamics of HgTe and HgSe

    DEFF Research Database (Denmark)

    Kepa, H.; Giebultowicz, T.; Buras, B.

    1982-01-01

    The dispersion relations for the acoustic and optic phonons in HgTe and for the acoustic phonons in HgSe were determined by neutron inelastic scattering in three high symmetry directions. The effect of the free-carrier screening of the long-range electric field of LO phonons in HgTe was observed....... The formalism of the rigid ion model is used for numerical calculations of the phonon dispersion relations and the phonon densities of states in HgTe and HgSe....

  16. Optical phonon modes of wurtzite InP

    Science.gov (United States)

    Gadret, E. G.; de Lima, M. M.; Madureira, J. R.; Chiaramonte, T.; Cotta, M. A.; Iikawa, F.; Cantarero, A.

    2013-03-01

    Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h, and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model, the complete dispersion relations of InP in the wurtzite phase have been calculated, showing a good agreement with the Raman experimental data.

  17. Energy transfer in coupled nonlinear phononic waveguides: transition from wandering breather to nonlinear self-trapping

    International Nuclear Information System (INIS)

    Kosevich, Y A; Manevitch, L I; Savin, A V

    2007-01-01

    We consider, both analytically and numerically, the dynamics of stationary and slowly-moving breathers (localized short-wavelength excitations) in two weakly coupled nonlinear oscillator chains (nonlinear phononic waveguides). We show that there are two qualitatively different dynamical regimes of the coupled breathers: the oscillatory exchange of the low-amplitude breather between the phononic waveguides (wandering breather), and one-waveguide-localization (nonlinear self-trapping) of the high-amplitude breather. We also show that phase-coherent dynamics of the coupled breathers in two weakly linked nonlinear phononic waveguides has a profound analogy, and is described by a similar pair of equations, to the tunnelling quantum dynamics of two weakly linked Bose-Einstein condensates in a symmetric double-well potential (single bosonic Josephson junction). The exchange of phonon energy and excitations between the coupled phononic waveguides takes on the role which the exchange of atoms via quantum tunnelling plays in the case of the coupled condensates. On the basis of this analogy, we predict a new tunnelling mode of the coupled Bose-Einstein condensates in a single bosonic Josephson junction in which their relative phase oscillates around π/2. The dynamics of relative phase of two weakly linked Bose-Einstein condensates can be studied by means of interference, while the dynamics of the exchange of lattice excitations in coupled nonlinear phononic waveguides can be observed by means of light scattering

  18. Hydrodynamic phonon drift and second sound in a (20,20) single-wall carbon nanotube

    International Nuclear Information System (INIS)

    Lee, Sangyeop; Lindsay, Lucas

    2017-01-01

    Here, two hydrodynamic features of phonon transport, phonon drift and second sound, in a (20,20) single wall carbon nanotube (SWCNT) are discussed using lattice dynamics calculations employing an optimized Tersoff potential for atomic interactions. We formally derive a formula for the contribution of drift motion of phonons to total heat flux at steady state. It is found that the drift motion of phonons carry more than 70% and 90% of heat at 300 K and 100 K, respectively, indicating that phonon flow can be reasonably approximated as hydrodynamic if the SWCNT is long enough to avoid ballistic phonon transport. The dispersion relation of second sound is derived from the Peierls-Boltzmann transport equation with Callaway s scattering model and quantifies the speed of second sound and its relaxation. The speed of second sound is around 4000 m/s in a (20,20) SWCNT and the second sound can propagate more than 10 m in an isotopically pure (20,20) SWCNT for frequency around 1 GHz at 100 K.

  19. Raman analysis of phonon modes in a short period AlN/GaN superlattice

    Science.gov (United States)

    Sarkar, Ketaki; Datta, Debopam; Gosztola, David J.; Shi, Fengyuan; Nicholls, Alan; Stroscio, Michael A.; Dutta, Mitra

    2018-03-01

    AlN/GaN-based optoelectronic devices have been the subject of intense research underlying the commercialization of efficient devices. Areas of considerable interest are the study of their lattice dynamics, phonon transport, and electron-phonon interactions specific to the interface of these heterostructures which results in additional optical phonon modes known as interface phonon modes. In this study, the framework of the dielectric continuum model (DCM) has been used to compare and analyze the optical phonon modes obtained from experimental Raman scattering measurements on AlN/GaN short-period superlattices. We have observed the localized E2(high), A1(LO) and the E1(TO) modes in superlattice measurements at frequencies shifted from their bulk values. To the best of our knowledge, the nanostructures used in these studies are among the smallest yielding useful Raman signatures for the interface modes. In addition, we have also identified an additional spread of interface phonon modes in the TO range resulting from the superlattice periodicity. The Raman signature contribution from the underlying AlxGa1-xN ternary has also been observed and analyzed. A temperature calibration was done based on Stokes/anti-Stokes ratio of A1(LO) using Raman spectroscopy in a broad operating temperature range. Good agreement between the experimental results and theoretically calculated calibration plot predicted using Bose-Einstein statistics was obtained.

  20. Effects of quantum statistics of phonons on the thermal conductivity of silicon and germanium nanoribbons

    Science.gov (United States)

    Kosevich, Yuriy A.; Savin, Alexander V.; Cantarero, Andrés

    2013-01-01

    We present molecular dynamics simulation of phonon thermal conductivity of semiconductor nanoribbons with an account for phonon quantum statistics. In our semiquantum molecular dynamics simulation, dynamics of the system is described with the use of classical Newtonian equations of motion where the effect of phonon quantum statistics is introduced through random Langevin-like forces with a specific power spectral density (color noise). The color noise describes interaction of the molecular system with the thermostat. The thermal transport of silicon and germanium nanoribbons with atomically smooth (perfect) and rough (porous) edges are studied. We show that the existence of rough (porous) edges and the quantum statistics of phonon change drastically the low-temperature thermal conductivity of the nanoribbon in comparison with that of the perfect nanoribbon with atomically smooth edges and classical phonon dynamics and statistics. The rough-edge phonon scattering and weak anharmonicity of the considered lattice produce a weakly pronounced maximum of thermal conductivity of the nanoribbon at low temperature.

  1. Magnetic ground state and magnon-phonon interaction in multiferroic h-YMnO3

    DEFF Research Database (Denmark)

    Holm, S. L.; Kreisel, A.; Schaeffer, T. K.

    2018-01-01

    Inelastic neutron scattering has been used to study the magnetoelastic excitations in the multiferroic manganite hexagonal YMnO3. An avoided crossing is found between magnon and phonon modes close to the Brillouin zone boundary in the (a,b) plane. Neutron polarization analysis reveals that this m......Inelastic neutron scattering has been used to study the magnetoelastic excitations in the multiferroic manganite hexagonal YMnO3. An avoided crossing is found between magnon and phonon modes close to the Brillouin zone boundary in the (a,b) plane. Neutron polarization analysis reveals...... that this mode has mixed magnon-phonon character. An external magnetic field along the c axis is observed to cause a linear field-induced splitting of one of the spin-wave branches. A theoretical description is performed, using a Heisenberg model of localized spins, acoustic phonon modes, and a magnetoelastic...... coupling via the single-ion magnetostriction. The model quantitatively reproduces the dispersion and intensities of all modes in the full Brillouin zone, describes the observed magnon-phonon hybridized modes, and quantifies the magnetoelastic coupling. The combined information, including the field...

  2. Coherent gigahertz phonons in Ge₂Sb₂Te₅ phase-change materials.

    Science.gov (United States)

    Hase, Muneaki; Fons, Paul; Kolobov, Alexander V; Tominaga, Junji

    2015-12-09

    Using ≈40 fs ultrashort laser pulses, we investigate the picosecond acoustic response from a prototypical phase change material, thin Ge2Sb2Te5 (GST) films with various thicknesses. After excitation with a 1.53 eV-energy pulse with a fluence of ≈5 mJ cm(-2), the time-resolved reflectivity change exhibits transient electronic response, followed by a combination of exponential-like strain and coherent acoustic phonons in the gigahertz (GHz) frequency range. The time-domain shape of the coherent acoustic pulse is well reproduced by the use of the strain model by Thomsen et al 1986 (Phys. Rev. B 34 4129). We found that the decay rate (the inverse of the relaxation time) of the acoustic phonon both in the amorphous and in the crystalline phases decreases as the film thickness increases. The thickness dependence of the acoustic phonon decay is well modeled based on both phonon-defect scattering and acoustic phonon attenuation at the GST/Si interface, and it is revealed that those scattering and attenuation are larger in crystalline GST films than those in amorphous GST films.

  3. Phonon spectra in SiO2 glasses

    International Nuclear Information System (INIS)

    Perez R, J.F.; Jimenez S, S.; Gonzalez H, J.; Vorobiev, Y.V.; Hernandez L, M.A.; Parga T, J.R.

    1999-01-01

    Phonon spectra in SiO 2 sol-gel made glasses annealed under different conditions are investigated using infrared absorption and Raman scattering. These data are compared with those obtained in commercial optical-quality quartz. All the materials exhibit the same phonon bands, the exact position and the intensity depend on the measuring technique and on the sample preparation method. The phonon spectra in this material are interpreted on the basis of a simple quasi-linear description of elastic waves in an O-Si-O chain. It is shown that the main features observed in the range 400-1400 cm -1 can be predicted using a quasi-linear chain model in which the band at 1070 cm -1 is assigned to the longitudinal optical waves in the O-Si-O chain with the smallest possible wavelength at the Brillouin zone boundary, the band located around 450 cm -1 is assigned to the transversal optical waves and the band at 800 cm -1 to the longitudinal acoustical waves with the same wavelength. The degree of structural disorder can be also deduced within the framework of the proposed model. (Author)

  4. Technical Evaluation Report, Part A - Vortex Flow and High Angle of Attack

    Science.gov (United States)

    Luckring, James M.

    2003-01-01

    A symposium entitled Vortex Flow and High Angle of Attack was held in Loen, Norway, from May 7 through May 11, 2001. The Applied Vehicle Technology (AVT) panel, under the auspices of the Research and Technology Organization (RTO), sponsored this symposium. Forty-eight papers, organized into nine sessions, addressed computational and experimental studies of vortex flows pertinent to both aircraft and maritime applications. The studies also ranged from fundamental fluids investigations to flight test results, and significant results were contributed from a broad range of countries. The principal emphasis of this symposium was on "the understanding and prediction of separation-induced vortex flows and their effects on military vehicle performance, stability, control, and structural design loads." It was further observed by the program committee that "separation- induced vortex flows are an important part of the design and off-design performance of conventional fighter aircraft and new conventional or unconventional manned or unmanned advanced vehicle designs (UAVs, manned aircraft, missiles, space planes, ground-based vehicles, and ships)." The nine sessions addressed the following topics: vortical flows on wings and bodies, experimental techniques for vortical flows, numerical simulations of vortical flows, vortex stability and breakdown, vortex flows in maritime applications, vortex interactions and control, vortex dynamics, flight testing, and vehicle design. The purpose of this paper is to provide brief reviews of these papers along with some synthesizing perspectives toward future vortex flow research opportunities. The paper includes the symposium program. (15 refs.)

  5. High Angle Mining System. Final research report, Sep 80-Jun 83

    Energy Technology Data Exchange (ETDEWEB)

    Christofferson, D.

    1983-06-01

    Under Bureau of Mines Contract JO-133925, ESD Corporation developed the High Angle Mining System (HAMS) as a method of extracting coal from seams varying widely in thickness and pitch. The system would normally be employed to extract coal lying beyond the economic limit of a strip or open-pit highwall. It is a surface-controlled operation involving no underground personnel. The HAMS can significantly increase the reserve base of coal that can be economically surface mined. A number of open-pit or surface mines which have moderately or steeply pitched seams were visited and studied. Existing technology was reviewed to identify systems or system components which merited further consideration for the development of the HAMS concept. Conventional and innovative approaches based on augering and two approaches based on slackline excavation were developed in sufficient detail to enable comparison on the basis of operational limitation, recovery ratio, productivity, and economy. The slackline excavator concept employing a projectile bucket was selected as the best approach. The capability of economically mining pitched seams of coal with the HAMS was demonstrated.

  6. Longitudinal polar optical phonons in InN/GaN single and double het- erostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ardali, Sukru; Tiras, Engin [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470 (Turkey); Gunes, Mustafa; Balkan, Naci [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Ajagunna, Adebowale Olufunso; Iliopoulos, Eleftherios; Georgakilas, Alexandros [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion-Crete (Greece)

    2011-05-15

    Longitudinal optical phonon energy in InN epi-layers has been determined independently from the Raman spectroscopy and temperature dependent Hall mobility measurements. Raman spectroscopy technique can be used to obtain directly the LO energy where LO phonon scattering dominates transport at high temperature. Moreover, the Hall mobility is determined by the scattering of electrons with LO phonons so the data for the temperature dependence of Hall mobility have been used to calculate the effective energy of longitudinal optical phonons.The samples investigated were (i) single heterojunction InN with thicknesses of 1.08, 2.07 and 4.7 {mu}m grown onto a 40 nm GaN buffer and (ii) GaN/InN/AlN double heterojunction samples with InN thicknesses of 0.4, 0.6 and 0.8 {mu}m. Hall Effect measurements were carried out as a function of temperature in the range between T = 1.7 and 275 K at fixed magnetic and electric fields. The Raman spectra were obtained at room temperature. In the experiments, the 532 nm line of a nitrogen laser was used as the excitation source and the light was incident onto the samples along of the growth direction (c-axis). The results, obtained from the two independent techniques suggest the following: (1) LO phonon energies obtained from momentum relaxation experiments are generally slightly higher than those obtained from the Raman spectra. (2) LO phonon energy for the single heterojunctions does not depend on the InN thickness. (3) In double heterostructures, with smaller InN thicknesses and hence with increased strain, LO phonon energy increases by 3% (experimental accuracy is < 1%) when the InN layer thickness increases from 400 to 800 nm (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Hydrothermal Upflow, Serpentinization and Talc Alteration Associated with a High Angle Normal Fault Cutting an Oceanic Detachment, Northern Apennines, Italy

    Science.gov (United States)

    Alt, J.; Crispini, L.; Gaggero, L.; Shanks, W. C., III; Gulbransen, C.; Lavagnino, G.

    2017-12-01

    Normal faults cutting oceanic core complexes are observed at the seafloor and through geophysics, and may act as flow pathways for hydrothermal fluids, but we know little about such faults in the subsurface. We present bulk rock geochemistry and stable isotope data for a fault that acted as a hydrothermal upflow zone in a seafloor ultramafic-hosted hydrothermal system in the northern Apennines, Italy. Peridotites were exposed on the seafloor by detachment faulting, intruded by MORB gabbros, and are overlain by MORB lavas and pelagic sediments. North of the village of Reppia are fault shear zones in serpentinite, oriented at a high angle to the detachment surface and extending 300 m below the paleo-seafloor. The paleo-seafloor strikes roughly east-west, dipping 30˚ to the north. At depth the fault zone occurs as an anticlinal form plunging 40˚ to the west. A second fault strikes approximately north-south, with a near vertical dip. The fault rock outcrops as reddish weathered talc + sulfide in 0.1-2 m wide anastomosing bands, with numerous splays. Talc replaces serpentinite in the fault rocks, and the talc rocks are enriched in Si, metals (Fe, Cu, Pb), Light Rare Earth Elements (LREE), have variable Eu anomalies, and have low Mg, Cr and Ni contents. In some cases gabbro dikes are associated with talc-alteration and may have enhanced fluid flow. Sulfide from a fault rock has d34S=5.7‰. The mineralogy and chemistry of the fault rocks indicate that the fault acted as the upflow pathway for high-T black-smoker type fluids. Traverses away from the fault (up to 1 km) and with depth below the seafloor (up to 500 m) reveal variable influences of hydrothermal fluids, but there are no consistent trends with distance. Background serpentinites 500 m beneath the paleoseafloor have LREE depleted trends. Other serpentinites exhibit correlations of LREE with HFSE as the result of melt percolation, but there is significant scatter, and hydrothermal effects include LREE enrichment

  8. Temperature dependence of phonons in pyrolitic graphite

    International Nuclear Information System (INIS)

    Brockhouse, B.N.; Shirane, G.

    1977-01-01

    Dispersion curves for longitudinal and transverse phonons propagating along and near the c-axis in pyrolitic graphite at temperatures between 4 0 K and 1500 0 C have been measured by neutron spectroscopy. The observed frequencies decrease markedly with increasing temperature (except for the transverse optical ''rippling'' modes in the hexagonal planes). The neutron groups show interesting asymmetrical broadening ascribed to interference between one phonon and many phonon processes

  9. Tunable infrared reflectance by phonon modulation

    Science.gov (United States)

    Ihlefeld, Jon F.; Sinclair, Michael B.; Beechem, III, Thomas E.

    2018-03-06

    The present invention pertains to the use of mobile coherent interfaces in a ferroelectric material to interact with optical phonons and, ultimately, to affect the material's optical properties. In altering the optical phonon properties, the optical properties of the ferroelectric material in the spectral range near-to the phonon mode frequency can dramatically change. This can result in a facile means to change to the optical response of the ferroelectric material in the infrared.

  10. Tunable infrared reflectance by phonon modulation

    Energy Technology Data Exchange (ETDEWEB)

    Ihlefeld, Jon F.; Sinclair, Michael B.; Beechem, III, Thomas E.

    2018-03-06

    The present invention pertains to the use of mobile coherent interfaces in a ferroelectric material to interact with optical phonons and, ultimately, to affect the material's optical properties. In altering the optical phonon properties, the optical properties of the ferroelectric material in the spectral range near-to the phonon mode frequency can dramatically change. This can result in a facile means to change to the optical response of the ferroelectric material in the infrared.

  11. Carrier-phonon interaction in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Seebeck, Jan

    2009-03-10

    In recent years semiconductor quantum dots have been studied extensively due to their wide range of possible applications, predominantly for light sources. For successful applications, efficient carrier scattering processes as well as a detailed understanding of the optical properties are of central importance. The aims of this thesis are theoretical investigations of carrier scattering processes in InGaAs/GaAs quantum dots on a quantum-kinetic basis. A consistent treatment of quasi-particle renormalizations and carrier kinetics for non-equilibrium conditions is presented, using the framework of non-equilibrium Green's functions. The focus of our investigations is the interaction of carriers with LO phonons. Important for the understanding of the scattering mechanism are the corresponding quasi-particle properties. Starting from a detailed study of quantum-dot polarons, scattering and dephasing processes are discussed for different temperature regimes. The inclusion of polaron and memory effects turns out to be essential for the description of the carrier kinetics in quantum-dot systems. They give rise to efficient scattering channels and the obtained results are in agreement with recent experiments. Furthermore, a consistent treatment of the carrier-LO-phonon and the carrier-carrier interaction is presented for the optical response of semiconductor quantum dots, both giving rise to equally important contributions to the dephasing. Beside the conventional GaAs material system, currently GaN based light sources are of high topical interest due to their wide range of possible emission frequencies. In this material additionally intrinsic properties like piezoelectric fields and strong band-mixing effects have to be considered. For the description of the optical properties of InN/GaN quantum dots a procedure is presented, where the material properties obtained from an atomistic tight-binding approach are combined with a many-body theory for non

  12. Search for the 3-phonon state of {sup 40}Ca; Recherche de l'etat a trois phonons dans le {sup 40}Ca

    Energy Technology Data Exchange (ETDEWEB)

    Fallot, M

    2002-09-01

    We study collective vibrational states of the nucleus: giant resonances and multiphonon states. It has been shown that multiphonon states, which are built with several superimposed giant resonances, can be excited in inelastic heavy ion scattering near the grazing angle. No three photon states have been observed until now. An experiment has been performed at GANIL, aiming at the observation of the 3-phonon state built with the giant quadrupole resonance (GQR) in {sup 40}Ca, with the reaction {sup 40}Ca + {sup 40}Ca at 50 A.Me.V. The ejectile was identified in the SPEG spectrometer. Light charged particles were detected in 240 CsI scintillators of the INDRA 4{pi} array. The analysis confirms the previous results about the GQR and the 2-phonon state in {sup 40}Ca. For the first time, we have measured an important direct decay branch of the GQR by alpha particles. Applying the so-called 'missing energy method' to events containing three protons measured in coincidence with the ejectile, we observe a direct decay branch revealing the presence of a 3-phonon state in the excitation energy region expected for the triple GQR. Dynamical processes are also studied in the inelastic channel, emphasizing a recently discovered mechanism named towing-mode. We observe for the first time the towing-mode of alpha particles. The energies of multiphonon states in {sup 40}Ca and {sup 208}Pb have been computed microscopically including some anharmonicities via boson mapping methods. The basis of the calculation has been extended to the 3-phonon states. Our results show large anharmonicities (several MeV), due to the coupling of 3-phonon states to 2-phonon states. The extension of the basis to 4-phonon states has been performed for the first time. The inclusion of the 4 phonon states in the calculation did not affect the previous observations concerning the 2-phonon states. Preliminary results on the anharmonicities of the 3-phonon states are presented. (author)

  13. Unified quantum theory of elastic and inelastic atomic scattering from a physisorbed monolayer solid

    DEFF Research Database (Denmark)

    Bruch, L. W.; Hansen, Flemming Yssing; Dammann, Bernd

    2017-01-01

    A unified quantum theory of the elastic and inelastic scattering of low energy He atoms by a physisorbed monolayer solid in the one-phonon approximation is given. It uses a time-dependent wave packet with phonon creation and annihilation components and has a self-consistent feedback between...... the wave functions for elastic and inelastic scattered atoms. An attenuation of diffraction scattering by inelastic processes thus is inherent in the theory. The atomic motion and monolayer vibrations in the harmonic approximation are treated quantum mechanically and unitarity is preserved. The evaluation...... of specific one-phonon events includes contributions from diffuse inelastic scattering in other phonon modes. Effects of thermally excited phonons are included using a mean field approximation. The theory is applied to an incommensurate Xe/Pt(111) monolayer (incident energy Ei = 4-16 meV), a commensurate Xe...

  14. Soft phonon modes driven huge difference on lattice thermal conductivity between topological semimetal WC and WN

    Science.gov (United States)

    Guo, San-Dong; Chen, Peng

    2018-04-01

    Topological semimetals are currently attracting increasing interest due to their potential applications in topological qubits and low-power electronics, which are closely related to their thermal transport properties. Recently, the triply degenerate nodal points near the Fermi level of WC are observed by using angle-resolved photoemission spectroscopy. In this work, by solving the Boltzmann transport equation based on first-principles calculations, we systematically investigate the phonon transport properties of topological semimetals WC and WN. The predicted room-temperature lattice thermal conductivities of WC (WN) along the a and c directions are 1140.64 (7.47) W m-1 K-1 and 1214.69 (5.39) W m-1 K-1. Considering the similar crystal structure of WC and WN, it is quite interesting to find that the thermal conductivity of WC is more than two orders of magnitude higher than that of WN. It is found that, different from WN, the large acoustic-optical (a-o) gap prohibits the acoustic+acoustic → optical (aao) scattering, which gives rise to very long phonon lifetimes, leading to ultrahigh lattice thermal conductivity in WC. For WN, the lack of an a-o gap is due to soft phonon modes in optical branches, which can provide more scattering channels for aao scattering, producing very short phonon lifetimes. Further deep insight can be attained from their different electronic structures. Distinctly different from that in WC, the density of states of WN at the Fermi level becomes very sharp, which leads to destabilization of WN, producing soft phonon modes. It is found that the small shear modulus G and C44 limit the stability of WN, compared with WC. Our studies provide valuable information for phonon transports in WC and WN, and motivate further experimental studies to study their lattice thermal conductivities.

  15. Effect of magnon-phonon interaction on transverse acoustic phonon excitation at finite temperature

    International Nuclear Information System (INIS)

    Cheng Taimin; Li Lin; Xianyu Ze

    2007-01-01

    A magnon-phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line Σ it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point Γ), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line Δ it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X) and there is hardening for transverse acoustic phonon nearby point M. The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon-phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon

  16. Modeling of phonon heat transfer in spherical segment of silica aerogel grains

    Energy Technology Data Exchange (ETDEWEB)

    Han, Ya-Fen; Xia, Xin-Lin, E-mail: xiaxl@hit.edu.cn; Tan, He-Ping, E-mail: tanheping@hit.edu.cn; Liu, Hai-Dong

    2013-07-01

    Phonon heat transfer in spherical segment of nano silica aerogel grains is investigated by the lattice Boltzmann method (LBM). For various sizes of grains, the temperature distribution and the thermal conductivity are obtained by the numerical simulation, in which the size effects of the gap surface are also considered. The results indicate that the temperature distribution in the silica aerogel grain depends strongly on the size. Both the decreases in the diameter of spherical segment and the ratio of the diameter of gap surface to the diameter of spherical segment reduce its effective thermal conductivity obviously. In addition, the phonon scattering at the boundary surfaces becomes more prominent when grain size decreases.

  17. Ab initio phonon dispersions of face centered cubic Pb: effects of spin-orbit coupling

    International Nuclear Information System (INIS)

    Dal Corso, Andrea

    2008-01-01

    I present the ab initio phonon dispersions of face centered cubic Pb calculated within the framework of density functional perturbation theory, with plane waves and a fully relativistic ultrasoft pseudopotential which includes spin-orbit coupling effects. I find that, within the local density approximation, the theory gives phonon frequencies close to the experimental inelastic neutron scattering data. Many of the anomalies present in these dispersions are well reproduced by the fully relativistic pseudopotential theory and can be shown to appear only for small values of the smearing parameter that controls the sharpness of the Fermi surface.

  18. LO-phonon and plasmon coupling in neutron-transmutation-doped GaAs

    International Nuclear Information System (INIS)

    Kuriyama, K.; Sakai, K.; Okada, M.

    1996-01-01

    Coupling between the longitudinal-optic (LO) phonon mode and the longitudinal plasma mode in neutron-transmutation-doped (NTD) semi-insulating GaAs was studied using Raman-scattering spectroscopy and a Fourier-transform infrared spectrometer. When the electron concentration due to the activation of NTD impurities (Ge Ga and Se As ) approaches ∼8x10 16 cm -3 , the LO-phonon endash plasmon coupling is observed. This behavior is consistent with the free-electron absorption due to the activation of NTD impurities in samples annealed above 600 degree C. copyright 1996 The American Physical Society

  19. The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

    Science.gov (United States)

    Zhu, Yun; Li, Zhen; Li, Yue-ming

    2018-05-01

    A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC's dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

  20. Manipulation of Squeezed Two-Phonon Bound States using Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Nakamura Kazutaka G.

    2013-03-01

    Full Text Available Two-phonon bound states have been excited exclusively in ZnTe(110 via impulsive stimulated second-order Raman scattering, essentially being squeezed states due to phase coherent excitation of two identical components anticorrelated in the wave vector. By using coherent control technique with a pair of femtosecond laser pulses, the manipulation of squeezed states has been demonstrated in which both the amplitude and lifetime of coherent oscillations of squeezed states are modulated, indicating the feasibility to control the quantum noise and the quantum nature of phonon squeezed states, respectively.

  1. Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films

    Energy Technology Data Exchange (ETDEWEB)

    Chase, T. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Trigo, M.; Reid, A. H.; Dürr, H. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Li, R.; Vecchione, T.; Shen, X.; Weathersby, S.; Coffee, R.; Hartmann, N.; Wang, X. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Reis, D. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States)

    2016-01-25

    We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement.

  2. Modeling of phonon heat transfer in spherical segment of silica aerogel grains

    International Nuclear Information System (INIS)

    Han, Ya-Fen; Xia, Xin-Lin; Tan, He-Ping; Liu, Hai-Dong

    2013-01-01

    Phonon heat transfer in spherical segment of nano silica aerogel grains is investigated by the lattice Boltzmann method (LBM). For various sizes of grains, the temperature distribution and the thermal conductivity are obtained by the numerical simulation, in which the size effects of the gap surface are also considered. The results indicate that the temperature distribution in the silica aerogel grain depends strongly on the size. Both the decreases in the diameter of spherical segment and the ratio of the diameter of gap surface to the diameter of spherical segment reduce its effective thermal conductivity obviously. In addition, the phonon scattering at the boundary surfaces becomes more prominent when grain size decreases

  3. Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

    International Nuclear Information System (INIS)

    Robb, Paul D.; Finnie, Michael; Longo, Paolo; Craven, Alan J.

    2012-01-01

    Aberration-corrected high angle annular dark field (HAADF) imaging in scanning transmission electron microscopy (STEM) can now be performed at atomic-resolution. This is an important tool for the characterisation of the latest semiconductor devices that require individual layers to be grown to an accuracy of a few atomic layers. However, the actual quantification of interfacial sharpness at the atomic-scale can be a complicated matter. For instance, it is not clear how the use of the total, atomic column or background HAADF signals can affect the measured sharpness or individual layer widths. Moreover, a reliable and consistent method of measurement is necessary. To highlight these issues, two types of AlAs/GaAs interfaces were studied in-depth by atomic-resolution HAADF imaging. A method of analysis was developed in order to map the various HAADF signals across an image and to reliably determine interfacial sharpness. The results demonstrated that the level of perceived interfacial sharpness can vary significantly with specimen thickness and the choice of HAADF signal. Individual layer widths were also shown to have some dependence on the choice of HAADF signal. Hence, it is crucial to have an awareness of which part of the HAADF signal is chosen for analysis along with possible specimen thickness effects for future HAADF studies performed at the scale of a few atomic layers. -- Highlights: ► Quantification of interfaces using atomic-scale HAADF imaging is considered. ► The sharpness of AlAs/GaAs interfaces is investigated. ► A method of analysis was developed to map the various HAADF signals in an image. ► Measured sharpness varies with specimen thickness and HAADF signal type.

  4. Investigation on asymmetric flow over a blunt-nose slender body at high angle of attack

    Science.gov (United States)

    Zhongyang, Qi; Yankui, Wang; Lei, Wang; Qian, Li

    2017-12-01

    The asymmetric vortices over a blunt-nose slender body are investigated experimentally and numerically at a high angle of attack (AoA, α = 50°) and a Reynolds number of Re D = 1.54 × 105 on the basis of an incoming free-stream velocity and diameter (D) of the model. A micro-perturbation in the form of a hemispherical protrusion with a radius of r = 0.012D is introduced and attached on the nose of the slender body to control the behavior of the asymmetric vortices. Given the predominant role of micro perturbation in the asymmetric vortex pattern, a square wave, which is singly periodic, is observed for side-force variation by setting the circumferential angle (θ) of the micro perturbation from 0° to 360°. The asymmetric vortex pattern and the corresponding side force are manageable and highly dependent on the location of perturbation. The flow structure over the blunt-nose slender body is clarified by building a physical model of asymmetric vortex flow structure in a regular state at a high AoA (α = 50°). This model is divided into several regions by flow structure development along the model body-axis, i.e., inception region at x/D ≤ 3.0, triple-vortex region at 3.0 ≤ x/D ≤ 6.0, four-vortex region at 6.0 ≤ x/D ≤ 8.5, and five-vortex region at 8.5 ≤ x/D ≤ 12. The model reveals a complicated multi-vortex system. The associated pressure distributions and flow characteristics are discussed in detail.

  5. Elucidating the Wavelength Dependence of Phonon Scattering in Nanoparticle-Matrix Composites using Phonon Spectroscopy

    Science.gov (United States)

    2016-07-11

    and a Stanford Research Systems SR830 lock -in amplifier was used to measure the 1st and 3rd harmonics of the voltage signal. The temperature...current source and a Stanford Research Systems SR830 lock -in amplifier was used to measure the 1st and 3rd harmonic voltage signals. 2.2.2...Taras, M. Martin, U. Chaitanya and T. Edwin , Physics World, 2005, 18, 24. 67. N. W. Ashcroft and N. D. Mermin, Appendix N, 2010. DISTRIBUTION A

  6. Raman scattering study of filled skutterudite compounds

    International Nuclear Information System (INIS)

    Ogita, N; Kojima, R; Hasegawa, T; Takasu, Y; Udagawa, M; Kondo, T; Takeda, N; Ikeno, T; Ishikawa, K; Sugawara, H; Kikuchi, D; Sato, H; Sekine, C; Shirotani, I

    2007-01-01

    Raman scattering of skutterudite compounds RT 4 X 12 (R=La, Ce, Pr, Nd, Sm and Yb, T=Fe, Ru and Os, X=P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnicogen vibrations. At the low energy region, the second-order phonons, due to the vibration of the rare earth ions with a flat phonon dispersion, are observed in the spectra of RRu 4 P 12 (R=La and Sm) and ROs 4 Sb 12 (R=La, Ce, Pr, Nd, and Sm). The appearance of the second-order phonons in the spectra is caused by an anharmonic vibrations of rare earth ions in large cage space and a large density of state due to the flat phonon dispersion. However, in spite of the similar cage space, the 2nd-order phonons are hardly observed for RFe 4 Sb 12 and RRu 4 Sb 12 . Thus, these results suggest that the dynamics of the rare earth ion is closely related to not only the cage size but also the electronic state due to the transition metals. Raman spectra of PrRu 4 P 12 show the drastic spectral change due to the metal-insulator transition. The phonon spectra and crystal field excitations due to the structural change have been assigned above and below the transition temperature

  7. Splash, pop, sizzle: Information processing with phononic computing

    Directory of Open Access Journals (Sweden)

    Sophia R. Sklan

    2015-05-01

    Full Text Available Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic.

  8. Resonant tunneling in a pulsed phonon field

    DEFF Research Database (Denmark)

    Kral, P.; Jauho, Antti-Pekka

    1999-01-01

    , The nonequilibrium spectral function for the resonance displays the formation and decay of the phonon sidebands on ultrashort time scales. The time-dependent tunneling current through the individual phonon satellites reflects this quasiparticle formation by oscillations, whose time scale is set by the frequency...

  9. Phononic crystals and elastodynamics: Some relevant points

    Directory of Open Access Journals (Sweden)

    N. Aravantinos-Zafiris

    2014-12-01

    Full Text Available In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.

  10. Fluid-structure interaction of a rolling restrained body of revolution at high angles of attack

    Science.gov (United States)

    Degani, D.; Ishay, M.; Gottlieb, O.

    2017-03-01

    The current work investigates numerically rolling instabilities of a free-to-roll slender rigid-body of revolution placed in a wind tunnel at a high angle of attack. The resistance to the roll moment is represented by a linear torsion spring and equivalent linear damping representing friction in the bearings of a simulated wind tunnel model. The body is subjected to a three-dimensional, compressible, laminar flow. The full Navier-Stokes equations are solved using the second-order implicit finite difference Beam-Warming scheme, adapted to a curvilinear coordinate system, whereas the coupled structural second order equation of motion for roll is solved by a fourth-order Runge-Kutta method. The body consists of a 3.5-diameter tangent ogive forebody with a 7.0-diameter long cylindrical afterbody extending aft of the nose-body junction to x/D = 10.5. We describe in detail the investigation of three angles of attack 20°, 40°, and 65°, at a Reynolds number of 30 000 (based on body diameter) and a Mach number of 0.2. Three distinct configurations are investigated as follows: a fixed body, a free-to-roll body with a weak torsion spring, and a free-to-roll body with a strong torsion spring. For each angle of attack the free-to-roll configuration portrays a distinct and different behavior pattern, including bi-stable limit-cycle oscillations. The bifurcation structure incorporates both large and small amplitude periodic roll oscillations where the latter lose their periodicity with increasing stiffness of the restraining spring culminating with distinct quasiperiodic oscillations. We note that removal of an applied upstream disturbance for a restrained body does not change the magnitude or complexity of the oscillations or of the flow patterns along the body. Depending on structure characteristics and flow conditions even a small rolling moment coefficient at the relatively low angle of attack of 20° may lead to large amplitude resonant roll oscillations.

  11. Hierarchical thermoelectrics : Crystal grain boundaries as scalable phonon scatterers

    NARCIS (Netherlands)

    Selli, Daniele; Boulfelfel, Salah Eddine; Schapotschnikow, PZ; Donadio, Davide; Leoni, Stefano

    2016-01-01

    Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier

  12. Electron mobility limited by optical phonons in wurtzite InGaN/GaN core-shell nanowires

    Science.gov (United States)

    Liu, W. H.; Qu, Y.; Ban, S. L.

    2017-09-01

    Based on the force-balance and energy-balance equations, the optical phonon-limited electron mobility in InxGa1-xN/GaN core-shell nanowires (CSNWs) is discussed. It is found that the electrons tend to distribute in the core of the CSNWs due to the strong quantum confinement. Thus, the scattering from first kind of the quasi-confined optical (CO) phonons is more important than that from the interface (IF) and propagating (PR) optical phonons. Ternary mixed crystal and size effects on the electron mobility are also investigated. The results show that the PR phonons exist while the IF phonons disappear when the indium composition x < 0.047, and vice versa. Accordingly, the total electron mobility μ first increases and then decreases with indium composition x, and reaches a peak value of approximately 3700 cm2/(V.s) when x = 0.047. The results also show that the mobility μ increases as increasing the core radius of CSNWs due to the weakened interaction between the electrons and CO phonons. The total electron mobility limited by the optical phonons exhibits an obvious enhancement as decreasing temperature or increasing line electron density. Our theoretical results are expected to be helpful to develop electronic devices based on CSNWs.

  13. Dephasing of LO-phonon-plasmon hybrid modes in n-type GaAs

    Science.gov (United States)

    Vallée, F.; Ganikhanov, F.; Bogani, F.

    1997-11-01

    The relaxation dynamics of coherent phononlike LO-phonon-plasmon hybrid modes is investigated in n-doped GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. Measurements performed for different crystal temperatures in the range 10-300 K as a function of the electron density injected by doping show a large reduction of the hybrid mode dephasing time compared to the bare LO-phonon one for densities larger than 1016 cm-3. The results are interpreted in terms of coherent decay of the LO-phonon-plasmon mixed mode in the weak-coupling regime and yield information on the plasmon and electron relaxation. The estimated average electron momentum relaxation times are smaller than those deduced from Hall mobility measurements, as expected from our theoretical model.

  14. Phonon spectrum of YBCO obtained by specific heat inversion method for real data

    CERN Document Server

    Tao Wen; Dai Xian Xi; Dai Ji Xin; Evenson, W E

    2003-01-01

    In this paper, the phonon spectrum of YBCO is obtained from experimental specific heat data by an exact inversion formula with a parameter for eliminating divergences. The results can be compared to those of neutron inelastic scattering, which can only be carried out in a few laboratories. Some key points of specific heat-phonon spectrum inversion (SPI) theory and a method of asymptotic behaviour control are discussed. An improved unique existence theorem is presented, and a universal function set for numerical calculation of SPI is calculated with high accuracy, which makes the inversion method applicable and convenient in practice. This is the first time specific heat-phonon SPI has been realized for a concrete system.

  15. Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling

    Science.gov (United States)

    Kim, Taehun; Leiner, Jonathan C.; Park, Kisoo; Oh, Joosung; Sim, Hasung; Iida, Kazuki; Kamazawa, Kazuya; Park, Je-Geun

    2018-05-01

    Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been studied via inelastic neutron scattering. A simple Heisenberg model with a single-ion anisotropy describes most features of the spin-wave dispersion curves. However, there is shown to be a renormalization of the magnon energies located at around 11 meV. Since both the magnon-magnon interaction and magnon-phonon coupling can affect the renormalization in a noncollinear magnet, we have accounted for both of these couplings by using a Heisenberg XXZ model with 1 /S expansions [1] and the Einstein site phonon model [13], respectively. This quantitative analysis leads to the conclusion that the renormalization effect primarily originates from the magnon-phonon coupling, while the spontaneous magnon decay due to the magnon-magnon interaction is suppressed by strong two-ion anisotropy.

  16. Phonon dynamics of the Sn/Ge(111)-(3 x 3) surface

    International Nuclear Information System (INIS)

    Farias, D.; Kaminski, W.; Lobo, J.; Ortega, J.; Hulpke, E.; Perez, R.; Flores, F.; Michel, E.G.

    2004-01-01

    We present a theoretical and experimental study on the phonon dynamics of the low-temperature Sn/Ge(111)-(3 x 3) structure. High-resolution helium atom scattering (HAS) data show that, besides the Rayleigh wave, there are three surface phonon branches with low dispersion related to the (3 x 3) surface phase. Their energies are approximately 6.5, 4, and 3meV at the Γ-bar point. In addition, we detect phonon peaks in the Q range 0.4-0.5A -1 at ∼2meV, which correspond to (3 x 3) folding of the Rayleigh wave. Ab initio DFT-GGA total energy calculations have been performed to determine the frequencies associated with the vertical displacements of the three Sn atoms in the unit cell. The values obtained are in good agreement with the experiment

  17. First-principles method for electron-phonon coupling and electron mobility

    DEFF Research Database (Denmark)

    Gunst, Tue; Markussen, Troels; Stokbro, Kurt

    2016-01-01

    We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...

  18. In rich In{sub 1-x}Ga{sub x}N: Composition dependence of longitudinal optical phonon energy

    Energy Technology Data Exchange (ETDEWEB)

    Tiras, E. [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, CO4 3SQ Colchester (United Kingdom); Faculty of Science, Department of Physics, Anadolu University, Yunus Emre Campus, 26470 Eskisehir (Turkey); Gunes, M.; Balkan, N. [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, CO4 3SQ Colchester (United Kingdom); Schaff, W.J. [Department of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853 (United States)

    2010-01-15

    The composition dependence of longitudinal optical (LO) phonon energies in undoped and Mg-doped In{sub 1-x}Ga{sub x}N samples are determined using Raman spectroscopy in the range of Ga fraction from x = 0 to x = 56%. The LO phonon energy varies from 73 meV for InN to 83 meV for In{sub 1-x}Ga{sub x}N with 56% Ga. Independent measurements of temperature dependent mobility at high temperatures where LO phonon scattering dominates the transport were also used to obtain the LO phonon energy for x = 0 and x = 20%. The results obtained from the two independent techniques compare extremely well. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  19. Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas

    2017-10-17

    We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving κInSe< κGaSe< κGaS. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, thermal transport is governed by in-plane vibrations in InSe, GaSe and GaS, similar to buckled monolayer materials such as silicene. Alloying of InSe, GaSe and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ~2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.

  20. Attenuation process of the longitudinal phonon mode in a TeO2 crystal in the 20-GHz range

    Science.gov (United States)

    Ohno, S.; Sonehara, T.; Tatsu, E.; Koreeda, A.; Saikan, S.

    2017-06-01

    We experimentally investigated the hypersonic attenuation process of a longitudinal mode (L-mode) sound wave in TeO2 from room temperature to a lower temperature using Brillouin scattering and impulsive stimulated thermal scattering (ISTS) measurements. For precise measurement of the Brillouin linewidth at low temperatures, whereby the mean free path of the phonon becomes longer than the sample length, it is indispensable that the phonon should propagate along the phonon-resonance direction. To figure out the suitable direction, we defined two indices characterizing a degree of phonon divergence and a purity of propagation direction. The best direction that we found from these indices is [110] direction in TeO2, and it was used to discuss the temperature and frequency dependences of Brillouin spectra. We extracted the temperature dependence of the attenuation rate of T4 from the modulated Brillouin spectra due to the phonon resonance below Debye temperature. The frequency dependence ω1 of the hypersonic attenuation was also estimated from the polarization dependence of the Brillouin linewidth. Theoretically, it predicted that the L-mode phonon attenuation at low temperatures in TeO2 is a result of Herring's process, which shows the attenuation behavior of ω2T3 . The ω1T4 dependence is not allowed in Herring's process but is allowed by the L +L →L process, which has been considered to be forbidden so far. We evaluated the thermal phonon lifetime using ISTS and established that it was finite even at 20 K, thereby allowing the L +L →L process. Therefore, we conclude that the L +L →L process dominates the attenuation of an L-mode phonon in TeO2 in the low-temperature region.

  1. Transition densities with electron scattering

    International Nuclear Information System (INIS)

    Heisenberg, J.

    1985-01-01

    This paper reviews the ground state and transition charge densities in nuclei via electron scattering. Using electrons as a spectroscopic tool in nuclear physics, these transition densities can be determined with high precision, also in the nuclear interior. These densities generally ask for a microscopic interpretation in terms of contributions from individual nucleons. The results for single particle transitions confirm the picture of particle-phonon coupling. (Auth.)

  2. The effect of n- and p-type doping on coherent phonons in GaN.

    Science.gov (United States)

    Ishioka, Kunie; Kato, Keiko; Ohashi, Naoki; Haneda, Hajime; Kitajima, Masahiro; Petek, Hrvoje

    2013-05-22

    The effect of doping on the carrier-phonon interaction in wurtzite GaN is investigated by pump-probe reflectivity measurements using 3.1 eV light in near resonance with the fundamental band gap of 3.39 eV. Coherent modulations of the reflectivity due to the E2 and A1(LO) modes, as well as the 2A1(LO) overtone are observed. Doping of acceptor and donor atoms enhances the dephasing of the polar A1(LO) phonon via coupling with plasmons, with the effect of donors being stronger. Doping also enhances the relative amplitude of the coherent A1(LO) phonon with respect to that of the high-frequency E2 phonon, though it does not affect the relative intensity in Raman spectroscopic measurements. We attribute this enhanced coherent amplitude to the transient depletion field screening (TDFS) excitation mechanism, which, in addition to impulsive stimulated Raman scattering (ISRS), contributes to the generation of coherent polar phonons even for sub-band gap excitation. Because the TDFS mechanism requires photoexcitation of carriers, we argue that the interband transition is made possible at a surface with photon energies below the bulk band gap through the Franz-Keldysh effect.

  3. Phonon-assisted damping of plasmons in three- and two-dimensional metals

    Science.gov (United States)

    Caruso, Fabio; Novko, Dino; Draxl, Claudia

    2018-05-01

    We investigate the effects of crystal lattice vibrations on the dispersion of plasmons. The loss function of the homogeneous electron gas (HEG) in two and three dimensions is evaluated numerically in the presence of electronic coupling to an optical phonon mode. Our calculations are based on many-body perturbation theory for the dielectric function as formulated by the Hedin-Baym equations in the Fan-Migdal approximation. The coupling to phonons broadens the spectral signatures of plasmons in the electron-energy loss spectrum (EELS) and it induces the decay of plasmons on timescales shorter than 1 ps. Our results further reveal the formation of a kink in the plasmon dispersion of the two-dimensional HEG, which marks the onset of plasmon-phonon scattering. Overall, these features constitute a fingerprint of plasmon-phonon coupling in EELS of simple metals. It is shown that these effects may be accounted for by resorting to a simplified treatment of the electron-phonon interaction which is amenable to first-principles calculations.

  4. Sensitivity Modulation of Upconverting Thermometry through Engineering Phonon Energy of a Matrix.

    Science.gov (United States)

    Suo, Hao; Guo, Chongfeng; Zheng, Jiming; Zhou, Bo; Ma, Chonggeng; Zhao, Xiaoqi; Li, Ting; Guo, Ping; Goldys, Ewa M

    2016-11-09

    Investigation of the unclear influential factors to thermal sensing capability is the only way to achieve highly sensitive thermometry, which is greatly needed to meet the growing demand for potential sensing applications. Here, the effect from the phonon energy of a matrix on the sensitivity of upconversion (UC) microthermometers is elaborately discussed using a controllable method. Uniform truncated octahedral YF 3 :Er 3+ /Yb 3+ microcrystals were prepared by a hydrothermal approach, and phase transformation from YF 3 to YOF and Y 2 O 3 with nearly unchanged morphology and size was successfully realized by controlling the annealing temperature. The phonon energies of blank matrixes were determined by FT-IR spectra and Raman scattering. Upon 980 nm excitation, phonon energy-dependent UC emitting color was finely tuned from green to yellow for three samples, and the mechanisms were proposed. Thermal sensing behaviors based on the TCLs ( 2 H 11/2 / 4 S 3/2 ) were evaluated, and the sensitivities gradually grew with the increase in the matrix's phonon energy. According to chemical bond theory and first-principle calculations, the most intrinsic factors associated with thermometric ability were qualitatively demonstrated through analyzing the inner relation between the phonon energy and bond covalency. The exciting results provide guiding insights into employing appropriate host materials with desired thermometric ability while offering the possibility of highly accurate measurement of temperature.

  5. Magnon and phonon dispersion, lifetime, and thermal conductivity of iron from spin-lattice dynamics simulations

    Science.gov (United States)

    Wu, Xufei; Liu, Zeyu; Luo, Tengfei

    2018-02-01

    In recent years, the fundamental physics of spin-lattice (e.g., magnon-phonon) interaction has attracted significant experimental and theoretical interests given its potential paradigm-shifting impacts in areas like spin-thermoelectrics, spin-caloritronics, and spintronics. Modelling studies of the transport of magnons and phonons in magnetic crystals are very rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model ferromagnetic crystalline iron, where the spin and lattice systems are coupled through the atomic position-dependent exchange function, and thus the interaction between magnons and phonons is naturally considered. We then present a method combining SLD simulations with spectral energy analysis to calculate the magnon and phonon harmonic (e.g., dispersion, specific heat, and group velocity) and anharmonic (e.g., scattering rate) properties, based on which their thermal conductivity values are calculated. This work represents an example of using SLD simulations to understand the transport properties involving coupled magnon and phonon dynamics.

  6. Electron-phonon coupling from finite differences

    Science.gov (United States)

    Monserrat, Bartomeu

    2018-02-01

    The interaction between electrons and phonons underlies multiple phenomena in physics, chemistry, and materials science. Examples include superconductivity, electronic transport, and the temperature dependence of optical spectra. A first-principles description of electron-phonon coupling enables the study of the above phenomena with accuracy and material specificity, which can be used to understand experiments and to predict novel effects and functionality. In this topical review, we describe the first-principles calculation of electron-phonon coupling from finite differences. The finite differences approach provides several advantages compared to alternative methods, in particular (i) any underlying electronic structure method can be used, and (ii) terms beyond the lowest order in the electron-phonon interaction can be readily incorporated. But these advantages are associated with a large computational cost that has until recently prevented the widespread adoption of this method. We describe some recent advances, including nondiagonal supercells and thermal lines, that resolve these difficulties, and make the calculation of electron-phonon coupling from finite differences a powerful tool. We review multiple applications of the calculation of electron-phonon coupling from finite differences, including the temperature dependence of optical spectra, superconductivity, charge transport, and the role of defects in semiconductors. These examples illustrate the advantages of finite differences, with cases where semilocal density functional theory is not appropriate for the calculation of electron-phonon coupling and many-body methods such as the GW approximation are required, as well as examples in which higher-order terms in the electron-phonon interaction are essential for an accurate description of the relevant phenomena. We expect that the finite difference approach will play a central role in future studies of the electron-phonon interaction.

  7. Lattice instability and soft phonons in single-crystal La/sub 2-//sub x/Sr/sub x/CuO4

    International Nuclear Information System (INIS)

    Boeni, P.; Axe, J.D.; Shirane, G.

    1988-01-01

    The dispersion of the low-lying phonon branches of several doped and undoped single crystals of La/sub 2-//sub x/Sr/sub x/CuO 4 have been investigated by using inelastic-neutron-scattering techniques. The zone-center modes are in good agreement with Raman measurements. The reported peaks in the phonon density of states show up at energies that correspond to extrema in the dispersion curves of the transverse and longitudinal acoustic branches near the zone boundary. The tetragonal-to-orthorhombic phase transition is caused by a softening of transverse-optic-phonon mode at the X point. The rotational nature of the soft mode leads to moderate weak electron-phonon coupling and the mode is unlikely to enhance significantly conventional phonon mediated superconductivity. We did not observe any evidence for the predicted breathing-mode instability near the zone boundary

  8. Effective electron mass and phonon modes in n-type hexagonal InN

    Science.gov (United States)

    Kasic, A.; Schubert, M.; Saito, Y.; Nanishi, Y.; Wagner, G.

    2002-03-01

    Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-μm-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m0. The resonantly excited zone center E1 (TO) phonon mode is observed at 477 cm-1 in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A1(LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm-1 constitutes a lower limit for the unscreened A1(LO) phonon frequency.

  9. Subterahertz Longitudinal Phonon Modes Propagating in a Lipid Bilayer Immersed in an Aqueous Medium

    Science.gov (United States)

    Zakhvataev, V. E.

    2018-04-01

    The properties of subterahertz longitudinal acoustic phonon modes in the hydrophobic region of a lipid bilayer immersed in a compressible viscous aqueous medium are investigated theoretically. An approximate expression is obtained for the Mandelstam-Brillouin components of the dynamic structure factor of a bilayer. The analysis is based on a generalized hydrodynamic model of the "two-dimensional lipid bilayer + three-dimensional fluid medium" system, as well as on known sharp estimates for the frequencies and lifetimes of long-wavelength longitudinal acoustic phonons in a free hydrated lipid bilayer and in water, obtained from inelastic X-ray scattering experiments and molecular dynamics simulations. It is shown that, for characteristic values of the parameters of the membrane system, subterahertz longitudinal phonon-like excitations in the hydrophobic part of the bilayer are underdamped. In this case, the contribution of the viscous flow of the aqueous medium to the damping of a longitudinal membrane mode is small compared with the contribution of the lipid bilayer. Quantitative estimates of the damping ratio agree well with the experimental results for the vibration mode of the enzyme lysozyme in aqueous solution [1]. It is also shown that a coupling between longitudinal phonon modes of the bilayer and relaxation processes in its fluid environment gives rise to an additional peak in the scattering spectrum, which corresponds to a non-propagating mode.

  10. One-dimensional hypersonic phononic crystals.

    Science.gov (United States)

    Gomopoulos, N; Maschke, D; Koh, C Y; Thomas, E L; Tremel, W; Butt, H-J; Fytas, G

    2010-03-10

    We report experimental observation of a normal incidence phononic band gap in one-dimensional periodic (SiO(2)/poly(methyl methacrylate)) multilayer film at gigahertz frequencies using Brillouin spectroscopy. The band gap to midgap ratio of 0.30 occurs for elastic wave propagation along the periodicity direction, whereas for inplane propagation the system displays an effective medium behavior. The phononic properties are well captured by numerical simulations. The porosity in the silica layers presents a structural scaffold for the introduction of secondary active media for potential coupling between phonons and other excitations, such as photons and electrons.

  11. Electron–phonon superconductivity in YIn3

    International Nuclear Information System (INIS)

    Billington, D; Llewellyn-Jones, T M; Maroso, G; Dugdale, S B

    2013-01-01

    First-principles calculations of the electron–phonon coupling were performed on the cubic intermetallic compound YIn 3 . The electron–phonon coupling constant was found to be λ ep = 0.42. Using the Allen–Dynes formula with a Coulomb pseudopotential of μ* = 0.10, a T c of approximately 0.77 K is obtained which is reasonably consistent with the experimentally observed temperature (between 0.8 and 1.1 K). The results indicate that conventional electron–phonon coupling is capable of producing the superconductivity in this compound. (paper)

  12. Electron-phonon superconductivity in YIn3

    Science.gov (United States)

    Billington, D.; Llewellyn-Jones, T. M.; Maroso, G.; Dugdale, S. B.

    2013-08-01

    First-principles calculations of the electron-phonon coupling were performed on the cubic intermetallic compound YIn3. The electron-phonon coupling constant was found to be λep = 0.42. Using the Allen-Dynes formula with a Coulomb pseudopotential of μ* = 0.10, a Tc of approximately 0.77 K is obtained which is reasonably consistent with the experimentally observed temperature (between 0.8 and 1.1 K). The results indicate that conventional electron-phonon coupling is capable of producing the superconductivity in this compound.

  13. Scattering of Neutrons by an Anharmonic Crystal

    Energy Technology Data Exchange (ETDEWEB)

    Hoegberg, T; Bohlin, L; Ebbsjoe, I

    1967-04-15

    Numerical calculations have been performed for the anharmonic effects in neutron scattering. The phonon frequency widths and shifts have been calculated as a function of neutron frequency at different wave numbers and temperatures for a potential with central symmetry and for a face-centered cubic lattice.

  14. Characterization of Materials by Raman Scattering

    Science.gov (United States)

    Kozielski, M.

    2007-03-01

    The paper reports on the use of phonon spectra obtained with the Raman spectroscopy for characterization of different materials. The Raman scattering spectra obtained for zinc selenide crystals, mixed crystals zinc selenide admixtured with magnesium or beryllium, oxide crystals including strontium lanthanum gallate, molecular crystals of triammonium hydrogen diseleniate and a homologous series of polyoxyethylene glycols are analysed.

  15. NEUTRON-SCATTERING STUDY OF DCN

    DEFF Research Database (Denmark)

    Mackenzie, Gordon A.; Pawley, G. S.

    1979-01-01

    Phonons in deuterium cyanide have been measured by neutron coherent inelastic scattering. The main subject of study was the transverse acoustic mode in the (110) direction polarised along (110) which is associated with the first-order structural phase transition at 160K. Measurements have shown...

  16. First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures

    International Nuclear Information System (INIS)

    Mazumder, Sandip; Li, Ju

    2010-01-01

    The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion

  17. Inelastic neutron scattering and lattice dynamics of minerals

    Indian Academy of Sciences (India)

    We review current research on minerals using inelastic neutron scattering and lattice dynamics calculations. Inelastic neutron scattering studies in combination with first principles and atomistic calculations provide a detailed understanding of the phonon dispersion relations, density of states and their manifestations in ...

  18. Inelastic neutron scattering and lattice dynamics of minerals

    Indian Academy of Sciences (India)

    Abstract. We review current research on minerals using inelastic neutron scattering and lattice dynamics calculations. Inelastic neutron scattering studies in combination with first principles and atomistic calculations provide a detailed understanding of the phonon dispersion relations, density of states and their ...

  19. Lattice and Molecular Vibrations in Single Crystal I2 at 77 K by Inelastic Neutron Scattering

    DEFF Research Database (Denmark)

    Smith, H. G.; Nielsen, Mourits; Clark, C. B.

    1975-01-01

    Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the other...

  20. Topological chiral phonons in center-stacked bilayer triangle lattices

    Science.gov (United States)

    Xu, Xifang; Zhang, Wei; Wang, Jiaojiao; Zhang, Lifa

    2018-06-01

    Since chiral phonons were found in an asymmetric two-dimensional hexagonal lattice, there has been growing interest in the study of phonon chirality, which were experimentally verified very recently in monolayer tungsten diselenide (2018 Science 359 579). In this work, we find chiral phonons with nontrivial topology in center-stacked bilayer triangle lattices. At the Brillouin-zone corners, (), circularly polarized phonons and nonzero phonon Berry curvature are observed. Moreover, we find that the phonon chirality remain robust with changing sublattice mass ratio and interlayer coupling. The chiral phonons at the valleys are demonstrated in doubler-layer sodium chloride along the [1 1 1] direction. We believe that the findings on topological chiral phonons in triangle lattices will give guidance in the study of chiral phonons in real materials and promote the phononic applications.

  1. [Inelastic electron scattering from surfaces

    International Nuclear Information System (INIS)

    1993-01-01

    This program uses ab-initio and multiple scattering to study surface dynamical processes; high-resolution electron-energy loss spectroscopy is used in particular. Off-specular excitation cross sections are much larger if electron energies are in the LEED range (50--300 eV). The analyses have been extended to surfaces of ordered alloys. Phonon eigenvectors and eigenfrequencies were used as inputs to electron-energy-loss multiple scattering cross section calculations. Work on low-energy electron and positron holography is mentioned

  2. Electromagnetic decay of two-phonon states

    International Nuclear Information System (INIS)

    Catara, F.; Chomaz, Ph.; Van Giai, N.; Paris-11 Univ., 91 - Orsay

    1991-01-01

    The electromagnetic decay of two-phonon states corresponding to the multi-excitation of giant resonances is studied. The calculations are performed within a boson expansion approach and the elementary modes are constructed in random phase approximation (RPA). The rates for direct transition of two-phonon states to the ground state turn out to be not negligibly smaller than those from the (single) giant resonances. The former transitions are accompanied by a γ-ray whose energy is equal to the sum of the two phonon energies. Thus the detection of such high energy γ-rays could provide a signature of the excitation of two-phonon states. (author) 9 refs., 3 tabs

  3. Toward stimulated interaction of surface phonon polaritons

    Energy Technology Data Exchange (ETDEWEB)

    Kong, B. D.; Trew, R. J.; Kim, K. W., E-mail: kwk@ncsu.edu [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695-7911 (United States)

    2013-12-21

    Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons.

  4. Phonon limited electronic transport in Pb

    Science.gov (United States)

    Rittweger, F.; Hinsche, N. F.; Mertig, I.

    2017-09-01

    We present a fully ab initio based scheme to compute electronic transport properties, i.e. the electrical conductivity σ and thermopower S, in the presence of electron-phonon interaction. We explicitly investigate the \

  5. Influence of phonons on semiconductor quantum emission

    Energy Technology Data Exchange (ETDEWEB)

    Feldtmann, Thomas

    2009-07-06

    A microscopic theory of interacting charge carriers, lattice vibrations, and light modes in semiconductor systems is presented. The theory is applied to study quantum dots and phonon-assisted luminescence in bulk semiconductors and heterostructures. (orig.)

  6. Theoretical Aspects of Phonon Dispersion Curves for Metals

    International Nuclear Information System (INIS)

    Cochran, W.

    1965-01-01

    Reasonably complete knowledge of the phonon dispersion curves for at least a dozen metallic elements and intermetallic compounds has now been obtained from neutron inelastic scattering experiments. The results have one feature in common: when analysed in terms of interatomic force constants they reveal the presence of comparatively long-range forces extending over several atomic spacings. The results for lead are particularly interesting; it did not prove possible to fit them by a force-constant model, but the dispersion curves for wave vectors in symmetry directions when analysed in terms of force constants between planes of atoms showed an oscillatory interatomic potential extending over distances of more than 20Å. This review is concerned with recent theoretical work which has a bearing on the calculation of phonon dispersion curves for metals and the explanation of the long range of the interatomic potential. The best hope at present for a general treatment of atomic interaction in metals appears to lie in the ''method of neutral pseudo-atoms'', (a description recently coined by Ziman). This approximate theory is outlined and its relevance to Kohn anomalies in phonon dispersion curves is discussed. Experimental data for sodium is consistent with the theory, and the interatomic potential in sodium varies periodically in a distance π/k F , where fik F is the Fermi momentum, as has already been demonstrated by Koenig in a different way. More exact calculations have been made for sodium by Toya and by Sham. The relationship between the different methods and other work of a more general character such as that of Harrison are discussed. (author) [fr

  7. Dynamical Cooper pairing in non-equilibrium electron-phonon systems

    Energy Technology Data Exchange (ETDEWEB)

    Knap, Michael [Technical University of Munich (Germany); Harvard University (United States); Babadi, Mehrtash; Refael, Gil [Caltech (United States); Martin, Ivar [Argonne National Laboratory (United States); Demler, Eugene [Harvard University (United States)

    2016-07-01

    Ultrafast laser pulses have been used to manipulate complex quantum materials and to induce dynamical phase transitions. One of the most striking examples is the transient enhancement of superconductivity in several classes of materials upon irradiating them with high intensity pulses of terahertz light. Motivated by these experiments we analyze the Cooper pairing instabilities in non-equilibrium electron-phonon systems. We demonstrate that the light induced non-equilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We analyze the competition between these effects and show that in a broad range of parameters the dynamic enhancement of Cooper pair formation dominates over the increase in the scattering rate. This opens the possibility of transient light induced superconductivity at temperatures that are considerably higher than the equilibrium transition temperatures. Our results pave new pathways for engineering high-temperature light-induced superconducting states.

  8. Phonon dispersion relations in PrBa2Cu3O6+x (x approximate to 0.2)

    DEFF Research Database (Denmark)

    Gardiner, C.H.; Boothroyd, A.T.; Larsen, B.H.

    2004-01-01

    We report measurements of the phonon dispersion relations in nonsuperconducting, oxygen-deficient PrBa2Cu3O6+x (xapproximate to0.2) by inelastic neutron scattering. The data are compared with a model of the lattice dynamics based on a common interatomic potential. Good agreement is achieved for all...

  9. Proposed Quenching of Phonon-Induced Processes in Photoexcited Quantum Dots due to Electron-Hole Asymmetries

    DEFF Research Database (Denmark)

    Nysteen, Anders; Nielsen, Per Kær; Mørk, Jesper

    2013-01-01

    by photoluminescence excitation spectroscopy of a single quantum dot. We also investigate the implications for cavity QED, i.e., a coupled quantum dot-cavity system, and demonstrate that the phonon scattering may be strongly quenched. The quenching is explained by a balancing between the deformation potential...

  10. Waveguiding in supported phononic crystal plates

    International Nuclear Information System (INIS)

    Vasseur, J; Hladky-Hennion, A-C; Deymier, P; Djafari-Rouhani, B; Duval, F; Dubus, B; Pennec, Y

    2007-01-01

    We investigate, with the help of the finite element method, the existence of absolute band gaps in the band structure of a free-standing phononic crystal plate and of a phononic crystal slab deposited on a substrate. The two-dimensional phononic crystal is constituted by a square array of holes drilled in an active piezoelectric (PZT5A or AlN) matrix. For both matrix materials, an absolute band gap occurs in the band structure of the free-standing plate provided the thickness of the plate is on the order of magnitude of the lattice parameter. When the plate is deposited on a Si substrate, the absolute band gap still remains when the matrix of the phononic crystal is made of PZT5A. The AlN phononic crystal plate losses its gap when supported by the Si substrate. In the case of the PZT5A matrix, we also study the possibility of localized modes associated with a linear defect created by removing one row of air holes in the deposited phononic crystal plate

  11. Theory of electron-phonon-dislon interacting system—toward a quantized theory of dislocations

    Science.gov (United States)

    Li, Mingda; Tsurimaki, Yoichiro; Meng, Qingping; Andrejevic, Nina; Zhu, Yimei; Mahan, Gerald D.; Chen, Gang

    2018-02-01

    We provide a comprehensive theoretical framework to study how crystal dislocations influence the functional properties of materials, based on the idea of a quantized dislocation, namely a ‘dislon’. In contrast to previous work on dislons which focused on exotic phenomenology, here we focus on their theoretical structure and computational power. We first provide a pedagogical introduction that explains the necessity and benefits of taking the dislon approach and why the dislon Hamiltonian takes its current form. Then, we study the electron-dislocation and phonon-dislocation scattering problems using the dislon formalism. Both the effective electron and phonon theories are derived, from which the role of dislocations on electronic and phononic transport properties is computed. Compared with traditional dislocation scattering studies, which are intrinsically single-particle, low-order perturbation and classical quenched defect in nature, the dislon theory not only allows easy incorporation of quantum many-body effects such as electron correlation, electron-phonon interaction, and higher-order scattering events, but also allows proper consideration of the dislocation’s long-range strain field and dynamic aspects on equal footing for arbitrary types of straight-line dislocations. This means that instead of developing individual models for specific dislocation scattering problems, the dislon theory allows for the calculation of electronic structure and electrical transport, thermal transport, optical and superconducting properties, etc, under one unified theory. Furthermore, the dislon theory has another advantage over empirical models in that it requires no fitting parameters. The dislon theory could serve as a major computational tool to understand the role of dislocations on multiple materials’ functional properties at an unprecedented level of clarity, and may have wide applications in dislocated energy materials.

  12. The temperature dependence of the phononic band gap of NaI

    Czech Academy of Sciences Publication Activity Database

    Kempa, Martin; Ondrejkovič, Petr; Bourges, P.; Ollivier, J.; Rols, S.; Kulda, J.; Margueron, S.; Hlinka, Jiří

    2013-01-01

    Roč. 25, č. 5 (2013), "055403-1"-"055403-4" ISSN 0953-8984 R&D Projects: GA ČR GPP204/11/P404 Grant - others:GA MŠk(CZ) LG11024 Institutional support: RVO:68378271 Keywords : alkali halides * phonon density of states * anharmonic lattice modes * inelastic neutron scattering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.223, year: 2013 http://stacks.iop.org/JPhysCM/25/055403

  13. Light Scattering in Solid IX

    CERN Document Server

    Cardona, Manuel

    2007-01-01

    This is the ninth volume of a well-established series in which expert practitioners discuss topical aspects of light scattering in solids. It reviews recent developments concerning mainly semiconductor nanostructures and inelastic x-ray scattering, including both coherent time-domain and spontaneous scattering studies. In the past few years, light scattering has become one of the most important research and characterization methods for studying carbon nanotubes and semiconducting quantum dots, and a crucial tool for exploring the coupled exciton--photon system in semiconductor cavities. Among the novel techniques discussed in this volume are pump--probe ultrafast measurements and those which use synchrotron radiation as light source. The book addresses improvements in the intensity, beam quality and time synchronization of modern synchrotron sources, which made it possible to measure the phonon dispersion in very small samples and to determine electronic energy bands as well as enabling real-time observations...

  14. Dynamical narrowing of the Rayleigh scattering ring from a semiconductor microcavity

    DEFF Research Database (Denmark)

    Langbein, W.; Hvam, Jørn Märcher

    2001-01-01

    In resonant secondary emission of light (SE), scattering by static disorder leads to coherent resonant Rayleigh scattering (RRS), while the scattering with other quasi-particles (e.g. phonons) leads to an incoherent emission called photoluminescence (PL). For a bare quantum well (QW) the SE does...

  15. Scattering of 20Ne atoms from the (001) face of LiF

    International Nuclear Information System (INIS)

    Semerad, E.; Hoerl, E.M.

    1983-01-01

    An apparatus for measurements of inelastic scattering processes of gas atoms from crystal surfaces is described. Scattering experiments with Neon atoms of thermal energy on the (001) LiF surface in the azimuth are discussed. Inelastic scattering shows large contributions of single phonon interactions as well as of modes originating from the bulk bands. (Author)

  16. Electron-phonon heat exchange in quasi-two-dimensional nanolayers

    Science.gov (United States)

    Anghel, Dragos-Victor; Cojocaru, Sergiu

    2017-12-01

    We study the heat power P transferred between electrons and phonons in thin metallic films deposited on free-standing dielectric membranes. The temperature range is typically below 1 K, such that the wavelengths of the excited phonon modes in the system is large enough so that the picture of a quasi-two-dimensional phonon gas is applicable. Moreover, due to the quantization of the components of the electron wavevectors perpendicular to the metal film's surface, the electrons spectrum forms also quasi two-dimensional sub-bands, as in a quantum well (QW). We describe in detail the contribution to the electron-phonon energy exchange of different electron scattering channels, as well as of different types of phonon modes. We find that heat flux oscillates strongly with thickness of the film d while having a much smoother variation with temperature (Te for the electrons temperature and Tph for the phonons temperature), so that one obtains a ridge-like landscape in the two coordinates, (d, Te) or (d, Tph), with crests and valleys aligned roughly parallel to the temperature axis. For the valley regions we find P ∝ Te3.5 - Tph3.5. From valley to crest, P increases by more than one order of magnitude and on the crests P cannot be represented by a simple power law. The strong dependence of P on d is indicative of the formation of the QW state and can be useful in controlling the heat transfer between electrons and crystal lattice in nano-electronic devices. Nevertheless, due to the small value of the Fermi wavelength in metals, the surface imperfections of the metallic films can reduce the magnitude of the oscillations of P vs. d, so this effect might be easier to observe experimentally in doped semiconductors.

  17. Thermal Properties and Phonon Spectral Characterization of Synthetic Boron Phosphide for High Thermal Conductivity Applications.

    Science.gov (United States)

    Kang, Joon Sang; Wu, Huan; Hu, Yongjie

    2017-12-13

    Heat dissipation is an increasingly critical technological challenge in modern electronics and photonics as devices continue to shrink to the nanoscale. To address this challenge, high thermal conductivity materials that can efficiently dissipate heat from hot spots and improve device performance are urgently needed. Boron phosphide is a unique high thermal conductivity and refractory material with exceptional chemical inertness, hardness, and high thermal stability, which holds high promises for many practical applications. So far, however, challenges with boron phosphide synthesis and characterization have hampered the understanding of its fundamental properties and potential applications. Here, we describe a systematic thermal transport study based on a synergistic synthesis-experimental-modeling approach: we have chemically synthesized high-quality boron phosphide single crystals and measured their thermal conductivity as a record-high 460 W/mK at room temperature. Through nanoscale ballistic transport, we have, for the first time, mapped the phonon spectra of boron phosphide and experimentally measured its phonon mean free-path spectra with consideration of both natural and isotope-pure abundances. We have also measured the temperature- and size-dependent thermal conductivity and performed corresponding calculations by solving the three-dimensional and spectral-dependent phonon Boltzmann transport equation using the variance-reduced Monte Carlo method. The experimental results are in good agreement with that predicted by multiscale simulations and density functional theory, which together quantify the heat conduction through the phonon mode dependent scattering process. Our finding underscores the promise of boron phosphide as a high thermal conductivity material for a wide range of applications, including thermal management and energy regulation, and provides a detailed, microscopic-level understanding of the phonon spectra and thermal transport mechanisms of

  18. Cryogenic phonon-mediated particle detectors for dark matter searches and neutrino physics

    International Nuclear Information System (INIS)

    Lee, A.T.J.

    1993-01-01

    This work describes the development of cryogenic phonon-mediated particle detectors for dark matter searches and neutrino detection. The detectors described in this work employ transition-edge sensors, which consist of a meander pattern of thin-film superconductor on a silicon substrate. When phonons from a particle interaction in the crystal impinge on the sensor in sufficient density, sections of the line are driven normal and provide a measurable resistance. A large fraction of the thesis describes work to fully characterize the phonon flux from particle interactions. In one set of experiments, ∼25% of the phonon energy from 59.54 keV gamma-ray events was found to propagate open-quotes ballisticallyclose quotes (i.e., with little or no scattering) across a 300 μm thick crystal of silicon. Gamma-rays produce electron recoils in silicon whereas with dark matter and neutrino experiments nuclear recoils are also of interest. Two experiments were done to measure the ballistic component that arises from neutron events, which interact via nuclear recoil. Measurements indicate that the fraction of energy that is ballistic is ∼50% greater for nuclear recoils than for electron recoils. Two novel detectors were fabricated and tested in an attempt to improve the sensitivity of the detectors. In the first detector, relatively large Al pads were linked by 2 μm wide Ti lines in a meander pattern. Phonons impinging on the Al pads create quasiparticles which diffuse in the Al pad until they are trapped in the lower gap Tl links. The sensitivity of the detector was found to be increased by this open-quotes funnelingclose quotes action. A second detector was built that incorporates 0.25 μm wide lines defined by direct electron-beam exposure of the photoresist. If the superconducting line is sufficiently narrow, single phonons are capable of driving sections normal which should improve the sensitivity and linearity of the detector

  19. Acoustic cloaking by a near-zero-index phononic crystal

    KAUST Repository

    Zheng, Li-Yang

    2014-04-21

    Zero-refractive-index materials may lead to promising applications in various fields. Here, we design and fabricate a near Zero-Refractive-Index (ZRI) material using a phononic crystal (PC) composed of a square array of densely packed square iron rods in air. The dispersion relation exhibits a nearly flat band across the Brillouin zone at the reduced frequency f  = 0.5443c/a, which is due to Fabry-Perot (FP) resonance. By using a retrieval method, we find that both the effective mass density and the reciprocal of the effective bulk modulus are close to zero at frequencies near the flat band. We also propose an equivalent tube network model to explain the mechanisms of the near ZRI effect. This FP-resonance-induced near ZRI material offers intriguing wave manipulation properties. We demonstrate both numerically and experimentally its ability to shield a scattering obstacle and guide acoustic waves through a bent structure.

  20. Engineering the hypersonic phononic band gap of hybrid Bragg stacks.

    Science.gov (United States)

    Schneider, Dirk; Liaqat, Faroha; El Boudouti, El Houssaine; El Hassouani, Youssef; Djafari-Rouhani, Bahram; Tremel, Wolfgang; Butt, Hans-Jürgen; Fytas, George

    2012-06-13

    We report on the full control of phononic band diagrams for periodic stacks of alternating layers of poly(methyl methacrylate) and porous silica combining Brillouin light scattering spectroscopy and theoretical calculations. These structures exhibit large and robust on-axis band gaps determined by the longitudinal sound velocities, densities, and spacing ratio. A facile tuning of the gap width is realized at oblique incidence utilizing the vector nature of the elastic wave propagation. Off-axis propagation involves sagittal waves in the individual layers, allowing access to shear moduli at nanoscale. The full theoretical description discerns the most important features of the hypersonic one-dimensional crystals forward to a detailed understanding, a precondition to engineer dispersion relations in such structures.

  1. Multi-channel unidirectional transmission of phononic crystal heterojunctions

    Science.gov (United States)

    Xu, Zhenlong; Tong, Jie; Wu, Fugen

    2018-02-01

    Two square steel columns are arranged in air to form two-dimensional square lattice phononic crystals (PNCs). Two PNCs can be combined into a non-orthogonal 45∘ heterojunction when the difference in the directional band gaps of the two PNC types is utilized. The finite element method is used to calculate the acoustic band structure, the heterogeneous junction transmission characteristics, acoustic field distribution, and many others. Results show that a non-orthogonal PNC heterojunction can produce a multi-channel unidirectional transmission of acoustic waves. With the square scatterer rotated, the heterojunction can select a frequency band for unidirectional transmission performance. This capability is particularly useful for constructing acoustic diodes with wide-bands and high-efficiency unidirectional transmission characteristics.

  2. Phonon instabilities in NaNbO3

    International Nuclear Information System (INIS)

    Mishra, S.K.; Gupta, M.K.; Mittal, R.; Chaplot, S.L.

    2012-01-01

    NaNbO 3 has antiferroelectric structure at room temperature and exhibits unusual complex sequence of temperature and pressure driven structural phase transitions. Temperature dependent measurements from 17 to 1075 K revealed that NaNbO 3 undergoes a series of phase transitions, ranging from non-polar antiferrodistortive to ferroelectric and antiferroelectric in nature. High pressure measurements carried out up to 11 GPa at ambient temperature indicate transition from antiferroelectric to paraelectric phase. These transitions are characterized by appearance and disappearance of superlattice reflections in the powder diffraction patterns. Numerous Raman and infrared measurements are also reported in literature to gain reliable insights into, and deeper understanding of phase transition behavior. The optical measurements are limited to the Brillouin zone centre, which does not give a complete picture of the dynamics. Inelastic neutron scattering and ab-initio calculations were carried out to understand the phase transitions behaviour and their relation to the phonon spectra

  3. Study of hot carrier relaxation in quantum wells by subpicosecond Raman scattering

    International Nuclear Information System (INIS)

    Kim, Dai-sik; Yu, P.Y.

    1990-03-01

    Relaxation of hot carriers excited by subpicosecond laser pulses has been studied by Raman scattering in GaAs/AlAs multiple quantum wells with well widths varying between 100 and 1000 Angstrom. The hot phonon population observed by Raman scattering is found to decrease with the well width despite the fact that the hot electron temperature remains constant. The results are explained in terms of confinement of both electrons and optical phonons in quantum wells

  4. A unified model for diffractive and inelastic scattering of a light atom from a solid surface

    International Nuclear Information System (INIS)

    Adams, J.E.; Miller, W.H.

    1979-01-01

    A simple model for gas-surface scattering is presented which permits treatment of inelastic effects in diffractive systems. The model, founded on an impulsive collision assumption, leads to an intensity distribution which is just a sum of contributions from n-phonon scattering events. Furthemore, by using a convenient form for the repulsive interaction potential, analytic expressions are obtained for the elastic and one-phonon intensities that are in qualitative agreement with experimental results. (Auth.)

  5. Phonon optimized interatomic potential for aluminum

    Directory of Open Access Journals (Sweden)

    Murali Gopal Muraleedharan

    2017-12-01

    Full Text Available We address the problem of generating a phonon optimized interatomic potential (POP for aluminum. The POP methodology, which has already been shown to work for semiconductors such as silicon and germanium, uses an evolutionary strategy based on a genetic algorithm (GA to optimize the free parameters in an empirical interatomic potential (EIP. For aluminum, we used the Vashishta functional form. The training data set was generated ab initio, consisting of forces, energy vs. volume, stresses, and harmonic and cubic force constants obtained from density functional theory (DFT calculations. Existing potentials for aluminum, such as the embedded atom method (EAM and charge-optimized many-body (COMB3 potential, show larger errors when the EIP forces are compared with those predicted by DFT, and thus they are not particularly well suited for reproducing phonon properties. Using a comprehensive Vashishta functional form, which involves short and long-ranged interactions, as well as three-body terms, we were able to better capture interactions that reproduce phonon properties accurately. Furthermore, the Vashishta potential is flexible enough to be extended to Al2O3 and the interface between Al-Al2O3, which is technologically important for combustion of solid Al nano powders. The POP developed here is tested for accuracy by comparing phonon thermal conductivity accumulation plots, density of states, and dispersion relations with DFT results. It is shown to perform well in molecular dynamics (MD simulations as well, where the phonon thermal conductivity is calculated via the Green-Kubo relation. The results are within 10% of the values obtained by solving the Boltzmann transport equation (BTE, employing Fermi’s Golden Rule to predict the phonon-phonon relaxation times.

  6. Phonon optimized interatomic potential for aluminum

    Science.gov (United States)

    Muraleedharan, Murali Gopal; Rohskopf, Andrew; Yang, Vigor; Henry, Asegun

    2017-12-01

    We address the problem of generating a phonon optimized interatomic potential (POP) for aluminum. The POP methodology, which has already been shown to work for semiconductors such as silicon and germanium, uses an evolutionary strategy based on a genetic algorithm (GA) to optimize the free parameters in an empirical interatomic potential (EIP). For aluminum, we used the Vashishta functional form. The training data set was generated ab initio, consisting of forces, energy vs. volume, stresses, and harmonic and cubic force constants obtained from density functional theory (DFT) calculations. Existing potentials for aluminum, such as the embedded atom method (EAM) and charge-optimized many-body (COMB3) potential, show larger errors when the EIP forces are compared with those predicted by DFT, and thus they are not particularly well suited for reproducing phonon properties. Using a comprehensive Vashishta functional form, which involves short and long-ranged interactions, as well as three-body terms, we were able to better capture interactions that reproduce phonon properties accurately. Furthermore, the Vashishta potential is flexible enough to be extended to Al2O3 and the interface between Al-Al2O3, which is technologically important for combustion of solid Al nano powders. The POP developed here is tested for accuracy by comparing phonon thermal conductivity accumulation plots, density of states, and dispersion relations with DFT results. It is shown to perform well in molecular dynamics (MD) simulations as well, where the phonon thermal conductivity is calculated via the Green-Kubo relation. The results are within 10% of the values obtained by solving the Boltzmann transport equation (BTE), employing Fermi's Golden Rule to predict the phonon-phonon relaxation times.

  7. Incoherent imaging using dynamically scattered coherent electrons

    International Nuclear Information System (INIS)

    Nellist, P.D.; Pennycook, S.J.

    1999-01-01

    We use a Bloch wave approach to show that, even for coherent dynamical scattering from a stationary lattice with no absorption, annular dark-field imaging in a scanning transmission electron microscope gives a direct incoherent structure image of the atomic-column positions of a zone-axis-aligned crystal. Although many Bloch waves may be excited by the probe, the detector provides a filtering effect so that the 1s-type bound states are found to dominate the image contrast for typical experimental conditions. We also find that the column intensity is related to the transverse kinetic energy of the 1s states, which gives atomic number, Z, contrast. The additional effects of phonon scattering are discussed, in particular the reasons why phonon scattering is not a prerequisite for transverse incoherence. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  8. Ionizing particle detection based on phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Aly, Arafa H., E-mail: arafa16@yahoo.com, E-mail: arafa.hussien@science.bsu.edu.eg; Mehaney, Ahmed; Eissa, Mostafa F. [Physics Department, Faculty of Science, Beni-Suef University, Beni-Suef (Egypt)

    2015-08-14

    Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.

  9. Phonon dispersion relations in PrBa2Cu3O6+x (x≅0.2)

    International Nuclear Information System (INIS)

    Gardiner, C.H.; Boothroyd, A.T.; Larsen, B.H.; Reichardt, W.; Zhokhov, A.A.; Andersen, N.H.; Lister, S.J.S.; Wildes, A.R.

    2004-01-01

    We report measurements of the phonon dispersion relations in nonsuperconducting, oxygen-deficient PrBa 2 Cu 3 O 6+x (x≅0.2) by inelastic neutron scattering. The data are compared with a model of the lattice dynamics based on a common interatomic potential. Good agreement is achieved for all but two phonon branches, which are significantly softer than predicted. These modes are found to arise predominantly from motion of the oxygen ions in the CuO 2 planes. Analogous modes in YBa 2 Cu 3 O 6 are well described by the common interatomic potential model

  10. Phonon renormalization at small q values in the high-temperature phase of CsCuCl sub 3

    CERN Document Server

    Foerster, U; Schotte, U; Stuhr, U

    1997-01-01

    The hexagonal perovskite CsCuCl sub 3 exhibits a structural phase transition from a dynamically disordered high-temperature phase to an ordered low-temperature phase due to the cooperative Jahn-Teller effect. The lattice dynamics of the high-temperature phase has been studied by inelastic neutron scattering experiments. The investigations concentrated on small wave vectors q, where for the first time renormalized phonons at q=0.02-0.05 A sup - sup 1 could be observed. The measurements confirm the predictions of a theoretical approach based on the coupling between dynamic reorientation processes and acoustic lattice waves (pseudo-spin phonon coupling). (author)

  11. Quantifying resistances across nanoscale low- and high-angle interspherulite boundaries in solution-processed organic semiconductor thin films.

    Science.gov (United States)

    Lee, Stephanie S; Mativetsky, Jeffrey M; Loth, Marsha A; Anthony, John E; Loo, Yueh-Lin

    2012-11-27

    The nanoscale boundaries formed when neighboring spherulites impinge in polycrystalline, solution-processed organic semiconductor thin films act as bottlenecks to charge transport, significantly reducing organic thin-film transistor mobility in devices comprising spherulitic thin films as the active layers. These interspherulite boundaries (ISBs) are structurally complex, with varying angles of molecular orientation mismatch along their lengths. We have successfully engineered exclusively low- and exclusively high-angle ISBs to elucidate how the angle of molecular orientation mismatch at ISBs affects their resistivities in triethylsilylethynyl anthradithiophene thin films. Conductive AFM and four-probe measurements reveal that current flow is unaffected by the presence of low-angle ISBs, whereas current flow is significantly disrupted across high-angle ISBs. In the latter case, we estimate the resistivity to be 22 MΩμm(2)/width of the ISB, only less than a quarter of the resistivity measured across low-angle grain boundaries in thermally evaporated sexithiophene thin films. This discrepancy in resistivities across ISBs in solution-processed organic semiconductor thin films and grain boundaries in thermally evaporated organic semiconductor thin films likely arises from inherent differences in the nature of film formation in the respective systems.

  12. Acoustic modes of the phonon dispersion relation of NbD/sub x/ alloys

    International Nuclear Information System (INIS)

    Rowe, J.M.; Vagelatos, N.; Rush, J.J.; Flotow, H.E.

    1975-01-01

    The acoustic modes of the phonon dispersion relation in Nb, NbD 0 . 15 , and NbD 0 . 45 were measured at 473 0 K for phonons with wave vectors along the [100], [110], and [111] axes by coherent neutron scattering. The observed neutron groups for both alloys were well defined, with little or no apparent broadening. Results are compared to similar data for Nb--Mo alloys and with previous lattice-dynamics results for PdD 0 . 63 . This comparison shows that despite differences in detail, the general features of the dispersion relations of NbD/sub x/ and Nb--Mo are similar after allowing for the differences in lattice parameters for the two alloys. The measured dispersion curves and derived phonon frequency distributions for the Nb--D alloys are quite different from the analogous results for PdD 0 . 63 in that the average acoustic phonon frequencies increase with increasing deuterium concentration and lattice parameter

  13. Thermal conductivity of graphene nanoribbons accounting for phonon dispersion and polarization

    International Nuclear Information System (INIS)

    Wang, Yingjun; Xie, Guofeng

    2015-01-01

    The relative contribution to heat conduction by different phonon branches is still an intriguing and open question in phonon transport of graphene nanoribbons (GNRs). By incorporating the direction–dependent phonon–boundary scattering into the linearized phonon Boltzmann transport equation, we find that because of lower Grüneisen parameter, the TA phonons have the major contribution to thermal conductivity of GNRs, and in the case of smooth edge and micron–length of GNRS, the relative contribution of TA branch to thermal conductivity is over 50%. The length and edge roughness of GNRs have distinct influences on the relative contribution of different polarization branches to thermal conductivity. The contribution of TA branch to thermal conductivity increases with increasing the length or decreasing the edge roughness of GNRs. On the contrary, the contribution of ZA branch to thermal conductivity increases with decreasing the length or increasing the edge roughness of GNRs. The contribution of LA branch is length and roughness insensitive. Our findings are helpful for understanding and engineering the thermal conductivity of GNRs.

  14. Ultrasonic investigation of phonon localization in a disordered three-dimensional 'mesoglass'

    International Nuclear Information System (INIS)

    Page, J H; Hu, H; Skipetrov, S; Tiggelen, B A van

    2007-01-01

    One of the long standing questions in phonon physics has been whether or not the Anderson localization of acoustic phonons can be demonstrated unambiguously in disordered materials. In this paper, this question is addressed by reporting signatures of the localization of ultrasonic waves in a 'mesoglass' made from a disordered three-dimensional network of aluminum beads. In the upper part of the intermediate frequency regime, which extends over the range of frequencies where the acoustic phonon wavelength is comparable with the sizes of the pores and beads, the intensity distributions of the speckle patterns due to strong multiple scattering show clear departures from Rayleigh statistics, with a variance that increases with frequency. This intensity distribution can be fitted with a stretched exponential, consistent with recent predictions for localization. In this frequency range, the time-of-flight profile of the transmitted intensity exhibits a non-exponential decay, which may be construed as a slowing down of the phonon diffusion coefficient with propagation time. These results are interpreted using recent theoretical predictions based on the self-consistent theory of the dynamics of localization, showing that our experimental data are consistent with the localization of acoustic waves in this mesoglass, and further elucidating their behaviour

  15. Magnetic ground state and magnon-phonon interaction in multiferroic h -YMnO3

    Science.gov (United States)

    Holm, S. L.; Kreisel, A.; Schäffer, T. K.; Bakke, A.; Bertelsen, M.; Hansen, U. B.; Retuerto, M.; Larsen, J.; Prabhakaran, D.; Deen, P. P.; Yamani, Z.; Birk, J. O.; Stuhr, U.; Niedermayer, Ch.; Fennell, A. L.; Andersen, B. M.; Lefmann, K.

    2018-04-01

    Inelastic neutron scattering has been used to study the magnetoelastic excitations in the multiferroic manganite hexagonal YMnO3. An avoided crossing is found between magnon and phonon modes close to the Brillouin zone boundary in the (a ,b ) plane. Neutron polarization analysis reveals that this mode has mixed magnon-phonon character. An external magnetic field along the c axis is observed to cause a linear field-induced splitting of one of the spin-wave branches. A theoretical description is performed, using a Heisenberg model of localized spins, acoustic phonon modes, and a magnetoelastic coupling via the single-ion magnetostriction. The model quantitatively reproduces the dispersion and intensities of all modes in the full Brillouin zone, describes the observed magnon-phonon hybridized modes, and quantifies the magnetoelastic coupling. The combined information, including the field-induced magnon splitting, allows us to exclude several of the earlier proposed models and point to the correct magnetic ground state symmetry, and provides an effective dynamic model relevant for the multiferroic hexagonal manganites.

  16. Research on bandgaps in two-dimensional phononic crystal with two resonators.

    Science.gov (United States)

    Gao, Nansha; Wu, Jiu Hui; Yu, Lie

    2015-02-01

    In this paper, the bandgap properties of a two-dimensional phononic crystal with the two resonators is studied and embedded in a homogenous matrix. The resonators are not connected with the matrix but linked with connectors directly. The dispersion relationship, transmission spectra, and displacement fields of the eigenmodes of this phononic crystal are studied with finite-element method. In contrast to the phononic crystals with one resonators and hollow structure, the proposed structures with two resonators can open bandgaps at lower frequencies. This is a very interesting and useful phenomenon. Results show that, the opening of the bandgaps is because of the local resonance and the scattering interaction between two resonators and matrix. An equivalent spring-pendulum model can be developed in order to evaluate the frequencies of the bandgap edge. The study in this paper is beneficial to the design of opening and tuning bandgaps in phononic crystals and isolators in low-frequency range. Copyright © 2014 Elsevier B.V. All rights reserved.

  17. Phonon tunneling through a double barrier system

    International Nuclear Information System (INIS)

    Villegas, Diosdado; León-Pérez, Fernando de; Pérez-Álvarez, R.; Arriaga, J.

    2015-01-01

    The tunneling of optical and acoustic phonons at normal incidence on a double-barrier is studied in this paper. Transmission coefficients and resonance conditions are derived theoretically under the assumption that the long-wavelength approximation is valid. It is shown that the behavior of the transmission coefficients for the symmetric double barrier has a Lorentzian form close to resonant frequencies and that Breit–Wigner's formula have a general validity in one-dimensional phonon tunneling. Authors also study the so-called generalized Hartman effect in the tunneling of long-wavelength phonons and show that this effect is a numerical artifact resulting from taking the opaque limit before exploring the variation with a finite barrier width. This study could be useful for the design of acoustic devices

  18. Single-photon indistinguishability: influence of phonons

    DEFF Research Database (Denmark)

    Nielsen, Per Kær; Lodahl, Peter; Jauho, Antti-Pekka

    2012-01-01

    of indistinguishability, absent in the approximate theories. The maximum arises due to virtual processes in the highly non-Markovian short-time regime, which dominate the decoherence for small QD-cavity coupling, and phonon-mediated real transitions between the upper and lower polariton branches in the long-time regime......Recent years have demonstrated that the interaction with phonons plays an important role in semiconductor based cavity QED systems [2], consisting of a quantum dot (QD) coupled to a single cavity mode [Fig. 1(a)], where the phonon interaction is the main decoherence mechanism. Avoiding decoherence...... as a function of the QD-cavity coupling strength for light emitted from the QD and the cavity, respectively, for all the employed methods. Both the Lindblad and TCL theories deviate significantly from our exact results, where, importantly, the exact results predict a pronounced maximum in the degree...

  19. Phonon tunneling through a double barrier system

    Energy Technology Data Exchange (ETDEWEB)

    Villegas, Diosdado [Departamento de Física, Universidad Central “Marta Abreu” de Las Villas, CP 54830, Santa Clara, Villa Clara (Cuba); Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico); León-Pérez, Fernando de [Centro Universitario de la Defensa de Zaragoza, Ctra. de Huesca s/n, E-50090 Zaragoza (Spain); Pérez-Álvarez, R. [Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca (Mexico); Arriaga, J., E-mail: arriaga@ifuap.buap.mx [Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico)

    2015-04-15

    The tunneling of optical and acoustic phonons at normal incidence on a double-barrier is studied in this paper. Transmission coefficients and resonance conditions are derived theoretically under the assumption that the long-wavelength approximation is valid. It is shown that the behavior of the transmission coefficients for the symmetric double barrier has a Lorentzian form close to resonant frequencies and that Breit–Wigner's formula have a general validity in one-dimensional phonon tunneling. Authors also study the so-called generalized Hartman effect in the tunneling of long-wavelength phonons and show that this effect is a numerical artifact resulting from taking the opaque limit before exploring the variation with a finite barrier width. This study could be useful for the design of acoustic devices.

  20. Effects of counterion valency on the damping of phonons propagating along the axial direction of liquid-crystalline DNA

    Science.gov (United States)

    Liu, Yun; Chen, Sow-Hsin; Berti, Debora; Baglioni, Piero; Alatas, Ahmet; Sinn, Harald; Alp, Ercan; Said, Ayman

    2005-12-01

    The phonon propagation and damping along the axial direction of films of aligned 40wt% calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS). The IXS spectra are analyzed with the generalized three effective eigenmode theory, from which we extract the dynamic structure factor S (Q,E) as a function of transferred energy E =ℏω, and the magnitude of the transferred wave vector Q. S (Q,E) of a DNA sample typically consists of three peaks, one central Rayleigh scattering peak, and two symmetric Stokes and anti-Stokes Brillouin side peaks. By analyzing the Brillouin peaks, the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30nm-1. A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q =4nm-1. The high-frequency sound speed obtained in this Q range is 3100m /s, which is about twice faster than the ultrasound speed of 1800m/s, measured by Brillouin light scattering at Q ˜0.01nm-1 at the similar hydration level. Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent. The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied. It is found that the added multivalent counterions introduce stronger phonon damping. The phonons at the range between ˜12.5 and ˜22.5nm-1 are overdamped by the added counterions according to our model analyses. The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4ps.

  1. Collective two-phonon states in deformed nuclei

    International Nuclear Information System (INIS)

    Solov'ev, V.G.; Shirikova, N.Y.

    1982-01-01

    The Pauli principle in the two-phonon components of the wave functions is taken into account within the framework of the quasiparticle-phonon model of the nucleus with phonon operators depending on the sign of the projection of the angular momentum. The centroid energies of collective two-phonon states in even-even deformed nuclei are calculated and it is shown that the inclusion of the Pauli principle shifts them by 1--3 MeV to higher energies. The shifts of the three-phonon poles due to the inclusion of the Pauli principle in the three-phonon components of the wave functions are calculated. Strong fragmentation of collective two-phonon states whose energy centroids are 3--5 MeV should be expected. It is concluded that collective two-phonon states need not exist in deformed nuclei. The situation with the 168 Er nucleus and the Th and U isotopes is analyzed

  2. Situation with collective two-phonon states in deformed nuclei

    International Nuclear Information System (INIS)

    Soloviev, V.G.; Shirikova, N.Yu.

    1982-01-01

    Within the quasiparticle-phonon nuclear model with the operators of phonons depending on the sign of the angular momentum projection, the Pauli principle is taken into account in the two-phonon components of the wave functions. The centroid energies of the collective two-phonon states in even-even deformed nuclei are calculated. It is shown that the inclusion of the Pauli principle leads to their shift by 1-3 MeV towards high energies. The shifts of three-phonon poles due to the Pauli principle are calculated in the three-phonon components of the wave functions. The collective two-phonon states, the centroid energies of which are 3-5 MeV, are expected to be strongly fragmented. The conclusion is confirmed that the collective two-phonon states should not exist in deformed nuclei. The situation in 168 Er and in the 228 Th isotopes is analysed

  3. Phonon structure in proximity tunnel junctions

    International Nuclear Information System (INIS)

    Zarate, H.G.; Carbotte, J.P.

    1985-01-01

    We have iterated to convergence, for the first time, a set of four coupled real axis Eliashberg equations for the superconducting gap and renormalization functions on each side of a proximity sandwich. We find that the phenomenological procedures developed to extract the size of the normal side electron-phonon interaction from tunneling data are often reasonable but may in some cases need modifications. In all the cases considered the superconducting phonon structure reflected on the normal side, as well as other structures, shows considerable agreement with experiment as to size, shape, and variation with barrier transmission coefficient. Finally, we study the effects of depairing on these structures

  4. Evidence for second-phonon nuclear wobbling

    International Nuclear Information System (INIS)

    Jensen, D.R.; Hagemann, G.B.; Herskind, B.; Sletten, G.; Wilson, J.N.; Hamamoto, I.; Odegaard, S.W.; Spohr, K.; Huebel, H.; Bringel, P.; Neusser, A.; Schoenwasser, G.; Singh, A.K.; Ma, W.C.; Amro, H.; Bracco, A.; Leoni, S.; Benzoni, G.; Maj, A.; Petrache, C.M.

    2002-01-01

    The nucleus 163 Lu has been populated through the reaction 139 La( 29 Si,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2) out /B(E2) in value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation

  5. Self-consistency in the phonon space of the particle-phonon coupling model

    Science.gov (United States)

    Tselyaev, V.; Lyutorovich, N.; Speth, J.; Reinhard, P.-G.

    2018-04-01

    In the paper the nonlinear generalization of the time blocking approximation (TBA) is presented. The TBA is one of the versions of the extended random-phase approximation (RPA) developed within the Green-function method and the particle-phonon coupling model. In the generalized version of the TBA the self-consistency principle is extended onto the phonon space of the model. The numerical examples show that this nonlinear version of the TBA leads to the convergence of results with respect to enlarging the phonon space of the model.

  6. Raman scattering of quasimodes in ZnO

    International Nuclear Information System (INIS)

    Alarcon-Llado, E; Cusco, R; Artus, L; Jimenez, J; Wang, B; Callahan, M

    2008-01-01

    The angular dependence of the optical phonons of high-quality bulk ZnO has been systematically studied by means of Raman scattering. We report the observation of quasi-TO and quasi-LO modes for propagation directions covering the whole a-c mixing plane using a beveled ZnO single crystal sample. Scattering experiments performed in two different configuration geometries indicate that birefringence effects are not relevant for the phonon analysis in this material. The observed angular dependence of the quasimode frequencies is in good agreement with Loudon's model.

  7. Neutron scattering treatise on materials science and technology

    CERN Document Server

    Kostorz, G

    1979-01-01

    Treatise on Materials Science and Technology, Volume 15: Neutron Scattering shows how neutron scattering methods can be used to obtain important information on materials. The book discusses the general principles of neutron scattering; the techniques used in neutron crystallography; and the applications of nuclear and magnetic scattering. The text also describes the measurement of phonons, their role in phase transformations, and their behavior in the presence of crystal defects; and quasi-elastic scattering, with its special merits in the study of microscopic dynamical phenomena in solids and

  8. Phonon emission in a degenerate semiconductor at low lattice temperatures

    International Nuclear Information System (INIS)

    Midday, S.; Nag, S.; Bhattacharya, D.P.

    2015-01-01

    The characteristics of phonon growth in a degenerate semiconductor at low lattice temperatures have been studied for inelastic interaction of non-equilibrium electrons with the intravalley acoustic phonons. The energy of the phonon and the full form of the phonon distribution are taken into account. The results reveal significant changes in the growth characteristics compared to the same for a non-degenerate material

  9. Effect of pressure on the second-order Raman scattering intensities of zincblende semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Trallero-Giner, C.; Syassen, K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)

    2010-01-15

    A microscopic description of the two-phonon scattering intensities in direct-gap zincblende-type semiconductors as a function of hydrostatic pressure and for non-resonant excitation is presented. The calculations were performed according to the electron-two-phonon deformation potential interaction for the {gamma}{sub 1} and {gamma}{sub 15} components of the Raman tensor. It is shown that the effect of pressure on the Raman scattering cross-section exhibits a complex behavior according to the contribution of the acoustical or optical phonons to the overtones and combinations. Second-order scattering intensities via acoustical modes could decrease or increase with increasing hydrostatic pressure, while for combinations or overtones of optical phonons a decreasing intensity is obtained. Calculations of the effect of pressure on second-order Raman intensities are compared to experimental results for ZnTe. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  10. Ballistic phonon and thermal radiation transport across a minute vacuum gap in between aluminum and silicon thin films: Effect of laser repetitive pulses on transport characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Yilbas, B.S., E-mail: bsyilbas@kfupm.edu.sa; Ali, H.

    2016-08-15

    Short-pulse laser heating of aluminum and silicon thin films pair with presence of a minute vacuum gap in between them is considered and energy transfer across the thin films pair is predicted. The frequency dependent Boltzmann equation is used to predict the phonon intensity distribution along the films pair for three cycles of the repetitive short-pulse laser irradiation on the aluminum film surface. Since the gap size considered is within the Casimir limit, thermal radiation and ballistic phonon contributions to energy transfer across the vacuum gap is incorporated. The laser irradiated field is formulated in line with the Lambert's Beer law and it is considered as the volumetric source in the governing equations of energy transport. In order to assess the phonon intensity distribution in the films pair, equivalent equilibrium temperature is introduced. It is demonstrated that thermal separation of electron and lattice sub-systems in the aluminum film, due to the short-pulse laser irradiation, takes place and electron temperature remains high in the aluminum film while equivalent equilibrium temperature for phonons decays sharply in the close region of the aluminum film interface. This behavior is attributed to the phonon boundary scattering at the interface and the ballistic phonon transfer to the silicon film across the vacuum gap. Energy transfer due to the ballistic phonon contribution is significantly higher than that of the thermal radiation across the vacuum gap.

  11. Ballistic phonon and thermal radiation transport across a minute vacuum gap in between aluminum and silicon thin films: Effect of laser repetitive pulses on transport characteristics

    Science.gov (United States)

    Yilbas, B. S.; Ali, H.

    2016-08-01

    Short-pulse laser heating of aluminum and silicon thin films pair with presence of a minute vacuum gap in between them is considered and energy transfer across the thin films pair is predicted. The frequency dependent Boltzmann equation is used to predict the phonon intensity distribution along the films pair for three cycles of the repetitive short-pulse laser irradiation on the aluminum film surface. Since the gap size considered is within the Casimir limit, thermal radiation and ballistic phonon contributions to energy transfer across the vacuum gap is incorporated. The laser irradiated field is formulated in line with the Lambert's Beer law and it is considered as the volumetric source in the governing equations of energy transport. In order to assess the phonon intensity distribution in the films pair, equivalent equilibrium temperature is introduced. It is demonstrated that thermal separation of electron and lattice sub-systems in the aluminum film, due to the short-pulse laser irradiation, takes place and electron temperature remains high in the aluminum film while equivalent equilibrium temperature for phonons decays sharply in the close region of the aluminum film interface. This behavior is attributed to the phonon boundary scattering at the interface and the ballistic phonon transfer to the silicon film across the vacuum gap. Energy transfer due to the ballistic phonon contribution is significantly higher than that of the thermal radiation across the vacuum gap.

  12. Ballistic phonon and thermal radiation transport across a minute vacuum gap in between aluminum and silicon thin films: Effect of laser repetitive pulses on transport characteristics

    International Nuclear Information System (INIS)

    Yilbas, B.S.; Ali, H.

    2016-01-01

    Short-pulse laser heating of aluminum and silicon thin films pair with presence of a minute vacuum gap in between them is considered and energy transfer across the thin films pair is predicted. The frequency dependent Boltzmann equation is used to predict the phonon intensity distribution along the films pair for three cycles of the repetitive short-pulse laser irradiation on the aluminum film surface. Since the gap size considered is within the Casimir limit, thermal radiation and ballistic phonon contributions to energy transfer across the vacuum gap is incorporated. The laser irradiated field is formulated in line with the Lambert's Beer law and it is considered as the volumetric source in the governing equations of energy transport. In order to assess the phonon intensity distribution in the films pair, equivalent equilibrium temperature is introduced. It is demonstrated that thermal separation of electron and lattice sub-systems in the aluminum film, due to the short-pulse laser irradiation, takes place and electron temperature remains high in the aluminum film while equivalent equilibrium temperature for phonons decays sharply in the close region of the aluminum film interface. This behavior is attributed to the phonon boundary scattering at the interface and the ballistic phonon transfer to the silicon film across the vacuum gap. Energy transfer due to the ballistic phonon contribution is significantly higher than that of the thermal radiation across the vacuum gap.

  13. Structure factors and phonon dispersion in liquid Li0.61Na0.39 alloy

    International Nuclear Information System (INIS)

    Pratap, Arun; Lad, Kirit N.; Raval, K.G.

    2004-01-01

    The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li 0.61 Na 0.39 alloy. Apart from the phonon spectra, the Ashcroft-Langreth structure factors in the alloy are derived in the Percus-Yevick approximation. (author)

  14. Comparative study of the two-phonon Raman bands of silicene and graphene

    International Nuclear Information System (INIS)

    Popov, Valentin N; Lambin, Philippe

    2016-01-01

    We present a computational study of the two-phonon Raman spectra of silicene and graphene within a density-functional non-orthogonal tight-binding model. Due to the presence of linear bands close to the Fermi energy in the electronic structure of both structures, the Raman scattering by phonons is resonant. We find that the Raman spectra exhibit a crossover behavior for laser excitation close to the π-plasmon energy. This phenomenon is explained by the disappearance of certain paths for resonant Raman scattering and the appearance of other paths beyond this energy. Besides that, the electronic joint density of states (DOS) is divergent at this energy, which is reflected on the behavior of the Raman bands of the two structures in a qualitatively different way. Additionally, a number of Raman bands, originating from divergent phonon DOS at the M point and at points, inside the Brillouin zone, is also predicted. The calculated spectra for graphene are in excellent agreement with available experimental data. The obtained Raman bands can be used for structural characterization of silicene and graphene samples by Raman spectroscopy. (paper)

  15. A possible high-mobility signal in bulk MoTe2: Temperature independent weak phonon decay

    Directory of Open Access Journals (Sweden)

    Titao Li

    2016-11-01

    Full Text Available Layered transition metal dichalcogenides (TMDs have attracted great attention due to their non-zero bandgap for potential application in high carrier mobility devices. Recent studies demonstrate that the carrier mobility of MoTe2 would decrease by orders of magnitude when used for few-layer transistors. As phonon scattering has a significant influence on carrier mobility of layered material, here, we first reported temperature-dependent Raman spectra of bulk 2H-MoTe2 from 80 to 300 K and discovered that the phonon lifetime of both E12g and A1g vibration modes are independent with temperature. These results were explained by the weak phonon decay in MoTe2. Our results imply the existence of a carrier mobility higher than the theoretical value in intrinsic bulk 2H-MoTe2 and the feasibility to obtain MoTe2-based transistors with sufficiently high carrier mobility.

  16. Phonon spectrum of single-crystalline FeSe probed by high-resolution electron energy-loss spectroscopy

    Science.gov (United States)

    Zakeri, Khalil; Engelhardt, Tobias; Le Tacon, Matthieu; Wolf, Thomas

    2018-06-01

    Utilizing high-resolution electron energy-loss spectroscopy (HREELS) we measure the phonon frequencies of β-FeSe(001), cleaved under ultra-high vacuum conditions. At the zone center (Γ bar-point) three prominent loss features are observed at loss energies of about ≃ 20.5 and 25.6 and 40 meV. Based on the scattering selection rules we assign the observed loss features to the A1g, B1g, and A2u phonon modes of β-FeSe(001). The experimentally measured phonon frequencies do not agree with the results of density functional based calculations in which a nonmagnetic, a checkerboard or a strip antiferromagnetic order is assumed for β-FeSe(001). Our measurements suggest that, similar to the other Fe-based materials, magnetism has a profound impact on the lattice dynamics of β-FeSe(001).

  17. Inelastic neutron scattering from high-density fcc 4He

    International Nuclear Information System (INIS)

    Thomlinson, W.; Eckert, J.; Shirane, G.

    1978-01-01

    The phonon dispersion relations in high-density crystals of fcc 4 He have been measured along high-symmetry directions by the neutron-inelastic-scattering technique. A recent study of the lattice dynamics of fcc 4 He by Eckert et al. has been extended to cover the fcc phase diagram at pressures below 5 kbar. Molar volumes of 9.03, 9.43, and 9.97 cm 3 /mole have been studied in the temperature range from near the melting curve to near the fcc-hcp transition line. The phonon dispersion relations are in good agreement with a first-order self-consistent phonon theory calculation by Goldman. The observed phonon-group line shapes at large energy and momentum transfers show evidence for multiphonon scattering in agreement with calculations by Glyde. Eckert et al. reported extremely large anharmonic isochoric temperature shifts of the phonon energies. The present work studied the shifts as a function of molar volume and temperature. Mode-Grueneisen-parameter dispersion curves have been measured using the present data and earlier measurements at lower density in the fcc phase by Traylor et al. Macroscopic Grueneisen parameters have been calculated from the phonon density of states obtained from the data

  18. Resonance effects in Raman scattering of quantum dots formed by the Langmuir-Blodgett method

    Energy Technology Data Exchange (ETDEWEB)

    Milekhin, A G; Sveshnikova, L L; Duda, T A [Institute of Semiconductor Physics, Lavrentjev av.13, 630090, Novosibirsk (Russian Federation); Surovtsev, N V; Adichtchev, S V [Institute of Automation and Electrometry, Koptyug av.1, 630090, Novosibirsk (Russian Federation); Azhniuk, Yu M [Institute of Electron Physics, Universytetska Str. 21, 88017, Uzhhorod (Ukraine); Himcinschi, C [Institut fuer Theoretische Physik, TU Bergakademie Freiberg, Leipziger Str. 23, 09596, Freiberg (Germany); Kehr, M; Zahn, D R T, E-mail: milekhin@thermo.isp.nsc.r [Semiconductor Physics, Chemnitz University of Technology, Chemnitz (Germany)

    2010-09-01

    The enhancement of Raman scattering by optical phonon modes in quantum dots was achieved in resonant and surface-enhanced Raman scattering experiments by approaching the laser energy to the energy of either the interband transitions or the localized surface plasmons in silver nanoclusters deposited onto the nanostructures. Resonant Raman scattering by TO, LO, and SO phonons as well as their overtones was observed for PbS, ZnS, and ZnO quantum dots while enhancement for LO and SO modes in CdS quantum dots with a factor of about 700 was measured in surface enhanced Raman scattering experiments. Multiple phonon Raman scattering observed up to 5th and 7th order for CdS and ZnO, respectively, confirms the high crystalline quality of the grown QDs.

  19. Electron-phonon interactions and the phonon anomaly in β-phase NiTi

    International Nuclear Information System (INIS)

    Zhao, G.L.; Harmon, B.N.

    1993-01-01

    The electronic structure of β-phase NiTi has been calculated using a first-principles linear-combination-of-atomic-orbitals method. The resulting band structure was fitted with a nonorthogonal tight-binding Hamiltonian from which electron-phonon matrix elements were evaluated. The soft phonon near Q 0 =(2/3, 2) / (3 ,0)π/a, which is responsible for the premartensitic phase transition in β-phase NiTi, is found to arise from the strong electron-phonon coupling of nested electronic states on the Fermi surface. Thermal vibrations and changes in electronic occupation cause a smearing of the nested features, which in turn cause a hardening of the phonon anomaly

  20. Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

    International Nuclear Information System (INIS)

    Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

    2012-01-01

    The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ► We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ► The results show the first PBGs start with zero Hz with low modes. ► Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.

  1. Hydrodynamic states of phonons in insulators

    Directory of Open Access Journals (Sweden)

    S.A. Sokolovsky

    2012-12-01

    Full Text Available The Chapman-Enskog method is generalized for accounting the effect of kinetic modes on hydrodynamic evolution. Hydrodynamic states of phonon system of insulators have been studied in a small drift velocity approximation. For simplicity, the investigation was carried out for crystals of the cubic class symmetry. It has been found that in phonon hydrodynamics, local equilibrium is violated even in the approximation linear in velocity. This is due to the absence of phonon momentum conservation law that leads to a drift velocity relaxation. Phonon hydrodynamic equations which take dissipative processes into account have been obtained. The results were compared with the standard theory based on the local equilibrium validity. Integral equations have been obtained for calculating the objects of the theory (including viscosity and heat conductivity. It has been shown that in low temperature limit, these equations are solvable by iterations. Steady states of the system have been considered and an expression for steady state heat conductivity has been obtained. It coincides with the famous result by Akhiezer in the leading low temperature approximation. It has been established that temperature distribution in the steady state of insulator satisfies a condition of heat source absence.

  2. Phonon limited electronic transport in Pb

    DEFF Research Database (Denmark)

    Rittweger, Florian; Hinsche, Nicki Frank; Mertig, Ingrid

    2017-01-01

    We present a fully ab initio based scheme to compute electronic transport properties, i.e. the electrical conductivity σ and thermopower S, in the presence of electron-phonon interaction. We explicitly investigate the k-dependent structure of the Éliashberg spectral function, the coupling strength...

  3. Phonon affected transport through molecular quantum

    Czech Academy of Sciences Publication Activity Database

    Loos, Jan; Koch, T.; Alvermann, A.; Bishop, A. R.; Fehske, H.

    2009-01-01

    Roč. 21, č. 39 (2009), 395601/1-395601/18 ISSN 0953-8984 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.964, year: 2009

  4. Electron-phonon interactions in correlated systems

    International Nuclear Information System (INIS)

    Wysokinski, K.I.

    1996-01-01

    There exist attempts to describe the superconducting mechanism operating in HTS as based on antiferromagnetic fluctuations. It is not our intention to dwell on the superconducting mechanism, even though this is very a important issue. The main aim is to discuss the problem of interplay between electron-phonon and electron-electron interactions in correlated systems. We believe such analysis can be of importance for various materials and not only HTS'S. We shall however mainly refer to experiments on this last class of superconductors. Severe complications are to be expected by studying the problem. As is well known electron correlations are very important in narrow band systems, where the relevant electronic scale E F is quite small. In those circumstances, the phonon energy scale ω D is of comparable magnitude, with the ratio ω D /E F of order 1 signalling a possible break down of the Migdal - Eliashberg description of the electron-phonon interaction in metals. Here we shall assume the validity of the Migdal-Eliashberg approximation and concentrate on the mutual influence of electron and phonon subsystems. In the next section we shall discuss experimental motivation for and theoretical work related to the present problem. Section 3 contains a brief discussion of our theory. It is a self-consistent theory a la Migdal with strong correlations treated with an auxiliary boson technique. We conclude with results and their discussion. (orig.)

  5. Phononic fluidics: acoustically activated droplet manipulations

    Science.gov (United States)

    Reboud, Julien; Wilson, Rab; Bourquin, Yannyk; Zhang, Yi; Neale, Steven L.; Cooper, Jonathan M.

    2011-02-01

    Microfluidic systems have faced challenges in handling real samples and the chip interconnection to other instruments. Here we present a simple interface, where surface acoustic waves (SAWs) from a piezoelectric device are coupled into a disposable acoustically responsive microfluidic chip. By manipulating droplets, SAW technologies have already shown their potential in microfluidics, but it has been limited by the need to rely upon mixed signal generation at multiple interdigitated electrode transducers (IDTs) and the problematic resulting reflections, to allow complex fluid operations. Here, a silicon chip was patterned with phononic structures, engineering the acoustic field by using a full band-gap. It was simply coupled to a piezoelectric LiNbO3 wafer, propagating the SAW, via a thin film of water. Contrary to the use of unstructured superstrates, phononic metamaterials allowed precise spatial control of the acoustic energy and hence its interaction with the liquids placed on the surface of the chip, as demonstrated by simulations. We further show that the acoustic frequency influences the interaction between the SAW and the phononic lattice, providing a route to programme complex fluidic manipulation onto the disposable chip. The centrifugation of cells from a blood sample is presented as a more practical demonstration of the potential of phononic crystals to realize diagnostic systems.

  6. Anomalous Doppler effects in bulk phononic crystal

    International Nuclear Information System (INIS)

    Cai Feiyan; He Zhaojian; Zhang Anqi; Ding Yiqun; Liu Zhengyou

    2010-01-01

    Doppler effects in simple cubic phononic crystal are studied theoretically and numerically. In addition to observing Doppler shifts from a moving source's frequencies inside the gap, we find that Doppler shifts can be multi-order, anisotropic, and the dominant order of shift depends on the band index that the source's frequency is in.

  7. Phononic band gap structures as optimal designs

    DEFF Research Database (Denmark)

    Jensen, Jakob Søndergaard; Sigmund, Ole

    2003-01-01

    In this paper we use topology optimization to design phononic band gap structures. We consider 2D structures subjected to periodic loading and obtain the distribution of two materials with high contrast in material properties that gives the minimal vibrational response of the structure. Both in...

  8. Kohn anomaly in phonon driven superconductors

    International Nuclear Information System (INIS)

    Das, M P; Chaudhury, R

    2014-01-01

    Anomalies often occur in the physical world. Sometimes quite unexpectedly anomalies may give rise to new insight to an unrecognized phenomenon. In this paper we shall discuss about Kohn anomaly in a conventional phonon-driven superconductor by using a microscopic approach. Recently Aynajian et al.'s experiment showed a striking feature; the energy of phonon at a particular wave-vector is almost exactly equal to twice the energy of the superconducting gap. Although the phonon mechanism of superconductivity is well known for many conventional superconductors, as has been noted by Scalapino, the new experimental results reveal a genuine puzzle. In our recent work we have presented a detailed theoretical analysis with the help of microscopic calculations to unravel this mystery. We probe this aspect of phonon behaviour from the properties of electronic polarizability function in the superconducting phase of a Fermi liquid metal, leading to the appearance of a Kohn singularity. We show the crossover to the standard Kohn anomaly of the normal phase for temperatures above the transition temperature. Our analysis provides a nearly complete explanation of this new experimentally discovered phenomenon. This report is a shorter version of our recent work in JPCM.

  9. Quasiparticles, phonons and beyond. Enlargement the basis of quasiparticle-phonon model

    International Nuclear Information System (INIS)

    Stoyanov, Ch.

    2000-01-01

    The version of Quasiparticle-Phonon Model (QPM) which accounts up to three-phonons is discussed. The new basis is used to study the low-lying isovector mode and the low-energy E1 transitions forbidden in the ideal boson picture. The coupling to the continuum is incorporated in the formalism of QPM. The phenomenon of trapping of states is studied in the case of high-lying states with large angular momentum. (author)

  10. Interpretation of resistivity of Nd1.85Ce0.15CuO4-y using the electron-phonon spectral function determined from tunneling data

    International Nuclear Information System (INIS)

    Tralshawala, N.; Zasadzinski, J.F.; Coffey, L.; Huang, Q.

    1991-01-01

    Tunneling measurements of α 2 F(ω) of Nd 1.85 Ce 0.15 CuO 4-y are shown to be in good agreement with recent published results of the phonon density of states F(ω) from neutron scattering. The locations of peaks and valleys in both functions are similar, but the spectral weights differ, suggesting that α 2 has a strong energy dependence. We have used α 2 F(ω) to estimate the phonon contribution, ρ phonon (T), to published data of the temperature-dependent resistivity, ρ(T), for thin films and single crystals of Nd 1.85 Ce 0.15 CuO 4-y . When the phonon contribution is subtracted from the experimental data, a clear T 2 contribution remains over most of the temperature range. The T 2 contribution is interpreted to be due to three-dimensional electron-electron scattering, ρ e-e . There is also a correlation between the magnitude of ρ e-e , and the value of the plasma frequency, ω p [obtained from the determination of ρ phonon (T)], with a scaling which approximates ω p -10/3 . Such a scaling is expected from the carrier-concentration dependence of electron-electron scattering

  11. Quantum scattering of neon from a nanotextured surface

    International Nuclear Information System (INIS)

    Levi, A C; Huang, C; Allison, W; MacLaren, D A

    2009-01-01

    Phonon exchange is the usual cause of decoherence in atom-surface scattering. By including quantum effects in the treatment of Debye-Waller scattering, we show that phonon exchange becomes ineffective when the relevant phonon frequencies are high. The result explains the surprising observation of strong elastic scattering of Ne from a Cu(100) surface nanotextured with a c(2 x 2) Li adsorbate structure. We extend a previous model to describe the phonon spectra by an Einstein oscillator component with an admixture of a Debye spectrum. The Einstein oscillator represents the dominant, high frequency vibration of the adsorbate, normal to the surface, while the Debye spectrum represents the substrate contribution. Neon scattering is so slow that exciting the adsorbate mode has a low probability and is impossible if the incident energy is below the threshold. Thus, adsorbate vibrations are averaged out. A theoretical discussion and calculation shows that under such circumstances the vibrations of a light adsorbate do not contribute to the Debye-Waller effect, with the result that Ne scattering at thermal energies is quantum mechanical and largely elastic, explaining the high reflectivity and the diffraction peaks observed experimentally.

  12. Origin of the "waterfall" effect in phonon dispersion of relaxor perovskites.

    Science.gov (United States)

    Hlinka, J; Kamba, S; Petzelt, J; Kulda, J; Randall, C A; Zhang, S J

    2003-09-05

    We have undertaken an inelastic neutron scattering study of the perovskite relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O3 with 8% PbTiO3 (PZN-8%PT) in order to elucidate the origin of the previously reported unusual kink on the low frequency transverse phonon dispersion curve (known as the "waterfall effect"). We show that its position (q(wf)) depends on the choice of the Brillouin zone and that the relation of q(wf) to the size of the polar nanoregions is highly improbable. The waterfall phenomenon is explained in the framework of a simple model of coupled damped harmonic oscillators representing the acoustic and optic phonon branches.

  13. Electronic response and longitudinal phonons of a charge-density-wave distorted linear chain

    International Nuclear Information System (INIS)

    Giuliani, G.

    1978-01-01

    The longitudinal-phonon spectrum of an incommensurate charge-density-wave distorted linear chain at T = 0 K are calculated. This is done by direct numerical evaluation of the full static-electronic-response matrix. The electronic band structure assumed for this purpose is that of a mean-field theory 1-D Peierls insulator. The present results show how, within this simplified, but self-consistent picture, the phase and amplitude modes connect to, and interact with, the ordinary longitudinal-phonon branch. Effects due to our inclusion of (0,2ksub(F)) scattering along with the usual (-2ksub(F), 2ksub(F)) are also pointed out. An alternative approximate expression for the 1-D electronic-response matrix is also given. (author)

  14. Compositional Variation of the Phonon Dispersion Curves of bcc Fe-Ga Alloys

    International Nuclear Information System (INIS)

    Zarestky, Jerel L.; Garlea, Vasile O.; Lograsso, Tom; Schlagel, D.L.; Stassis, C.

    2005-01-01

    Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of bcc Fe1-xGax x=10.8, 13.3, 16.0, 22.5 alloys as a function of Ga concentration. The phonon frequencies of every branch were found to decrease significantly with increasing Ga concentration. The softening was most pronounced for the T2 0 branch and, to a lesser extent, the L branch in the vicinity of = 2 3. The concentration dependence of the shear elastic constant C =1/2 C11-C12 , calculated from the slope of the T2 0 branch, was found to agree with the results of sound velocity measurements. For the higher concentration sample measured, 22.5 at. % Ga, new branches appeared, an effect associated with the increase in the number of atoms per unit cell.

  15. A new class of tunable hypersonic phononic crystals based on polymer-tethered colloids.

    Science.gov (United States)

    Alonso-Redondo, E; Schmitt, M; Urbach, Z; Hui, C M; Sainidou, R; Rembert, P; Matyjaszewski, K; Bockstaller, M R; Fytas, G

    2015-09-22

    The design and engineering of hybrid materials exhibiting tailored phononic band gaps are fundamentally relevant to innovative material technologies in areas ranging from acoustics to thermo-optic devices. Phononic hybridization gaps, originating from the anti-crossing between local resonant and propagating modes, have attracted particular interest because of their relative robustness to structural disorder and the associated benefit to 'manufacturability'. Although hybridization gap materials are well known, their economic fabrication and efficient control of the gap frequency have remained elusive because of the limited property variability and expensive fabrication methodologies. Here we report a new strategy to realize hybridization gap materials by harnessing the 'anisotropic elasticity' across the particle-polymer interface in densely polymer-tethered colloidal particles. Theoretical and Brillouin scattering analysis confirm both the robustness to disorder and the tunability of the resulting hybridization gap and provide guidelines for the economic synthesis of new materials with deliberately controlled gap position and width frequencies.

  16. Imaging off-plane shear waves with a two-dimensional phononic crystal lens

    International Nuclear Information System (INIS)

    Chiang Chenyu; Luan Pigang

    2010-01-01

    A two-dimensional flat phononic crystal (PC) lens for focusing off-plane shear waves is proposed. The lens consists of a triangular lattice hole-array, embedded in a solid matrix. The self-collimation effect is employed to guide the shear waves propagating through the lens along specific directions. The Dirichlet-to-Neumann maps (DtN) method is employed to calculate the band structure of the PC, which can avoid the problems of bad convergence and fake bands automatically in the void-solid PC structure. When the lens is illuminated by the off-plane shear waves emanating from a point source, a subwavelength image appears in the far-field zone. The imaging characteristics are investigated by calculating the displacement fields explicitly using the multiple scattering method, and the results are in good agreement with the ray-trace predictions. Our results may provide insights for designing new phononic devices.

  17. A new class of tunable hypersonic phononic crystals based on polymer-tethered colloids

    Science.gov (United States)

    Alonso-Redondo, E.; Schmitt, M.; Urbach, Z.; Hui, C. M.; Sainidou, R.; Rembert, P.; Matyjaszewski, K.; Bockstaller, M. R.; Fytas, G.

    2015-09-01

    The design and engineering of hybrid materials exhibiting tailored phononic band gaps are fundamentally relevant to innovative material technologies in areas ranging from acoustics to thermo-optic devices. Phononic hybridization gaps, originating from the anti-crossing between local resonant and propagating modes, have attracted particular interest because of their relative robustness to structural disorder and the associated benefit to `manufacturability'. Although hybridization gap materials are well known, their economic fabrication and efficient control of the gap frequency have remained elusive because of the limited property variability and expensive fabrication methodologies. Here we report a new strategy to realize hybridization gap materials by harnessing the `anisotropic elasticity' across the particle-polymer interface in densely polymer-tethered colloidal particles. Theoretical and Brillouin scattering analysis confirm both the robustness to disorder and the tunability of the resulting hybridization gap and provide guidelines for the economic synthesis of new materials with deliberately controlled gap position and width frequencies.

  18. Negative refraction imaging of solid acoustic waves by two-dimensional three-component phononic crystal

    International Nuclear Information System (INIS)

    Li Jing; Liu Zhengyou; Qiu Chunyin

    2008-01-01

    By using of the multiple scattering methods, we study the negative refraction imaging effect of solid acoustic waves by two-dimensional three-component phononic crystals composed of coated solid inclusions placed in solid matrix. We show that localized resonance mechanism brings on a group of flat single-mode bands in low-frequency region, which provides two equivalent frequency surfaces (EFS) close to circular. The two constant frequency surfaces correspond to two Bloch modes, a right-handed and a left-handed, whose leading mode are respectively transverse (T) and longitudinal (L) modes. The negative refraction behaviors of the two kinds of modes have been demonstrated by simulation of a Gaussian beam through a finite system. High-quality far-field imaging by a planar lens for transverse or longitudinal waves has been realized separately. This three-component phononic crystal may thus serve as a mode selector in negative refraction imaging of solid acoustic waves

  19. The Role of C-axis Polarized Phonons in High Temperature Superconductors

    International Nuclear Information System (INIS)

    Timusk, T.; Homes, C. C.; Reichardt, W.

    1995-01-01

    We report on the optical conductivity of c-axis phonons in YBa 2 Cu 3 O 7-σ as a function of doping and temperature. At room temperature the frequencies and strengths of the modes are in good agreement with results from shell models based on neutron scattering. We discuss the apical oxygen mode which becomes asymmetric in underdoped materials and argue, with Burns, that the Au mode shifts from 570 cm -1 to 610 cm -1 for the two-fold coordinated copper sites in the chain layer in oxygen depleted materials. At low temperature there is a large transfer of c-axis phonon oscillator strength from O(4) apical and O (2, 3,) plane bending modes, to a very broad at 400 cm -1

  20. Interface plasmon-phonons modes in ion-beam synthesized Mg2Si nanolayers

    International Nuclear Information System (INIS)

    Baleva, M.; Zlateva, G.

    2009-01-01

    Raman scattering of samples, representing n- and p-type Si matrix with unburied Mg 2 Si nanolayers, formed by ion-beam synthesis, are studied. Despite the features in the Raman spectra attributed to the polariton modes with frequencies between those of the TO and LO phonons, additional features outside this interval are detected. The frequencies of these features are very sensitive to the plasma frequency, being different in the n- and p-type Si matrix and to the annealing time. The latter implies the generation of interface plasmonphonons modes. The frequencies of the interface plasmon-phonon modes are calculated and compared with the experimental results. The order of the carrier concentration in Mg 2 Si, the data of which are not available in the literature, is evaluated. (authors)

  1. A micromorphic model for monolayer hexagonal boron nitride with determined constitutive constants by phonon dispersions

    International Nuclear Information System (INIS)

    Zhang, Bin; Yang, Gang

    2014-01-01

    A two dimensional (2D) micromorphic model is developed for monolayer hexagonal boron nitride (h-BN). Theoretical expressions of phonon dispersions for 2D crystals are derived based on the simplified governing equations of specialized three dimensional micromorphic crystals. The constitutive constants of governing equations of the h-BN micromorphic model are determined, which is performed by fitting the available phonon dispersions data of experimental measurements and first-principles calculations with our theoretical expressions. The obtained Young’s modulus and Poisson’s ratio of h-BN are comparable with the results of ab initio calculations and inelastic x-ray scattering experiments, thus the constitutive relations of the h-BN model are verified, which also indicates that mechanical properties of monolayer h-BN could be characterized by our 2D micromorphic model

  2. Properties of thermal neutron scattering on the nucleus of hydrogen atom of methane molecule; Osobine rasejanja termalnih neutrona na jezgru vodonikovog atoma molekula metana

    Energy Technology Data Exchange (ETDEWEB)

    Miloradovic, M M [Tehnicki fakultet, Cacak (Yugoslavia); Markovic, M I [Elektrotehnicki fakultet, Beograd (Yugoslavia)

    1987-07-01

    On the basis of derived quantum-mechanical expression for the microscopic nucleus scattering the single and collective influences of translational, rotational and intravibrational motions of the methane molecule on the thermal neutron scattering are established. When incident neutron energy is E{sub 0} {<=} 0.1 eV, it is found that only translational and rotational motion of the methane molecule influences the thermal neutron scattering. The influence of these motions for E{sub 0} . 0.1 eV decreases rapidly with the increase of the incident neutron energy and then the significant influence on the thermal neutron scattering exerts inelastic scattering on the combined rotational with single intravibrational phonons of the methane molecule, while the inelastic scattering on single intravibrational phonons is significantly less. In the combination with rotational phonons the biggest influence has threefold degenerated deformed intravibrational phonons, somehow less influence has twofold degenerated deformed intravibrational phonons, and the least influence has valent intravibrational phonons. All the effects of quasielastic and quantum inelastic scattering are clearly expressed with the thermal neutron scattering at small angles, so that for E{sub 0} =1 eV practically there is no scattering backward. (author)

  3. Inelastic light scattering spectroscopy of semiconductor nitride nanocolumns

    Energy Technology Data Exchange (ETDEWEB)

    Calleja, J.M.; Lazic, S.; Sanchez-Paramo, J. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Agullo-Rueda, F. [Materials Science Institute of Madrid, CSIC, 28049 Madrid (Spain); Cerutti, L.; Ristic, J.; Fernandez-Garrido, S.; Sanchez-Garcia, M.A.; Grandal, J.; Calleja, E. [ISOM and Departamento de Ingenieria Electronica, ETSIT, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Trampert, A.; Jahn, U. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2007-08-15

    A review of inelastic light scattering measurements on group III-nitride nanocolumns grown by molecular beam epitaxy is presented. The nanocolumns are hexagonal, high quality single crystals with diameters in the range of 20 to 100 nm, with no traces of extended defects. GaN nanocolumns grown on bare Si substrates with both (111) and (100) orientation display narrow phonon peaks, indicating the absence of strain inhomogeneities. This opens the possibility of efficient integration of the nanocolumns as optoelectronic devices with the complementary metal oxide semiconductor technology. Measurements of the E{sub 2} phonon frequency on AlGaN nanocolumns indicate a linear dependence of the Al concentration on the Al relative flux, up to 60%. The E{sub 2} peak width increases with Al content due to phonon damping by alloy scattering. Inelastic light scattering measurements in InN nanocolumns display a coupled LO phonon-plasmon mode together with uncoupled phonons. The coupled mode is not observed in a reference compact sample. The origin of the coupled mode is attributed to spontaneous accumulation of electrons at the lateral surfaces of the nanocolumns. The presence of free electrons in the nanocolumns is confirmed by infrared reflectance measurements. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Inelastic light scattering spectroscopy of semiconductor nitride nanocolumns

    International Nuclear Information System (INIS)

    Calleja, J.M.; Lazic, S.; Sanchez-Paramo, J.; Agullo-Rueda, F.; Cerutti, L.; Ristic, J.; Fernandez-Garrido, S.; Sanchez-Garcia, M.A.; Grandal, J.; Calleja, E.; Trampert, A.; Jahn, U.

    2007-01-01

    A review of inelastic light scattering measurements on group III-nitride nanocolumns grown by molecular beam epitaxy is presented. The nanocolumns are hexagonal, high quality single crystals with diameters in the range of 20 to 100 nm, with no traces of extended defects. GaN nanocolumns grown on bare Si substrates with both (111) and (100) orientation display narrow phonon peaks, indicating the absence of strain inhomogeneities. This opens the possibility of efficient integration of the nanocolumns as optoelectronic devices with the complementary metal oxide semiconductor technology. Measurements of the E 2 phonon frequency on AlGaN nanocolumns indicate a linear dependence of the Al concentration on the Al relative flux, up to 60%. The E 2 peak width increases with Al content due to phonon damping by alloy scattering. Inelastic light scattering measurements in InN nanocolumns display a coupled LO phonon-plasmon mode together with uncoupled phonons. The coupled mode is not observed in a reference compact sample. The origin of the coupled mode is attributed to spontaneous accumulation of electrons at the lateral surfaces of the nanocolumns. The presence of free electrons in the nanocolumns is confirmed by infrared reflectance measurements. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Phonon dynamics and Urbach energy studies of MgZnO alloys

    Energy Technology Data Exchange (ETDEWEB)

    Huso, Jesse, E-mail: jhuso@vandals.uidaho.edu; Che, Hui; Thapa, Dinesh; Canul, Amrah; Bergman, Leah [Department of Physics, University of Idaho, Moscow, Idaho 83844-0903 (United States); McCluskey, M. D. [Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)

    2015-03-28

    The Mg{sub x}Zn{sub 1−x}O alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of Mg{sub x}Zn{sub 1−x}O thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0–68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2–5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47–66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.

  6. Strong Carrier–Phonon Coupling in Lead Halide Perovskite Nanocrystals

    Science.gov (United States)

    2017-01-01

    We highlight the importance of carrier–phonon coupling in inorganic lead halide perovskite nanocrystals. The low-temperature photoluminescence (PL) spectrum of CsPbBr3 has been investigated under a nonresonant and a nonstandard, quasi-resonant excitation scheme, and phonon replicas of the main PL band have been identified as due to the Fröhlich interaction. The energy of longitudinal optical (LO) phonons has been determined from the separation of the zero phonon band and phonon replicas. We reason that the observed LO phonon coupling can only be related to an orthorhombically distorted crystal structure of the perovskite nanocrystals. Additionally, the strength of carrier–phonon coupling has been characterized using the ratio between the intensities of the first phonon replica and the zero-phonon band. PL emission from localized versus delocalized carriers has been identified as the source of the observed discrepancies between the LO phonon energy and phonon coupling strength under quasi-resonant and nonresonant excitation conditions, respectively. PMID:29019652

  7. RAMAN LIGHT SCATTERING IN PSEUDOSPIN-ELECTRON MODEL AT STRONG PSEUDOSPIN-ELECTRON INTERACTION

    Directory of Open Access Journals (Sweden)

    T.S.Mysakovych

    2004-01-01

    Full Text Available Anharmonic phonon contributions to Raman scattering in locally anharmonic crystal systems in the framework of the pseudospin-electron model with tunneling splitting of levels are investigated. The case of strong pseudospin-electron coupling is considered. Pseudospin and electron contributions to scattering are taken into account. Frequency dependences of Raman scattering intensity for different values of model parameters and for different polarization of scattering and incident light are investigated.

  8. Fuchs-Kliewer phonons of H-covered and clean GaN(1 1 bar 00)

    Science.gov (United States)

    Rink, M.; Himmerlich, M.; Krischok, S.; Kröger, J.

    2018-01-01

    Inelastic electron scattering is used to study surface phonon polaritons on H-covered and clean GaN(1 1 bar 00) surfaces. The Fuchs-Kliewer phonon of GaN(1 1 bar 00) -H gives rise to characteristic signatures of its single and multiple excitation in specular electron energy loss spectra. The loss intensities for multi-phonon scattering processes decrease according to a Poisson distribution. Vibrational spectra of this surface are invariant on the time scale of days reflecting its chemical passivation by the H layer. In contrast, vibrational spectra of pristine GaN(1 1 bar 00) are subject to a pronounced temporal evolution where spectroscopic weight is gradually shifted towards the multiple excitation of the Fuchs-Kliewer phonon. As a consequence, the monotonous decrease of the cross section for multiple quantum excitation as observed for the H-covered surface is not applicable. This remarkable effect is particularly strong in spectra acquired at low primary energies of incident electrons, which hints at processes occurring in the very surface region. Scenarios that may contribute to these observations are discussed.

  9. Equilibrium limit of thermal conduction and boundary scattering in nanostructures.

    Science.gov (United States)

    Haskins, Justin B; Kınacı, Alper; Sevik, Cem; Çağın, Tahir

    2014-06-28

    Determining the lattice thermal conductivity (κ) of nanostructures is especially challenging in that, aside from the phonon-phonon scattering present in large systems, the scattering of phonons from the system boundary greatly influences heat transport, particularly when system length (L) is less than the average phonon mean free path (MFP). One possible route to modeling κ in these systems is through molecular dynamics (MD) simulations, inherently including both phonon-phonon and phonon-boundary scattering effects in the classical limit. Here, we compare current MD methods for computing κ in nanostructures with both L ⩽ MFP and L ≫ MFP, referred to as mean free path constrained (cMFP) and unconstrained (uMFP), respectively. Using a (10,0) CNT (carbon nanotube) as a benchmark case, we find that while the uMFP limit of κ is well-defined through the use of equilibrium MD and the time-correlation formalism, the standard equilibrium procedure for κ is not appropriate for the treatment of the cMFP limit because of the large influence of boundary scattering. To address this issue, we define an appropriate equilibrium procedure for cMFP systems that, through comparison to high-fidelity non-equilibrium methods, is shown to be the low thermal gradient limit to non-equilibrium results. Further, as a means of predicting κ in systems having L ≫ MFP from cMFP results, we employ an extrapolation procedure based on the phenomenological, boundary scattering inclusive expression of Callaway [Phys. Rev. 113, 1046 (1959)]. Using κ from systems with L ⩽ 3 μm in the extrapolation, we find that the equilibrium uMFP κ of a (10,0) CNT can be predicted within 5%. The equilibrium procedure is then applied to a variety of carbon-based nanostructures, such as graphene flakes (GF), graphene nanoribbons (GNRs), CNTs, and icosahedral fullerenes, to determine the influence of size and environment (suspended versus supported) on κ. Concerning the GF and GNR systems, we find that

  10. Nanomesh phononic structures for low thermal conductivity and thermoelectric energy conversion materials

    Science.gov (United States)

    Yu, Jen-Kan; Mitrovic, Slobodan; Heath, James R.

    2016-08-16

    A nanomesh phononic structure includes: a sheet including a first material, the sheet having a plurality of phononic-sized features spaced apart at a phononic pitch, the phononic pitch being smaller than or equal to twice a maximum phonon mean free path of the first material and the phononic size being smaller than or equal to the maximum phonon mean free path of the first material.

  11. ATA and the electron phonon coupling constant in calculating TA of super conducting alloys [Paper No. : V-2

    International Nuclear Information System (INIS)

    Chatterjee, P.; Chatterjee, S.

    1978-01-01

    The theoretical formula of McMillan has been very successful in explaining the superconducting transition temperature. In this theory the electron-phonon coupling constant was very difficult to calculate from a purely theoretical stand point until Gyorffy and Gaspari gave a theoretical formulation from the multiple scattering point of view. This theory has been very successful in explaining Tsub(c) of many superconducting elements and compounds. For the disordered solid, such as substitution alloys, this theory fails because of the breakdown of the translational symmetry used in the multiple scattering theory of Gyorffy and Gaspari. This problem can however be solved if we average the Green's function in random phase approximation (ATA). In this work we have reformulated Gyorffy and Gaspari's expression of the electron phonon coupling constant in the random phase approximation. This theory has been utilised to alloys of Nb and Mo with different concentrations. The agreement between theory and experiment appears to be very good. (author)

  12. Phonon interference control of atomic-scale metamirrors, meta-absorbers, and heat transfer through crystal interfaces

    Science.gov (United States)

    Kosevich, Yu. A.; Potyomina, L. G.; Darinskii, A. N.; Strelnikov, I. A.

    2018-03-01

    The paper theoretically studies the possibility of using the effects of phonon interference between paths through different interatomic bonds for the control of phonon heat transfer through internal crystal interfaces and for the design of phonon metamirrors and meta-absorbers. These metamirrors and meta-absorbers are considered to be defect nanolayers of atomic-scale thicknesses embedded in a crystal. Several analytically solvable three-dimensional lattice-dynamics models of the phonon metamirrors and meta-absorbers at the internal crystal planes are described. It is shown that due to destructive interference in the two or more phonon paths, the internal crystal planes, fully or partially filled with weakly bound or heavy-isotope defect atoms, can completely reflect or completely absorb phonons at the transmission antiresonances, whose wavelengths are larger than the effective thickness of the metamirror or meta-absorber. Due to cooperative superradiant effect, the spectral widths of the two-path interference antiresonances for the plane waves are given by the square of partial filling fraction in the defect crystal plane. Our analysis reveals that the presence of two or more phonon paths plays the dominant role in the emergence of the transmission antiresonances in phonon scattering at the defect crystal planes and in reduction of the thermal interface conductance in comparison with the Fano-resonance concept. We study analytically phonon transmission through internal crystal plane in a model cubic lattice of Si-like atoms, partially filled with Ge-like defect atoms. Such a plane can serve as interference phonon metamirror with the transmission antiresonances in the vicinities of eigenmode frequencies of Ge-like defect atoms in the terahertz frequency range. We predict the extraordinary phonon transmission induced by the two-path constructive interference of the lattice waves in resonance with the vibrations of rare host atoms, periodically distributed in the

  13. Electron-phonon coupling at metal surfaces

    International Nuclear Information System (INIS)

    Hellsing, B.; Eiguren, A.; Chulkov, E.V.

    2002-01-01

    Chemical reactions at metal surfaces are influenced by inherent dissipative processes which involve energy transfer between the conduction electrons and the nuclear motion. We shall discuss how it is possible to model this electron-phonon coupling in order to estimate its importance. A relevant quantity for this investigation is the lifetime of surface-localized electron states. A surface state, quantum well state or surface image state is located in a surface-projected bandgap and becomes relatively sharp in energy. This makes a comparison between calculations and experimental data most attractive, with a possibility of resolving the origin of the lifetime broadening of electron states. To achieve more than an order of magnitude estimate we point out the importance of taking into account the phonon spectrum, electron surface state wavefunctions and screening of the electron-ion potential. (author)

  14. Phonon spectroscopy with superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Grimshaw, J.M.

    1984-02-01

    Superconducting tunnel junctions can be used as generators and detectors of monochromatic phonons of frequency larger than 80 GHz, as was first devised by Eisenmenger and Dayem (1967) and Kinder (1972a, 1973). In this report, we intend to give a general outline of this type of spectroscopy and to present the results obtained so far. The basic physics underlying phonon generation and detection are described in chapter I, a wider approach being given in the references therein. In chapter II, the different types of junctions are considered with respect to their use. Chapter III deals with the evaporation technique for the superconducting junctions. The last part of this report is devoted to the results that we have obtained on γ-irradiated LiF, pure Si and Phosphorous implanted Si. In these chapters, the limitations of the spectrometer are brought out and suggestions for further work are given [fr

  15. Electron and Phonon Transport in Molecular Junctions

    DEFF Research Database (Denmark)

    Li, Qian

    Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions....... The system we are interested in here are π-stacked molecules connected with two semi-infinite leads. π-stacked aromatic rings, connected via π-π electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport...... transmission at the Fermi energy. We propose and analyze a way of using π   stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific...

  16. Multiple topological phases in phononic crystals

    KAUST Repository

    Chen, Zeguo; Wu, Ying

    2017-01-01

    We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.

  17. Magnon rainbows filtered through phonon clouds

    Science.gov (United States)

    Boona, Stephen R.

    2016-06-01

    The study of heat flow in magnetic insulators is a topic of significant interest in spin caloritronics, especially for understanding the nuanced origins of the spin Seebeck effect (SSE). Recent work by Diniz and Costa (2016 New J. Phys. 18 052002) provides insight into this subject by presenting a microscopic model for the spectral dependence of magnon-phonon interactions in magnetic insulators, which has been a challenging puzzle for decades. Their new paper shows that phonon-mediated magnon-magnon interactions affect the lifetime of magnons differently depending on the magnon wavelength. As a result, low energy magnons transport spin more efficiently, and are more sensitive to applied magnetic fields. These results help explain some unexpected behavior in the SSE recently reported in several experiments.

  18. From Planck's quanta to phonon in solids

    International Nuclear Information System (INIS)

    Martinez- Duart, J. M; Melo, O. de

    2008-01-01

    Planck's 1900 published results on the black body radiation had the first application in the quantification of radiation. This quantum hypothesis explained several noteworthy light- matter interaction effects in 1905. These were the electron emission, Stokes law and gas ionization. As soon as two years later, A. Einstein derived an expression for the specific heat of solids, applying the quantum hypothesis to the mechanical oscillation of the atoms. In the present work, the main ideas which led to the concept of phonon are discussed. From an historical point of view, the developments due to Einstein, Born, Debye, among others are analyzed and most important properties of the phonons are presented. Finally, the importance of this entity in the theory of solids is explained, in particular regarding the thermal and optical properties as well as the electrical conductivity

  19. Multiple topological phases in phononic crystals

    KAUST Repository

    Chen, Zeguo

    2017-11-20

    We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.

  20. Photon-phonon interaction in photonic crystals

    International Nuclear Information System (INIS)

    Ueta, T

    2010-01-01

    Photon-phonon interaction on the analogy of electron-phonon interaction is considered in one-dimensional photonic crystal. When lattice vibration is artificially introduced to the photonic crystal, a governing equation of electromagnetic field is derived. A simple model is numerically analysed and the following novel phenomena are found out. The lattice vibration generates the light of frequency which added the integral multiple of the vibration frequency to that of the incident wave and also amplifies the incident wave resonantly. On a resonance, the amplification factor increases very rapidly with the number of layers increases. Resonance frequencies change with the phases of lattice vibration. The amplification phenomenon is analytically discussed for low frequency of the lattice vibration.

  1. Thermodynamics of phonon-modulated tunneling centers

    International Nuclear Information System (INIS)

    Junker, W.; Wagner, M.

    1989-01-01

    In recent years tunneling centers have frequently been used to explain the unusual thermodynamic properties of disordered materials; in these approaches, however, the effect of the tunneling-phonon interaction is neglected. The present study considers the archetype model of phono-assisted tunneling, which is well known from other areas of tunneling physics (quantum diffusion, etc.). It is shown that the full thermodynamic information can be rigorously extracted from a single Green function. An extended factorization procedure beyond Hartree-Fock is introduced, which is checked by sum rules as well as by exact Goldberger-Adams expansions. The phonon-modulated internal energy and specific heat are calculated for different power-law coupling setups

  2. Phonons as building blocks in nuclear structure

    International Nuclear Information System (INIS)

    Silvestre-Brac, B.

    1980-01-01

    The structure of a nuclear system in terms of eigenmodes (phonons) of subsystems is investigated in three different approaches. In the frame of nuclear field theory the three identical particle system is analysed and the elimination of spurious states due to the violation of the Pauli principle is emphasized. In terms of weak coupling, a new approach of the shell model is proposed which is shown to be rapidly convergent with the number of basis vectors. Applications of three particle systems in the lead region are made. Lastly, a microscopic multiphonon theorie of collective K=0 states in deformed nuclei based on a Tamm Dancoff phonon is developed. The role of the Pauli principle as well as comparisons with boson expansion methods are deeply analysed [fr

  3. Understanding photon sideband statistics and correlation for determining phonon coherence

    Science.gov (United States)

    Ding, Ding; Yin, Xiaobo; Li, Baowen

    2018-01-01

    Generating and detecting coherent high-frequency heat-carrying phonons have been topics of great interest in recent years. Although there have been successful attempts in generating and observing coherent phonons, rigorous techniques to characterize and detect phonon coherence in a crystalline material have been lagging compared to what has been achieved for photons. One main challenge is a lack of detailed understanding of how detection signals for phonons can be related to coherence. The quantum theory of photoelectric detection has greatly advanced the ability to characterize photon coherence in the past century, and a similar theory for phonon detection is necessary. Here, we reexamine the optical sideband fluorescence technique that has been used to detect high-frequency phonons in materials with optically active defects. We propose a quantum theory of phonon detection using the sideband technique and found that there are distinct differences in sideband counting statistics between thermal and coherent phonons. We further propose a second-order correlation function unique to sideband signals that allows for a rigorous distinction between thermal and coherent phonons. Our theory is relevant to a correlation measurement with nontrivial response functions at the quantum level and can potentially bridge the gap of experimentally determining phonon coherence to be on par with that of photons.

  4. Counting Tm dopant atoms around GaN dots using high-angle annular dark field images

    International Nuclear Information System (INIS)

    Rouvière, J-L; Okuno, H; Jouneau, P H; Bayle-Guillemaud, P; Daudin, B

    2011-01-01

    High resolution Z-contrast STEM imaging is used to study the Tm doping of GaN quantum dots grown in AlN by molecular beam epitaxy (MBE). High-angle annular dark field (HAADF) imaging allows us to visualize directly individual Tm atoms in the AlN matrix and even to count the number of Tm atoms in a given AlN atomic column. A new visibility coefficient to determine quantitatively the number of Tm atoms in a given atomic column is introduced. It is based on locally integrated intensities rather than on peak intensities of HAADF images. STEM image simulations shows that this new visibility is less sensitive to the defocus-induced blurring or to the position of the Tm atom within the thin lamella. Most of the Tm atoms diffuse out of GaN dots. Tm atoms are found at different positions in the AlN matrix, (i) Above the wetting layer, Tm atoms are spread within a thickness of 14 AlN monolayers (MLs). (ii) Above the quantum dots all the Tm are located in the same plane situated at 2-3 MLs above the apex of the GaN dot, i.e. at a distance of 14 MLs from the wetting layer, (iii) In addition, Tm can diffuse very far from the GaN dot by following threading dislocations lines.

  5. Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

    Science.gov (United States)

    Puzyrev, Vladimir; Torres-Verdín, Carlos; Calo, Victor

    2018-05-01

    The interpretation of resistivity measurements acquired in high-angle and horizontal wells is a critical technical problem in formation evaluation. We develop an efficient parallel 3-D inversion method to estimate the spatial distribution of electrical resistivity in the neighbourhood of a well from deep directional electromagnetic induction measurements. The methodology places no restriction on the spatial distribution of the electrical resistivity around arbitrary well trajectories. The fast forward modelling of triaxial induction measurements performed with multiple transmitter-receiver configurations employs a parallel direct solver. The inversion uses a pre-conditioned gradient-based method whose accuracy is improved using the Wolfe conditions to estimate optimal step lengths at each iteration. The large transmitter-receiver offsets, used in the latest generation of commercial directional resistivity tools, improve the depth of investigation to over 30 m from the wellbore. Several challenging synthetic examples confirm the feasibility of the full 3-D inversion-based interpretations for these distances, hence enabling the integration of resistivity measurements with seismic amplitude data to improve the forecast of the petrophysical and fluid properties. Employing parallel direct solvers for the triaxial induction problems allows for large reductions in computational effort, thereby opening the possibility to invert multiposition 3-D data in practical CPU times.

  6. High angle-of-attack aerodynamics of a strake-canard-wing V/STOL fighter configuration

    Science.gov (United States)

    Durston, D. A.; Schreiner, J. A.

    1983-01-01

    High angle-of-attack aerodynamic data are analyzed for a strake-canard-wing V/STOL fighter configuration. The configuration represents a twin-engine supersonic V/STOL fighter aircraft which uses four longitudinal thrust-augmenting ejectors to provide vertical lift. The data were obtained in tests of a 9.39 percent scale model of the configuration in the NASA Ames 12-Foot Pressure Wind Tunnel, at a Mach number of 0.2. Trimmed aerodynamic characteristics, longitudinal control power, longitudinal and lateral/directional stability, and effects of alternate strake and canard configurations are analyzed. The configuration could not be trimmed (power-off) above 12 deg angle of attack because of the limited pitch control power and the high degree of longitudinal instability (28 percent) at this Mach number. Aerodynamic center location was found to be controllable by varying strake size and canard location without significantly affecting lift and drag. These configuration variations had relatively little effect on the lateral/directional stability up to 10 deg angle of attack.

  7. PIV-based estimation of unsteady loads on a flat plate at high angle of attack using momentum equation approaches

    Science.gov (United States)

    Guissart, A.; Bernal, L. P.; Dimitriadis, G.; Terrapon, V. E.

    2017-05-01

    This work presents, compares and discusses results obtained with two indirect methods for the calculation of aerodynamic forces and pitching moment from 2D Particle Image Velocimetry (PIV) measurements. Both methodologies are based on the formulations of the momentum balance: the integral Navier-Stokes equations and the "flux equation" proposed by Noca et al. (J Fluids Struct 13(5):551-578, 1999), which has been extended to the computation of moments. The indirect methods are applied to spatio-temporal data for different separated flows around a plate with a 16:1 chord-to-thickness ratio. Experimental data are obtained in a water channel for both a plate undergoing a large amplitude imposed pitching motion and a static plate at high angle of attack. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculations. It is found that indirect methods are able to compute the mean and the temporal evolution of the loads for two-dimensional flows with a reasonable accuracy. Nonetheless, both methodologies are noise sensitive, and the parameters impacting the computation should thus be chosen carefully. It is also shown that results can be improved through the use of dynamic mode decomposition (DMD) as a pre-processing step.

  8. Column ratio mapping: a processing technique for atomic resolution high-angle annular dark-field (HAADF) images.

    Science.gov (United States)

    Robb, Paul D; Craven, Alan J

    2008-12-01

    An image processing technique is presented for atomic resolution high-angle annular dark-field (HAADF) images that have been acquired using scanning transmission electron microscopy (STEM). This technique is termed column ratio mapping and involves the automated process of measuring atomic column intensity ratios in high-resolution HAADF images. This technique was developed to provide a fuller analysis of HAADF images than the usual method of drawing single intensity line profiles across a few areas of interest. For instance, column ratio mapping reveals the compositional distribution across the whole HAADF image and allows a statistical analysis and an estimation of errors. This has proven to be a very valuable technique as it can provide a more detailed assessment of the sharpness of interfacial structures from HAADF images. The technique of column ratio mapping is described in terms of a [110]-oriented zinc-blende structured AlAs/GaAs superlattice using the 1 angstroms-scale resolution capability of the aberration-corrected SuperSTEM 1 instrument.

  9. Column ratio mapping: A processing technique for atomic resolution high-angle annular dark-field (HAADF) images

    International Nuclear Information System (INIS)

    Robb, Paul D.; Craven, Alan J.

    2008-01-01

    An image processing technique is presented for atomic resolution high-angle annular dark-field (HAADF) images that have been acquired using scanning transmission electron microscopy (STEM). This technique is termed column ratio mapping and involves the automated process of measuring atomic column intensity ratios in high-resolution HAADF images. This technique was developed to provide a fuller analysis of HAADF images than the usual method of drawing single intensity line profiles across a few areas of interest. For instance, column ratio mapping reveals the compositional distribution across the whole HAADF image and allows a statistical analysis and an estimation of errors. This has proven to be a very valuable technique as it can provide a more detailed assessment of the sharpness of interfacial structures from HAADF images. The technique of column ratio mapping is described in terms of a [1 1 0]-oriented zinc-blende structured AlAs/GaAs superlattice using the 1 A-scale resolution capability of the aberration-corrected SuperSTEM 1 instrument.

  10. Quantum mode phonon forces between chainmolecules

    DEFF Research Database (Denmark)

    Bohr, Jakob

    2001-01-01

    bimolecular interaction is a truly many-body force that is temperature dependent and can be of the order of 1 eV. These phonon forces depend on molecular shape, composition, and density. They may therefore also be important for large molecular conformational changes, including the unfolding of chain molecules....... For the later case, a significant change in zero-point energy is found. This may be the underlying cause for cold denaturation of proteins. (C) 2001 John Wiley & Sons, Inc....

  11. Comments on exciton-phonon coupling. II

    International Nuclear Information System (INIS)

    Allen, J.W.; Silbey, R.

    1979-01-01

    Two variational calculations of the energy and correlation functions for a simple exciton-phonon coupled system are presented and contrasted to the adiabatic solution and the exact solution. The simpler variational solution leads to two minima and abrupt changes in the properties of the system; an asymmetric variational wavefunction, motivated by the form of perturbation theory for this problem, leads to smooth behavior in agreement with the exact result. (Auth.)

  12. Phonon studies of intercalated conductive polymers

    Energy Technology Data Exchange (ETDEWEB)

    Prassides, K; Bell, C J [School of Chemistry and Molecular Sciences, Univ. of Sussex, Brighton (United Kingdom); Dianoux, A J [Inst. Laue-Langevin, 38 - Grenoble (France); Chunguey, Wu; Kanatzidis, M G [Dept. of Chemistry, Michigan State Univ., East Lansing (United States)

    1992-06-01

    The phonon density-of-states of FeOCl, the conductive form of polyaniline and the intercalation compound (polyaniline)[sub 0.20]FeOCl(I) have been measured by the neutron time-of-flight technique. The results are discussed in the light of the conducting and structural properties of the materials. Compound I is oxidised by standing in air and the neutron measurements reveal substantial changes in the inorganic host skeleton. (orig.).

  13. Nuclear wobbling-phonon excitations with alignments

    International Nuclear Information System (INIS)

    Hamamoto, I.

    2003-01-01

    Wobbling-phonon excitations, which are recently observed in 71 163 Lu 92 , are studied. The presence of alignments in nuclei makes it easier for wobbling excitations to appear at lower angular momenta of the yrast spectra. A family of rotational bands with wobbling excitations, which have nearly the same nuclear intrinsic structure, have been pinned down by observing specific electromagnetic decay properties between them. The triaxiality parameter γ = +20 deg. is obtained for the nuclear shape from measured E2 transition probabilities

  14. Electron-electron scattering and mobilities in semiconductors and quantum wells

    International Nuclear Information System (INIS)

    Lyo, S.K.

    1986-01-01

    The effect of electron-electron scattering on the mobility in semiconductors and semiconductor quantum wells is examined. A general exact formula is derived for the mobility, when the electron-electron collision rate is much faster than other scattering rates such as those by ionized impurities and phonons. In this limit, the transport relaxation rate is independent of the carrier's energy and contributions to the inverse mobility from individual scattering mechanism add up. The mobility becomes significantly reduced from its value in the absence of electron-electron scattering. When the collision rates are not necessarily dominated by electron-electron scattering, the mobility is calculated by the Kohler-Sondheimer variational method in the presence of ionized-impurity scattering and acoustic-phonon scattering in a nondegenerate two-dimensional quantum well

  15. Neutron scattering and the 1994 Nobel Physics Prize

    International Nuclear Information System (INIS)

    Sun Xiangdong

    1995-01-01

    Neutron scattering is an efficient method for detecting the microstructure of matter by which we can study, for example, details of the phonon spectrum in solids, and the isotopic effect. Bertram N. Brockhouse and Clifford G. Shull earned the Nobel Physics Prize in 1994 for their significant contributions in this domain

  16. Lattice dynamics of solid deuterium by inelastic neutron scattering

    DEFF Research Database (Denmark)

    Nielsen, Mourits; Bjerrum Møller, Hans

    1971-01-01

    The dispersion relations for phonons in solid ortho-deuterium have been measured at 5 °K by inelastic neutron scattering. The results are in good agreement with recent calculations in which quantum effects are taken into account. The data have been fitted to a third-neighbor general force model...

  17. Inelastic neutron scattering an ab-initio calculation of negative thermal expansion in Ag2O

    International Nuclear Information System (INIS)

    Gupta, M.K.; Mittal, R.; Rols, S.; Chaplot, S.L.

    2012-01-01

    The compound Ag 2 O undergoes large and isotropic negative thermal expansion over 0-500 K. We report temperature dependent inelastic neutron scattering measurements and ab-initio calculations of the phonon spectrum. The temperature dependence of the experimental phonon spectrum shows strong anharmonic nature of phonon modes of energy around 2.4 meV. The ab-initio calculations reveal that the maximum negative Grüneisen parameter, which is a measure of the relevant anharmonicity, occurs for the transverse phonon modes that involve bending motions of the Ag 4 O tetrahedra. The thermal expansion is evaluated from the ab-initio calculation of the pressure dependence of the phonon modes, and found in good agreement with available experimental data.

  18. Novel information theory techniques for phonon spectroscopy

    International Nuclear Information System (INIS)

    Hague, J P

    2007-01-01

    The maximum entropy method (MEM) and spectral reverse Monte Carlo (SRMC) techniques are applied to the determination of the phonon density of states (PDOS) from heat-capacity data. The approach presented here takes advantage of the standard integral transform relating the PDOS with the specific heat at constant volume. MEM and SRMC are highly successful numerical approaches for inverting integral transforms. The formalism and algorithms necessary to carry out the inversion of specific heat curves are introduced, and where possible, I have concentrated on algorithms and experimental details for practical usage. Simulated data are used to demonstrate the accuracy of the approach. The main strength of the techniques presented here is that the resulting spectra are always physical: Computed PDOS is always positive and properly applied information theory techniques only show statistically significant detail. The treatment set out here provides a simple, cost-effective and reliable method to determine phonon properties of new materials. In particular, the new technique is expected to be very useful for establishing where interesting phonon modes and properties can be found, before spending time at large scale facilities

  19. Optimization of phononic filters via genetic algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Hussein, M I [University of Colorado, Department of Aerospace Engineering Sciences, Boulder, Colorado 80309-0429 (United States); El-Beltagy, M A [Cairo University, Faculty of Computers and Information, 5 Dr. Ahmed Zewail Street, 12613 Giza (Egypt)

    2007-12-15

    A phononic crystal is commonly characterized by its dispersive frequency spectrum. With appropriate spatial distribution of the constituent material phases, spectral stop bands could be generated. Moreover, it is possible to control the number, the width, and the location of these bands within a frequency range of interest. This study aims at exploring the relationship between unit cell configuration and frequency spectrum characteristics. Focusing on 1D layered phononic crystals, and longitudinal wave propagation in the direction normal to the layering, the unit cell features of interest are the number of layers and the material phase and relative thickness of each layer. An evolutionary search for binary- and ternary-phase cell designs exhibiting a series of stop bands at predetermined frequencies is conducted. A specially formulated representation and set of genetic operators that break the symmetries in the problem are developed for this purpose. An array of optimal designs for a range of ratios in Young's modulus and density are obtained and the corresponding objective values (the degrees to which the resulting bands match the predetermined targets) are examined as a function of these ratios. It is shown that a rather complex filtering objective could be met with a high degree of success. Structures composed of the designed phononic crystals are excellent candidates for use in a wide range of applications including sound and vibration filtering.

  20. Optimization of phononic filters via genetic algorithms

    International Nuclear Information System (INIS)

    Hussein, M I; El-Beltagy, M A

    2007-01-01

    A phononic crystal is commonly characterized by its dispersive frequency spectrum. With appropriate spatial distribution of the constituent material phases, spectral stop bands could be generated. Moreover, it is possible to control the number, the width, and the location of these bands within a frequency range of interest. This study aims at exploring the relationship between unit cell configuration and frequency spectrum characteristics. Focusing on 1D layered phononic crystals, and longitudinal wave propagation in the direction normal to the layering, the unit cell features of interest are the number of layers and the material phase and relative thickness of each layer. An evolutionary search for binary- and ternary-phase cell designs exhibiting a series of stop bands at predetermined frequencies is conducted. A specially formulated representation and set of genetic operators that break the symmetries in the problem are developed for this purpose. An array of optimal designs for a range of ratios in Young's modulus and density are obtained and the corresponding objective values (the degrees to which the resulting bands match the predetermined targets) are examined as a function of these ratios. It is shown that a rather complex filtering objective could be met with a high degree of success. Structures composed of the designed phononic crystals are excellent candidates for use in a wide range of applications including sound and vibration filtering

  1. Phonon dispersion curves determination in (delta)-phase Pu-Ga alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wong, J; Clatterbuck, D; Occelli, F; Farber, D; Schwartz, A; Wall, M; Boro, C; Krisch, M; Beraud, A; Chiang, T; Xu, R; Hong, H; Zschack, P; Tamura, N

    2006-02-07

    We have designed and successfully employed a novel microbeam on large grain sample concept to conduct high resolution inelastic x-ray scattering (HRIXS) experiments to map the full phonon dispersion curves of an fcc {delta}-phase Pu-Ga alloy. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common {sup 239}Pu isotope and the non-availability of large (mm size) single crystal materials for Pu and its alloys. A classical Born von-Karman force constant model was used to model the experimental results, and no less than 4th nearest neighbor interactions had to be included to account for the observation. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus, (C{sub 11}-C{sub 12})/2, a Kohn-like anomaly in the T{sub 1}[011] branch, and a pronounced softening of the T[111] branch towards the L point in the Brillouin are found. These features may be related to the phase transitions of plutonium and to strong coupling between the crystal structure and the 5f valence instabilities. Our results represent the first full phonon dispersions ever obtained for any Pu-bearing material, thus ending a 40-year quest for this fundamental data. The phonon data also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for {delta}-plutonium. We also conducted thermal diffuse scattering experiments to study the T(111) dispersion at low temperatures with an attempt to gain insight into bending of the T(111) branch in relationship to the {delta} {yields} {alpha}{prime} transformation.

  2. Electron Raman scattering in quantum well wires

    International Nuclear Information System (INIS)

    Zhao Xiangfu; Liu Cuihong

    2007-01-01

    Electron Raman scattering (ERS) is investigated in a semiconductor quantum well wire (QWW) of cylindrical geometry for T=0K and neglecting phonon-assisted transitions. The differential cross-section (DCS) involved in this process is calculated as a function of a scattering frequency and the cylindrical radius. Electron states are confined within a QWW. Single parabolic conduction and valence bands are assumed. The selection rules are studied. Singularities in the spectra are interpreted for various cylindrical radii. ERS discussed here can provide direct information about the electron band structure of the system

  3. Research on low-frequency band gap property of a hybrid phononic crystal

    Science.gov (United States)

    Dong, Yake; Yao, Hong; Du, Jun; Zhao, Jingbo; Chao, Ding; Wang, Benchi

    2018-05-01

    A hybrid phononic crystal has been investigated. The characteristic frequency of XY mode, transmission loss and displacement vector have been calculated by the finite element method. There are Bragg scattering band gap and local resonance band gap in the band structures. We studied the influence factors of band gap. There are many flat bands in the eigenfrequencies curve. There are many flat bands in the curve. The band gap covers a large range in low frequency. The band gaps cover more than 95% below 3000 Hz.

  4. Isotope effect on superconductivity and Raman phonons of Pyrochlore Cd2Re2O7

    Science.gov (United States)

    Razavi, F. S.; Hajialamdari, M.; Reedyk, M.; Kremer, R. K.

    2018-06-01

    Cd2Re2O7 is the only α-Pyrochlore exhibiting superconductivity with a transition temperature (Tc) of ∼ 1 K. In this study, we present the effect of oxygen isotope (18O) as well as combined 18O and cadmium isotope (116Cd) substitution on the superconductivity and Raman scattering spectrum of Cd2Re2O7. The change of Tc and the energy gap Δ(T) are reported using various techniques including point contact spectroscopy. The shift in Raman phonon frequencies upon isotope substitution will be compared with measurement of the isotope effect on the superconducting transition temperature.

  5. Copper plasmonics and catalysis: role of electron-phonon interactions in dephasing localized surface plasmons

    Science.gov (United States)

    Sun, Qi-C.; Ding, Yuchen; Goodman, Samuel M.; H. Funke, Hans; Nagpal, Prashant

    2014-10-01

    Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain

  6. The non-pair forces and phonon dispersion in heavy alkali metals

    International Nuclear Information System (INIS)

    Aradhana, Km.; Rathore, R.P.S.

    1990-01-01

    Two types of non-pair forces, one from the Born-Mayer and the other from the Morse potential, are derived to discuss the response of electrons in heavy alkali metals, i.e., rubidium and cesium. The potentials are added to the two-body potential of Morse to account also for the ion-ion interactions. The potentials so obtained are employed to predict the phonon dispersion relations in bcc metals, which are also compared with recent precise neutron scattering data. (author). 1 fig, 3 tabs., 24 refs

  7. International Conference on Phonon Physics, 31 August-3 September 1981. Bloomington, Indiana,

    Science.gov (United States)

    1981-12-01

    semi-metal [11-12]. Such a behaviour is gene - rally ascribed either to (intravalley) electron-phonon interaction or *o scattering by static...and electric field dependence of the nonlinear coupling co- efficient ijk " For the first process, which involves the mixing of ultrasonic waves to gene ...DYNAMICS OF THE CUBIC-TETRAGONAL PHASE TRANSITION IN KNbO3 M.D. Fontana, G.E. Kugel and C. Carabatos University of Metz, Ile du Saulcy, 57045 Metz, Fance

  8. Analytical approach to phonons and electron-phonon interactions in single-walled zigzag carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Kandemir, B S; Keskin, M [Department of Physics, Faculty of Sciences, Ankara University, 06100 Tandogan, Ankara (Turkey)

    2008-08-13

    In this paper, exact analytical expressions for the entire phonon spectra in single-walled carbon nanotubes with zigzag geometry are presented by using a new approach, originally developed by Kandemir and Altanhan. This approach is based on the concept of construction of a classical lattice Hamiltonian of single-walled carbon nanotubes, wherein the nearest and next nearest neighbor and bond bending interactions are all included, then its quantization and finally diagonalization of the resulting second quantized Hamiltonian. Furthermore, within this context, explicit analytical expressions for the relevant electron-phonon interaction coefficients are also investigated for single-walled carbon nanotubes having this geometry, by the phonon modulation of the hopping interaction.

  9. Analytical approach to phonons and electron-phonon interactions in single-walled zigzag carbon nanotubes

    International Nuclear Information System (INIS)

    Kandemir, B S; Keskin, M

    2008-01-01

    In this paper, exact analytical expressions for the entire phonon spectra in single-walled carbon nanotubes with zigzag geometry are presented by using a new approach, originally developed by Kandemir and Altanhan. This approach is based on the concept of construction of a classical lattice Hamiltonian of single-walled carbon nanotubes, wherein the nearest and next nearest neighbor and bond bending interactions are all included, then its quantization and finally diagonalization of the resulting second quantized Hamiltonian. Furthermore, within this context, explicit analytical expressions for the relevant electron-phonon interaction coefficients are also investigated for single-walled carbon nanotubes having this geometry, by the phonon modulation of the hopping interaction

  10. Electron-Mediated Phonon-Phonon Coupling Drives the Vibrational Relaxation of CO on Cu(100)

    Science.gov (United States)

    Novko, D.; Alducin, M.; Juaristi, J. I.

    2018-04-01

    We bring forth a consistent theory for the electron-mediated vibrational intermode coupling that clarifies the microscopic mechanism behind the vibrational relaxation of adsorbates on metal surfaces. Our analysis points out the inability of state-of-the-art nonadiabatic theories to quantitatively reproduce the experimental linewidth of the CO internal stretch mode on Cu(100) and it emphasizes the crucial role of the electron-mediated phonon-phonon coupling in this regard. The results demonstrate a strong electron-mediated coupling between the internal stretch and low-energy CO modes, but also a significant role of surface motion. Our nonadiabatic theory is also able to explain the temperature dependence of the internal stretch phonon linewidth, thus far considered a sign of the direct anharmonic coupling.

  11. [Morphological analysis of alveolar bone of anterior mandible in high-angle skeletal class II and class III malocclusions assessed with cone-beam computed tomography].

    Science.gov (United States)

    Ma, J; Jiang, J H

    2018-02-18

    To evaluate the difference of features of alveolar bone support under lower anterior teeth between high-angle adults with skeletal class II malocclusions and high-angle adults presenting skeletal class III malocclusions by using cone-beam computed tomography (CBCT). Patients who had taken the images of CBCT were selected from the Peking University School and Hospital of Stomatology between October 2015 and August 2017. The CBCT archives from 62 high-angle adult cases without orthodontic treatment were divided into two groups based on their sagittal jaw relationships: skeletal class II and skeletal class III. vertical bone level (VBL), alveolar bone area (ABA), and the width of alveolar bone were measured respectively at the 2 mm, 4 mm, 6 mm below the cemento-enamel junction (CEJ) level and at the apical level. After that, independent samples t-tests were conducted for statistical comparisons. The ABA of the mandibular alveolar bone in the area of lower anterior teeth was significantly thinner in the patients of skeletal class III than those of skeletal class II, especially in terms of the apical ABA, total ABA on the labial and lingual sides and the ABA at 6 mm below CEJ level on the lingual side (Pclass III than those of skeletal class II, especially regarding the apical level on the labial and lingual side and at the level of 4 mm, 6 mm below CEJ level on the lingual side (Pclass III adult patients with high-angle when compared with the sample of high-angle skeletal class II adult cases. We recommend orthodontists to be more cautious in treatment of high-angle skeletal class III patients, especially pay attention to control the torque of lower anterior teeth during forward and backward movement, in case that the apical root might be absorbed or fenestration happen in the area of lower anterior teeth.

  12. High mobility In0.75Ga0.25As quantum wells in an InAs phonon lattice

    Science.gov (United States)

    Chen, C.; Holmes, S. N.; Farrer, I.; Beere, H. E.; Ritchie, D. A.

    2018-03-01

    InGaAs based devices are great complements to silicon for CMOS, as they provide an increased carrier saturation velocity, lower operating voltage and reduced power dissipation (International technology roadmap for semiconductors (www.itrs2.net)). In this work we show that In0.75Ga0.25As quantum wells with a high mobility, 15 000 to 20 000 cm2 V-1 s-1 at ambient temperature, show an InAs-like phonon with an energy of 28.8 meV, frequency of 232 cm-1 that dominates the polar-optical mode scattering from  ˜70 K to 300 K. The measured optical phonon frequency is insensitive to the carrier density modulated with a surface gate or LED illumination. We model the electron scattering mechanisms as a function of temperature and identify mechanisms that limit the electron mobility in In0.75Ga0.25As quantum wells. Background impurity scattering starts to dominate for temperatures  <100 K. In the high mobility In0.75Ga0.25As quantum well, GaAs-like phonons do not couple to the electron gas unlike the case of In0.53Ga0.47As quantum wells.

  13. Electron-phonon coupling and superconductivity in the (4/3)-monolayer of Pb on Si(111): Role of spin-orbit interaction

    Science.gov (United States)

    Sklyadneva, I. Yu.; Heid, R.; Bohnen, K.-P.; Echenique, P. M.; Chulkov, E. V.

    2018-05-01

    The effect of spin-orbit coupling on the electron-phonon interaction in a (4/3)-monolayer of Pb on Si(111) is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. We show that the spin-orbit interaction produces a large weakening of the electron-phonon coupling strength, which appears to be strongly overestimated in the scalar relativistic calculations. The effect of spin-orbit interaction is largely determined by the induced modification of Pb electronic bands and a stiffening of the low-energy part of phonon spectrum, which favor a weakening of the electron-phonon coupling strength. The state-dependent strength of the electron-phonon interaction in occupied Pb electronic bands varies depending on binding energy rather than electronic momentum. It is markedly larger than the value averaged over electron momentum because substrate electronic bands make a small contribution to the phonon-mediated scattering and agrees well with the experimental data.

  14. On the Debye-Waller factor in atom-surface scattering

    International Nuclear Information System (INIS)

    Garcia, N.; Maradudin, A.A.; Celli, V.

    1982-01-01

    A theory for the Debye-Waller factor in atom-surface scattering is presented, to lowest order in the phonon contributions. Multiple-scattering effects as well as the cross-correlated surface atom displacements are included. The theory accounts for experimental data without the necessity of introducing the Armand effect, which is due to the finite size of the incident atom. The work presented here implies that the Kirchhoff approximation fails when the energy of the incident particle is in the energy range of the phonon spectrum. The results of the calculation are presented in the high-temperature limit, and it is observed that the Rayleigh surface phonons contribute three-quarters of the Debye-Waller factor, while the bulk phonons account for the rest. This result is interesting because the calculation of the former contribution is simpler than that of the latter. (author)

  15. A thermal neutron scattering law for yttrium hydride

    Science.gov (United States)

    Zerkle, Michael; Holmes, Jesse

    2017-09-01

    Yttrium hydride (YH2) is of interest as a high temperature moderator material because of its superior ability to retain hydrogen at elevated temperatures. Thermal neutron scattering laws for hydrogen bound in yttrium hydride (H-YH2) and yttrium bound in yttrium hydride (Y-YH2) prepared using the ab initio approach are presented. Density functional theory, incorporating the generalized gradient approximation (GGA) for the exchange-correlation energy, is used to simulate the face-centered cubic structure of YH2 and calculate the interatomic Hellmann-Feynman forces for a 2 × 2 × 2 supercell containing 96 atoms. Lattice dynamics calculations using PHONON are then used to determine the phonon dispersion relations and density of states. The calculated phonon density of states for H and Y in YH2 are used to prepare H-YH2 and Y-YH2 thermal scattering laws using the LEAPR module of NJOY2012. Analysis of the resulting integral and differential scattering cross sections demonstrates adequate resolution of the S(α,β) function. Comparison of experimental lattice constant, heat capacity, inelastic neutron scattering spectra and total scattering cross section measurements to calculated values are used to validate the thermal scattering laws.

  16. Pump pulse duration dependence of coherent phonon amplitudes in antimony

    Energy Technology Data Exchange (ETDEWEB)

    Misochko, O. V., E-mail: misochko@issp.ac.ru [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)

    2016-08-15

    Coherent optical phonons of A{sub 1k} and E{sub k} symmetry in antimony have been studied using the femtosecond pump–probe technique. By varying the pump-pulse duration and keeping the probe duration constant, it was shown that the amplitude of coherent phonons of both symmetries exponentially decreases with increasing pulse width. It was found that the amplitude decay rate for the fully symmetric phonons with larger frequency is greater than that of the doubly degenerate phonons, whereas the frequency and lifetime for coherent phonons of both symmetries do not depend on the pump-pulse duration. Based on this data, the possibility of separation between dynamic and kinematic contributions to the generation mechanism of coherent phonons is discussed.

  17. NATO Advanced Study Institute on Nonequilibrium Phonon Dynamics

    CERN Document Server

    1985-01-01

    Phonons are always present in the solid state even at an absolute temperature of 0 K where zero point vibrations still abound. Moreover, phonons interact with all other excitations of the solid state and, thereby, influence most of its properties. Historically experimental information on phonon transport came from measurements of thermal conductivity. Over the past two decades much more, and much more detailed, information on phonon transport and on many of the inherent phonon interaction processes have come to light from experiments which use nonequilibrium phonons to study their dynamics. The resultant research field has most recently blossomed with the development of ever more sophisticated experimental and theoretical methods which can be applied to it. In fact, the field is moving so rapidly that new members of the research community have difficulties in keeping up to date. This NATO Advanced Study Institute (ASI) was organized with the objective of overcoming the information barrier between those expert...

  18. Phonon response of some heavy Fermion systems in dynamic limit

    Science.gov (United States)

    Sahoo, Jitendra; Shadangi, Namita; Nayak, Pratibindhya

    2017-05-01

    The phonon excitation spectrum of some Heavy Fermion (HF) systems in the presence of electron-phonon interaction is studied in the dynamic limit (ω≠0). The renormalized excitation phonon frequencies (ω˜ = ω/ω0) are evaluated through Periodic Anderson Model (PAM) in the presence of electron-phonon interaction using Zubarev-type double time temperature-dependent Green function. The calculated renormalized phonon energy is analyzed through the plots of (ω˜ = ω/ω0) against temperature for different system parameters like effective coupling strength ‘g’ and the position of f-level ‘d’. The observed behavior is analyzed and found to agree with the general features of HF systems found in experiments. Further, it is observed that in finite but small q-values the propagating phonons harden and change to localized peaks.

  19. Ultrafast optical generation of squeezed magnon states and long lifetime coherent LO phonons

    Science.gov (United States)

    Zhao, Jimin

    2005-12-01

    Ultrafast optical pulses have been used to generate, probe, and control low-energy elementary excitations in crystals. In particular, we report the first experimental demonstration of the generation of quantum squeezed states of magnons (collective spin-wave excitations) in a magnetic material, and new progress in experimental investigation of anharmonic interactions in a semiconductor. The mechanism for the magnon squeezing is two-magnon impulsive stimulated Raman scattering (ISRS). Femtosecond laser pulses have been used to coherently correlate degenerate counter-propagating magnons in the antiferromagnetic insulator MnF2. In the squeezed state, fluctuations of the magnetization of a crystallographic unit cell vary periodically in time and are reduced below that of the ground-state quantum noise. Similar experiments were also performed in another antiferromagnetic insulator, FeF2, for which the squeezing effect is one order of magnitude larger. We have also investigated the anharmonic interaction of the low-frequency E2 phonon in ZnO through ISRS. Temperature dependence of the linewidth and frequency indicates that the two-phonon up-conversion process is the dominant decay channel and isotopic disorder may be the main limit on the lifetime at low temperature. We have observed the longest lifetime of an optical phonon mode in a solid (211 ps at 5 K). And we have found that pump-probe experiments, compared with spontaneous Raman spectroscopy, have extremely high accuracy in determining the frequency of a low-lying excitation.

  20. The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Mardaani, Mohammad, E-mail: mohammad-m@sci.sku.ac.ir; Rabani, Hassan, E-mail: rabani-h@sci.sku.ac.ir [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, 8818634141 Shahrekord (Iran, Islamic Republic of); Esmaili, Esmat; Shariati, Ashrafalsadat [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of)

    2015-08-07

    A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.