WorldWideScience
 
 
1

Phonon recycling in ion-doped lasers  

Science.gov (United States)

Phonon emission is an energy-conversion efficiency loss in photonic transition processes. Phonon recycling by the anti-Stokes cooling results in a lower operating temperature. Transmitted optical phonons cross heterogeneous boundary and the upconverted acoustic phonons contribute to higher occupancy of the optical phonon and increase the second-order transition rate. Optimization of phonon spectra makes upconversion favorable. We present theoretical study and quantitative efficiency results for phonon recycling in Yb3+ doped yttria alumina garnet lasing layer and its adjacent Yb3+:ZrF2 cooling layers and examine the thermodynamic limits. It is predicted that 30% of emitted phonons are recycled and further improvement is possible.

Kim, Jedo; Kaviany, Massoud

2009-08-01

2

Coherent phonon detection in Ge with a femtosecond laser  

International Nuclear Information System (INIS)

[en] A highly sensitive femtosecond photo deflection spectroscopy technique was first developed experimentally. Using femtosecond laser pulses the authors have detected ultrafast coherent phonon emission in a Ge plate. It is found that the ultrafast femtosecond laser pulses generate coherent phonons in the plate via the electronic mechanism. Supersonic expansion of photo-excited electron-hole plasma is observed

2001-01-01

3

Origin of coherent phonons in Bi2Te3 excited by ultrafast laser pulses  

Science.gov (United States)

Femtosecond laser pulses are used to excite coherent optical phonons in single crystal Bi2Te3 thin films. Oscillations from low- and high-frequency A1g phonon modes are observed. A perturbation model based on molecular dynamics reveals various possibilities of phonon generation due to complex interactions among different phonon modes. In order to elucidate the process of phonon generation, measurements on thin films with thicknesses below the optical absorption depth are carried out, showing that a gradient force is necessary to excite the observed A1g phonon modes, which provides a refined picture of displacive excitation of coherent phonon.

Wang, Yaguo; Guo, Liang; Xu, Xianfan; Pierce, Jonathan; Venkatasubramanian, Rama

2013-08-01

4

Electron and phonon distribution relaxation in metal films under a femtosecond laser pulse  

Energy Technology Data Exchange (ETDEWEB)

The simultaneous time evolution of electron and phonon distributions in a gold film submitted to a femtosecond laser pulse has been theoretically investigated. A system of two coupled time-dependent Boltzmann equations describing electron and phonon dynamics has been solved by considering electron-electron (e-e) and electron-phonon (e-p) collisions. Phonon-phonon (p-p) collisions have been neglected. The collision probability of each process is derived by quantum-mechanical first order perturbation theory. The injected laser energy (source term) is directly absorbed by the electron gas through electron-photon collisions and a perturbation term is added to the Boltzmann equation for electrons. However, phonons do not directly absorb energy from the laser but they are affected by the irradiation due to their collisional interaction with electrons. The results emphasize the transient non-equilibrium behavior of the electron distribution function and details of electron and phonon relaxation dynamics.

Pietanza, L.D.; Colonna, G.; Longo, S.; Capitelli, M

2004-04-01

5

Dynamics of a vertical cavity quantum cascade phonon laser structure.  

UK PubMed Central (United Kingdom)

Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325 GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic output of the device as a function of time after applying electrical pumping. The emission builds in intensity reaching a steady state on a timescale of order 0.1 ?s. We show that the results are consistent with a model of the dynamics of a saser cavity exactly analogous to the models used for describing laser dynamics. We also obtain estimates for the gain coefficient, steady-state acoustic power output and efficiency of the device.

Maryam W; Akimov AV; Campion RP; Kent AJ

2013-01-01

6

Phonon contribution to double-heterojunction laser operation  

Energy Technology Data Exchange (ETDEWEB)

Laser data (77 and 300 K) are presented on two photopumped undoped metallorganic chemical vapor deposition Al/sub x/Ga/sub 1-x/As -GaAs heterostructures with active regions consisting of: (i) a thick GaAs layer (L/sub z/1 approx.1500 A) coupled to an auxiliary quantum-well array of seven small L/sub z/2 approx.50 A coupled GaAs layers, and (ii) a comparison single thick GaAs layer (L/sub z/2 approx.600 A) in the form of a conventional double heterostructure (DH). Because of the strengthening of phonon-assisted recombination with temperature, laser operation of the bulk (L/sub z/ > or approx. =500 A) GaAs layers is shifted from h..omega..approx.E/sub g/ at 77 K to E/sub g/ -h..omega../sub L/0 < or =h..omega..phonon assisted.

Holonyak, N. Jr.; Vojak, B.A.; Laidig, W.D.; Hess, K.; Coleman, J.J.; Dapkus, P.D.

1980-07-15

7

Tunable hypersonic-phonon emission from semiconductor quantum wire systems under free-electron laser radiations  

International Nuclear Information System (INIS)

[en] Full text: Recently, electrical generation of high-frequency ultrasonic phonons from low-dimensional semiconductor systems (LDSSs) has been studied both experimentally and theoretically by Australian research teams. It has been found that by electrical generation of the phonon emission from a LDSS device with fixed sample parameters, it is difficult to tune the frequency and the angle of the phonon emission. Here, we propose a novel scheme for generating tunable hypersonic phonon sources (i.e., the phonon frequency generated is far above 109 Hz) by optical means. This is motivated by recent availability of the free-electron laser radiations. In this work, a theoretical study of generation of high-frequency acoustic phonons by electrons in GaAs-based quantum wire (QWi) systems, subject to intense terahertz (THz) electromagnetic (EM) radiations, is conducted. We have studied the frequency and angular distribution of the phonon emission generated optically via deformation potential coupling. The distinctive nature for electron-photon-phonon interactions in a QWi device results in a strong dependence of the acoustic phonon emission on strength E0 and frequency ? of the THz EM field. Consequently, the frequency and the angle for THz phonon emission can be tuned by varying E0 and/or ?). We find that the tunable hypersonic generation from semiconductor QWi systems can be achieved by using recently developed free-electron laser radiations

1998-01-01

8

Terahertz time domain spectroscopy of phonon-depopulation based quantum cascade lasers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The gain and loss in a terahertz quantum cascade laser based on a longitudinal optical phonon depopulation scheme is studied using terahertz time domain spectroscopy. At laser threshold the gain is found to be clamped at 25 cm?1 for a 1 mm long device and the full width at half maximum of the spectr...

Jukam, Nathan; Dhillon, Sukhdeep; Oustinov, Dimitri; Madéo, Julien; Tignon, Jérôme; Colombelli, Raffaele; Dean, Paul

9

Terahertz Time Domain Spectroscopy of Phonon-Depopulation Based Quantum Cascade Lasers  

International Nuclear Information System (INIS)

A 3.1 THz phonon depopulation-based quantum-cascade-laser is investigated using terahertz time domain spectroscopy. A gain of 25 cm-1 and absorption features due to the lower laser level being populated from a parasitic electronic channel are highlighted.

2011-12-23

10

Laser heating versus phonon confinement effect in the Raman spectra of diamond nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Nanodiamond particles with typical diameters of 20 and 6 nm produced by high pressure high temperature or detonation processes have been studied by micro-Raman spectroscopy. We show that the frequency downshift and broadening of the first-order diamond phonon band is not uniquely related to phonon confinement, as commonly assumed. Local heating caused by the focused laser light must be also taken in account, since it may affect the Raman spectrum in a similar fashion, even at relatively low laser power levels. A combined theoretical model considering both effects (quantum confinement and local heating) on the excited phonon modes is presented and adopted for the simulation of the experimental data. We observe different heating behaviours upon laser illumination depending on the particles origin, thus underscoring the importance to compensate for this effect before retrieving structural parameters.

Chaigneau, Marc; Picardi, Gennaro, E-mail: gennaro.picardi@poly.polytechnique.fr [LPICM, Ecole Polytechnique, CNRS (France); Girard, Hugues A.; Arnault, Jean-Charles [LIST, Diamond Sensors Laboratory, CEA (France); Ossikovski, Razvigor [LPICM, Ecole Polytechnique, CNRS (France)

2012-06-15

11

The effect of phonon extraction level separation on the performance of three-well resonant-phonon terahertz quantum-cascade lasers  

International Nuclear Information System (INIS)

The authors present a simulation and experimental study on the effect of phonon extraction level separation on the performance of GaAs-based three-well resonant-phonon terahertz quantum-cascade lasers (QCLs). The phonon extraction level separation is varied from 30 to 42 meV. Because of the efficient longitudinal-optical phonon scattering, the 36 meV QCL shows the largest gain, the best temperature performance and the highest output power. As for the lower (30 meV) or higher (42 meV) energy separation QCLs, the electron–longitudinal-optical phonon interaction still works by involving a transfer of in-plane momentum. The measured lasing characteristics are in qualitative agreement with simulation

2009-06-10

12

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation  

Science.gov (United States)

The transient reflectivity response of phase-change Ge2Sb2Te5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases (amorphous, fcc-, and hcp-crystalline), as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investigated for the fcc-crystalline phase and the laser-crystallized material, revealing strong differences. We find evidence that a considerable fraction of amorphous phase remains in the laser-crystallized material, which features a different phonon frequency, not related to other phases. These results are important for emerging strategies aimed at driving ultrafast phase transitions via coherent phonon excitation for applications in data storage.

Hernandez-Rueda, J.; Savoia, A.; Gawelda, W.; Solis, J.; Mansart, B.; Boschetto, D.; Siegel, J.

2011-06-01

13

Coupled carrier–phonon nonequilibrium dynamics in terahertz quantum cascade lasers: a Monte Carlo analysis  

Science.gov (United States)

The operation of state-of-the-art optoelectronic quantum devices may be significantly affected by the presence of a nonequilibrium quasiparticle population to which the carrier subsystem is unavoidably coupled. This situation is particularly evident in new-generation semiconductor-heterostructure-based quantum emitters, operating both in the mid-infrared as well as in the terahertz (THz) region of the electromagnetic spectrum. In this paper, we present a Monte Carlo-based global kinetic approach, suitable for the investigation of a combined carrier–phonon nonequilibrium dynamics in realistic devices, and discuss its application with a prototypical resonant-phonon THz emitting quantum cascade laser design.

Iotti, Rita C.; Rossi, Fausto

2013-07-01

14

On the amplification of sound (acoustic phonons) by absorption of laser radiation in cylindrical quantum wires  

CERN Multimedia

Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of laser radiation in cylindrical quantum wires is calculated for the case of monophoton absorption process and the case of multiphoton absorption process. Analytical expressions and conditions for the absorption of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption are discussed; numerical computations and plots are carried out for a GaAs/GaAsAl quantum wire. The results are compared with bulk semiconductors and quantum wells.

Hung, N Q; Bau, N Q; Hung, Nguyen Quoc; Nhan, Nguyen Vu; Bau, Nguyen Quang

2002-01-01

15

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

Directory of Open Access Journals (Sweden)

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.

Hu Jianbo; Misochko Oleg V.; Nakamura Kazutaka G.

2013-01-01

16

Resonance laser-plasma excitation of coherent terahertz phonons in the bulk of fluorine-bearing crystals under high-intensity femtosecond laser irradiation  

Science.gov (United States)

The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation.

Potemkin, F. V.; Mareev, E. I.; Mikheev, P. M.; Khodakovskii, N. G.

2013-08-01

17

A route from the negative-effective-mass generators to the phonon-difference FIR lasers  

Science.gov (United States)

Solid-state sources covering the wave number range from 5 to 120 cm-1 are considered. Experimental data on the negative effective masses, the inverted cyclotron resonance transitions, as well as the light-to-heavy hole band transition inversion are compared with existing theoretical models. On the basis of this comparison, the phonon-difference process inversion is proposed as a new mechanism of stimulated FIR radiation. Contrary to the previous models which require complicated carrier-energy band structures, like that in p-type Ge, the two-phonon difference radiation is expected to act both inp and n-type materials. Magnetic fields and cooling down to liquid helium temperatures are not necessary for its operation. Crystalline Si, Ge, A3B5, A2B6 and other semiconductor compounds are candidates for creating lasers on phonons.

Brazis, R.

1995-01-01

18

Non-equilibrium electron and phonon dynamics in metals under femtosecond laser pulses  

Energy Technology Data Exchange (ETDEWEB)

Different models for relaxation dynamics of electrons and phonons in a thin metal film heated by femto-pico second laser pulses have been discussed. The traditional two-temperature approach reveals to be inaccurate due to deviations of electrons and phonons from Fermi-Dirac and Bose-Einstein distributions, respectively. Coupled Boltzmann kinetic equations have been adapted for the quantum statistics to study the energy distribution of electrons and phonons in metals. Theoretical details have been discussed and a new solution method has been proposed overcoming numerical problems and improving stability, allowing the study of the dynamics until the complete relaxation. Numerical results have been compared with photoemission spectroscopy experimental data. (authors)

Pietanza, L.D.; Colonna, G.; Longo, S.; Capitelli, M. [Istituto di Metodologie Inorganiche e dei Plasmi (IMIP), CNR, Bari (Italy); Longo, S.; Capitelli, M. [Degli Studi di Bari Univ., Dipt. di Chimica (Italy)

2007-11-15

19

Non-equilibrium electron and phonon dynamics in metals under femtosecond laser pulses  

International Nuclear Information System (INIS)

Different models for relaxation dynamics of electrons and phonons in a thin metal film heated by femto-pico second laser pulses have been discussed. The traditional two-temperature approach reveals to be inaccurate due to deviations of electrons and phonons from Fermi-Dirac and Bose-Einstein distributions, respectively. Coupled Boltzmann kinetic equations have been adapted for the quantum statistics to study the energy distribution of electrons and phonons in metals. Theoretical details have been discussed and a new solution method has been proposed overcoming numerical problems and improving stability, allowing the study of the dynamics until the complete relaxation. Numerical results have been compared with photoemission spectroscopy experimental data. (authors)

2007-01-01

20

Low-phonon-frequency chalcogenide crystalline hosts for rare earth lasers operating beyond three microns  

Energy Technology Data Exchange (ETDEWEB)

The invention comprises a RE-doped MA.sub.2 X.sub.4 crystalline gain medium, where M includes a divalent ion such as Mg, Ca, Sr, Ba, Pb, Eu, or Yb; A is selected from trivalent ions including Al, Ga, and In; X is one of the chalcogenide ions S, Se, and Te; and RE represents the trivalent rare earth ions. The MA.sub.2 X.sub.4 gain medium can be employed in a laser oscillator or a laser amplifier. Possible pump sources include diode lasers, as well as other laser pump sources. The laser wavelengths generated are greater than 3 microns, as becomes possible because of the low phonon frequency of this host medium. The invention may be used to seed optical devices such as optical parametric oscillators and other lasers.

Payne, Stephen A. (Castro Valley, CA); Page, Ralph H. (San Ramon, CA); Schaffers, Kathleen I. (Pleasanton, CA); Nostrand, Michael C. (Livermore, CA); Krupke, William F. (Pleasanton, CA); Schunemann, Peter G. (Malden, MA)

2000-01-01

 
 
 
 
21

Electron- and phonon-coupling in femtosecond laser-induced desorption of CO from Ru(0001)  

Science.gov (United States)

We studied femtosecond laser-induced desorption of CO from Ru(0001) using intense near-infrared and visible femtosecond laser pulses. We find a pronounced wavelength dependence with a factor 3-4 higher desorption yield at comparable fluence when desorption is induced via 400 nm light, compared to 800 nm and attribute this difference to the difference in penetration depth of the incident light. All our data can be described using empirical friction-modeling to determine the desorption mechanism with the same mechanism for both wavelengths. We find that both hot electrons and phonons contribute to the desorption process.

Gladh, J.; Hansson, T.; Öström, H.

2013-09-01

22

Evidence from Laser ARPES of Electron-Optical Phonon Coupling Near the Node of Optimally Doped Bi2212  

Science.gov (United States)

Laser based photoemission with photons of energy 6 eV is used to examine the fine details of the very low energy electron dispersion and associated dynamics in the nodal region of optimally doped Bi2212. A ``kink'' in the dispersion in the immediate vicinity of the Fermi energy is associated with scattering from an optical phonon previously identified in Raman studies. The identification of this phonon as the appropriate mode is confirmed by comparing the scattering rates observed experimentally with the results of calculated scattering rates based on the properties of the phonon mode as well as the mode's observed dispersion with respect to Fermi surface angle at low temperature.

Rameau, Jonathan; Yang, Hongbo; Johnson, Peter

2010-03-01

23

Characterization of Femtosecond laser-irradiation crystallization and structure of multiple periodic Si/Sb??Te?? nanocomposite films by coherent phonon spectroscopy.  

UK PubMed Central (United Kingdom)

Multiple parameters of nanocomposite Si/Sb??Te?? multilayer films are possibly optimized simultaneously to satisfy the development of ideal phase-change memory devices by adjusting chemical composition and physical structure of multilayer films. The crystallization and structure of the films are studied by coherent phonon spectroscopy. Laser irradiation power dependence of coherent optical phonon spectroscopy reveals laser-induced crystallization of the amorphous multilayer film, while coherent acoustic phonon spectroscopy reveals the presence of folded acoustic phonons which suggests a good periodic structure of the multilayer films. Laser irradiation-induced crystallization shows applicable potentials of the multilayer films in optical phase change storage.

Zhu W; Wang C; Sun M; Li S; Zhai J; Lai T

2011-11-01

24

Effect of periodic number of [Si/Sb80Te20]x multilayer film on its laser-induced crystallization studied by coherent phonon spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The periodic number dependence of the femtosecond laser-induced crystallization threshold of [Si(5nm)/Sb80Te20(5nm)]x nanocomposite multilayer films has been investigated by coherent phonon spectroscopy. Coherent optical phonon spectra show that femtosecond laser-irradiated crystallization threshold...

Zhu, Weiling; Wang, Changzhou; Sun, Mingcheng; Li, Simian; Zhai, Jiwei; Lai, Tianshu

25

Phonon Assisted Laser Transitions and Energy Transfer in Rare Earth Laser Crystals.  

Science.gov (United States)

An extensive study of energy transfer and phonon interaction in rare earth doped LiYF4 has been conducted. The trivalent rare earth ions Pr, Nd, Dy, Ho, Er, Tm and Yb were used as the optically active ions. Y2Ti2O7, also doped with rare earth ions, was ex...

H. P. Jenssen

1971-01-01

26

Laser action on corona pulses  

International Nuclear Information System (INIS)

The influence of UV laser radiation on the formation and development of corona pulses was investigated. In the case of a positive point a non-branched streamer was obtained which had good reproducibility in time and space. In the case of a negative point the formation of discharge pulses below the onset potential is explained by thermionic emission; at higher voltages electron explosive emission is supposed to be active in pulse formation. (author) 8 figs., 11 refs

1990-06-01

27

Theory of amplification of sound (acoustic phonons) by absorption of laser radiation in quantum wires with parabolic potential  

CERN Multimedia

Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of a laser radiation in quantum wires with parabolic potential is calculated for the case of monophoton absorption and the case of multiphoton absorption. Analytical expressions and conditions for the absorption coefficient of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption are discussed; numerical computations and plots are carried out for a GaAs/GaAsAl quantum wire. The results are compared with bulk semiconductors and quantum wells.

Hung, N Q; Bau, N Q; Hung, Nguyen Quoc; Vuong, Dinh Quoc; Bau, Nguyen Quang

2002-01-01

28

Optical phonons in laser-deposited CdS{sub x}Te{sub 1{minus}x} films  

Energy Technology Data Exchange (ETDEWEB)

We report the longitudinal optical (LO) phonon frequencies for thin films of the ternary alloy CdS{sub x}Te{sub 1{minus}x} and their composition dependence for the full range of x values from pure CdTe to pure CdS. Pulsed laser deposition was used to prepare the polycrystalline thin films including compositions well inside the miscibility gap. We find that this ternary system exhibits a {open_quotes}two-mode{close_quotes} behavior with CdS- and CdTe-like longitudinal optic phonon modes. The modified random-element isodisplacement model yields a good description of the composition dependence of the LO phonon frequencies. {copyright} {ital 1997 American Institute of Physics.}

Fischer, A.; Feng, Z.; Bykov, E.; Contreras-Puente, G.; Compaan, A. [The University of Toledo, Toledo, Ohio 43606 (United States); de Landa Castillo-Alvarado, F.; Avendano, J. [ESFM-IPN, Mexico City, 07738 (Mexico); Mason, A. [NREL, Golden, Colorado 80401 (United States)

1997-06-01

29

Laser action by optically depumping lower states  

Science.gov (United States)

A method and apparatus are described for obtaining laser action between an upper energy level and a lower energy level of a gaseous medium. The upper energy level is populated to some degree (short of achieving a conventional inverted population) by any suitable pumping means, and an inverted population is established by transiently and selectively depumping the lower energy level. The depumping may be done by exposing the medium to an intense source of radiation which selectively causes the transformation of the lower energy level species to some other energy level. Thus, a thermally pumped/optically depumped gas laser system is produced.

Krupke, W.F.

1975-11-26

30

The impact of hot-phonons on the performance of 1.3{mu}m dilute nitride edge-emitting quantum well lasers  

Energy Technology Data Exchange (ETDEWEB)

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3{mu}m InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power.

MacKenzie, R [School of Electrical and Electronic Engineering University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Lim, J J [School of Electrical and Electronic Engineering University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Bull, S [School of Electrical and Electronic Engineering University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Sujecki, S [School of Electrical and Electronic Engineering University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Kent, A J [School of Physics and Astronomy University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Larkins, E C [School of Electrical and Electronic Engineering University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom)

2007-12-15

31

The impact of hot-phonons on the performance of 1.3?m dilute nitride edge-emitting quantum well lasers  

International Nuclear Information System (INIS)

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3?m InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power.

2007-01-01

32

The impact of hot-phonons on the performance of 1.3µm dilute nitride edge-emitting quantum well lasers  

Science.gov (United States)

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3µm InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power.

MacKenzie, R.; Lim, J. J.; Bull, S.; Sujecki, S.; Kent, A. J.; Larkins, E. C.

2007-12-01

33

Effects of electron-phonon coupling and electron diffusion on ripples growth on ultrafast-laser-irradiated metals  

Energy Technology Data Exchange (ETDEWEB)

Metals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 {mu}m) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature.

Colombier, J. P.; Garrelie, F.; Faure, N.; Reynaud, S.; Bounhalli, M.; Audouard, E.; Stoian, R.; Pigeon, F. [Universite de Lyon, Laboratoire Hubert Curien, UMR 5516 CNRS, Universite Jean Monnet, 42000 Saint-Etienne (France)

2012-01-15

34

Effects of electron-phonon coupling and electron diffusion on ripples growth on ultrafast-laser-irradiated metals  

Science.gov (United States)

Metals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 ?m) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature.

Colombier, J. P.; Garrelie, F.; Faure, N.; Reynaud, S.; Bounhalli, M.; Audouard, E.; Stoian, R.; Pigeon, F.

2012-01-01

35

Effects of electron-phonon coupling and electron diffusion on ripples growth on ultrafast-laser-irradiated metals  

International Nuclear Information System (INIS)

Metals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 ?m) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature.

2012-01-15

36

Superslow Self-Organized Motions in a Multimode Microwave Phonon Laser (Phaser) under Resonant Destabilization of Stationary Acoustic Stimulated Emission  

CERN Multimedia

Two qualitatively different kinds of resonant destabilization of phonon stimulated emission (SE) are experimentally revealed for periodically forced multimode ruby phaser (phonon laser) operating at SE frequencies about 9 GHz, i.e. at microwave acoustic wavelengths of 1 micron. The inversion state of Cromium(3+) spin-system in ruby was created by electromagnetic pump at 23 GHz. Under deep modulation of pump power at low frequencies OMEGA_m = 70-200 Hz deterministic chaotic reconfigurations of the acoustic microwave power spectra (AMPS) were observed. This range of SE destabilization corresponds to the relaxational resonance that is well known for optical class-B lasers. Outside the relaxational resonance range, namely at ultra-low (infrasonic) frequencies OMEGA_m about 10 Hz, the other type of resonant destabilization of stationary phonon SE was observed by us for the first time. This new nonlinear resonance (we call it lambda-resonance) manifests itself as very slow and periodically repeated self-reconfigura...

Makovetskii, D N

2004-01-01

37

Femtosecond laser-irradiated crystallization of amorphous Si2Sb2Te3 films and its in-situ characterization by coherent phonon spectroscopy.  

UK PubMed Central (United Kingdom)

Femtosecond laser-irradiation-induced phase change of a new amorphous Si(2)Sb(2)Te(3) film with a good thermal stability and low reset current is studied by coherent phonon spectroscopy. New coherent optical phonons (COP) occur as laser irradiation fluence reaches some threshold, implying laser-induced phase change emerged. The compositions in phase-changed area revealed by COP modes agree well with ones in reported annealed crystallized film, implying laser-induced phase change as crystallization. Pump fluence dependence of COP dynamics reveals good crystallization quality of the phase-changed film, exhibiting promising application of Si(2)Sb(2)Te(3) films in optical phase change memory. Acoustic phonons are also found and identified.

Li S; Zhou D; Wen T; Zhu W; Song Z; Lai T

2013-04-01

38

Terahertz quantum cascade lasers with thin resonant-phonon depopulation active regions and surface-plasmon waveguides  

CERN Document Server

We report three-well, resonant-phonon depopulation terahertz quantum cascade lasers with semi-insulating surface-plasmon waveguides and reduced active region (AR) thicknesses. Devices with thicknesses of 10, 7.5, 6, and 5 {\\mu}m are compared in terms of threshold current density, maximum operating temperature, output power and AR temperature. Thinner ARs are technologically less demanding for epitaxial growth and result in reduced electrical heating of devices. However, it is found that 7.5-{\\mu}m-thick devices give the lowest electrical power densities at threshold, as they represent the optimal trade-off between low electrical resistance and low threshold gain.

Salih, M; Valavanis, A; Khanna, S P; Li, L H; Cunningham, J E; Davies, A G; Linfield, E H

2013-01-01

39

New laser action of optically pumped atomic vanadium vapor  

Science.gov (United States)

Laser action has been observed on the vanadium 560.4-, 575.3-, 581.7-, and 637.9-nm lines. Vanadium vapor is produced from vanadium metal plate by YAG laser (2.0 J/pulse) irradiation, and optically pumped by an XeCl excimer laser of 25-mJ energy. The vanadium laser pulse has a duration of 50 ns and peak output power of about 7 W.

Yoshida, H.; Takashima, N.; Ninomiya, H.

1992-01-01

40

Phonon engineering for nanostructures.  

Energy Technology Data Exchange (ETDEWEB)

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.

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

 
 
 
 
41

354-nm laser action on XeF  

International Nuclear Information System (INIS)

[en] This letter reports laser action on the xenon monofluoride 2?1/2?2?1/2 band at 354 nm. Lasing on discrete vibrational bands has been achieved by pulse excitation of high-pressure mixtures of F2/Xe/Ar with an electron beam. XeF is a member of a new class of diatmoic molecules, the noble gas monohalides, which all exhibit similar molecular structure and spectra, and laser action should be attainable on the various bands of other members of this class of molecules. The kinetics and loss mechanisms of these laser candidates are briefly discussed

1975-10-15

42

Laser action of optically pumped atomic vanadium vapor  

Science.gov (United States)

Vanadium vapor is generated from a vanadium metal by irradiation of a pulsed YAG laser of 2.2 J energy, and the vanadium atoms are optically pumped by a XeCl laser of 7.3 mJ energy. Laser action has been observed on the vanadium 409.5 nm 4F(7/2)-4D(5/2) transition. This laser pulse has a pulse width of 4 ns and peak power of 1.08 W, and the optical gain is 0.46/cm.

Ninomiya, H.; Abe, M.; Takashima, N.

1991-04-01

43

Laser action from syn-(methyl,methyl) bimane  

Energy Technology Data Exchange (ETDEWEB)

At the present, the Coumarin laser dyes are the ones most widely used for the spectral region stretching from 440 to 550 nm. However, the Coumarin dyes have rather poor photochemical stability. While searching for more stable and efficient laser dyes, the authors 3,4,6,7-tetramethyl-1, 5-diazabicyclo(3.3.0)octa-3, 6-diene-2, 8-dion (SYN-(CH/sub 3/,Ch/sub 3/)B for short). This new heterocyclic molecule was first reported by Kosower, Pazhenchevsky, and Hershkowitz in 1978. Their work included the observation of strong and striking fluorescence properties, as well as good photochemical stability, for these compounds. It should be emphasized that strong fluorescence (high quantum fluorescence yield) of organic compounds which are not benzene derivatives is rare. The quantum fluorescence yield of the syn-(R2,R1)B ranges from 0.7 to 0.9. The isomer anti-(R2,R1)B is only weakly fluorescent. There are two specific spectroscopic parameters of laser dyes that critically determine the laser action efficiency of flashlamp and cw laser-pumped dye lasers: (a) a high quantum fluorescence yield and (b) low triplet-triplet (T-T) absorption over the fluorescence (laser action) spectral region of the laser dye. The author, therefore, recorded the T-T absorption spectrum of syn-(CH/sub 3/,CH/sub 3/)B. We compared the laser action parameters of syn-(CH/sub 3/,CH/sub 3/)B with those of Coumarin 30. Both syn-(CH/sub 3/,CH/sub 3/)B and Coumarin 30 showed laser action in the same spectral region. syn-(CH/sub 3/,Ch/sub 3/)B lased only 30% less efficient than did Coumarin 30. Reprints. (mjm)

Pavlopoulos, T.G.; Boyer, J.H.; Politzer, I.R.; Lau, C.M.

1986-12-01

44

Phonon-assisted stimulated emission and ultra-thin active layers in cleaved-cavity and vertical-cavity surface emitting lasers  

Energy Technology Data Exchange (ETDEWEB)

Unique lasing processes in III-V semiconductor lasers are examined. The dynamics of stimulated photon emissions in thin AlGaAs/GaAs single quantum well lasers are observed experimentally and modeled by rate equations describing the electron and photon densities. Agreement between experiment and theory are achieved when the transition probability matrix, calculated with the spreading out of electron and hole wave functions taken into account, is used. The phonon assisted stimulated photon emission observed in this work is delayed with respect to the unassisted emission. This observation is modeled by using a weaker matrix element for the unassisted process which is expected from theory and thus supports the author' claim that this emission is phonon assisted. Rate equations developed to simulate doubly stimulated emission of photons and phonons do not describe the experimental data so the possibility of stimulated phonon emission is ruled out for the samples studied in this work. Vertical Cavity Surface Emitting Lasers are also studied since they can be designed to support unique lasing processes. The design and growth of vertical cavity surface emitting lasers are discussed and these concepts are applied to the realization of a vertical cavity surface emitting laser with the thinnest active layer of any laser yet reported. Stimulated emission supported across the sub-monolayer thick InAs single quantum well active region can be understood by considering the spreading of the electron and hole wavefunctions beyond the confines of the quantum well to increase the length of the effective gain region.

Benjamin, S.D.

1991-01-01

45

Bound-to-continuum terahertz quantum cascade laser with a single-quantum-well phonon extraction/injection stage  

Energy Technology Data Exchange (ETDEWEB)

A terahertz quantum cascade laser design that combines a wide gain bandwidth, large photon-driven transport and good high-temperature characteristics is presented. It relies on a diagonal transition between a bound state and doublet of states tunnel coupled to the upper state of a phonon extraction stage. The high optical efficiency of this design enables the observation of photon-driven transport over a wide current density range. The relative tolerance of the design to small variations in the barrier thicknesses made it suitable for testing different growth techniques and materials. In particular, we compared the performances of devices grown using molecular-beam epitaxy with those achieved using organometallic chemical vapor deposition. The low-threshold current density and the high slope efficiency makes this device an attractive active region for the development of single-mode quantum cascade lasers based on third-order-distributed feedback structures. Single-mode, high power was achieved with good continuous and pulsed wave operation.

Amanti, Maria I; Scalari, Giacomo; Terazzi, Romain; Fischer, Milan; Beck, Mattias; Faist, Jerome [Institute of Quantum Electronics, ETH Zurich (Switzerland); Rudra, Alok; Gallo, Pascal; Kapon, Eli [Laboratory of Physics of Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL) (Switzerland)], E-mail: jerome.faist@phys.ethz.ch

2009-12-15

46

Femtosecond laser-induced crystallization of amorphous Sb2Te3 film and coherent phonon spectroscopy characterization and optical injection of electron spins  

International Nuclear Information System (INIS)

[en] A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A1g1 and Eg) of crystalline Sb2Te3 enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb2Te3-like topological insulators.

2011-09-01

47

Femtosecond laser-induced crystallization of amorphous Sb{sub 2}Te{sub 3} film and coherent phonon spectroscopy characterization and optical injection of electron spins  

Energy Technology Data Exchange (ETDEWEB)

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb{sub 2}Te{sub 3} film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb{sub 2}Te{sub 3} film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A{sub 1g}{sup 1} and E{sub g}) of crystalline Sb{sub 2}Te{sub 3} enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb{sub 2}Te{sub 3} film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb{sub 2}Te{sub 3}-like topological insulators.

Li Simian [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Hebei Key Laboratory of Optoelectronic Information and Geo-detection Technology Shijiazhuang University of Economics, Shijiazhuang 050031 (China); Huang Huan; Wang Yang; Wu Yiqun; Gan Fuxi [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhu Weiling; Wang Wenfang; Chen Ke; Yao Daoxin; Lai Tianshu [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

2011-09-01

48

Common causes of injury and legal action in laser surgery.  

UK PubMed Central (United Kingdom)

OBJECTIVE: To identify common causes of legal action, injuries, claims, and decisions related to medical professional liability claims stemming from cutaneous laser surgery. DESIGN: Search of online public legal documents using a national database. MAIN OUTCOME MEASURES: Frequency and nature of cases, including year of litigation, location and certification of provider, injury sustained, cause of legal action, verdict, and indemnity payment. RESULTS: From 1985 to 2012, the authors identified 174 cases related to injury stemming from cutaneous laser surgery. The incidence of litigation related to laser surgery shows an increasing trend, with peak occurrence in 2010. Laser hair removal was the most common litigated procedure. Nonphysician operators accounted for a substantial subset of these cases, with their physician supervisors named as defendants, despite not performing the procedure. Plastic surgery was the specialty most frequently litigated against. Of the preventable causes of action, the most common was failure to obtain an informed consent. Of the 120 cases with public decisions, 61 (50.8%) resulted in decisions in favor of the plaintiff. The mean indemnity payment was $380 719. CONCLUSIONS: Claims related to cutaneous laser surgery are increasing and result in indemnity payments that exceed the previously reported average across all medical specialties. Nonphysicians performing these procedures will be held to a standard of care corresponding to an individual with appropriate training; thus, physicians are ultimately responsible for the actions of their nonphysician agents.

Jalian HR; Jalian CA; Avram MM

2013-02-01

49

Coherent anti-Stokes Raman scattering and normal anti-Stokes Raman scattering due to LO phonons in GaP using cw diode lasers  

Science.gov (United States)

Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm -1 LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were laser beams in the focal plane of the focusing lens was determined to 40±5 ?m. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm -1 , using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions.

Aggarwal, R. L.; Farrar, L. W.; Polla, D. L.

2011-10-01

50

Laser excitation of stationary states in molecules: the coupling of real eigenstates to phonons and photons  

International Nuclear Information System (INIS)

Experimental evidence is presented for the laser excitation of true eigenstates in molecules. The theoretical treatment and the experimental findings on thermal broadening of electronic resonances which result in the loss of ''identity'' of molecular states are discussed, and it is shown that vibrational relaxation and magnetic field induced couplings depend crucially on the preparation of the state

1977-01-01

51

Yoctocalorimetry phonon counting in nanostructures  

CERN Document Server

It appears feasible with nanostructures to perform calorimetry at the level of individual thermal phonons. Here I outline an approach employing monocrystalline mesoscopic insulators, which can now be patterned from semiconductor heterostructures into complex geometries with full, three- dimensional relief. Successive application of these techniques also enables definition of integrated nanoscale thermal transducers; coupling these to a dc SQUID readout yields the requisite energy sensitivity and temporal resolution with minimal back action. The prospect of phonon counting opens intriguing experimental possibilities with analogies in quantum optics. These include fluctuation-based phonon spectroscopy, phonon shot noise in the energy relaxation of nanoscale systems, and quantum statistical phenomena such as phonon bunching and anticorrelated electron-phonon exchange.

Roukes, M L

1998-01-01

52

Endovenous laser ablation: a review of mechanisms of action.  

UK PubMed Central (United Kingdom)

BACKGROUND: The aim of this article is to summarize and review the proposed theories on the laser action during endovenous ablation. METHODS: Laser mechanics and laser-tissue interaction are summarized from articles found in literature. Several theories, like the "steam bubble theory," the "direct contact theory," the "heat pipe," and "direct light energy absorption" are discussed. RESULTS: The laser light emitted intraluminally can be absorbed, scattered, or reflected. Reflection is negligible in the near-infrared spectrum. By combining absorption and scattering, the optical extinction of different wavelengths related to different biological tissues can be determined. The direct contact of the fiber tip and the vein wall may be a way of destroying the vein wall, but results in ulcerations and perforations of the vein wall. Avoiding this contact, and allowing direct light absorption into the vein wall, results in a more homogenous vein wall destruction. If the energy is mainly absorbed by the intraluminal blood, the laser fiber will act as a heat pipe. Histological studies show that a more circumferential vein wall destruction can be obtained when the vein is emptied of its intraluminal blood. The use of tumescent liquid reinforces spasm of the vein and protects the perivenous tissue. CONCLUSION: Several factors play an important role in the mechanism of endovenous laser ablation. Direct energy absorption by the vein wall is the most efficient mechanism. It is important to empty the vein of its intraluminal blood and to inject tumescent liquid around the vein.

Vuylsteke ME; Mordon SR

2012-04-01

53

Nonadiabatic generation of coherent phonons  

CERN Multimedia

The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonons, despite its unsatisfactory performance on reproducing the observed dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent phonon generation is also examined and compared with the TDDFT calculations.

Shinohara, Y; Yabana, K; Iwata, J -I; Otobe, T; Bertsch, G F

2012-01-01

54

Laser characteristics of KCL:O2(-)  

Science.gov (United States)

Amplified spontaneous emission and laser action have been observed at 77 K in KCl crystals containing the superoxide ion (O2/-/). The laser operates in two bands of width approximately 50 A centered at 6350 A and 5984 A. These bands are the (lattice) phonon sidebands of vibronic transitions of the superoxide ion. At lower temperatures (approximately 6 K) amplified spontaneous emission is observed in the zero phonon line at 6294 A.

Wilk, S. R.; Boyd, R. W.; Teegarden, K. J.

1983-10-01

55

Trapped phonons  

CERN Document Server

We analyze the effect of restricted geometries on the contribution of Nambu-Goldstone bosons (phonons) to the shear viscosity, $\\eta$, of a superfluid. For illustrative purpose we examine a simplified system consisting of a circular boundary of radius $R$, confining a two-dimensional rarefied gas of phonons. Considering the Maxwell-type conditions, we show that phonons that are not in equilibrium with the boundary and that are not specularly reflected exert a shear stress on the boundary. In this case it is possible to define an effective (ballistic) shear viscosity coefficient $\\eta \\propto \\rho_{\\rm ph} \\chi R$, where $\\rho_{\\rm ph}$ is the density of phonons and $\\chi$ is a parameter which characterizes the type of scattering at the boundary. For an optically trapped superfluid our results corroborate the findings of Refs. \\cite{Mannarelli:2012su, Mannarelli:2012eg}, which imply that at very low temperature the shear viscosity correlates with the size of the optical trap and decreases with decreasing tempe...

Mannarelli, Massimo

2013-01-01

56

Phonons with orbital angular momentum  

Energy Technology Data Exchange (ETDEWEB)

Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

Ayub, M. K. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

2011-10-15

57

Induced phonon-sideband laser operation of large-quantum-well Al/sub x/Ga/sub 1-x/As-GaAs heterostructures (L/sub z/ approx. 200--500 A)  

Energy Technology Data Exchange (ETDEWEB)

Data are presented on photopumped metallorganic chemically vapor-deposited Al/sub x/Ga/sub 1-x/As-GaAs quantum-well heterostructures with active regions consisting of a large GaAs quantum well (L/sub z/1approx.200, 500 A) coupled to a phonon generating array of seven small GaAs wells (L/sub z/2approx.50 A). Phonon-sideband laser operation below the confined-carrier transitions of the large GaAs quantum well(s) is induced by the large number of phonons generated in the smaller GaAs wells. The induced phonon-sideband laser operation (of a larger quantum well by an array of smaller wells) leads to a measurement of the energy difference between the first-state light- and heavy-hole energies of a 200-A GaAs quantum well (4.9 meV) and directly to the GaAs L0-phonon energy h..omega../sub L/0approx. =41.0-4.9=36.1 meV.

Coleman, J.J.; Dapkus, P.D.; Vojak, B.A.; Laidig, W.D.; Holonyak, N. Jr.; Hess, K.

1980-07-01

58

Phonon manipulation with phononic crystals.  

Energy Technology Data Exchange (ETDEWEB)

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 factor. In addition, the techniques and scientific understanding developed in the research can be applied to a wide range of materials, with the caveat that the thermal conductivity of such a material be dominated by phonon, rather than electron, transport. In particular, this includes several thermoelectric materials with attractive properties at elevated temperatures (i.e., greater than room temperature), such as silicon germanium and silicon carbide. It is reasonable that phononic crystal patterning could be used for high-temperature thermoelectric devices using such materials, with applications in energy scavenging via waste-heat recovery and thermoelectric cooling for high-performance microelectronic circuits. The only part of the ZT picture missing in this work was the experimental measurement of the Seebeck coefficient of our phononic crystal devices. While a first-order approximation indicates that the Seebeck coefficient should not change significantly from that of bulk silicon, we were not able to actually verify this assumption within the timeframe of the project. Additionally, with regards to future high-temperature applications of this technology, we plan to measure the thermal conductivity reduction factor of our phononic crystals as elevated temperatures to confirm that it does not diminish, given that the nominal thermal conductivity of most semiconductors, including silicon, decreases with temperature above room temperature. We hope to have the opportunity to address these concerns and further advance the state-of-the-art of thermoelectric materials in future projects.

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

59

Surface temperature evolution in pulsed laser action of millisecond range  

International Nuclear Information System (INIS)

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001-1.573 ?m, 50 ?s acquisition time for each photodiode, 800 ?m spatial resolution, 900-3500 deg. Cbrightness temperature range) is used to measure brightness temperature under the pulsed action of Nd:YAG laser (HAAS-HL62P) on stainless steel (INOX 304L) substrates. Specially developed 'notch' filters (10-6 transparency at 1.06 ?m wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored on the basis of method of multi-colour pyrometry. The accuracy of brightness temperature measurements is examined by comparing the temperature evolution for pulses with different durations but with the same value of energy density flux. The influence of the following parameters is studied keeping the remaining ones constant: pulse duration (6-20 ms, rectangular pulse shape), energy per pulse (10-33 J, rectangular pulse shape), pulse shape (three types of triangulars and one rectangular). Finally the evolution of surface temperature for pulses with more complex shapes but with the same pulse duration and energy per pulse is compared.

2006-04-30

60

Effect of thermal expansion on the possibility of gamma-ray laser action  

Energy Technology Data Exchange (ETDEWEB)

The necessity of maintaining the time-stable temperature of a gamma-ray laser working body is shown. Attention is given to the effect on the expansion of a laser rod cooled by liquid helium on the possibility of laser action under heat evolution caused by electron, X-ray quanta, and cascade gamma quanta absorption.

Bushuev, V.A.; Mantsyzov, B.I.; Kuzmin, R.N.

1980-05-01

 
 
 
 
61

Laser action on the 342-nm molecular iodine band  

International Nuclear Information System (INIS)

[en] A new laser operating on the 342-nm band of I2 is reported. Electron-beam-excited mixtures of argon with CF3I and HI produced this I2 laser. The excited state of this laser is probably formed by ion recombination reactions, and a plausible mechanism is given

1975-11-15

62

Analgesic action of laser therapy (LLLT) in an animal model  

Digital Repository Infrastructure Vision for European Research (DRIVER)

OBJECTIVES: To evaluate the analgesic effect of laser therapy on healthy tissue of mice. STUDY DESIGN: Forty-five animals were divided in three groups of 15: A--infrared laser irradiation (830 nm, Kondortech, São Carlos, SP, Brazil); B--red laser irradiation (660 nm, Kondortech, São Carlos, SP, Bra...

Daniel Pozza; Patricia Fregapani; João Weber; Marília Gerhardt de Oliveira; Marcos André de Oliveira; Nelson Ribeiro Neto

63

Coherent phonons in bismuth film observed by ultrafast electron diffraction  

Directory of Open Access Journals (Sweden)

Full Text Available The generation of coherent phonons in polycrystalline bismuth film excited with femtosecond laser pulse is observed by ultrafast time-resolved electron diffraction. The dynamics of the diffracted intensities from the (110), (202), and (024) lattice planes show pronounced oscillations at 130–150 GHz. The origin of these coherent acoustic phonons is discussed in view of optical phonon decay into two acoustic phonons. Different drop times in the intensity of the diffraction orders are observed and interpreted as anisotropy in the energy transfer rate of coherent optical phonons.

A. Bugayev; A. Esmail; M. Abdel-Fattah; H. E. Elsayed-Ali

2011-01-01

64

Study of Phonon Modes in Germanium Nanowires  

CERN Multimedia

The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nanowires for the first time.

Wang, X; Shakouri, A; Sun, X; Yu, B; Meyyappan, Meyya; Shakouri, Ali; Sun, Xuhui; Wang, Xi; Yu, Bin

2007-01-01

65

Tunable vacuum ultraviolet laser action by argon excimers  

Energy Technology Data Exchange (ETDEWEB)

Vacuum ultraviolet lasing was achieved in electron-beam-pumped high-density argon gas (25--65 bars). With a diffraction grating, the argon excimer laser (126 nm) could be tuned between 123.2 and 127.4 nm. The line width of the tuned laser was 0.6 nm and the output power approx.1 kW.

Wrobel, W.; Roehr, H.; Steuer, K.

1980-01-15

66

Laser activity at 1.18 um, 1.07 um, and 0.97 umin the low phonon energy crystalline hosts KPb2Br5 and RbPb2Br5 doped with Nd3+  

Energy Technology Data Exchange (ETDEWEB)

For the first time laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2} + {sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. Rare earth- doped MPb{sub 2}Br{sub 5} (M=K, Rb) is a promising candidate for long wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd{sup 3+}:MPb{sub 2}Br{sub 5} has high potential for laser operation at new wavelengths as well as for the realization of short-wavelength lasing due to upconversion processes.

Rademaker, K; Heumann, E; Payne, S A; Huber, G; Krupke, W F; Isaenko, L I; Burger, A

2004-09-15

67

Immunomodulation action of ultraviolet N2-laser radiation  

Science.gov (United States)

The report deals with the investigation of the influence of N2-laser radiation on the kinetics of the initial specimens of the respiratory chain -- reactive oxygen forms (ROFs) -- depending on its parameters. It was shown, that the energy of N2-laser radiation promotes to the correction of the ROF generation and leads to an immunomodulation effect. We suppose that the immunomodulation effect is connected with a key molecule of the respiratory chain -NADP(H) and with the regulation role of ROF. We emphasize the necessity of correction of the pathological processes with hypo- and hyperfunction of granulocyte- macrophage cells by N2-laser radiation under the ROF generation kinetics control.

Pukhova, Yana; Provorov, Alexander S.; Salmin, Vladimir V.

1995-01-01

68

Plasma and Shock Generation by Indirect Laser Pulse Action  

International Nuclear Information System (INIS)

[en] In the paper the results of our experiment with flyer disks, accelerated to high velocities by the PALS iodine laser and subsequently creating craters when hitting massive targets , are presented. We have carried out experiments with the double targets consisted of a disk placed in front of a massive target part at distances of either 200 or 500 ?m. Both elements of the targets were made of Al. The following disk irradiation conditions were used: laser energy of 130 J, laser wavelength of 1.315 ?m, pulse duration of 0.4 ns, and laser spot diameter of 250 ?m. To measure some plasma parameters and accelerated disk velocity a three frame interferometric system was used. Efficiency of crater creation by a disk impact was determined from the crater parameters, which were obtained by means of a crater replica technique. The experimental results concern two main stages: (a) ablative plasma generation and disk acceleration and (b) disk impact and crater creation. Spatial density distributions at different moments of plasma generation and expansion are shown. Discussion of the experimental results on the basis of a 2-D theoretical model of the laser -- solid target interaction is carried out

2006-01-15

69

Excitation of coherent nondiagonal combination-active phonons at interaction of femto-second laser pulses with high-temperature superconductors YBa2Cu3O7-x  

International Nuclear Information System (INIS)

[en] One studied time resolved optical response of different crystallographic faces of YBa2Cu3O7-x single crystal. When conducting such measurements the first ultrashort subpicosecond pulse switches the phonon system to the coherent state and the second pulse sound it with the given time delay within the time range. Comparison of the periodograms of time response with light combination scattering spontaneous spectra demonstrates that nondiagonal modes contribute into time response alongside with totally-symmetrical phonons. One discusses mechanism of generation of coherent phonons in high-temperature super conductors

2001-01-01

70

Study on modes of energy action in laser-induction hybrid cladding  

International Nuclear Information System (INIS)

The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.

2009-11-15

71

Whispering-gallery mode resonators for highly unidirectional laser action.  

UK PubMed Central (United Kingdom)

Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (? ? 10 ?m) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of ?5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers.

Wang QJ; Yan C; Yu N; Unterhinninghofen J; Wiersig J; Pflügl C; Diehl L; Edamura T; Yamanishi M; Kan H; Capasso F

2010-12-01

72

Quasiparticle-phonon model  

International Nuclear Information System (INIS)

Formalism of quasiparticle-phonon nuclear model for odd spherical nuclei is presented consistently. Taking into account exact commutation relations of quasiparticle- and phonon operators and anharmonic corrections for phonon excitations, equations are obtained for energies and structural coefficients of wave functions of excited states, comprising ''quasiparticle+phonon'' and ''quasiparticle+ two phonons'' components. Influence of different physical effects and phonon basis sire on fragmentation of the monoquasiparticle and ''quasiparticle+phonon'' states is studied. The role of the corrections to meet the Pauli principle requirement is studied. The description of the method of strength functions to calculate fragmentation of low-quasiparticle component strength is given. Iterative method of numerical solution of the equations obtained is described.

1985-01-01

73

Laser action due to strontium ion transitions in a discharge with an electron beam  

Energy Technology Data Exchange (ETDEWEB)

Laser action due to a transition in Sr II at 430.5 nm was achieved in an Sr-He mixture under pumping caused by recombination of Sr(2+) ions in an open transverse discharge of coaxial design with an electron beam. In an Sr-He-Kr mixture, laser action due to transitions in Sr II was achieved simultaneously with three types of pumping: by electron impact (1033, 1092 nm), by charge transfer (1087, 1123, 1202 nm), and by recombination (430.5 nm). 11 refs.

Koptev, IU.V.; Latush, E.L.; Sem, M.F. (Rostovskii Gosudarstvennyi Universitet, Rostov-on-Don (USSR))

1990-04-01

74

Lasing action in water vapor induced by ultrashort laser filamentation  

Science.gov (United States)

The water vapor fluorescence in air from filaments generated by intense ultrashort Ti:sapphire laser pulses is experimentally studied. The backscattered fluorescence from OH shows an exponential increase with increasing filament length, indicating amplified spontaneous emission. By measuring the intensity inside the filament and the fluorescence intensity of OH, a high degree of nonlinearity is obtained, indicating a highly nonlinear field dissociation of H2O molecule.

Yuan, Shuai; Wang, Tiejun; Teranishi, Yoshiaki; Sridharan, Aravindan; Hsien Lin, Sheng; Zeng, Heping; Leang Chin, See

2013-06-01

75

Crystal-host Gd0.5Lu0.5VO4 for Ln3+-lasants: a new high-gain many-phonon ?(3)-active tetragonal vanadate—SRS spectroscopy and nonlinear-laser effects  

Science.gov (United States)

We found that tetragonal Gd0.5Lu0.5VO4—known as host-crystal for Ln3+-lasants—is an attractive optical material for Raman laser converters. We discovered and investigated its almost sesqui-octave Stokes and anti-Stokes lasing comb resulting from four SRS-promoting vibration modes in combination with cascaded and cross-cascaded many-phonon ?(3)-nonlinear interactions. Furthermore, estimations of the steady-state Raman gain coefficient have been performed.

Kaminskii, A. A.; Lux, O.; Rhee, H.; Eichler, H. J.; Yoneda, H.; Shirakawa, A.; Ueda, K.; Zhao, B.; Chen, J.; Dong, J.; Zhang, J.

2012-12-01

76

Coherent generation of acoustic phonons in an optical microcavity.  

UK PubMed Central (United Kingdom)

Ultrafast coherent generation of acoustic phonons is studied in a semiconductor optical microcavity. The confinement of the light pulse amplifies both the generation and the detection of phonons. In addition, the standing wave character of the photon field modifies the generation and detection phonon bandwidth. Coherent generation experiments in an acoustic nanocavity embedded in an optical microcavity are reported as a function of laser energy and incidence angle to evidence the separate role of the optical and exciton resonances. Amplified signals and phonon spectra modified by the optical confinement are demonstrated.

Lanzillotti-Kimura ND; Fainstein A; Huynh A; Perrin B; Jusserand B; Miard A; Lemaître A

2007-11-01

77

Rapid-flow combined-action industrial CO/sub 2/ laser  

Energy Technology Data Exchange (ETDEWEB)

An investigation was made into the characteristics of a combined-action (pulse-periodic and cw) high-power CO/sub 2/ discharge laser, and of its construction. In forming the discharge the gas was preionized by high voltage electrodeless pulses.

Generalov, N.A.; Zimakov, V.P.; Kosynkin, V.D.; Raizer, Y.P.; Solov' ev, N.G.

1982-08-01

78

Blazed phononic crystal grating  

Science.gov (United States)

It is well known that blazed optical diffraction gratings can significantly increase the diffraction efficiency of plane waves for a selected angle of incidence. We show that by combining blazing with a phononic band gap, diffraction efficiency approaching 100% can be achieved for acoustic waves. We obtain experimentally 98% diffraction efficiency with a two-dimensional phononic crystal of rotated steel rods of square cross-section immersed in water. This result opens the way toward the design of efficient phononic crystal gratings.

Moiseyenko, Rayisa P.; Liu, Jingfei; Declercq, Nico F.; Laude, Vincent

2013-01-01

79

Imitrines. III. Laser action in the 500 nm band in solutions and vapors of organic dyes in the imitrine class  

Energy Technology Data Exchange (ETDEWEB)

Laser action has been achieved in solutions of nine new organic dyes in the imidazotriazine (imitrine) class excited by the third (355 nm) harmonic of a neodymium laser. The free-lasing spectra covered the 485--546 nm range and the lasing efficiency was up to 17%. Laser action in the 470 and 525 nm ranges was obtained in imitrine 3 and imitrine 9 vapors.

Zuev, V.S.; Kruglenko, V.P.; Logunov, O.A.; Povstyanoi, M.V.; Startsev, A.V.; Stoilov, Y.Y.

1981-07-01

80

Phonon anomalies in ?-uranium  

International Nuclear Information System (INIS)

[en] The temperature dependence of the phonon spectra of ?-uranium has recently been measured by inelastic neutron scattering and inelastic X-ray scattering. Although there is little evidence of any anharmonicity, the phonon shows some softening in the optic modes at the zone boundary. Furthermore, an extra mode forms at high temperatures, which is incompatible with a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode

2007-01-01

 
 
 
 
81

Hypersonic phononic crystals.  

UK PubMed Central (United Kingdom)

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.

Gorishnyy T; Ullal CK; Maldovan M; Fytas G; Thomas EL

2005-03-01

82

Hypersonic phononic crystals.  

Science.gov (United States)

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. PMID:15903869

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

2005-03-22

83

Tunable room-temperature CW laser action in Cr(3+):GdScAl-garnet  

Energy Technology Data Exchange (ETDEWEB)

For the first time, CW room temperature laser action of Cr(3+):Gd3Sc2Al3O12 is reported. These crystals show a strong band fluorescence due to the 4T2 to 4A2 transition with a lifetime of 150 microns. Laser pumping in the blue and red spectral range yields a minimum threshold of 170 mW and slope efficiencies up to 18.5 percent. The emission of the free running laser is centered at 784 nm with a FWHM of 5 nm. The extension of the Ga-garnets to Al-garnets as suitable host lattices for Cr(3+) reveals the variety of garnet-structured crystals having an appropriate ligand field for continuously tunable laser operation.

Drube, J.; Struve, B.; Huber, G.

1984-05-01

84

PHONONS IN AMORPHOUS MATERIALS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A brief review is given of phonons in amorphous materials as seen in Raman scattering, infrared absorption and inelastic neutron scattering. It is shown that phonons (i.e. quantised harmonic vibrations) are well defined in network structures and a description is given of the standard theoretical tec...

Thorpe, M.

85

Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity  

CERN Document Server

We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2{\\lambda} microcavity containing 8 ZnO/Zn(0.92)Mg(0.08)O quantum wells embedded in epitaxially grown Zn(0.92)Mg(0.08)O/Zn(0.65)Mg(0.35)O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral range are discussed.

Kalusniak, S; Halm, S; Henneberger, F

2010-01-01

86

Some new laser dyes: solvent effect on QE and lasing action  

Energy Technology Data Exchange (ETDEWEB)

With a view to extend the tunability range and maximum output with the coumarin series of dyes, eleven new coumarins differing in the nature of substituents and their positions are synthesized. Two of these are found to be capable of laser action. Optical spectra and quantum efficiencies of these two dyes in various solvents are studied. Correlation between lasing capability structure of the dye and its optical characteristics is discussed.

Padhye, M.R.; Varadarajan, T.S.; Deshpande, A.V.

1982-08-01

87

Single-mode dye laser with a double-action Fizeau interferometer.  

UK PubMed Central (United Kingdom)

The peculiar properties of the high-reflectivity Fizeau wedge used in reflection are pointed out and used to obtain single-mode operation of a Nd:YAG-pumped dye laser. It is demonstrated that the reflecting Fizeau wedge can have, as a cavity output coupler, the double action of selective-feedback mirror and an output filter, thus producing a background-free tunable narrow line.

Meyer YH; Nenchev MN

1981-03-01

88

Single-mode dye laser with a double-action Fizeau interferometer.  

Science.gov (United States)

The peculiar properties of the high-reflectivity Fizeau wedge used in reflection are pointed out and used to obtain single-mode operation of a Nd:YAG-pumped dye laser. It is demonstrated that the reflecting Fizeau wedge can have, as a cavity output coupler, the double action of selective-feedback mirror and an output filter, thus producing a background-free tunable narrow line. PMID:19701347

Meyer, Y H; Nenchev, M N

1981-03-01

89

Phonon-induced polariton superlattices  

DEFF Research Database (Denmark)

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.

de Lima, Jr., M. M.; Poel, Mike van der

2006-01-01

90

Coherent generation of acoustic phonons in an optical microcavity  

International Nuclear Information System (INIS)

Coherent acoustic phonons confined in a nanocavity are generated in an optical microcavity. The confinement of the femtosecond light pulse in the optical resonator amplifies both processes, generation and detection of the acoustic phonons. In addition, due to the standing wave character of the photon field, phonons of wavevector q = 0 and q = 2k (k is the light wavenumber) contribute to both the generation and detection in time resolved reflectivity measurements, further optimizing the pump and probe experiments. Time resolved differential reflectivity experiments are reported as a function of laser energy. The optical cavity resonance is apparent in the amplitude and spectral features of the Fourier transformed signals.

2007-01-01

91

Deformation of a laser plasma corona under the action of a ponderomotive force and accompanying effects  

International Nuclear Information System (INIS)

The pattern of deformation of the density profile of an inhomogeneous laser plasma flow due to the action of a ponderomotive force is identified. The dynamic pattern of generation of non-linear potential fields in the plasma, including caviton-trapped fields, is demonstrated. By isolating the dissipative mechanisms, it was possible to determine the proportion of the energy dissipated in the plasma as a result of the Cherenkov mechanism of interaction between the potential fields and electrons, and thus, the energy which results in the generation of hot electrons. It was shown that a comparatively low plasma flow rate qualitatively alters the pattern of interaction between laser radiation and a plasma. In particular, the formation of cavitons is impeded, the generation of short-wavelength longitudinal fields is suppressed, and the proportion of electromagnetic radiation energy absorbed as a result of the Cherenkov interaction is reduced, i.e., the energy transferred to the fast electrons is reduced. (author)

1979-01-01

92

Ablated matter expansion and crater formation under the action of ultrashort laser pulse  

International Nuclear Information System (INIS)

The action of a subpicosecond laser pulse on a target made of an absorbing condensed substance is considered. The propagation of an electron heat conduction wave and the crystal lattice heating prior to the hydrodynamic expansion of the target are analyzed. In these initial interaction stages, a heated layer with a thickness of dT is formed at the target surface. The dependence of dT on the absorbed laser energy density F[J/cm2] is evaluated. The motion of ablated matter in the expansion stage is described using a numerical solution of the equations of gasdynamics and the results of molecular dynamics (MD) simulations. The MD simulations are performed using a large number (?103) of parallel processors, which allows the number of model atoms to be increased up to a level (about 3.5 x 107) close to that encountered under real experimental conditions.

2006-01-01

93

Diffusionless oxidation and structure modification of thin Cr films by the action of ultrashort laser pulses  

Science.gov (United States)

Results of impact on Cr thin metal films by ultrashort laser pulses are investigated in the paper. For the first time thermochemical action of such pulses is shown and confirmed by analytical approaches (micro-Raman spectroscopy, CAES and others) and selective chemical etching both. It is impossible to ascribe this effect to well-known mechanism of heterogeneous diffusion at the irradiation specified conditions. Possible reasons of Cr thin films diffusionless oxidation and structure modification are observed. Discovered phenomena open up new opportunities for developing of optical thermochemical data recording on Cr thin films, which are widely used in microelectronics as photomasks and in the process of diffractive optical elements manufacturing.

Veiko, V. P.; Jarchuk, M. V.; Ivanov, A. I.

2012-08-01

94

ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS : PHONON TRANSPORT AND DECAY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Stationary charge transport in semiconductors implies steady flow of directed momentum and excess energy from the coupled system of electrons and phonons to the external heatsink. Bulk phonons mediate the momentum and energy transfer. This article will survey recent developments in phonon spectrosco...

Ulbrich, R.

95

Phonon-Assisted Incoherent Excitation of a Quantum Dot and its Emission Properties  

CERN Multimedia

We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally-detuned laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20 % with respect to strictly resonant excitation can be achieved at T = 9 K. Laser frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the photoluminescence is introduced which predicts a broadband incoherent coupling process when electron-phonon scattering is in the strong phonon coupling (polaronic) regime. Additionally, we investigate the coherence properties of the emitted light and study the impact of the relevant pump and phonon bath parameters.

Weiler, S; Roy, C; Ulrich, S M; Richter, D; Jetter, M; Hughes, S; Michler, P

2012-01-01

96

The action of powerful laser radiation on 1-2-3 superconducting thin films and bulk materials. [Y-Ba-Cu-O  

Energy Technology Data Exchange (ETDEWEB)

Laser induced decomposition, evaporation, and ablation processes in 1-2-3 superconductors are experimentally and theoretically studied. A model of laser beam action on 1-2-3 superconductors is developed. This model explains the low-energy mechanism of ablation, the processes of the high temperature superconductor film modification under laser action and the origination of the drops on the film surface deposited by a laser ablation technique. The model is in good agreement with experimental results. (orig.).

Zherikhin, A.; Bagratashvili, V.; Burimov, V.; Sobol, E.; Shubnii, G.; Sviridov, A. (Scientific Research Center for Technological Lasers, Troitsk (Russia))

1992-08-01

97

PHONONS IN AMORPHOUS MATERIALS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The study of the propagation of phonons is an important tool to investigate the sometimes unexpected and puzzling dynamic properties of amorphous solids. At first, as a typical example, we shall discuss the acoustic properties of vitreous silica. In the second part of the review emphasis will be giv...

Hunklinger, S.

98

Influence of physicochemical properties of ammonium uranates on formation of uranium oxides by the action of laser radiation  

International Nuclear Information System (INIS)

Spectroscopic studies of the surface laser plasma formed by the action of sequential high-power double laser pulses close to a porous body containing microquantities of ammonium polyuranates showed that the intensities of uranium spectral lines that are proportional to the elemental content in the plasma depend significantly on the physicochemical properties of the uranium compounds. The line intensities increase by several times with almost the same increase in the formation enthalpy of the compounds. (authors)

2011-01-01

99

The heat-pipe resembling action of boiling bubbles in endovenous laser ablation.  

Science.gov (United States)

Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100 degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100 degrees C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100 degrees C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall. PMID:20644976

van der Geld, Cees W M; van den Bos, Renate R; van Ruijven, Peter W M; Nijsten, Tamar; Neumann, H A Martino; van Gemert, Martin J C

2010-07-20

100

The heat-pipe resembling action of boiling bubbles in endovenous laser ablation.  

UK PubMed Central (United Kingdom)

Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100 degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100 degrees C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100 degrees C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall.

van der Geld CW; van den Bos RR; van Ruijven PW; Nijsten T; Neumann HA; van Gemert MJ

2010-11-01

 
 
 
 
101

Phonons in amorphous materials  

Energy Technology Data Exchange (ETDEWEB)

A general introduction is given to phonons in amorphous materials. It is shown that phonons are well defined in network structures and a description is given of the standard theoretical technique which is to build a finite model and then use one of the number of numerical techniques to obtain the eigenvalue spectrum of the dynamical matrix. Particular emphasis is given to theoretical techniques that do not require the building of a model. These are a) the analysis of normal models of a network with nearest neighbour forces only. The application of these ideas to real systems and experiments will be discussed by FL Galeener. b) the use of Bethe lattices to simulate networks. These are used to examine the ''defect modes'' associated with H in an Si.

Thorpe, M.F. (Michigan State Univ., East Lansing (USA). Dept. of Physics)

1982-01-01

102

Phonons in amorphous materials  

International Nuclear Information System (INIS)

[en] A general introduction is given to phonons in amorphous materials. It is shown that phonons are well defined in network structures and a description is given of the standard theoretical technique which is to build a finite model and then use one of the number of numerical techniques to obtain the eigenvalue spectrum of the dynamical matrix. Particular emphasis is given to theoretical techniques that do not require the building of a model. These are a) the analysis of normal models of a network with nearest neighbour forces only. The application of these ideas to real systems and experiments will be discussed by FL Galeener. b) the use of Bethe lattices to simulate networks. These are used to examine the ''defect modes'' associated with H in an Si. (author)

1982-01-01

103

Phonon dispersion in Be  

International Nuclear Information System (INIS)

In a study of the lattice dynamics of Be a simple scheme has been developed in which the pairwise and long range forces are accounted on the lines of nonlocal theory and the short range three-body forces are included. This procedure of calculations has been applied to compute the phonon dispersion in Be and the results of investigation have been compared with the experimental data. (author)

1979-01-01

104

High energy phonons: overview  

International Nuclear Information System (INIS)

[en] Neutron scattering has been important in the measurement and interpretation of phonon dispersion relations. As these measurements are extended to higher energies they may yield new types of information or information about different types of systems. Several examples are discussed including: dispersion in high frequency internal modes, application to molecular crystals and the use of vibrational modes of hydrogen as a structural probe

1984-01-01

105

Ultrafast coherent phonon dynamics in Ge2Sb2Te5 thin films  

Science.gov (United States)

We investigated the coherent acoustic and optical phonon dynamics in a Ge2Sb2Te5 phase change material by using pump-probe spectroscopy. Oscillating reflectivity changes with oscillation period and de-phasing time on a timescale of tens of picoseconds were observed and could be consistently explained by coherent acoustic phonon generation in the form of a strain pulse propagating into substrate. The temperature-dependent frequency shift of the coherent optical A 1 phonon mode was due to a three-phonon anharmonic decay while its de-phasing was dominated by temperatureindependent phonon-vacancy scattering at low temperature. A laser-fluence-dependent A 1 phonon mode softening and a dephasing rate increase were observed and attributed to the high density of electrons and the accompanying lattice distortion, as well as the increase in the lattice temperature.

Kim, Dong Hak; Park, J. W.; Lee, Hosun; Lim, D.

2013-03-01

106

Phonon Scattering of Composite Fermions  

CERN Document Server

We study the principal aspects of the interaction between acoustic phonons and two-dimensional electrons in quantizing magnetic fields corresponding to even denominator fractions. Using the composite fermion approach we derive the vertex of the electron-phonon coupling mediated by the Chern-Simons gauge field. We estimate acoustic phonon contribution to electronic mobility, phonon-drag thermopower, and hot electron energy loss rate, which all, depending on the temperature regime, are either proportional to lower powers of T than their zero field counterparts, or enhanced by the same numerical factor as the coefficient of surface acoustic wave attenuation.

Khveshchenko, D V

1997-01-01

107

Quasiparticle-phonon nuclear model  

International Nuclear Information System (INIS)

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

1977-01-01

108

Phononic Amorphous Silicon: Theory, Material, and Devices  

Energy Technology Data Exchange (ETDEWEB)

The field of phononic-engineered amorphous silicon is introduced. Specifically the construction of devices and waveguides for information conveyance and manipulation via phonons are considered. Typically the phononic properties of a given material are immutable and the phonons have such a limited diffusion length (nanometers) as to be unsuitable for engineering purposes. Crystalline silicon on the other hand has a reasonably large thermal conductivity and phonon diffusion length at sufficiently low temperatures. Phonon diffusion lengths can measure up to centimeters (e.g., crystalline SiO2) at temperature less than 10K but drop to sub microns at room temperature. Amorphous silicon, owing to the inherent scattering structures and owing to localization (of at least some phonon bands), has an anomalously large phonon lifetime [1]. This lifetime maybe indicative of a large phonon diffusion length and/or a fast phonon hop rate from one domain to the next and/or an indication that more than the typical three phonons (umklapp process) are involved in phonon scattering. Techniques involving small-scaled devices and phonon bands to control umklapp phonon-phonon scattering are described. The potential to exploit inherent amorphous silicon structure as well as the engineering (post film deposition) of di-hydride distributions to induce phonon forbidden bands for significantly reduced multi-phonon scattering is explored. The indirect optical band gap of small domain (and possibly amorphous) silicon [3] provides the physical basis for the transduction of phonon and optical energies. Experimental methods for the post-deposition introduction of phonon scattering structure, the transduction of phononic information to optical information, and experimental approaches including the use of micro-Raman to probe phonon spectra and transport are described. The prospects of a fully integrated phononic, photonic, electronic amorphous silicon technology have been described.

Chawda, S.; Mawyin, J.; Mahan, H.; Fortmann, C.; Halada, G.

2006-01-01

109

Ab initio simulation of coherent phonons in BN-nanotubes  

Energy Technology Data Exchange (ETDEWEB)

BN nanotubes are isostructural to carbon nanotubes with boron and nitrogen atoms occupying the even and odd sublattices, respectively. An intense ultrashort laser pulse excites the electronic system to very high temperatures, whereas the ions remain close to their initial state. The ensuing laser-induced processes of electronic origin include bond softening, phonon frequency changes (hardening or softening), and the excitation of coherent phonons. We study these processes by means of large-scale molecular dynamics simulations based on density functional theory, including levels of excitation where the nanotube breaks. Our results show a strong radial breathing mode, increasing in amplitude with the laser-induced electronic temperature. We also determine the damage threshold.

Bauerhenne, Bernd; Zijlstra, Eeuwe S.; Garcia, Martin E. [Theoretische Physik, Universitaet Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany)

2011-07-01

110

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Analysis of the absorption spectra and spectral hole burning in zero-phonon lines of F+3 and N1 colour centres in LiF crystals  

Science.gov (United States)

The temperature dependences and mechanisms of broadening of zero-phonon lines of F+3 (488 nm) and N1 (523 nm) colour centres in LiF crystals are investigated. The results obtained make it possible to determine the quadratic electronic—vibrational coupling constant for N1 colour centres. The experimental data on the spectral hole burning in zero-phonon lines of F+3 and N1 colour centres indicate that the latter are positively charged.

Fedorov, A. V.; Martyshkin, D. V.; Fedorov, V. V.

2010-09-01

111

Effect of phonons in mixed valence systems  

International Nuclear Information System (INIS)

The effect of electron-phonon coupling on valence fluctuations in rare-earth systems is studied. It is shown that the electron-phonon coupling affects both the important electronic parameters and the phonon-frequencies, in particular the short-wavelength longitudinal optical phonons.

1978-09-07

112

Phonon properties of plutonium pnictides  

International Nuclear Information System (INIS)

The phonon properties of plutonium pnictides (PuX; X= As, Sb ) have been studied by using rigid ion (RIM) and breathing shell models (BSM) which includes breathing motion of electron of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of f-electron. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report, for the first time specific heat for these compounds. (author)

2008-01-01

113

Antimicrobial Action of Minocycline Microspheres Versus 810 nm Diode Laser on Human Dental Plaque Microcosm Biofilms.  

UK PubMed Central (United Kingdom)

Background: The purpose of this study was to investigate the antimicrobial effects of minocycline hydrochloride microspheres vs. infrared light at 810 nm from a diode laser on multi-species oral biofilms in vitro. These biofilms were evolved from dental plaque inoculum (oral microcosms) obtained from six systemically healthy human individuals with generalized chronic periodontitis. Methods: Multi-species biofilms were derived using supra- and subgingival plaque samples from mesiobuccal aspects of premolars and molars exhibiting probing depths in the 4-5mm range and 1-2 mm loss of attachment. Biofilms were developed anaerobically on blood agar surfaces in 96-well plates using a growth medium of PRAS brain heart infusion with 2% horse serum. Minocycline HCl 1 mg microspheres were applied on biofilms on day 2 and day 5 of their development. Biofilms were also exposed on day 2 and 5 of their growth to 810 nm light for 30 seconds using power of 0.8 Watts in a continuous wave mode. The susceptibility of microorganisms to minocycline or infrared light was evaluated by a colony forming assay and DNA probe analysis at different time points. Results: At all time points of survival assessment, minocycline was more effective (>2 log10 CFU reduction) compared with light treatment (P<0.002). Microbial analysis did not reveal susceptibility of certain dental plaque pathogens to light and was not possible following treatment with minocycline due to lack of bacterial growth. Conclusion: The cumulative action of minocycline microspheres on multi-species oral biofilms in vitro led to enhanced killing of microorganisms, whereas a single exposure of light at 810 nm exhibited minimal and non-selective antimicrobial effects.

Song X; Yaskell T; Klepac-Ceraj V; Lynch MC; Soukos NS

2013-06-01

114

Gigahertz coherent guided acoustic phonons in AlN/GaN nanowire superlattices.  

UK PubMed Central (United Kingdom)

The generation of guided acoustic phonons in the GHz range in GaN/AlN superlattices grown atop a GaN nanowire is presented. Combined with a femtosecond laser, ultrafast pump-probe spectroscopy allows the generation and detection of guided acoustic phonons at different frequencies in the nanowire superlattices. The capability of the nanowire superlattices to be excellent detectors of acoustic phonons at specific frequencies is then used to observe the strong dispersion, as a result of nanoconfinement, of guided acoustic phonons after their propagation in the nanowire. The generation of high frequency coherent guided acoustic phonons could be useful not only to realize an acoustic transducer with a nanolateral size but also as a source to understand the thermal behavior of nanowires.

Mante PA; Wu YC; Lin YT; Ho CY; Tu LW; Sun CK

2013-03-01

115

Gigahertz coherent guided acoustic phonons in AlN/GaN nanowire superlattices.  

Science.gov (United States)

The generation of guided acoustic phonons in the GHz range in GaN/AlN superlattices grown atop a GaN nanowire is presented. Combined with a femtosecond laser, ultrafast pump-probe spectroscopy allows the generation and detection of guided acoustic phonons at different frequencies in the nanowire superlattices. The capability of the nanowire superlattices to be excellent detectors of acoustic phonons at specific frequencies is then used to observe the strong dispersion, as a result of nanoconfinement, of guided acoustic phonons after their propagation in the nanowire. The generation of high frequency coherent guided acoustic phonons could be useful not only to realize an acoustic transducer with a nanolateral size but also as a source to understand the thermal behavior of nanowires. PMID:23394396

Mante, Pierre-Adrien; Wu, Yueh-Chun; Lin, Yuan-Ting; Ho, Cheng-Ying; Tu, Li-Wei; Sun, Chi-Kuang

2013-02-13

116

LIFETIMES OF HIGH FREQUENCY PHONONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the inhibition of anharmonic spontaneous multiphonon decay by energy-momentum conservation and the reduction of isotope scattering by the sharing of ionic motion to permit a frequency window for long-lived transverse acoustic phonons.

Lax, M.; Narayanamurti, V.; Hu, P.; Weber, W.

117

2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate  

International Nuclear Information System (INIS)

[en] Graphical abstract: Modeling the lattice dynamics of a triangular plate with the arrows indicating the direction of impulsive thermal stress. We investigated ultrafast structural dynamics of triangular nanoplates based on 2-D Fermi-Pasta-Ulam model to explain coherent acoustic phonon excitation in nanoprisms. - Abstract: In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes.

2010-08-23

118

Photonic and phononic quasicrystals  

Energy Technology Data Exchange (ETDEWEB)

This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. (topical review)

Steurer, Walter; Sutter-Widmer, Daniel [Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich (Switzerland)

2007-07-07

119

Dephasing times in quantum dots due to elastic LO phonon-carrier collisions  

DEFF Research Database (Denmark)

Interpretation of experiments on quantum dot (QD) lasers presents a challenge: the phonon bottleneck, which should strongly suppress relaxation and dephasing of the discrete energy states, often seems to be inoperative. We suggest and develop a theory for an intrinsic mechanism for dephasing in QDs: second-order elastic interaction between quantum dot charge carriers and LO phonons. The calculated dephasing times are of the order of 200 fs at room temperature, consistent with experiments. The phonon bottleneck thus does not prevent significant room temperature dephasing.

Uskov, A. V.; Jauho, Antti-Pekka

2000-01-01

120

Optical Investigations of Powerful Laser Actions on Massive and Flyer Targets  

International Nuclear Information System (INIS)

[en] In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets, and double targets consisting of a foil or disk (6 ?m thick for both cases) placed in front of the massive target part at a distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameters on the target surface from 70 ?m up to 1200 ?m (i.e. moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J focused always on a diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. 3-frame interferometry was employed to investigate the plasma dynamics through measurements of the electron density distribution time development as well as of the disks and foil fragments velocities. The dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. The experiments were complemented by a 2-D analytical theory and computer simulations, which helped at interpretation of the results. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer, as well as two-dimensional shock wave generation at the laser-driven macroparticle impact were obtained from the measured crater parameters for both the wavelengths of laser radiation

2006-01-15

 
 
 
 
121

Phonon populations by nanosecond-pulsed Raman scattering in Si  

International Nuclear Information System (INIS)

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.

1985-01-01

122

Phonon populations by nanosecond-pulsed Raman scattering in Si  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1985-11-15

123

[The mechanism of the action of laser therapy in rheumatoid arthritis  

UK PubMed Central (United Kingdom)

48 patients with rheumatoid arthritis (RA) were exposed to He-Ne laser radiation. Due to the course of the above laser therapy the patients displayed reduced levels of E and F2 alpha prostaglandins, a trend to a decrease of lipid peroxidation products, glycosaminoglycans and collagen-peptidase activity. This evidences for suppression of the inflammation and destruction in the connective tissue. Catalase activity in red cells enhanced. The authors point to high efficacy of low-intensity He-Ne laser in moderate rheumatoid inflammation.

Kozlova IS; Tsurko VV; Piriazeva NA; Volkova ZI; Kariakina EV; Nikolaev VI; Mul'diiarov PIa

1994-01-01

124

Polymorphism, phonon dynamics and carrier-phonon coupling in pentacene  

CERN Multimedia

The crystal structure and phonon dynamics of pentacene is computed with the Quasi Harmonic Lattice Dynamics (QHLD) method, based on atom-atom potential. We show that two crystalline phases of pentacene exist, rather similar in thermodynamic stability and in molecular density. The two phases can be easily distinguished by Raman spectroscopy in the 10-100 cm-1 spectral region. We have not found any temperature induced phase transition, whereas a sluggish phase change to the denser phase is induced by pressure. The bandwidths of the two phases are slightly different. The charge carrier coupling to low-frequency phonons is calculated.

Della Valle, R G; Farina, L; Venuti, E; Masino, M; Girlando, A; Brillante, Aldo; Farina, Luca; Girlando, Alberto; Masino, Matteo; Valle, Raffaele G. Della; Venuti, Elisabetta

2003-01-01

125

Influence of thermal expansion on the feasibility of gamma-ray laser action  

Energy Technology Data Exchange (ETDEWEB)

It is shown that a stable temperature of the active medium of a gamma-ray laser is essential for its operation. An analysis is made of the influence of thermal expansion of a laser rod cooled with liquid helium on the feasibility of lasing in the presence of heat evolution because of the absorption of electrons and x-ray conversion photons, as well as of cascade gamma photons.

Bushuev, V.A.; Mantsyzov, B.I.; Kuz' min, R.N.

1980-05-01

126

Suppressing electron-phonon interactions in semiconductor quantum dot systems by engineering the electronic wavefunctions  

DEFF Research Database (Denmark)

It is well-known that decoherence deteriorates the efficiency of cavity QED systems containing quantum dots (QDs), and that a major contribution stems from the coupling between the electrical carriers in the QD and acoustic phonons [1]. Employing a recently published model [2], we demonstrate how a proper matching between the electronic wavefuntion and the phonon-induced energy shift of valence and conduction band may be exploited to change the decoherence and decay properties of the QD by suppressing the phonon-induced processes. This effect may be addressed in a photoluminescence experiment, where a CW laser excites a two-level QD which interacts with a non-Markovian reservoir of acoustical phonons, see Fig. 1a. We assume a simple harmonic confinement of the electronic carriers, resulting in Gaussian wavefunctions, (r) / exp[?r2/(2W2 )], withWe (Wg) being the width of the electron (hole) wavefunction. In Fig. 1b we plot the stationary QD population vs. the laser frequency. We observe that for non-equal electron and hole wavefunction, the phonon-induced effect on the population surprisingly is fully suppressed at specific detunings. In a coupled QD–cavity system [2, 3], see Fig. 2a, this effect causes the QD lifetime to be unaffected by phonon processes at specific QD-cavity detunings. Furthermore, as shown in Fig. 2b, a proper choice of the QD wavefunction minimizes the phonon-induced pure dephasing rate, both in terms of the short-time magnitude and the long-time constant value. Furthermore we show, that even for realistic QDs, where We and Wg are determined by the QD shape and material composition, a significant suppression of phonon-induced processes is possible. Thus, more efficient quantum systems may be obtained if the QD wavefunctions are properly matched with the phononic properties of the surroundings.

Nysteen, Anders; Nielsen, Per Kær

2012-01-01

127

Phonons from neutron powder diffraction  

CERN Document Server

The spherically averaged structure function $\\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off--center phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure (dynamics from powder diffraction(DPD)) has been successfully implemented for two systems, a simple metal, fcc Ni, and an ionic crystal, CaF$_{2}$. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from powder neutron diffraction.

Dimitrov, D A; Röder, H

1998-01-01

128

Phonon spectra in quantum wires  

Directory of Open Access Journals (Sweden)

Full Text Available Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most important feature is that, beside the allowed energy zones (which are continuous as in the bulk structure), zones of forbidden states appear. Different values of the boundary parameters lead to the appearance of lower and upper energy gaps, or dispersion branches spreading out of the bulk energy zone. The spectra of phonons in corresponding unbound structures were correlated to those in bound structures.

Ili? Dušan; Rakovi? Dejan; Šetraj?i? Jovan

2007-01-01

129

Phonon Scattering of Composite Fermions  

UK PubMed Central (United Kingdom)

We study the principal aspects of the interaction between acoustic phononsand two-dimensional electrons in quantizing magnetic fields correspondingto even denominator fractions. Using the composite fermion approach wederive the vertex of the electron-phonon coupling mediated by the ChernSimonsgauge field. We estimate acoustic phonon contribution to electronicmobility, phonon-drag thermopower, and hot electron energy loss rate, whichall, depending on the temperature regime, are either proportional to lowerpowers of T than their zero field counterparts, or enhanced by the samenumerical factor as the coefficient of surface acoustic wave attenuation.The discovery of gapless compressible states at even denominator fractions (EDF) ¸ 1=Phi,Phi = 2; 4; etc became a new challenge for the theory of the interacting two-dimensionalelectron gas (2DEG) in quantizing magnetic fields. A number of metal-like features exhibitedby strongly correlated EDF electronic states [1] motivated t...

D. V. Khveshchenko

130

Scattering of phonons by vacancies  

International Nuclear Information System (INIS)

The scattering of phonons by vacancies is estimated by a perturbation technique in terms of the missing mass and the missing linkages. An argument is given why distortion effects can be disregarded. The resonance frequency of the defect is sufficiently high so that resonance effects can be disregarded for phonons in the important frequency range for thermal conduction. The theory is applied to the thermal resistance by vacancies in cases where the vacancy concentration is known: potassium chloride with divalent cations, nonstoichiometric zirconium carbide, and tin telluride.

1987-01-01

131

Scattering of phonons by vacancies  

Science.gov (United States)

The scattering of phonons by vacancies is estimated by a perturbation technique in terms of the missing mass and the missing linkages. An argument is given why distortion effects can be disregarded. The resonance frequency of the defect is sufficiently high so that resonance effects can be disregarded for phonons in the important frequency range for thermal conduction. The theory is applied to the thermal resistance by vacancies in cases where the vacancy concentration is known: potassium chloride with divalent cations, nonstoichiometric zirconium carbide, and tin telluride.

Ratsifaritana, C. A.; Klemens, P. G.

1987-11-01

132

Mechanism for critical behavior of a chemically reactive system under the action of laser radiation  

Energy Technology Data Exchange (ETDEWEB)

Several mechanisms, such as thermal vibration instability, have been proposed to describe critical phenomena in the threshold behavior of reactions, but none for laser initiation. A mechanism based on the competition between thermal acceleration of reaction and retardation of reaction due to annihilation is suggested. Laser initiation with excitation of low-atom molecules is examined. A typical two-center chain reaction is schematically represented, and equations are derived in a model analysis. The analysis indicates that pulsed initiation behavior as a function of initial conditions has a critical character. The criticality of laser initiation is not fundamentally different from other forms of pulsed initiation. A threshold dependence on the absorbed energies is not necessary. General analysis carried out in this paper provides a calculation for determining the photothermal explosion mechanism.

Vasil' ev, G.K.; Chernyshev, Yu.A.; Makarov, E.F.; Yakushev, V.G.

1982-07-01

133

Phonon tunnelling from a sonic black hole  

CERN Multimedia

We investigate the phonon radiation from a spherically symmetrical, stationary, viscid-free sonic black hole by using a semi-classical method. The backreaction of the radiated phonon is taken into account. We obtain the phonon emission temperature which is consistent with the Hawking's formula.

Fang, Hengzhong

2011-01-01

134

Correction of eye refraction by nonablative laser action on thermomechanical properties of cornea and sclera  

International Nuclear Information System (INIS)

A new approach is proposed for correcting the eye refraction by controlled variation of the mechanical properties of the sclera and cornea upon nondestructive laser heating. Experimental ex vivo studies of rabbit and pig eyes show that laser-induced local denaturation of the sclera changes the refraction of the cornea by 3 diopters on the average, and the subsequent nondestructive irradiation of the cornea increases its plasticity, which leads to a further increase in its radius of curvature and a decrease in refraction down to 7 diopters.

2002-10-31

135

Vibrational frequencies via frozen phonons  

Energy Technology Data Exchange (ETDEWEB)

We have used a first principles linear combination of atomic orbitals (LCAO) method to calculate the total ground state energy for crystals of Si, Nb and Mo involving lattice distortions. From these calculations the equilibrium lattice constant, cohesive energy, and bulk modulus as well as the vibrational frequencies for selected phonons were determined.

Harmon, B.N.; Weber, W.; Hamann, D.R.

1981-01-01

136

Vibrational frequencies via frozen phonons  

Energy Technology Data Exchange (ETDEWEB)

A first principles linear combination of atomic orbitals (LCAO) method has been used to calculate the total ground state energy for crystals of Si, Nb, and Mo involving lattice distortions. From these calculations the equilibrium lattice constant, cohesive energy, and bulk modulus as well as the vibrational frequencies for selected phonons were determined.

Harmon, B.N. (Kernforschungszentrum, Karlsruhe, Germany); Weber, W.; Hamann, D.R.

1981-12-01

137

PHONONS IN MIXED VALENCE COMPOUNDS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several mixed-valence NaCl-structure compounds show strong anomalies in the phonon dispersion curves. These anomalies are related to the interaction of localized f-electrons with delocalized band electrons near the Fermi surface and to the iso-structural phase transitions characterized by a softenin...

Kress, W.; Bilz, H.; Güntherodt, G.; Jayaraman, A.

138

Changes in the refractive indices of absorbing liquids under the action of pulsed laser radiation  

International Nuclear Information System (INIS)

Changes in the refractive indices of weakly absorbing liquids exposed to pulsed laser radiation have been calculated as functions of space and time based on numerical solution of equations for continuous media motion in the Lagrange form, the heat-conduction equation, and the Lorentz-Lorenz formula. (authors)

2011-01-01

139

The heat-pipe resembling action of boiling bubbles in endovenous laser ablation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a con...

Geld, C.W.M. van der; Bos, R.R. van den; Ruijven, P.W.M. van; Nijsten, T.E.C.; Neumann, H.A.M.; Gemert, M.J.C. van

140

Ultrafast acoustics in the middle UV range: coherent phonons at higher frequencies and in smaller objects.  

UK PubMed Central (United Kingdom)

We show that the propagation of coherent acoustic phonons generated by femtosecond optical excitation can be clearly resolved using a probe laser in the middle UV (MUV) range. The MUV probe is easily produced from a high-repetition-rate femtosecond laser and a homemade frequency tripler. We present various experimental results that demonstrate efficient and high frequency detection of acoustic phonons. Thus, we show that the MUV range offers a unique way to reach higher frequencies and probe smaller objects in ultrafast acoustics.

Ayrinhac S; Devos A; Le Louarn A; Mante PA; Emery P

2010-10-01

 
 
 
 
141

Tunable infrared phonon anomalies in trilayer graphene.  

UK PubMed Central (United Kingdom)

Trilayer graphene in both ABA (Bernal) and ABC (rhombohedral) stacking sequences is shown to exhibit intense infrared absorption from in-plane optical phonons. The phonon feature, lying at ~1580 cm(-1), changes strongly with electrostatic gating. For ABC-stacked graphene trilayers, we observed a large enhancement in phonon absorption amplitude, as well as softening of the phonon mode, as the Fermi level is tuned away from charge neutrality. A similar, but substantially weaker, effect is seen in samples with the more common ABA stacking order. The strong infrared response of the optical phonons and the pronounced variation with electrostatic gating and stacking order reflect the interactions of the phonons and electronic excitations in the two systems. The key experimental findings can be reproduced within a simplified charged-phonon model that considers the influence of charging through Pauli blocking of the electronic transitions.

Lui CH; Cappelluti E; Li Z; Heinz TF

2013-05-01

142

Multiphoton dissociation of formic acid molecules under action of free electron laser  

International Nuclear Information System (INIS)

The successful experiments on the isotopic-selective infra-red multiphoton dissociation (IR MPD) of the formic acid molecules have been performed with the radiation of a free electron laser (FEL) for the first time. Upon irradiating the H12COOH + H13COOH (50% + 50%) mixture in the spectral region of the C=O stretch vibrational band in the dissociation product CO either 13C or 12C isotope predominates that depends on the laser radiation frequency. In the sample with the natural isotopic content the enrichment of CO by the 13C isotopic has been attained 19.5% compared with 1.1% of natural content. Also the about fivefold enrichment of CO by the 18O isotope has been observed.

1996-01-01

143

Influence of the electron--phonon interaction on an inverted population in a semiconductor superlattice and a semiconductor size-quantized film in a magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Analytic expressions are obtained for the coefficient representing phonon emission as a result of transitions between magnetic film levels and the magnetoacoustic subbands, and also for the coefficient of absorption of electromagnetic radiation under the electron--phonon interaction conditions. It is shown that under certain conditions these transitions cannot influence the self-excitation of a semiconductor laser.

Aleksanyan, A.G.

1985-04-01

144

Selective transmission and enhanced thermal conductance of ballistic phonon by nanocavities embedded in a narrow constriction  

Energy Technology Data Exchange (ETDEWEB)

The effects of nanocavities embedded in a narrow constriction on ballistic phonon transport in a semiconductor nanowire are investigated. It is shown that when more than one nanocavity is embedded in a narrow constriction with a fixed length, the nanowire has selective transmission and filter actions for the ballistic phonon. The number of resonant transmission peaks increases with the number n of cavities, while the frequencies of the main peaks are independent of n. The thermal conductance can be enhanced significantly, and the enhancement alters in different temperature ranges with the number n of cavities, depending on the competition between the transmission enhancement and scatter enhancement of the ballistic phonon. This structure may be a promising candidate for selective frequency generator and filter for the ballistic phonon in nanophononics.

Huang Weiqing; Huang Baiyun; Yi Danqing; Wang Mingpu [College of Materials Science and Engineering, Central South University, Changsha 410083 (China); Huang Guifang [CCAST (World Laboratory), PO Box 8730, Beijing 100080 (China); Wang Lingling [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: wqhuang2000@yahoo.com, E-mail: weiqinghuang@hnu.cn

2009-01-07

145

Massively parallel Hamiltonian action in pseudospectral algorithms applied to quantum dynamics of laser induced desorption  

International Nuclear Information System (INIS)

The Hamiltonian action upon a wavefunction is the basic operation in iterative propagation schemes. Aiming at high-dimensional quantum dynamics, we introduce a parallel algorithm for a Hamiltonian action utilizing pseudospectral schemes on multi-dimensional grids. This algorithm is exemplified for a six-dimensional (6D) quantum dynamical system described in Fourier coordinates. The performance outcome of our parallel implementation is revealed by an almost linear overall scaled speedup that is only limited by present hardware resources. Our parallelization strategy is realized in ab initio four-dimensional (4D) quantum dynamical studies investigating the lateral dynamics of CO photodesorbing from a Cr2O3(0 0 0 1) surface.

2004-09-13

146

Massively parallel Hamiltonian action in pseudospectral algorithms applied to quantum dynamics of laser induced desorption  

Energy Technology Data Exchange (ETDEWEB)

The Hamiltonian action upon a wavefunction is the basic operation in iterative propagation schemes. Aiming at high-dimensional quantum dynamics, we introduce a parallel algorithm for a Hamiltonian action utilizing pseudospectral schemes on multi-dimensional grids. This algorithm is exemplified for a six-dimensional (6D) quantum dynamical system described in Fourier coordinates. The performance outcome of our parallel implementation is revealed by an almost linear overall scaled speedup that is only limited by present hardware resources. Our parallelization strategy is realized in ab initio four-dimensional (4D) quantum dynamical studies investigating the lateral dynamics of CO photodesorbing from a Cr{sub 2}O{sub 3}(0 0 0 1) surface.

Borowski, S.; Kluener, T

2004-09-13

147

New Mid-IR Lasers Based on Rare-Earth-Doped Sulfide and Chloride Materials  

Energy Technology Data Exchange (ETDEWEB)

Applications in remote-sensing and military countermeasures have driven a need for compact, solid-state mid-IR lasers. Due to multi-phonon quenching, non-traditional hosts are needed to extend current solid-state, room-temperature lasing capabilities beyond {approx} 4 {micro}m. Traditional oxide and fluoride hosts have effective phonon energies in the neighborhood of 1000 cm{sup -1} and 500 cm{sup -1}, respectively. These phonons can effectively quench radiation above 2 and 4 {micro}m, respectively. Materials with lower effective phonon energies such as sulfides and chlorides are the logical candidates for mid-IR (4-10 {micro}m) operation. In this report, laser action is demonstrated in two such hosts, CaGa{sub 2}S{sub 4} and KPb{sub 2}Cl{sub 5}. The CaGa{sub 2}S{sub 4}:Dy{sup 3+} laser operating at 4.3 {micro}m represents the first sulfide laser operating beyond 2 {micro}m. The KPb{sub 2}Cl{sub 5}:Dy{sup 3+} laser operating at 2.4 {micro}m represents the first operation of a chloride-host laser in ambient conditions. Laser action is also reported for CaGa{sub 2}S{sub 4}:Dy{sup 3+} at 2.4 {micro}m, CaGa{sub 2}S{sub 4}:Dy{sup 3+} at 1.4 {micro}m, and KPb{sub 2}Cl{sub 5}:Nd{sup 3+} at 1.06 {micro}m. Both host materials have been fully characterized, including lifetimes, absorption and emission cross sections, radiative branching ratios, and radiative quantum efficiencies. Radiative branching ratios and radiative quantum efficiencies have been determined both by the Judd-Ofelt method (which is based on absorption measurements), and by a novel method described herein which is based on emission measurements. Modeling has been performed to predict laser performance, and a new method to determine emission cross section from slope efficiency and threshold data is developed. With the introduction and laser demonstration of rare-earth-doped CaGa{sub 2}S{sub 4} and KPb{sub 2}Cl{sub 5}, direct generation of mid-IR laser radiation in a solid-state host has been demonstrated. In KPb{sub 2}Cl{sub 5}, predictions indicate that laser operation to 9 {micro}m may be possible, a wavelength previously considered unreachable in a room-temperature, solid-state host.

Nostrand, M

2000-09-01

148

Spin Bath Decoherence Mediated by Phonons  

CERN Multimedia

We introduce an exactly solvable model to study decoherence of a central spin interacting with a spin bath where the coupling is mediated by phonons which we assume to be in a coherent state or thermal distribution. For the coherent state case, we find that the decoherence factor decays in a Gaussian fashion and it becomes independent of the phonon frequencies at short times. If the phonon energies are much larger than spin-phonon coupling or bath spins are fully polarized, decoherence time becomes independent of the initial phonon state. For the thermal state case, phonons play more important role in decoherence with increasing temperature. We also discuss possible effects of the temperature on spin bath contribution to decoherence.

Bozat, O

2008-01-01

149

Phonon lineshapes in atom-surface scattering  

Energy Technology Data Exchange (ETDEWEB)

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.

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

150

Phononic Frequency Combs via Nonlinear Resonances  

CERN Multimedia

We study the analogue of optical frequency combs in driven nonlinear phononic systems, and present a new generation mechanism for phononic frequency combs via nonlinear resonances. The nonlinear resonance refers to the simultaneous excitation of a set of phonon modes by the external driving, and thereby generated frequency combs are characterized by an array of equidistant spectral lines in the spectrum of each nonlinearly excited phonon mode. Frequency combs via nonlinear resonance of different orders are investigated, and particularly we reveal the possibility for correlation tailoring in higher order cases. The investigation contributes to potential applications in various nonlinear acoustic processes, such as harvesting phonons and generating phonon entanglements, and can also be generalized to other nonlinear systems.

Cao, Lushuai; Peng, Ruwen; Wang, Mu; Schmelcher, Peter

2013-01-01

151

Spin temperature and non-equilibrium phonons  

Energy Technology Data Exchange (ETDEWEB)

The concept of spin temperature is used to describe the electron paramagnetic resonance saturation in solids having a strong phonon bottleneck effect. Unusual features of the spin system and hot phonon behavior are analyzed on the basis of a set of kinetic equations derived for the spin and Zeeman temperatures and for the number of phonons. Most of the phenomena considered are observed experimentally. (author). 7 figs., 21 refs.

Kochelaev, B.I. [AN SSSR, Kazan (Russian Federation). Fiziko-Tekhnicheskij Inst.

1994-12-31

152

Polaronic signatures in phonon isotopic shifts  

Energy Technology Data Exchange (ETDEWEB)

The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa{sub 2}Cu{sub 3}O{sub 7}, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure.

Mustre de Leon, J.; Coss, R. de; Rubio-Ponce, A. [Inst. Politecnico Nacional, Merida (Mexico). Centro de Investigacion y de Estudios Avanzados; Bishop, A.R.; Trugman, S.A. [Los Alamos National Lab., NM (United States)

1998-12-31

153

Polaronic Signatures in Phonon Isotopic Shifts  

Energy Technology Data Exchange (ETDEWEB)

The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa{sub 2}Cu{sub 3}O{sub 7}, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure.

de Leon, J.M.; de Coss, R.; Rubio-Ponce, A.; Bishop, A.R.; Trugman, S.A.

1998-06-01

154

Two-dimensional phonon transport in graphene  

International Nuclear Information System (INIS)

Properties of phonons - quanta of the crystal lattice vibrations - in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. (topical review)

2012-06-13

155

Phononic Molecules Studied by Raman Scattering  

International Nuclear Information System (INIS)

An acoustic nanocavity can confine phonons in such a way that they act like electrons in an atom. By combining two of these phononic-atoms, it is possible to form a phononic 'molecule', with acoustic modes that are similar to the electronic states in a hydrogen molecule. We report Raman scattering experiments performed in a monolithic structure formed by a phononic molecule embedded in an optical cavity. The acoustic mode splitting becomes evident through both the amplification and change of selection rules induced by the optical cavity confinement. The results are in perfect agreement with photoelastic model simulations.

2010-01-04

156

Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire  

Directory of Open Access Journals (Sweden)

Full Text Available A model for phonon heat conduction in a molecular nanowire is developed. The calculation takes into account modification of the acoustic phonon dispersion relation due to the electron-phonon interaction. The results obtained are compared with models based upon a simpler, Callaway formula.

Galovi? Slobodanka P.; ?evizovi? D.; Zekovi? S.; Ivi? Z.

2006-01-01

157

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

International Nuclear Information System (INIS)

[en] 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 ? it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point ?), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line ? 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

2007-03-01

158

Phonon drag in ballistic quantum wires  

CERN Document Server

A drag current created in the ballistic transport regime in a one-dimensional nanowire by phonons generated by a current-carrying ballistic channel in a nearby nanowire is calculated. A threshold of the phonon-mediated drag current with respect to bias or gate voltage is predicted.

Muradov, M I

2001-01-01

159

Double-? phonon excitation in the Os nuclei  

Science.gov (United States)

We investigate double-? phonon excitation in the Os nuclei within the framework of the proton-neutron Interacting Boson Model (IBM-2). We decompose the IBM-2 wave-functions into multiphonon states, and see the contributions of zero, one and two phonon components in the low lying levels of the Os nuclei.

Sugita, M.; Otsuka, T.

1993-05-01

160

Electron-phonon interaction and the generalized kinetic equation for systems interacting with high-intensity electromagnetic wave fields  

International Nuclear Information System (INIS)

The generalized kinetic equation for an electron-phonon system subjected to the action of an intense electromagnetic wave field is derived on the basis of the Bogolubov method of elimination of boson operators, taking into account the electron-phonon collision effects. The conditions are considered under which the collision integral allows the introduction of the relaxation time, and the latter is calculated as a function of the frequency and intensity of the pumping field

1983-01-01

 
 
 
 
161

Phonon line emission revealed by self-assembly of colloidal nanoplatelets.  

UK PubMed Central (United Kingdom)

We show that colloidal nanoplatelets can self-assemble to form a 1D superlattice. When self-assembled, an additional emission line appears in the photoluminescence spectrum at low temperatures. This emission line is a collective effect, greatly enhanced when the NPLs are self-assembled. It is attributed to the longitudinal optical (LO) phonon replica of the band-edge exciton, and its presence in self-assembled nanoplatelets is explained using a model based on an efficient photons reabsorption between neighboring nanoplatelets. The presence of phonon replica at low temperatures in ensemble measurements suggests the possibility to design a laser, based on self-assembled nanoplatelets.

Tessier MD; Biadala L; Bouet C; Ithurria S; Abecassis B; Dubertret B

2013-04-01

162

Dynamics of internal electric and phonon fields in n-GaAs pumped with ultrashort pulses  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english We investigate the ultrafast dynamics of an electron-hole plasma coupled to phonons in bulk GaAs excited with femtosecond laser pulses. Our approach is based on balance equations directly derived from the Boltzmann equation within the relaxation-time approximation. Poisson's equation together with a phenomenological driven-harmonic-oscillator equation supplements our description by accounting for time-dependent electric and vibrational fields. Our calculated internal fiel (more) ds show oscillations at frequencies characteristic of those of coupled plasmon-phonon modes. Our results are consistent with recent experimental data.

Souza, Fabrício M.; Egues, J. Carlos

1999-12-01

163

Dynamics of internal electric and phonon fields in n-GaAs pumped with ultrashort pulses  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the ultrafast dynamics of an electron-hole plasma coupled to phonons in bulk GaAs excited with femtosecond laser pulses. Our approach is based on balance equations directly derived from the Boltzmann equation within the relaxation-time approximation. Poisson's equation together with a phenomenological driven-harmonic-oscillator equation supplements our description by accounting for time-dependent electric and vibrational fields. Our calculated internal fields show oscillations at frequencies characteristic of those of coupled plasmon-phonon modes. Our results are consistent with recent experimental data.

Souza Fabrício M.; Egues J. Carlos

1999-01-01

164

Phonon dynamics of plutonium chalcogenides and pnictides  

International Nuclear Information System (INIS)

We have investigated the phonon dynamics of the plutonium compounds (PuX; X = S, Se, Te, As, and Sb) by using rigid ion (RIM) and breathing shell models (BSM), later includes breathing motion of the electrons of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of electron-phonon interactions. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report the one phonon density of states and first time calculated the lattice specific heat for these compounds.

2009-09-15

165

Phonon Drag Dislocations at High Pressures  

Energy Technology Data Exchange (ETDEWEB)

Phonon drag on dislocations is the dominant process which determines the flow stress of metals at elevated temperatures and at very high plastic deformation rates. The dependence of the phonon drag on pressure or density is derived using a Mie-Grueneisen equation of state. The phonon drag is shown to increase nearly linearly with temperature but to decrease with density or pressure. Numerical results are presented for its variation for shock-loaded copper and aluminum. In these cases, density and temperature increase simultaneously, resulting in a more modest net increase in the dislocation drag coefficient. Nevertheless, phonon drag increases by more than an order of magnitude during shock deformations which approach melting. Since the dependencies of elastic moduli and of the phonon drag coefficient on pressure and temperature are fundamentally different, the effect of pressure on the constitutive law for plastic deformation can not simply be accounted for by its effect on the elastic shear modulus.

Wolfer, W.G.

1999-10-19

166

Sound-Particles and Phonons with Spin 1  

Directory of Open Access Journals (Sweden)

Full Text Available We present a new model for solids which is based on the stimulated vibration of independent neutral Fermi-atoms, representing independent harmonic oscillators with natural frequencies, which are excited by actions of the longitudinal and transverse elastic waves. Due to application of the principle of elastic wave-particle duality, we predict that the lattice of a solid consists of two type Sound Boson-Particles with spin 1 with finite masses. Namely, these lattice Boson-Particles excite the longitudinal and transverse phonons with spin 1. In this letter, we estimate the masses of Sound Boson-Particles which are around 500 times smaller than the atom mass.

Minasyan V.; Samoilov V.

2011-01-01

167

Coherent phonon frequency comb generated by few-cycle femtosecond pulses in Si  

Science.gov (United States)

We explore the coherent phonon induced refractive index modulation of a Si(001) surface upon the excitation in near-resonance with the direct band gap of Si. Through the anisotropic e-h pair generation and coherent Raman scattering, ˜ 10-fs laser pulses exert a sudden electrostrictive force on Si lattice launching coherent LO phonon oscillations at 15.6 THz frequency. The concomitant oscillatory change in the optical constants modulates the reflected probe light at the fundamental LO phonon frequency, generating a broad comb of frequencies at exact integer multiples of the fundamental frequency extending to beyond 100 THz. On the basis of an analytical model, we show that the simultaneous amplitude and phase modulation of the reflected light by the coherent lattice polarization at 15.6 THz generates the frequency comb.

Hase, Muneaki; Katsuragawa, Masayuki; Monia Constantinescu, Anca; Petek, Hrvoje

2013-03-01

168

LO-phonon generation rate with electron energy collision broadening in polar semiconductors  

International Nuclear Information System (INIS)

Rate equations for the LO-phonon distribution function and mean electron energy with the electron energy collision broadening effect included are derived in the frame of Zubarev's theory of non-equilibrium statistical operators. A numerical evaluation of the rate of change of the LO-phonon distribution function is performed for a typical process of laser-excited hot electron relaxation in several polar semiconductors (GaSb, GaAs, InP, CdSe, ZnS). The electron energy collision broadening is found to lead to a new feature in the wave vector dependence of the LO-phonon generation rate. This feature provides an example of an effect which is clearly beyond the Boltzmann equation level of description. (author). 6 figs., 1 tab., 29 refs.

1989-01-01

169

Phonons of Metallic Vicinal Surfaces  

CERN Document Server

We present an analysis of the vibrational dynamics of metal vicinal surfaces using the embedded atom method to describe the interaction potential and both a real space Green's function method and a slab method to calculate the phonons. We report two main general characteristics : a global shift of the surface vibrational density of states resulting from a softening of the force field. The latter is a direct result of the reduction of coordination for the different type of surface atoms; and an appearance of high frequency modes above the bulk band, resulting from a stiffening of the force field near the step atom. The latter is due to a rearrangement of the atomic positions during the relaxation of the surface atoms yielding a large shortening of the nearest neighbor distances near the step atoms.

Kara, A; Kara, Abdelkader; Rahman, Talat S.

2001-01-01

170

Three-phonon excitations in 124Sn  

International Nuclear Information System (INIS)

[en] The low-lying levels of 124Sn have been explored using the (n,n'?) reaction to identify multiphonon quadrupole excitations. Yields of ? rays as a function of incident neutron energy, ?-? coincidences, and ?-ray angular distributions have been measured. From the excitation functions and coincidence measurements, the level and decay schemes were determined with good confidence in the ?-ray placements. The angular distributions provide multipolarity information on the decay ? rays which lead to spin assignments for levels and also enable the determination of lifetimes or lifetime limits from Doppler shifts. A close-lying triplet of levels, representing the two-phonon multiplet, occurs near an additional 4+ level which mixes with the 4+ two-phonon excitation. A three-phonon quintet of levels has been found, including one new level, which decays almost exclusively to the two-phonon triplet. No other levels in the three-phonon energy region decay other than weakly to the two-phonon excitations; only one other level has observable decays to the two-phonon triplet

2005-01-24

171

Cooperative two-phonon phenomena in superconductivity  

Energy Technology Data Exchange (ETDEWEB)

The problem of the two-photon coherent generation of entanglement photon pairs in quantum optics has been intensively studied over the passing years. It is important to note that the two-quanta cooperative effects also play a main role in other fields of physics. One example is superconductivity, where the Cooper pairs are created due to the simultaneous two-phonon exchange between electrons. It occurs when the one-phonon exchange integral between the band electrons is smaller than that of the two-phonon exchange. This is possible in many-band superconducting materials, in which the two-phonon exchange integral arises through the virtual bands of the material. Some estimates of the two-phonon superconductivity have already been given. A more realistic model which takes into account the specificities of the many-band aspects of superconductor materials will be proposed. In two-phonon processes, a more complicated temperature dependence on the order parameter is expected. A rigorous study of this anomalous temperature dependence on the order parameter of superconductors is presented. One expects that the two-phonon exchange effects can amplify the superconductivity in a way similar to the way the thermal field amplifies the two-photon super-radiance in a microcavity.

Enaki, N A [Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, Chisinau (Moldova, Republic of); Eremeev, V V [Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, Chisinau (Moldova, Republic of)

2002-10-01

172

Nonlinear response function for two-phonon polaritons  

International Nuclear Information System (INIS)

[en] A nonlinear response function describing three-polariton processes (two single-phonon polaritons and two-phonon polariton) is derived for a system of interaction phonons and photons. The main features of the nonlinear optical spectra in the two-phonon polariton region are analyzed. (author). 17 refs

1992-01-01

173

The Phonon Drag Effect in Single-Walled Carbon Nanotubes  

CERN Multimedia

A variational solution of the coupled electron-phonon Boltzmann equations is used to calculate the phonon drag contribution to the thermopower in a 1-D system. A simple formula is derived for the temperature dependence of the phonon drag in metallic, single-walled carbon nanotubes. Scattering between different electronic bands yields nonzero values for the phonon drag as the Fermi level varies.

Scarola, V W

2002-01-01

174

The hot phonon spot in the film  

International Nuclear Information System (INIS)

The possibility of hot phonon spot (HPS) formation and the further study of dynamics of HPS development at the excitation of phonon system as a result of cooling down of the photoexcited current carriers in the semiconductor films are discussed. The adequately defective and thick films are considered. It is assumed that the loss of energy via boundaries may be neglected and the density of states of excited phonons through the depth of film will be uniform. (author). 3 refs, 2 figs, 3 tabs

1990-01-01

175

One-dimensional hypersonic phononic crystals.  

Science.gov (United States)

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. PMID:20141118

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

2010-03-10

176

One-dimensional hypersonic phononic crystals.  

UK PubMed Central (United Kingdom)

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.

Gomopoulos N; Maschke D; Koh CY; Thomas EL; Tremel W; Butt HJ; Fytas G

2010-03-01

177

Equations of the quasiparticle-phonon nuclear model with the phonon scattering effects at finite temperature  

International Nuclear Information System (INIS)

[en] A generalization of the quasiparticle-phonon nuclear model (QPNM) for describing the interaction with (2p-2h) configurations at finite temperature is presented. By taking exactly into account the occupation numbers of one-phonon energy levels a closed system of approximate equations for Green functions with one- to two-phonon transition, phonon-ground state correlation and phonon scattering propagators in even-even spherical nuclei is explicitly derived. A one-to-one correspondence between this system and the system of QPNM equations of the coefficients of the excited state wave function is established. It is shown that in the zero temperature limit one obtains the standard basic equations employed so far within the QPNM. The numerical evaluation of the phonon scattering effects has shown that for temperatures T

1984-01-01

178

Energy resolved phonon scattering in thin film amorphous solids  

International Nuclear Information System (INIS)

[en] Energy resolved phonon scattering measurements were performed using a novel heat pulse technique. Two thin film phonon generators were deposited on one face of a sapphire crystal substrate and two phonon detectors were deposited on the opposite face, under one of which a thin film amorphous material was deposited. The phonon detectors were superconducting tunnel heterojunctions. A comparison of the number of phonons detected at each junction gave information on the fraction of phonons transmitted through the amorphous film as a function of energy from which the phonon mean free path as a function of energy could be deduced. Materials investigated were silicon monoxide and germanium. (author)

1980-01-01

179

Effects of phonon-phonon coupling on properties of pygmy resonance in $^{124-132}$Sn  

CERN Multimedia

Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in $^{124-132}$Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy $E1$ strength distribution.

Arsenyev, N N; Voronov, V V; Van Giai, Nguyen

2012-01-01

180

Effects of phonon-phonon coupling on properties of pygmy resonance in 124-132Sn  

Directory of Open Access Journals (Sweden)

Full Text Available Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in 124-132Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy E1 strength distribution.

Arsenyev N. N.; Severyukhin A. P.; Voronov V. V.; Van Giai Nguyen

2012-01-01

 
 
 
 
181

Análise histológica da cicatrização de feridas cutâneas experimentais sob ação do laser de baixa potência =Histological analysis of experimental wound healing under the action of low power laser  

Directory of Open Access Journals (Sweden)

Full Text Available Objetivos: verificar histologicamente a cicatrização de feridas cutâneas experimentais em Rattus norvergicus quando empregado o laser de baixa potência. Métodos: foram utilizados 45 animais machos, distribuídos em três grupos conforme a terapêutica adotada (não tratados, tratados com laser na dose de 4 J/cm2 e tratados com laser na dose de 8 J/cm2), os quais foram divididos em três subgrupos conforme o período de eutanásia (7, 14 e 21 dias). Foi removido um fragmento cutâneo de 2 cm de diâmetro do dorso de cada animal e a cada 24 horas foi irradiado laser nos fragmentos dos grupos tratados, com a dose estabelecida previamente. Resultados: aos sete dias após o experimento, os grupos irradiados com laser de baixa potência apresentaram uma reepitelização mais eficiente quando comparados ao grupo não tratado. Além disso, os grupos tratados com laser apresentaram uma deposição de colágeno mais acentuada quando transcorridos 14 dias. A dose ajustada em 4 J/cm2 foi mais efetiva. Conclusões: o laser de baixa potência otimizou o processo de cicatrização de feridas cutâneas experimentais em Rattus norvergicus. A dose ajustada em 4 J/cm2 foi mais efetiva. Aims: To assess histologically the healing of experimental skin wounds in Rattus norvergicus using low-power laser. Methods: Forty-five males were divided into three groups according to the adopted therapy (untreated, treated with laser at a dose of 4 J/cm2 and treated with laser at a dose of 8 J/cm2), which were divided into three subgroups according to time of euthanasia (7, 14 and 21 days). A fragment of 2 cm in diameter of skin was removed from the back of each animal, and laser was irradiated every 24 hours in the fragments of the treated groups, with the previously established dose. Results: At seven days after the experiment, the low-power laser irradiated groups showed a more efficient reepithelialization when compared with the untreated group. Furthermore, the groups treated with laser showed a more marked deposition of collagen at 14 days. Dose adjusted in 4 J/cm2 was more effective. Conclusions: Low-power laser has enhanced the healing of experimental skin wounds in Rattus norvergicus. The adjusted dose in 4 J/cm2 was more effective.

Abreu, Jesus Antônio de Carvalho et al.

2011-01-01

182

Strong optical-mechanical coupling in a vertical GaAs/AlAs microcavity for subterahertz phonons and near-infrared light.  

UK PubMed Central (United Kingdom)

We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-Q optical cavity mode. Large optomechanical factors are reported (~THz/nm range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range ?W-mW, opening the way for the demonstration of phonon "lasing" by parametric instability in these devices.

Fainstein A; Lanzillotti-Kimura ND; Jusserand B; Perrin B

2013-01-01

183

Single electron-phonon interaction in a suspended quantum dot phonon cavity  

CERN Document Server

An electron-phonon cavity consisting of a quantum dot embedded in a free-standing GaAs/AlGaAs membrane is characterized in Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.

Höhberger, E M; Brandes, T; Kirschbaum, J; Wegscheider, W; Bichler, M; Kotthaus, J P

2003-01-01

184

Single-electron-phonon interaction in a suspended quantum dot phonon cavity.  

UK PubMed Central (United Kingdom)

An electron-phonon cavity consisting of a quantum dot embedded in a freestanding GaAs/AlGaAs membrane is characterized using Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at discrete magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.

Weig EM; Blick RH; Brandes T; Kirschbaum J; Wegscheider W; Bichler M; Kotthaus JP

2004-01-01

185

LO-phonon overheating in quantum dots  

CERN Multimedia

Longitudinal optical phonons have been used to interpret the electronic energy relaxation in quantum dots and at the same time they served as a reservoir, with which the electronic subsystem is in contact. Such a phonon subsystem is expected to be passive, namely, in a long-time limit the whole system should be able to achieve such a stationary state, in which statistical distributions of both subsystems do not change in time. We pay attention to this property of the LO phonon bath. We show the passivity property of the so far used approximations to electronic transport in quantum dots. Also we show a way how to improve the passivity of LO phonon bath using canonical Lang-Firsov transformation.

Kral, K

2005-01-01

186

Phonon spectra of a Fibonacci chain  

Energy Technology Data Exchange (ETDEWEB)

Based on more realistic physics we study the phonon spectra of the Fibonacci chain by taking into account a nonlinear resistance. It is found that the nonlinear force should be very weak and consequently, the continuity, range and gaps of the phonon spectra would be still controlled dominantly by the relative strength of spring constants and chain length. It means that even if no additional nonlinear resistance was taken into account, the conventional results of phonon spectra are exactly correct. On the other hand, in the framework of a conventional model we investigated the relationship between the biggest gaps of phonon spectra and defects of Fibonacci-like aperiodic chains. By means of numerical calculations one can obtain quantitatively the maximum of the length of a one-dimensional aperiodic chain sensitive to boundaries. This method would be useful for the calculation of quasiperiodic and aperiodic lattices.

Li Liqin [MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, South China Normal University, Guangzhou 510631 (China); Yang Xiangbo [MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, South China Normal University, Guangzhou 510631 (China); Laboratory of Photonic Information Technology, South China Normal University, Guangzhou 510631 (China)], E-mail: xbyang@scnu.edu.cn

2008-08-01

187

Phonon spectra of a Fibonacci chain  

International Nuclear Information System (INIS)

Based on more realistic physics we study the phonon spectra of the Fibonacci chain by taking into account a nonlinear resistance. It is found that the nonlinear force should be very weak and consequently, the continuity, range and gaps of the phonon spectra would be still controlled dominantly by the relative strength of spring constants and chain length. It means that even if no additional nonlinear resistance was taken into account, the conventional results of phonon spectra are exactly correct. On the other hand, in the framework of a conventional model we investigated the relationship between the biggest gaps of phonon spectra and defects of Fibonacci-like aperiodic chains. By means of numerical calculations one can obtain quantitatively the maximum of the length of a one-dimensional aperiodic chain sensitive to boundaries. This method would be useful for the calculation of quasiperiodic and aperiodic lattices

2008-08-01

188

Gap anisotropy and phonon renormalization in HTS  

International Nuclear Information System (INIS)

[en] Anisotropy of the order parameter (gap) in high-Tc superconductors is explained by unscreened interaction of charge carriers with long-wave optical phonons. Screening is absent due to the low frequency of long-wave plasmons in layered structures. Numerical calculations of the gap anisotropy caused by the unscreened interaction show good agreement of the model with the experiment. The influence of the superconducting gap anisotropy on the phonon dispersion is discussed. It is found that along specific directions of the Brillouin zone the lineshape (energy and linewidth) of phonons depends strongly on the type of anisotropy of the gap. In this context, the recent experimental results performed on YBa2Cu3O7 single crystals are discussed. The data can be well described in terms of the anisotropic gap function obtained from the non-totally screened interaction of charge carriers with long-wave optical phonons. (orig.)

1997-01-01

189

Phonon squeezing in a superconducting molecular transistor.  

UK PubMed Central (United Kingdom)

Josephson transport through a single molecule or carbon nanotube is considered in the presence of a local vibrational mode coupled to the electronic charge. The ground-state solution is obtained exactly in the limit of a large superconducting gap and is extended by variational analysis. The Josephson current induces squeezing of the phonon mode, which is controlled by the superconducting phase difference and by the junction asymmetry. Optical probes of nonclassical phonon states are briefly discussed.

Zazunov A; Feinberg D; Martin T

2006-11-01

190

Phonon squeezing in a superconducting molecular transistor.  

Science.gov (United States)

Josephson transport through a single molecule or carbon nanotube is considered in the presence of a local vibrational mode coupled to the electronic charge. The ground-state solution is obtained exactly in the limit of a large superconducting gap and is extended by variational analysis. The Josephson current induces squeezing of the phonon mode, which is controlled by the superconducting phase difference and by the junction asymmetry. Optical probes of nonclassical phonon states are briefly discussed. PMID:17155648

Zazunov, A; Feinberg, D; Martin, T

2006-11-09

191

Forward Electron-Phonon Scattering and HTS  

CERN Multimedia

Tunneling and point contact spectroscopy show clear phonon features and together with optic measurements give strong support that the electron-phonon interaction (EPI) is large in HTS oxides. Strong correlations in HTS oxides renormalize the EPI (and interaction with impurities) so that the forward scattering peak (FSP) develops for small hole doping \\delta<<1. The FSP mechanism explains important properties of the normal and superconducting state.

Kulic, M L; Kulic, Miodrag L.; Dolgov, Oleg V.

1999-01-01

192

Frequency dependence of dispersive phonon images  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english In the past, lattice dynamics models have been used in interpreting dispersive phonon focusing patterns of crystals. They have had mixed success in accounting for observed images and, moreover, different models applied to the same crystal tend to differ significantly in their predictions. In this paper we interpret observed phonon focusing images of two cubic crystals, germanium and silicon, through an extension of continuum elasticity theory that takes into account the f (more) irst deviation from linearity of the phonon dispersion relation. This is done by incorporating fourth-order spatial derivatives of the displacement field in the wave equation. The coefficients of the higher-order derivatives are determined by fitting to phonon dispersion relations for the acoustic branches measured by neutron scattering in the [100], [111] and [110] symmetry directions. With this model we simulate phonon images of Si and Ge projected onto the (100), (110) and (111) observation planes. These are able to account well for the observed phonon images.

Jakata, K.; Every, A.G.

2008-10-01

193

Coupling of low-energy electrons in the optimally doped Bi2Sr2CaCu2O8+? superconductor to an optical phonon mode  

Science.gov (United States)

Laser-based photoemission with photons of energy 6 eV is used to examine the fine details of the very low-energy electron dispersion and associated dynamics in the nodal region of optimally doped Bi2212. A “kink” in the dispersion in the immediate vicinity of the Fermi energy is associated with scattering from an optical phonon previously identified in Raman studies. The identification of this phonon as the appropriate mode is confirmed by comparing the scattering rates observed experimentally with the results of calculated scattering rates based on the properties of the phonon mode.

Rameau, J. D.; Yang, H.-B.; Gu, G. D.; Johnson, P. D.

2009-11-01

194

Lasers.  

UK PubMed Central (United Kingdom)

Lasers are a very effective approach for treating many hyperpigmented lesions. They are the gold standard treatment for actinic lentigos and dermal hypermelanocytosis, such as Ota nevus. Becker nevus, hyperpigmented mosaicisms, and lentigines can also be successfully treated with lasers, but they could be less effective and relapses can be observed. However, lasers cannot be proposed for all types of hyperpigmentation. Thus, freckles and café-au-lait macules should not be treated as the relapses are nearly constant. Due to its complex pathophysiology, melasma has a special place in hyperpigmented dermatoses. Q-switched lasers (using standard parameters or low fluency) should not be used because of consistent relapses and the high risk of post-inflammatory hyperpigmentation. Paradoxically, targeting the vascular component of the melasma lesion with lasers could have a beneficial effect. However, these results have yet to be confirmed. In all cases, a precise diagnosis of the type of hyperpigmentation is mandatory before any laser treatment, and the limits and the potential side effects of the treatment must be clearly explained to patients.

Passeron T

2012-12-01

195

[Lasers].  

UK PubMed Central (United Kingdom)

Lasers are a very effective approach for treating many hyperpigmented lesions. They are the gold standard treatment for actinic lentigos and dermal hypermelanocytosis, such as Ota nevus. Becker nevus, hyperpigmented mosaicisms, and lentigines can also be successfully treated with lasers, but they could be less effective and relapses can be observed. However, lasers cannot be proposed for all types of hyperpigmentation. Thus, freckles and café-au-lait macules should not be treated as the relapses are nearly constant. Due to its complex pathophysiology, melasma has a special place in hyperpigmented dermatoses. Q-switched lasers (using standard parameters or low fluency) should not be used because of consistent relapses and the high risk of post-inflammatory hyperpigmentation. Paradoxically, targeting the vascular component of the melasma lesion with lasers could have a beneficial effect. However, these results have yet to be confirmed. In all cases, a precise diagnosis of the type of hyperpigmentation is mandatory before any laser treatment, and the limits and the potential side effects of the treatment must be clearly explained to patients.

Passeron T

2012-11-01

196

Coherent phonon dynamics in semiconducting carbon nanotubes: a quantitative study of electron-phonon coupling.  

UK PubMed Central (United Kingdom)

We excite and detect coherent phonons in semiconducting (6,5) carbon nanotubes via a sub-10-fs pump-probe technique. Simulation of the amplitude and phase profile via time-dependent wave packet theory yields excellent agreement with experimental results under the assumption of molecular excitonic states and allows determining the electron-phonon coupling strength for the two dominant vibrational modes.

Lüer L; Gadermaier C; Crochet J; Hertel T; Brida D; Lanzani G

2009-03-01

197

Magnon-phonon interactions in ferromagnetic thin films Magnon-Phonon Wechselwirkungen in ferromagnetischen Dünnfilmen  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis is concerned with the interaction of magnons and phonons for spin current generation. We experimentally demonstrate resonant magnon-phonon interaction in the GHz frequency range by studying the magnetoelastically driven magnetization precession induced by a sound wave in ferromagnetic th...

Weiler, Mathias

198

Investigation of the degradation of the antireflection coatings of the nonlinear crystal under the action of the high average power laser radiation  

Energy Technology Data Exchange (ETDEWEB)

The analysis of the local heating role in the processes of the degradation of the antireflection coatings of the nonlinear crystals when they have been used in the CW and quasi-CW YAG lasers was carried out. The broad sample range of the oxide, nitride and fluoride films deposited on the LiNbO{sub 3}, BaNaNbO{sub 5}, LiIO{sub 3} KTP and BBO crystals was considered. Investigation of these samples was carried out under the intense heating of their surfaces by the action of the CO{sub 2} laser pulses. The analysis of the obtained results with account for the chemical reaction thermodynamics, thermotension and other factors is presented.

Sidoryuk, O.E.; Volpyan, O.D.; Zilov, A.A. [Polus Research Institute, Moscow (Russian Federation)

1997-12-01

199

Effect of pulsed laser action on hole-energy spectrum of Ge/Si self-assembled quantum dots  

Science.gov (United States)

Space-charge spectroscopy has been used to study the hole energy spectrum of an array of Ge quantum dots (QD’s) coherently embedded in a Si matrix and subjected to a ruby laser (?=694nm) nanosecond irradiation ex situ. The laser energy density in a single pulse was near the melting threshold of the Si surface. The number of laser pulses was varied from 1 to 10, and the duration of each pulse was 80ns . From the capacitance-voltage characteristics, temperature- and frequency-dependent admittance measurements, the energies of holes confined in Ge QD’s were determined. The pulsed laser annealing was found to result in a deepening of the hole energy level relative to the bulk Si valence band edge and in a decrease of the hole energy dispersion. After the treatment with ten laser pulses, the spread of the hole energies due to varying sizes of the QD’s within the ensemble was reduced by a factor of about 2. The obtained results give evidence for a substantial reduction of the QD’s size dispersion and for a narrowing distribution of the hole energy levels stimulated by nanosecond laser irradiation. A possible explanation of the improved uniformity of QD’s sizes involves dissolving small size Ge QD’s in a Si matrix by pulsed laser melting of the Ge nanoclusters and their subsequent intermixing with surrounding solid Si.

Yakimov, A. I.; Dvurechenskii, A. V.; Volodin, V. A.; Efremov, M. D.; Nikiforov, A. I.; Mikhalyov, G. Yu.; Gatskevich, E. I.; Ivlev, G. D.

2005-09-01

200

Thermal conductivities of one-dimensional anharmonic/nonlinear lattices: renormalized phonons and effective phonon theory  

Directory of Open Access Journals (Sweden)

Full Text Available Heat transport in low-dimensional systems has attracted enormous attention from both theoretical and experimental aspects due to its significance to the perception of fundamental energy transport theory and its potential applications in the emerging field of phononics: manipulating heat flow with electronic anologs. We consider the heat conduction of one-dimensional nonlinear lattice models. The energy carriers responsible for the heat transport have been identified as the renormalized phonons. Within the framework of renormalized phonons, a phenomenological theory, effective phonon theory, has been developed to explain the heat transport in general one-dimensional nonlinear lattices. With the help of numerical simulations, it has been verified that this effective phonon theory is able to predict the scaling exponents of temperature-dependent thermal conductivities quantitatively and consistently.

Nianbei Li; Baowen Li

2012-01-01

 
 
 
 
201

Anisotropic phonon anomaly in Bi2212 manifested by electron-phonon coupling  

Science.gov (United States)

Electron-phonon coupling (EPC) is one of the important issues in condensed matter physics. Angle-resolved photoemission spectroscopy has been recognized as a powerful tool for the study of EPC by determining the renormalization of electron self energy. For the phonon counterpart, we measure the momentum-dependent phonon spectra of an optimal doped cuprate Bi2212 with high-resolution electron energy loss spectroscopy. The apical oxygen vibration mode at 80 meV exhibits distinct anisotropic anomaly due to EPC. By analyzing the phonon lifetime, the momentum-dependent EPC strength is determined with the knowledge of electron band structure. It is emphasized that the combination of analyses of phonon and electron structures leads to an unambiguous and comprehensive description of EPC.

Guo, Jiandong; Qin, Huajun; Shi, Junren; Cao, Yanwei; Wu, Kehui; Zhang, Jiandi; Plummer, E. W.; Wen, J.; Gu, G. D.

2010-03-01

202

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe2  

Science.gov (United States)

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe2. We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5,0,0.5), at T?TCDW. Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3,0,0.5)?q?(0.5,0,0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe2 although other mechanisms might further boost the transition temperature.

Weber, F.; Rosenkranz, S.; Castellan, J.-P.; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K.-P.; Alatas, A.

2011-12-01

203

Electron-phonon coupling and the soft phonon mode in TiSe2.  

UK PubMed Central (United Kingdom)

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe(2). We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5, 0, 0.5), at T?T(CDW). Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe(2) are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3, 0, 0.5)?q?(0.5, 0, 0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe(2) although other mechanisms might further boost the transition temperature.

Weber F; Rosenkranz S; Castellan JP; Osborn R; Karapetrov G; Hott R; Heid R; Bohnen KP; Alatas A

2011-12-01

204

Plasmon broadening and temperature effects on the plasmon-phonon-assisted recombination in silicon  

Energy Technology Data Exchange (ETDEWEB)

We present a detailed theoretical calculation of the plasmon-phonon-assisted recombination (PPAR) in a highly laser excited electron-hole plasma of silicon. We present results for PPAR as a function of carrier density, lattice temperature, and carrier temperature and show that the results are consistent with reflectivity measurements in Si in the picosecond and femtosecond pump- to probe-beam delay time.

Rasolt, M.; Perrot, F.

1988-02-15

205

Electron and phonon interactions a novel semiclassical approach  

CERN Document Server

This monograph is a radical departure from the conventional quantum mechanical approach to electron-phonon interactions. It translates the customary quantum mechanical analysis of the electron-phonon interactions carried out in Fourier space into a predominantly classical analysis carried out in real space. Various electron-phonon interactions such as the polar and nonpolar optical phonons, acoustic phonons that interact via deformation potential and via the piezoelectric effect and phonons in metals, are treated in this monograph by a single, relatively simple "classical" model. This model is

Rose, A

1989-01-01

206

Thermodynamics of anisotropic phonon systems in superfluid helium  

International Nuclear Information System (INIS)

The thermodynamic functions of anisotropic phonon systems in superfluid helium are calculated for all levels of anisotropy. The results show that the thermodynamic functions of strongly anisotropic phonon systems are essentially different from isotropic ones. It is shown that for strongly anisotropic phonon systems, in thermodynamic equilibrium, the energy density of high-energy phonons, ?/kB?10 K, is more than ten times higher than in a cone with the same total energy density and with the Bose-Einstein distribution for an isotropic system. The stability curve for anisotropic phonon systems is derived and it is shown that strongly anisotropic phonon systems are thermodynamically stable over a wide temperature range

2006-03-15

207

Thermodynamics of anisotropic phonon systems in superfluid helium  

Science.gov (United States)

The thermodynamic functions of anisotropic phonon systems in superfluid helium are calculated for all levels of anisotropy. The results show that the thermodynamic functions of strongly anisotropic phonon systems are essentially different from isotropic ones. It is shown that for strongly anisotropic phonon systems, in thermodynamic equilibrium, the energy density of high-energy phonons, ?/kB>=10 K, is more than ten times higher than in a cone with the same total energy density and with the Bose-Einstein distribution for an isotropic system. The stability curve for anisotropic phonon systems is derived and it is shown that strongly anisotropic phonon systems are thermodynamically stable over a wide temperature range.

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

2006-03-01

208

Phonon Frequency Distribution of Vanadium  

International Nuclear Information System (INIS)

[en] The phonon frequency distribution of vanadium has been measured several times using the beryllium filter time-of-flight method. The results of the various authors agree more or less satisfactorily. But there have been objections against this method; for instance it does not start with monochromatic neutrons, and multiphonon processes are corrected only in a crude way. It seems worth while to determine the frequency distribution of vanadium by a different method. In the present work the authors tried to obtain this frequency distribution by a method which covers a larger part of the energy-transfer, momentum-transfer plane. Using the rotating crystal time-of-flight spectrometer at Karlsruhe with incident neutron energies between 0.018 and 0.08 eV energy transfers in the range from 0 to 2kBT and Q-values between 0 and 14Å-1 (where nQ is the momentum transfer) have been measured. Scattering-law values have been calculated and the frequency distribution was determined with the extrapolation method proposed by Egelstaff in an iterative way with the help of LEAP calculations. Taking into account the experimental errors the results agree very satisfactorily with the cold neutron work for energy transfers greater than 0.5 kBT. Below 0.5 kBT we have found an additional peak, the origin of which is not yet explained. Results are discussed and compared with existing theoretical calculations. (author)[fr] La distribution de'fréquence des phonons dans le vanadium a été mesurée, à plusieurs reprises, par la méthode du temps de vol faisant appel à un filtre en béryllium. Les résultats obtenus par les divers auteurs concordent de façon plus ou moins satisfaisante. Cependant, on a élevé des objections contre cette méthode, en faisant valoir notamment que la source de neutrons n’est pas monochromatique et que les processus à plusieurs phonons ne font l’objet que d'une correction approximative. Ils semble donc utile d’établir la distribution de fréquence dans le vanadium par une méthode différente. Les auteurs ont essayé d’appliquer une méthode qui couvre une plus grande partie du plan transfert d’énergie - transfert de quantité de mouvement. En utilisant le spectromètre à temps de vol à cristal tournant de Karlsruhe avec des énergies des neutrons incidents de 0,018 et 0,08 eV, ils ont mesuré des transferts d'énergie entre 0 et 2kBT et les valeurs de Q entre 0 et 14Å-1 (nQ étant le transfert de quantité de mouvement). Les auteurs ont calculé les valeurs relatives à la loi de diffusion et déterminé la distribution de fréquence par la méthode d'extrapolation d'Egelstaff employée itérativement à l'aide du code LEAP. Compte tenu des erreurs expérimentales, les résultats concordent de manière très satisfaisante avec ceux que fournit l'étude, par les neutron froids, des transferts d'énergie T. Au-dessous de 0,5 kBT, les auteurs ont constaté la présence d‘un pic supplémentairedont l'origine n’est pas encore élucidée. Les résultats obtenus font l'objet d'un examen critique et sont comparés à ceux des calculs théoriques dont on dispose actuellement. (author)[es] La distribución de las frecuencias fonÓnicas en el vanadio se ha medido en diversas ocasiones por el método de tiempo de vuelo y filtro de berilio. Los resultados obtenidos por los distintos investigadores concuerdan de una manera relativamente satisfactoria. Ahora bien, se han formulado objeciones al empleo de ese método, ya que, por ejemplo, la fuente neutrónica no es monocromática y, por otra parte, la corrección aplicada a los procesos multifonónicos es poco precisa. Parece justificado, por tanto, determinar la distribución de las frecuencias en el vanadio recurriendo a otro método. Los autores han procurado determinar la distribución de las frecuencias con ayuda de un método que abarca un sector más amplio del plano de la transferencia de energía en función de la transferencia de impulso (curva de dispersión). Empleando el espectrómetro de cristal giratorio de Karlsruhe y el méto

1965-01-01

209

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

International Nuclear Information System (INIS)

[en] 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 = 0oK) ), 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 interatomic or interionic distance in the crystal). Approximate calculations are performed to give some insight into the orders of magnitude of the effects under study. (author)[fr] Comme le predit la theorie harmonique, le spectre de la diffusion inelastique coherente de neutrons par un monocristal non conducteur, pour un angle de diffusion donne, se compose d'une serie de pics de fonction delta, qui se superposent a un bruit de fond continu. Les pics correspondent a des phenomenes a un phonon, dans lesquels un phonon est absorbe ou emis par le neutron; le bruit de fond provient de phenomenes a plusieurs phonons. Lorsqu'il existe des forces anharmoniques (interaction phonon-phonon) les pics de fonction delta s'elargissent pour former des pics finis et leur frequence centrale est dephasee par rapport aux valeurs harmoniques. Dans le cas d'un metal il y a, en plus des interactions phonon-phonon, une interaction entre les phonons et les electrons de conduction, laquelle contribue a dephaser et elargir encore davantage les pics a un phonon. Continuant les travaux de Van Hove (qui avait considere le cas relativement simple d'un cristal non conducteur a l'etat fondamental, soit T = 0oK) l'auteut a etudie les deplacements et les largeurs des pics de diffusion resultant des interactions indiquees plus haut, a l'aide de la theorie de la perturbation a plusieurs particules, en ayant largement recours a la methode des diagrammes. Il admet, avant tout examen du probleme, que quelle que soit la force des interactions, la largeur de chaque pic est petite par rapport a la valeur de la frequence en son centres dans ces conditions seulement, on peut considerer que les pics sont bien definis par rapport au bruit de fond, si les calculs d'interaction sont pousses jusqu'aux ordres superieurs. On estime que cette hipothbse est realisee tant que les temperatures ne sont pas trop elevees et que les valeurs du vecteur d'onde des phonons ne sont pas trop considerables. La methode appliquee par l'auteur lui permet d'obtenir des formules fermees pour la fonction de diffusion pa

1963-01-01

210

Role of primary photoacceptors in low-power laser effects: action of He-Ne laser radiation on bacteriophage T4-Escherichia coli interaction  

Energy Technology Data Exchange (ETDEWEB)

The effect of He-Ne laser radiation (lambda = 632.8 nm) on bacteriophage T4-Escherichia coli WP2 interactions was studied. Irradiation of bacteria having respiratory chain components as primary photoacceptors accelerated their division in a dose-dependent manner, but irradiation had no effect on the properties of the phage (measured as its ability to infect host cells). At the same time, exposure of bacteria to stimulating doses of He-Ne laser radiation (from 10(3) to 6 x 10(4) J/m2) increased their ability to promote the growth of unexposed phages. These results clearly indicate that low-power laser effects require primary photoacceptors (phage contains no chromophores for red light).

Tiphlova, O.; Karu, T.

1989-01-01

211

Phonon dispersion in quasiperiodic semiconductor superlattices  

International Nuclear Information System (INIS)

The phonon spectra of unstrained and strained quasiperiodic semiconductor superlattices (QSSL) have been calculated using one-dimensional linear chain model. Two types of quasiperiodic systems, namely cantor triadic bar (CTB) and Fibonacci sequences (FS), constituting of AlAs, GaAs and GaSb of which the latter two have a lattice mismatch of about 7% is considered. The calculations have been made using transfer matrix method and also with and without the inclusion of strain. The results on phonon spectra of two component CTB and two as well as three component FS semiconductor superlattices (SSL), thickness and order dependence on LO mode of GaAs, effect of strain on LO frequency of GaAs are presented. The calculated results show that the strain generated due to lattice mismatch reduces significantly the magnitudes of the confined optical phonon frequency of GaAs. (author). 27 refs., 5 figs.

1995-01-01

212

Phonon multiplexing through 1D chains  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english Recently, phonon propagation through atomic structures has become a relevant study issue. The most important applications arise in the thermal field, since phonons can carry thermal and acoustic energy. It is expected that technological advances will make possible the engineering of thermal paths according to convenience. A simple phonon multiplexer was analyzed as a spring-mass model. It consists of mono-atomic chains of atoms with a coupling structure between them. Forc (more) es between atoms follow Hooke's law and are restricted to be first nearest neighbor interaction. It was possible to establish simple rules on constitutive parameters such as atom masses and bonding forces that enable one to select a wavelength of transmission. The method used enables the study of structures of much greater complexity than the one presented here.

Avila, A.; Reyes, D.

2008-12-01

213

Electron-phonon decoupling and superconducting grains  

International Nuclear Information System (INIS)

Well below Tc the electronic heat capacity of a superconductor gets dramatically small. If it were possible to use this small heat capacity for calorimetry one would have a system of very great sensitivity. The difficulty is that in a real superconductor there is also the phonon contribution to the specific heat, which will become dominant once the electronic part gets small. However, at low temperature the coupling between electrons and phonons gets progressively weaker. The isolation of the electron and phonon systems from each other may lead to a large jump in the electron temperature. Some ideas on possibly heating only the electrons in certain processes and then observing the correspondingly great jump in the electron temperature Te are examined. A test using superconducting grains is reported. (R.P.) 4 refs.; 3 figs.; 3 tabs.

1992-01-01

214

Assessment of the Holland model for silicon phonon-phonon relaxation times using lattice dynamics calculations  

Science.gov (United States)

We assess the ability of the Holland model to accurately predict phonon-phonon relaxation times from bulk thermal conductivity values. First, lattice dynamics calculations are used to obtain phonon-phonon relaxation times and thermal conductivities for temperatures ranging from 10 K to 1000 K for Stillinger-Weber silicon. The Holland model is then fitted to these thermal conductivities and used to predict relaxation times, which are compared to the relaxation times obtained by lattice dynamics calculations. We find that fitting the Holland model to both total and mode-dependent thermal conductivities does not result in accurate mode-dependent phonon-phonon relaxation times. Introduction of Umklapp scattering for longitudinal modes resulted in improved prediction of mode-dependent relative contributions to thermal conductivity, especially at high temperatures. However, assumptions made by Holland regarding the frequency-dependence of phonon scattering mechanisms are found to be inconsistent with lattice dynamics data. Instead, we introduce a simple method based on using cumulative thermal conductivity functions to obtain better predictions of the frequency-dependence of relaxation times.

Zhu, Zimu; Romero, David A.; Sellan, Daniel P.; Nabovati, Aydin; Amon, Cristina H.

2013-05-01

215

Evidence for pervasive phonon structure of nuclear excitations  

Energy Technology Data Exchange (ETDEWEB)

Recent work suggests that phonon and intact multiphonon excitations are pervasive in nuclei whose structures run the gamut of collective types. Some of this evidence for a nearly universal phonon description of low energy nuclear spectra will be summarized. (orig.).

Casten, R.F. [Brookhaven National Lab., Upton, NY (United States); Zamfir, N.V. [Brookhaven National Lab., Upton, NY (United States)]|[Clark Univ., Worcester, MA (United States)]|[Institutul de Fizica Atomica, Bucharest (Romania)

1996-01-01

216

Resonant scattering of phonons in GaInSb  

International Nuclear Information System (INIS)

An attempt has been made to study the nature of the observed resonance scattering of phonons in doped InSb by calculating the phonon thermal conductivity of pure and Ga doped samples using modified resonant scattering relaxation times.

1985-01-01

217

Electron-Phonon Interaction in Mixed Valence Systems.  

Science.gov (United States)

One considers an Hamiltonian describing mixed valence compounds and including d and f electron-phonon coupling. One shows that the renormalization of the electronic energy parameters induced by the electron-phonon interaction depends strongly on the natur...

F. Brouers O. L. T. de Menezes

1980-01-01

218

Phonon thermal conductivity in single layered manganites  

International Nuclear Information System (INIS)

[en] We present measurements of the thermal transport in single crystals of single-layered manganites La1-xSr1+xMnO4 with 0=ph upon hole-doping. The suppression of ?ph originates from scattering of phonons by polaronic holes. The suppression is particularly strong when charge and orbital degrees of freedom are disordered and rather weak in the case of long-range charge and orbital ordering. Moreover, slight anomalies are found in the vicinity of antiferromagnetic phase transitions, probably due to scattering of phonons by magnetic fluctuations

2005-01-01

219

Phonon dispersion curves for CsCN  

International Nuclear Information System (INIS)

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)

2004-01-01

220

Effect of anisotropic phonons on superconductivity. [Zn  

Energy Technology Data Exchange (ETDEWEB)

Effect of crystal anisotropy which results in the anisotropic phonon frequency distribution function has been studied on superconductivity in a strongly coupled superconductor. The dependence of the superconducting critical temperature, Tc, on the degree of anisotropy is quite involved. In highly anisotropic systems superconductivity is suppressed. The expression for Tc is related to the total mean square displacement of the vibrating ion, yielding the result that, for superconductivity, the phonon frequency distribution function from mean square displacement is preferred to that obtained from other studies for consistent physical parameters. Explicit calculations for {sup 67}Zn are reported. (orig.).

Tewari, S.P.; Gumber, P.K. (Dept. of Physics and Astrophysics, Univ. of Delhi (India))

1990-11-15

 
 
 
 
221

LEAP, Scattering Law for Continuous Phonon Spectra  

International Nuclear Information System (INIS)

1 - Nature of physical problem solved: The scattering law S(alpha,beta) for an input continuous or piece-wise continuous phonon frequency function rho(beta) is calculated. 2 - Method of solution: The phonon expansion and steepest descents methods described in AERE R 3803 (UKAEA report) are used. 3 - Restrictions on the complexity of the problem: The arrays can easily be increased in size to incorporate larger problems. Currently the output S(alpha,beta) can be described using a 90 x 90 alpha/beta mesh

1979-01-01

222

Electronic structure, phonon spectra and electron-phonon interaction in ScB2  

Science.gov (United States)

The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron-phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.

Sichkar, S. M.; Antonov, V. N.

2013-07-01

223

Detection of Random Laser Action from Silica Xerogel Matrices Containing Rhodamine 610 Dye and Titanium Dioxide Nanoparticles  

Directory of Open Access Journals (Sweden)

Full Text Available The synthesis, structural characterization, and amplified spontaneous emission spectroscopy of dye-scattering particles in inorganic medium based on Rhodamine 610-TiO2 nanoparticles confined in silica xerogel matrix have been reported. Optimum concentrations have been determined depending on the normal fluorescence spectra for laser dye, in order to provide amplification, and TiO2 nanoparticals as scatter center. Random Laser has been studied under second harmonic Nd: YAG laser excitation. At the optimum concentrations, the results show that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 11 nm and 3 mJ respectively. The scattered and amplified probe light has been collected on a PC-interfaced CCD camera system.

Firas J. Al-Maliki

2012-01-01

224

Electron-phonon interaction in mixed valence systems  

International Nuclear Information System (INIS)

One considers an Hamiltonian describing mixed valence compounds and including d and f electron-phonon coupling. One shows that the renormalization of the electronic energy parameters induced by the electron-phonon interaction depends strongly on the nature (static or adiabatic) of the approximation used. One discusses the importance of the d-electron-phonon coupling on the narrowing of the f-level and the softening of the phonon modes. (author).

1980-01-01

225

Ação do laser terapêutico e do ultrassom na regeneração nervosa periférica Action of therapeutic laser and ultrasound in peripheral nerve regeneration  

Directory of Open Access Journals (Sweden)

Full Text Available OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fossa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm), para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do tratamentoOBJECTIVE: To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats. METHODS: We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed Ultrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days. RESULTS: In assessing the girth of the muscles of the right they, the following average decrease (in mm) for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII. CONCLUSION: The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.

Fabrício Borges Oliveira; Valéria Martins Dias Pereira; Ana Paula Nassif Tondato da Trindade; Antônio Carlos Shimano; Ronaldo Eugênio Calçada Dias Gabriel; Ana Paula Oliveira Borges

2012-01-01

226

Ação do laser terapêutico e do ultrassom na regeneração nervosa periférica/ Action of therapeutic laser and ultrasound in peripheral nerve regeneration  

Scientific Electronic Library Online (English)

Full Text Available Abstract in portuguese OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fossa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: (more) intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm), para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do tratamento Abstract in english OBJECTIVE: To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats. METHODS: We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed U (more) ltrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days. RESULTS: In assessing the girth of the muscles of the right they, the following average decrease (in mm) for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII. CONCLUSION: The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.

Oliveira, Fabrício Borges; Pereira, Valéria Martins Dias; Trindade, Ana Paula Nassif Tondato da; Shimano, Antônio Carlos; Gabriel, Ronaldo Eugênio Calçada Dias; Borges, Ana Paula Oliveira

2012-01-01

227

Evolution of Electrical Resistivity, Thermal Conductivity, and Temperature of a solid under the action of Intense Ultrashort Laser pulse  

CERN Multimedia

The dynamical properties of Cu in a regime relevant to femtosecond micro machining are obtained on picosecond time scales using pump-probe reflectivity study for 100fs, 1015 W cm-2 laser pulses. The electrical resistivity is obtained by solving Helmoltz equations. The dissipation mechanisms and scaling laws are obtained in high and low temperature limits. The 'resistivity saturation' effect in an unexplored regime intermediate to hot plasma and cold solid is studied in detail. The temperature evolution and thermal conductivity is obtained in the temporal range 0 to 30ps after the interaction of laser pulse with solid Cu.

Singh-Sandhu, A; Kumar, G R; Sandhu, Arvinder S.

2002-01-01

228

Modified Sharma-Joshi model and phonon dispersion in ?-zirconium  

International Nuclear Information System (INIS)

A new model is proposed. This model assumes the ion-ion interaction to be purely central and expresses the ion-ion coupling through the first and second derivatives of the potential. An equilibrium criterion, considering the volume dependent energies of ions and electrons, makes the model quite sound in its applicability. The volume-term due to Sharma-Joshi is modified to include the factors like G2 and Ksub(c)sup(2) ? (q). The latter factor accounts for the exchange and correlation effects of conduction electrons in their screening-action and the former factor includes the Umklapp processes, which essentially control the symmetry of the lattice. The model thus developed reproduces the phonon-dispersion in bcc zirconium quite successfully. (author)

1980-01-01

229

A NOTE ON TWO-PHONON COHERENT ANTISTOKES RAMAN SCATTERING  

Energy Technology Data Exchange (ETDEWEB)

Difference-frequency mixing of two pump waves can in principle excite two coherent phonon waves via the parametric process. Only when the phonon excitation is small, can the nonlinear susceptibility of two-phonon coherent antiStokes Raman scattering be described as proportional to the product of two Raman tensors.

Shen, Y.R.

1980-04-01

230

Size-dependent phonon transmission across dissimilar material interfaces.  

UK PubMed Central (United Kingdom)

In this paper, we study the size effects on the phonon transmission across material interfaces using the atomistic Green's function method. Layered Si and Ge or Ge-like structures are modeled with a variety of confined sizes in both transverse and longitudinal directions. The dynamical equation of the lattice vibration (phonon waves) is solved using the Green's function method and the phonon transmission is calculated through the obtained Green's function. Phonon transmission across a single interface of semi-infinite Si and Ge materials is studied first for the validation of the methodology. We show that phonon transmission across an interface can be tuned by changing the mass ratio of the two materials. Multi-layered superlattice-like structures with longitudinal size confinement are then studied. Frequency-dependent phonon transmission as a function of both the number of periods and the period thickness is reported. A converged phonon transmission after ten periods is observed due to the formation of phonon minibands. Frequency-dependent phonon transmission with transverse size confinement is also studied for the interface of Si and Ge nanowire-like structures. The phonon confinement induces new dips and peaks of phonon transmission when compared with the results for a bulk interface. With increasing size in the transverse direction, the phonon transmission approaches that of a bulk Si/Ge interface.

Li X; Yang R

2012-04-01

231

Phonon-imaging search for spin density waves in Pb  

Energy Technology Data Exchange (ETDEWEB)

Phonon imaging is particularly suited to measuring the quasiparticle density in superconducting Pb because the absorption of ballistic phonons by quasiparticles is highly anisotropic. The temperature dependence of the phonon absorption over the 1.4 - 2.1 K temperature range yields a superconducting gap in accord with the conventional electronic ground state of Pb.

Wolfe, J P; Head, T L [Physics Department and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 W. Green St., Urbana, IL 61801, (United States)

2007-12-15

232

Calculation of the kinetics of heating and structural changes in the cartilaginous tissue under the action of laser radiation  

International Nuclear Information System (INIS)

A theoretical model is developed for the calculation of the temperature fields and determination of the size of a zone with structural changes in the cartilaginous tissue. The model is based on a simultaneous analysis of the heat and mass transfer processes and it takes into account the bulk absorption of laser radiation by the tissue, surface evaporation of water, and temperature dependences of the diffusion coefficients. It is assumed that under the influence of a phase transition between free and bound water, caused by heating of the cartilage to 700C, the proteoglycans of the cartilage matrix become mobile and, as a result of such mass transfer, structural changes are induced in the cartilaginous tissue causing relaxation of stresses or denaturation. It is shown that the maximum temperature is then reached not on the irradiated surface but at some distance from it, and that the size of the zones of structural changes (denaturation depth) depends strongly on the energy density of the laser radiation and its wavelength, on the duration of the irradiation, and on the cartilage thickness. This model makes it possible to calculate the temperature fields and the depth of structural changes in laser-induced relaxation of stresses and changes in the shape of the cartilaginous tissue. (interaction of laser radiation with matter)

1998-07-31

233

Contribution of the decay of optical phonons into acoustic phonons to the thermal conductivity of AlN  

Science.gov (United States)

The thermal conductivity along two high-symmetry directions of several aluminum nitride (AlN) single crystals differing in their mass-fluctuation phonon-scattering parameter is described accurately in the full temperature range by taking into account the contribution of optical phonon decay into acoustic phonon. The accuracy of the proposed model shows the fundamental role of the optical phonon in the thermal conductivity of semiconductor materials.

Kazan, M.; Pereira, S.; Correia, M. R.; Masri, P.

2008-05-01

234

Coherent acoustic phonons in phonon cavities investigated by asynchronous optical sampling  

International Nuclear Information System (INIS)

Using a recently introduced measurement technique, called asynchronous optical sampling (ASOPS), we have investigated the dynamics of coherent acoustic phonons in a semiconductor heterostructure composed of a GaAs film between two GaAs/AlAs superlattices, serving as a cavity for acoustic phonons. Measurements were performed at liquid helium temperatures. The possibility to perform two-color pump-probe spectroscopy allowed us to tune the probe pulse energy to the cavity band gap, while sweeping the pump pulse energy over the superlattice resonance. The large measurement window of 1 ns in combination with a resolution of about 150 fs made a detailed analysis of the observed phonon dynamics possible. We observed a long lived oscillation in the gap of the phonon dispersion at 466 GHz, which we attribute to a cavity mode.

2007-01-01

235

Action of diode laser (830 nm) on cutaneous wound healing process: biometrical and histological study in rats  

International Nuclear Information System (INIS)

In this research, it was analyzed the acceleration of the healing process of cutaneous lesions in mice, using a diode laser emitting in 830 nm. The 64 selected animals in this study were randomically divided into four groups of 16 animals each (G1, G2, G3 and G4). Biometric and histological comparisons were accomplished in the following periods: 3, 7 and 14 days after the surgery and laser application. Three laser irradiation configurations were used: a punctual contact (G2) and two non-contact and uniform (G3 and G4). For group G2, the laser intensity was 428 mW/cm2 , and for groups G3 and G4 it was 53 mW/cm2. The total doses were D = 3 J/cm2 for groups G2 and G4, and D = 1,3 J/cm2 for G3. The first group, G1, was considered control and thus not submitted to any treatment after the surgery. All irradiated lesions presented acceleration of the healing process with regard to the control group. However, our results clearly indicate that the smaller laser intensity (uniform irradiation) leaded to the best results. On the other hand, the smaller used dose also leaded to the more significant and expressive results. The combination of the intensity value of 53 mW/cm2 and the dose of 1,3 J/cm2 leaded to optimal results, regarding the Biometric and histological analysis, presenting faster lesion contraction, quicker neoformation of epithelial and conjunctive tissue (with more collagen fibers ). (author)

2001-01-01

236

Clinical and morphologic evaluation of Er:YAG laser action at the front of cervical dentinal hypersensitivity  

International Nuclear Information System (INIS)

This work was achieved in vivo and in vitro to evaluate the efficiency of Er:YAG laser in the cervical dentinal hypersensitivity treatment (HSDC). The Clinical study was achieved in patients with HSDC. The treatment was realized in five sessions: the first for selection, the second for exams (clinic and X-Ray) and trying to remove the etiologic factors that could cause the HSDC. The third and fourth sessions were subjected to the radiation with that protocol: 60 mJ energy ,2 Hz frequency, 6 mm out of focus, under air cooling, 20 seconds each application which the same was repeated four times with one minute breaks, which scanning movements and without using anaesthetics. The fifth was evaluation. The patients were evaluated and registered in a subject scale of pain 0 to 3, in the beginning and end of each session of irradiation, and one month after the last session. The results showed that for the irradiated group occurs significant differences in the beginning of each session and between. For the control group did not occur significant differences in the beginning and after each session, but did show a difference between the sessions. As the control group as the irradiated group, had reduction of sensibility between the session. For the morphologic study nine teeth were selected, 7 molars and 2 pre-molars from operative dentistry discipline. Half of the surface was irradiated with Er:YAG laser, the same protocol used in vivo, and the other half was used as a control without receiving any laser irradiation. Subsequently, specimens were prepared for SEM examinations. The results showed that laser treated surfaces showed a reduction of dentine tubular diameter with partial or total closure of the dentine tubules. For the control group, it was observed bigger amounts smear layer and open dentine tubular. The results obtained indicated that the Er:YAG laser can contribute to the HSDC treatment. (author)

2001-01-01

237

Stimulated phonon echoes in resonant powders  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Experiments on stimulated phonon echoes in resonant quartz powders are reported. Angular dependence and power dependence studies give new information about their behaviour. Sieving the powder does not completely destroy the echo. The nature of the frozen state is not yet understood.

Billmann, A.; Frénois, Ch.; Guillot, G.; Levelut, A.

238

Synthetic thermoelectric materials comprising phononic crystals  

Energy Technology Data Exchange (ETDEWEB)

Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.

El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

2013-08-13

239

Magnetic polarization and two-phonon states  

International Nuclear Information System (INIS)

[en] Influence of magnetic core polarization on properties of 2- member of two-phonon quintet of states 21+ x 31- is analyzed. Like for recently identified lowest 1- member of this quintet, an excitation probability of 2- state is strongly affected by polarization of the nucleus

1997-01-01

240

Phononic properties of hexagonal chiral lattices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The manuscript reports the outcome of investigations on the phononic properties of a chiral cellular structure. The considered geometry features in-plane hexagonal symmetry, whereby circular nodes are connected through six ligaments tangent to the nodes themselves. in-plane wave propagation is analy...

Spadoni, Alessandro; Ruzzene, Massimo; Gonella, Stefano; Scarpa, Fabrizio

 
 
 
 
241

Anomalous Doppler effects in bulk phononic crystal  

International Nuclear Information System (INIS)

[en] 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.

2010-08-23

242

Anomalous Doppler effects in bulk phononic crystal  

Energy Technology Data Exchange (ETDEWEB)

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.

Cai Feiyan [Key Lab of Acoustic and Photonic Materials and Devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072 (China); Paul. C. Lauterbur Research Center for Biomedical Imaging, Institute of Biomedical and Health Engineering, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055 (China); Key Laboratory of Biomedical Informatics and Health Engineering, Chinese Academy of Sciences, Shenzhen 518055 (China); He Zhaojian; Zhang Anqi; Ding Yiqun [Key Lab of Acoustic and Photonic Materials and Devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072 (China); Liu Zhengyou, E-mail: zyliu@whu.edu.c [Key Lab of Acoustic and Photonic Materials and Devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072 (China)

2010-08-23

243

Hydrodynamic states of phonons in insulators  

Directory of Open Access Journals (Sweden)

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.

S.A. Sokolovsky

2012-01-01

244

Electron-phonon and spin-phonon coupling in $NaV_{2}O_{5}  

CERN Multimedia

We show that the asymmetric crystal environment of the V site in the ladder compound NaV$_{2}$O$_{5}$ leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the charge on the V ions, and favors a transition to a charge-ordered state at low temperatures. In the low temperature phase the charge fluctuations modulate the spin-spin superexchange interaction, resulting in a strong spin-phonon coupling.

Sherman, E Y; Lemmens, P; Van Loosdrecht, P H M; Güntherodt, G

1999-01-01

245

Coherent phonon dynamics in semiconducting carbon nanotubes: a quantitative study of electron-phonon coupling.  

Science.gov (United States)

We excite and detect coherent phonons in semiconducting (6,5) carbon nanotubes via a sub-10-fs pump-probe technique. Simulation of the amplitude and phase profile via time-dependent wave packet theory yields excellent agreement with experimental results under the assumption of molecular excitonic states and allows determining the electron-phonon coupling strength for the two dominant vibrational modes. PMID:19392321

Lüer, Larry; Gadermaier, Christoph; Crochet, Jared; Hertel, Tobias; Brida, Daniele; Lanzani, Guglielmo

2009-03-24

246

Quantum spin ladder with dynamic phonons Bound states of magnons and phonons  

CERN Document Server

We consider the two-chain Heisenberg ladder with antiferromagnetic interactions. Our approach is based on the description of spin excitations as triplets above a strong-coupling singlet ground state. It is shown that interaction with dynamic phonons drastically changes the dispersion of the elementary triplet excitation (magnon) and the spin structure factor. It is also shown that a new triplet excitation appears in the spectrum: the bound state of a magnon and a phonon.

Sushkov, O P

1999-01-01

247

Electron-phonon coupling strength of specific phonons from first principles LAPW calculations  

International Nuclear Information System (INIS)

Electron-phonon matrix elements, phonon linewidths and mode coupling strengths are being calculated for La2 - xMxCuO4 (M=divalent cation, for paramagnetic x = 0.0 and for x = 0.15 in a rigid band picture) from first principles local density calculations. The change in potential due to a particular phonon mode is calculated from the difference of self-consistent one-electron potentials, and appropriate Fermi surface averages are carried out for selected modes, allowing us to obtain the phonon linewidth due to the electron-phonon interaction, and the corresponding coupling strength ?. The authors establish the numerical accuracy within the dual representation of the potential used in the linearized augmented plane wave (LAPW) method. Evaluations of phonon linewidths and mode coupling strengths are presented for Al and Nb and compared with previous information on these modes. The authors present preliminary results for the full matrix elements and coupling of the LA2CuO4 oxygen planar X-point breathing mode, and compare with a simpler approximation.

1989-01-01

248

Interfacial and Confined Optical Phonons in Wurtzite Nanocrystals  

CERN Multimedia

We derive within the dielectric-continuum model an integral equation that defines interface and confined polar optical-phonon modes in nanocrystals with wurtzite crystal structure. It is demonstrated theoretically, that while the frequency of confined polar optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals have a discrete spectrum of frequencies different from those of the bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO nanocrystals are found to be in an excellent agreement with the experimental resonant Raman scattering spectra of spherical ZnO quantum dots.

Fonoberov, V A; Fonoberov, Vladimir A.; Balandin, Alexander A.

2004-01-01

249

The phonon and thermal properties of a ladder nanostructure  

Directory of Open Access Journals (Sweden)

Full Text Available  In this paper, we study the phonon thermal properties of a ladder nanostructure in harmonic approximation. We present a model consisting of two infinite chains with different masses. Then, we investigate the effect of different masses on the phonon spectrum. Moreover, as a specific case, in the absence of the second neighbor interaction, we calculate the phonon density of states/modes. Finally, we consider the thermal conductivity of the system. The results show that the phonon spectrum shifts down to the lower frequencies by increasing the masses. Furthermore, a frequency gap appears in the phonon spectrum. By increasing the springs constants, the thermal conductance decreases.

M Mardaani; H Rabani; M Keshavarz

2011-01-01

250

Phonon transport in an initially twisted polyvinyl acetate nanofiber  

Science.gov (United States)

A reduction in phonon thermal conductivity enhances thermoelectric performance. One method to accomplish this is by applying mechanical stress to a nanostructure. We consider an initially twisted 20 nm polyvinyl acetate nanofiber undergoing torsion. Our analytical method uses the continuum approach of Mooney's model. Torsion modifies the phonon dispersion. Angles of twist between 45° and 70° reduce the averaged phonon group velocity and the phonon thermal conductivity but when these angles are increased further, this conductivity increases. This suggests a phonon engineering approach to tune the thermal conductivity of nanomaterials.

Liangruksa, Monrudee; Puri, Ishwar K.

2013-05-01

251

High Pressure Study on The Phonon Spectra in Hafnium Nitrides  

Science.gov (United States)

We report ab initio calculations of the phonon spectra for hafnium nitride (HfN) at ambient and high pressures. The calculation of phonon density of states using the density functional perturbation theory including external perturbations like strains and electric fields in periodic systems carried out for full Brillouin zone. The lattice constant obtained for the HfN is in agreement with the experimental value. The calculated pressure variation of the phonon density of states show trend similar to the pressure dependent Raman spectra. The results regarding zone-center phonon modes for HfN shows generally good agreement with Raman measurements phonon.

Gupta, Sanjay D.; Gupta, Sanjeev K.; Jha, Prafulla K.

2011-07-01

252

Optical Phonon Lasing in Semiconductor Double Quantum Dots  

Science.gov (United States)

We propose optical phonon lasing for a double quantum dot (DQD) fabricated in a semiconductor substrate. We show that the DQD is weakly coupled to only two LO phonon modes that act as a natural cavity. The lasing occurs for pumping the DQD via electronic tunneling at rates much higher than the phonon decay rate, whereas an antibunching of phonon emission is observed in the opposite regime of slow tunneling. Both effects disappear with an effective thermalization induced by the Franck--Condon effect in a DQD fabricated in a carbon nanotube with a strong electron--phonon coupling.

Okuyama, Rin; Eto, Mikio; Brandes, Tobias

2013-01-01

253

Mechanism of conversion of ethanol by the action of pulsed IR radiation from a CO/sub 2/ laser  

Energy Technology Data Exchange (ETDEWEB)

This article presents data comparing the possible reaction channels--photochemical and thermochemical as well as molecular and chain dominated--open to ethanol during irradiation with pulsed infrared radiation from a carbon dioxide laser. The channels are investigated in light of the various yields, determined by gas chromatography, of ethane, methane, ethylene, and acetaldehyde, and the dependence of the yields and kinetics on ethanol vapor pressure.

Zhitneva, G.P.; Pshezhetskii, S.Ya.

1987-04-01

254

Recording mechanism of photochemical holograms in a thiazine-dye-polyvinyl-alcohol medium under the action of a helium-neon laser  

Science.gov (United States)

This paper discusses the mechanism of amplitude holographic recording in polyvinyl alcohol films with additives of thiazine dyes (thionine, methylene blue) under the action of a helium-neon laser. It is proposed to describe the photochemical transformations of the dye by a sequential reaction scheme with one reversible stage. It is shown that the presence of associates (dimers) of the dyes in the films has a substantial effect on the bleaching kinetics. Plasticization of the polymer makes it possible to control the ratio of the rate constants of the reaction scheme and also results in complete breakdown of the holographic gratings after the recording is completed. The kinetics of spontaneous erasure of the holograms in the test medium are compared with those of the thiazine-dye-deoxyribonucleic-acid (DNA) film system.

Lantukh, Yu. D.; Ketsle, G. A.; Pashkevich, S. N.; Letuta, S. N.; Razdobreev, D. A.

2006-07-01

255

High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons  

International Nuclear Information System (INIS)

A new optical pump-probe technique is implemented for the investigation of coherent acoustic phonon dynamics in the GHz to THz frequency range which is based on two asynchronously linked femtosecond lasers. Asynchronous optical sampling (ASOPS) provides the performance of on all-optical oscilloscope and allows us to record optically induced lattice dynamics over nanosecond times with femtosecond resolution at scan rates of 10 kHz without any moving part in the set-up. Within 1 minute of data acquisition time signal-to-noise ratios better than 107 are achieved. We present examples of the high-sensitivity detection of coherent phonons in superlattices and of the coherent acoustic vibration of metallic nanoparticles.

2007-01-01

256

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells  

CERN Multimedia

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.

Sanders, G D; Kim, C S; Kim, Chang-Sub

2001-01-01

257

Saturation effects in semiconductor lasers  

Energy Technology Data Exchange (ETDEWEB)

This paper describes a theory for a semiconductor active medium interacting with a laser field. In a semiconductor laser, the charge carrier transitions are inhomogeneously broadened, and electron-electron and electron-phonon collisions tend to dephase the laser transitions and maintain thermal equilibrium among the carriers. These properties cause semiconductor lasers to frequency tune as though they are inhomogeneously broadened and to saturate as though they are homogeneously broadened. A theory that contains these two aspects of semiconductor laser behavior is presented. From it, the authors are able to calculate the loaded gain, efficiency, intensity, and carrier-induced refractive index of a semiconductor active medium.

Chow, W.W.; Dente, G.C.; Depatie, D.

1987-08-01

258

Single-photon indistinguishability: influence of phonons  

DEFF Research Database (Denmark)

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 effects is important in linear optical quantum computing [1], where a device emitting fully coherent indistinguishable single photons on demand, is the essential ingredient. In this contribution we present a numerically exact simulation of the effect of phonons on the degree of indistinguishability of photons emitted from a solid-state cavity QED system. Our model rigorously describes non-Markovian effects to all orders in the phonon coupling constant, being based on an exact diagonalization procedure accounting for the time evoluiton of one-time and two-time photon correlation funcitons. We compare to standard approaches for treating the phonon interaction, namely the Markovian Lindblad formalism and the long-time limit of the non-Markovian timeconvolution-less (TCL) approach, and find large quantitative and qualitative differences [3]. Figures 1(b) and (c) show the calculated indistingusihability 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 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, dominating the decoherence for large QD-cavity coupling. Our method captures the physics of the regime of small and as well as large QD-cavity coupling, both corresponding to experimentally relevant situations. Importantly, the commonly used Lindblad formalism fails completely in describing the variations of the indistinguishability predicted by the two other models.

Nielsen, Per Kær; Lodahl, Peter

2012-01-01

259

A simple model for the rotation of a trapped chiral nematic droplet under the action of a linearly polarized laser beam.  

UK PubMed Central (United Kingdom)

There have been recent reports of continuous rotation of chiral nematic droplets in restricted ranges of diameter/pitch (d /p) values, trapped by a linearly polarized laser beam. We have developed a simple model to calculate the distortion in the helical structure of a set of flat layers, caused by the action of the strong electric field of the propagating laser beam on the dielectric anisotropy of the medium. The resulting change in the polarization state of the beam passing through the sample is then used to calculate the torque on the sample as a function of the azimuthal angle of the first layer. The main results are: i) the torque tends to zero even with circularly polarized beam for samples with thicknesses around integral multiples of 0.5p ; ii) the undistorted sample takes an equilibrium orientation for linearly polarized beam, which jumps by ?/2 rad at the same sample thicknesses; iii) these samples will have a nonzero torque at all azimuthal angles of the first slice when the helical structure is distorted by the linearly polarized beam. The calculations show that a propagating accordion mode, in which the helical pitch alternately expands and contracts, gives rise to the nonzero torque. The theoretical predictions are in broad agreement with experimental results.

Mosallaeipour M; Ananthamurthy S; Madhusudana NV

2013-08-01

260

A simple model for the rotation of a trapped chiral nematic droplet under the action of a linearly polarized laser beam.  

Science.gov (United States)

There have been recent reports of continuous rotation of chiral nematic droplets in restricted ranges of diameter/pitch (d /p) values, trapped by a linearly polarized laser beam. We have developed a simple model to calculate the distortion in the helical structure of a set of flat layers, caused by the action of the strong electric field of the propagating laser beam on the dielectric anisotropy of the medium. The resulting change in the polarization state of the beam passing through the sample is then used to calculate the torque on the sample as a function of the azimuthal angle of the first layer. The main results are: i) the torque tends to zero even with circularly polarized beam for samples with thicknesses around integral multiples of 0.5p ; ii) the undistorted sample takes an equilibrium orientation for linearly polarized beam, which jumps by ?/2 rad at the same sample thicknesses; iii) these samples will have a nonzero torque at all azimuthal angles of the first slice when the helical structure is distorted by the linearly polarized beam. The calculations show that a propagating accordion mode, in which the helical pitch alternately expands and contracts, gives rise to the nonzero torque. The theoretical predictions are in broad agreement with experimental results. PMID:23989758

Mosallaeipour, Marjan; Ananthamurthy, Sharath; Madhusudana, N V

2013-08-30

 
 
 
 
261

Phonon Squeezing in a Superconducting Molecular Transistor  

CERN Multimedia

Josephson transport through a double junction formed by a single molecule or carbon nanotube is considered in the presence of a local vibrational mode which is linearly coupled to the charge on the molecule. An exact solution is obtained in the limit of a large superconducting gap, and it is complemented by a variational analysis in the general case. Coherent charge fluctuations involve polaron dressing and are entangled with non-classical phonon states. The flow of a Josephson current induces squeezing of the phonon mode, controlled by the superconducting phase difference and by the junction asymmetry. Squeezing is maximal in the polaron crossover regime, where a nearly minimum-uncertainty state with about 40 per cent squeezing can be obtained. Optical probes of non-classical states are briefly discussed.

Zazunov, A; Martin, T; Martin, Thierry

2006-01-01

262

Quantum mode phonon forces between chainmolecules  

DEFF Research Database (Denmark)

A phenomenological description of the contributions of phonons to molecular force is developed. It uses an approximation to consider macromolecules as solid continua. The molecular modes of a molecule can then be characterized by a Debye-like description of the partition function. The resulting 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.

Bohr, Jakob

2001-01-01

263

Thermodynamics of phonon-modulated tunneling centers  

Energy Technology Data Exchange (ETDEWEB)

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.

Junker, W.; Wagner, M. (Universitaet Stuttgart (West Germany))

1989-08-01

264

Thermodynamics of phonon-modulated tunneling centers  

International Nuclear Information System (INIS)

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.

1989-01-01

265

Phonon Frequencies from a Local Pseudopotential  

Science.gov (United States)

We calculated phonon frequencies using a recently developed local pseudopotential for simple metals.( C. Fiolhais, J.P. Perdew, S.Q. Armster, J.M. MacLaren, and M. Brajczewska, Phys. Rev. B 51), 14001 (1995) (erratum submitted). The advantages of a local pseudopotential are that it provides greater computational simplicity than a nonlocal one and that density functional theory in principle requires a local external potential. We will report on the phonon frequencies of sixteen simple metals and compare these results to a nonlocal pseudopotential. (J.A. Moriarty, Phys. Rev. B 26), 4 (1982). Because we have examined several different crystal structures for each metal, we also report on structural instabilities.

Pollack, Lisa; Perdew, John P.

1996-03-01

266

Phonons as building blocks in nuclear structure  

International Nuclear Information System (INIS)

[en] 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

1980-01-01

267

Electron-phonon coupling and the soft phonon mode in TiSe{<_2}.  

Energy Technology Data Exchange (ETDEWEB)

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe{sub 2}. We observe a complete softening of a transverse optic phonon at the L point, i.e., q = (0.5,0,0.5), at T {approx} T{sub CDW}. Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe{sub 2} are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3,0,0.5) {<=} q {<=} (0.5,0,0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe{sub 2} although other mechanisms might further boost the transition temperature.

Weber, F.; Rosenkranz, S.; Castellan, J.-P.; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K.-P.; Alatas, A. (Materials Science Division); ( XSD); (Institut fur Festkorperphysik)

2011-01-01

268

Semiconductor laser  

Energy Technology Data Exchange (ETDEWEB)

A semiconductor laser of the rib guide type having the thickness of an active layer within a stripe-shaped region thicker than that of the outside, and thus the stripe-shaped region is made to have a waveguide action and, thereby, fundamental mode laser may be achieved.

Sakuma, I.; Furuse, T.; Kawano, H.; Matsumoto, S.; Matsumoto, Y.; Nishida, K.; Ueno, M.

1984-02-28

269

Theory of coherent phonons in carbon nanotubes and graphene nanoribbons  

International Nuclear Information System (INIS)

We survey our recent theoretical studies on the generation and detection of coherent radial breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial breathing like mode (RBLM) phonons in graphene nanoribbons. We present a microscopic theory for the electronic states, phonon modes, optical matrix elements and electron–phonon interaction matrix elements that allows us to calculate the coherent phonon spectrum. An extended tight-binding (ETB) model has been used for the electronic structure and a valence force field (VFF) model has been used for the phonon modes. The coherent phonon amplitudes satisfy a driven oscillator equation with the driving term depending on the photoexcited carrier density. We discuss the dependence of the coherent phonon spectrum on the nanotube chirality and type, and also on the graphene nanoribbon mod number and class (armchair versus zigzag). We compare these results with a simpler effective mass theory where reasonable agreement with the main features of the coherent phonon spectrum is found. In particular, the effective mass theory helps us to understand the initial phase of the coherent phonon oscillations for a given nanotube chirality and type. We compare these results to two different experiments for nanotubes: (i) micelle suspended tubes and (ii) aligned nanotube films. In the case of graphene nanoribbons, there are no experimental observations to date. We also discuss, based on the evaluation of the electron–phonon interaction matrix elements, the initial phase of the coherent phonon amplitude and its dependence on the chirality and type. Finally, we discuss previously unpublished results for coherent phonon amplitudes in zigzag nanoribbons obtained using an effective mass theory. (topical review)

2013-04-10

270

Photon phonon entanglement in coupled optomechanical arrays  

CERN Multimedia

We consider three optomechanical cavities coupled irreversibly as well as reversibly to each other and explore entanglement between the different optical and mechanical modes in the collective system. Each cavity is driven by a coherent field and the optomechanical coupling in each cavity is treated in the linearised regime. The composite system exhibits robust intercavity photon-phonon entanglement, in bipartite form, well into the steady state.

Akram, Uzma

2011-01-01

271

Phonon tunnels across a sonic horizon  

CERN Multimedia

We consider phonon tunneling in sonic black hole by WKB approximation method without the backreaction, in which the relativistic momentum-energy equation is used. We also study the WKB loop (closed path) integral [B. D. Chowdhury, Pramana70:3-26, 2008] in sonic black hole case and discuss the equivalence of the results of some cases from the two different tunneling probability expression in Painlev\\'e-like coordinates.

Fang, H Z

2011-01-01

272

On the quantization of strongly interacting phonons  

CERN Multimedia

The assumption is considered that the strong interaction between phonons makes a certain contribution to the formation of Cooper pairs. Heisenberg's old idea about the quantization of strong nonlinear fields using the Tamm-Dankoff method is discussed. The approximate solution method of infinite Tamm-Dankoff equations system is suggested. This allows us to obtain an equation for the fixed deformation of the lattice between two Cooper electrons. Such deformations can introduce a significant contribution to the energy of Cooper pairs.

Dzhunushaliev, V D

1997-01-01

273

Phonon dispersion relations for caesium thiocyanate  

Energy Technology Data Exchange (ETDEWEB)

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.

Irving, M.A.; Smith, T.F. (Monash Univ., Clayton (Australia). Dept. of Physics); Elcombe, M.M. (Australian Atomic Energy Commission Research Establishment, Lucas Heights)

1984-05-01

274

Partition Functions for Electron-Phonon Interactions  

Science.gov (United States)

The well-known cummulant summation formula is applied to the calculation of the grand canonical partition function for the electron-phonon interaction. The method is, in principle, exact and does not depend on any restrictions to the relevant parameter range nor on the particulars of the Hamiltonian. Another advantage of our approach is that the systematic ordering of terms yields levels of approximation which are dictated by the physics of the system rather than just a numerical truncation.

Zhou, Yu; Mancini, Jay D.; Fessatidis, Vassilios; Bowen, Samuel P.

2002-03-01

275

Phonon drag in thermal conductivity of antiferromagnets  

Science.gov (United States)

We use Boltzmann equation approach to the thermal transport in low-dimensional antiferromagnets with spin-lattice coupling. We consider the limit of fast spin excitations, relevant to many compounds with J>>?D, where ?D is the Debye energy. We discuss the ``off-diagonal'' contribution to the heat current due to the drag of spin excitations on phonons. We calculate this effect for the one-dimensional spin chain materials.

Gangadharaiah, Suhas; Chernyshev, Alexander

2010-03-01

276

Optimization of phononic filters via genetic algorithms  

Energy Technology Data Exchange (ETDEWEB)

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.

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

277

Phonons of the anomalous element cerium.  

UK PubMed Central (United Kingdom)

Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of f electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural ? - ? transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion scheme of elemental cerium across the ? ? ? transition, and compared it with theoretical results using ab initio lattice dynamics. Several phonon branches show strong changes in the dispersion shape, indicating large modifications in the interactions between phonons and conduction electrons. This is reflected as well by the lattice Grüneisen parameters, particularly around the X point. We derive a vibrational entropy change ?S(?-?)(vib) ? (0.33+/-0.03)k(B), illustrating the importance of the lattice contribution to the transition. Additionally, we compare first principles calculations with the experiments to shed light on the mechanism underlying the isostructural volume collapse in cerium under pressure.

Krisch M; Farber DL; Xu R; Antonangeli D; Aracne CM; Beraud A; Chiang TC; Zarestky J; Kim DY; Isaev EI; Ahuja R; Johansson B

2011-06-01

278

Phonon drag thermopower and weak localization  

CERN Multimedia

Previous experimental work on a two-dimensional (2D) electron gas in a Si-on-sapphire device led to the conclusion that both conductivity and phonon drag thermopower $S^g$ are affected to the same relative extent by weak localization. The present paper presents further experimental and theoretical results on these transport coefficients for two very low mobility 2D electron gases in $\\delta-$doped GaAs/Ga$_x$Al$_{1-x}$As quantum wells. The experiments were carried out in the temperature range 3-7K where phonon drag dominates the thermopower and, contrary to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of magnitude less than those in the conductivity. A theoretical framework for phonon drag thermopower in 2D and 3D semiconductors is presented which accounts for this insensitivity of $S^g$ to weak localization. It also provides transparent physical explanations of many previous experimental and theoretical results.

Miele, A; Zaremba, E; Feng, Y; Foxon, C T; Harris, J J

1998-01-01

279

Coherent phonon in superconductor iron pnictide  

Science.gov (United States)

The role of phonons in high critical temperature superconductivity has been subjected to a large debate and the description of the superconductivity mechanism is still controversial. Recently, the attention of the scientific community has been focused on the new family of iron pnictide superconductors, in which all the degrees of freedom of the crystal, such as spin, lattice and charges, compete giving rise to a fascinating phase diagram. However, such strong correlations make harder to assert on the mechanism of the electrons pair formation. In order to shine light on this key point linked to the occurrence of superconductivity, we study a coherent A1g optical phonon mode in time domain by measuring the transient reflectivity in iron pnictide Ba(Fe1-xCox)2As2 (x=0.06 and 0.08) across the superconducting phase transition [1]. The phonon parameters such as frequency, amplitude and damping time are discussed as a function of both sample temperature and doping. [1] Mansart et al., Pys. Rev. B 80, 172504 (2009)

Boschetto, Davide; Mansart, Barbara; Savoia, Annunziata; Marsi, Marino

2010-03-01

280

Optimization of phononic filters via genetic algorithms  

International Nuclear Information System (INIS)

[en] 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

2007-01-01

 
 
 
 
281

Laser-rate-equation description of optomechanical oscillators.  

UK PubMed Central (United Kingdom)

We develop a set of laser rate equations that accurately describes mechanical amplification in optomechanical oscillators driven by photothermal or radiation pressure forces. In the process we introduce a set of parameters describing gain, stored energy, slope efficiency, and saturation power of the mechanical laser. We identify the three-phonon parametric interactions as a microscopic mechanism enabling self-oscillation. Our theory shows remarkable agreement with our experimental data, demonstrating that optomechanical self-oscillation is essentially a "phonon lasing" process in which an optical pump generates coherent acoustic phonons.

Khurgin JB; Pruessner MW; Stievater TH; Rabinovich WS

2012-06-01

282

Inhibitory effects of visible 650-nm and infrared 808-nm laser irradiation on somatosensory and compound muscle action potentials in rat sciatic nerve: implications for laser-induced analgesia.  

UK PubMed Central (United Kingdom)

Low-level laser therapy (LLLT) has been shown in clinical trials to relieve chronic pain and the World Health Organization has added LLLT to their guidelines for treatment of chronic neck pain. The mechanisms for the pain-relieving effects of LLLT are however poorly understood. We therefore assessed the effects of laser irradiation (LI) on somatosensory-evoked potentials (SSEPs) and compound muscle action potentials (CMAPs) in a series of experiments using visible (? = 650 nm) or infrared (? = 808 nm) LI applied transcutaneously to points on the hind limbs of rats overlying the course of the sciatic nerve. This approximates the clinical application of LLLT. The 650-nm LI decreased SSEP amplitudes and increased latency after 20 min. CMAP proximal amplitudes and hip/ankle (H/A) ratios decreased at 10 and 20 min with increases in proximal latencies approaching significance. The 808-nm LI decreased SSEP amplitudes and increased latencies at 10 and 20 min. CMAP proximal amplitudes and H/A ratios decreased at 10 and 20 min. Latencies were not significantly increased. All LI changes for both wavelengths returned to baseline by 48 h. These results strengthen the hypothesis that a neural mechanism underlies the clinical effectiveness of LLLT for painful conditions.

Yan W; Chow R; Armati PJ

2011-06-01

283

A step closer to visualizing the electron___phonon interplay  

Energy Technology Data Exchange (ETDEWEB)

The origin of the very high superconducting transition temperature (Tc) in ceramic copper oxide superconductors is one of the greatest mysteries in modern physics. In the superconducting state, electrons form pairs (known as Cooper pairs) and condense into the superfluid state to conduct electric current with zero resistance. For conventional superconductors, it is well established that the 2 electrons in a Cooper pair are 'bonded' by lattice vibrations (phonons), whereas in high-Tc superconductors, the 'glue' for the Cooper pairs is still under intense discussion. Although the high transition temperature and the unconventional pairing symmetry (d-wave symmetry) have led many researchers to believe that the pairing mechanism results from electron-electron interaction, increasing evidence shows that electron-phonon coupling also significantly influences the low-energy electronic structures and hence may also play an important role in high-Tc superconductivity. In a recent issue of PNAS, Carbone et al. use ultrafast electron diffraction, a recently developed experimental technique, to attack this problem from a new angle, the dynamics of the electronic relaxation process involving phonons. Their results provide fresh evidence for the strong interplay between electronic and atomic degrees of freedom in high-Tc superconductivity. In general, ultrafast spectroscopy makes use of the pump-probe method to study the dynamic process in material. In such experiments, one first shoots an ultrafast (typically 10-100 fs) 'pumping' pulse at the sample to drive its electronic system out of the equilibrium state. Then after a brief time delay ({Delta}t) of typically tens of femtoseconds to tens of picoseconds, a 'probing' pulse of either photons or electrons is sent in to probe the sample's transient state. By varying {Delta}t, one can study the process by which the system relaxes back to the equilibrium state, thus acquiring the related dynamic information. This pump-probe experiment is reminiscent of the standard method used by bell makers for hundreds of years to judge the quality of their products (hitting a bell then listening to how the sound would fade away), albeit the relevant time scale here is way beyond tens of femtoseconds. Traditionally, ultrafast spectroscopy was carried out to study gas-phase reactions, but it has also been applied to study condensed phase systems since the development of reliable solid-state ultrafast lasers approximately a decade ago. In addition, the ability to control pulse width, wavelength, and amplification of the output of Ti:Sapphire lasers has further increased the capability of this experimental method. During the past decade, many ultrafast pump-probe experiments have been carried out in various fields by using different probing methods, such as photo-resistivity, fluorescence yield, and photoemission, and they have revealed much new information complementary to the equilibrium spectroscopy methods used before. Carbone et al. used the photon-pump, electron (diffraction)-probe method. The pumping photon pulse first drives the electrons in the sample into an oscillating mode along its polarization direction. Then during the delay time, these excited electrons can transfer excess energy to the adjacent nuclei and cause crystal lattice vibration on their way back to the equilibrium state. An ultrashort electron pulse is shot at the sample at various time delays {Delta}t and the diffraction pattern is collected. Because the electron diffraction pattern is directly related to the crystal lattice structure and its motion, this technique provides a natural way to study the electron-phonon coupling problem. Furthermore, by adjusting the pump pulse's relative polarization with respect to the Cu-O bond direction, Carbone et al. were able to acquire the electron-phonon coupling strength along different directions. Focusing on the lattice dynamic along the c axis, Carbone et al. found that the c-axis phonons in the optimally-doped Bi{sub 2}Sr{sub 2}CaCu{sub

Chen, Y.L.; Lee, W.S.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept. /SLAC, PULSE

2011-01-04

284

Analytical approach to phonons and electron-phonon interactions in single-walled zigzag carbon nanotubes  

International Nuclear Information System (INIS)

[en] 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

2008-08-13

285

Phonon energy inversion in graphene during transient thermal transport  

Science.gov (United States)

This work reports on the phonon energy inversion in graphene nanoribbons: after initial localized thermal excitation, the energy of initial cold phonons (flexural mode: FM) becomes higher than that of local hot phonons (longitudinal and transverse modes: LM/TM). Such energy inversion holds for about 50 picoseconds. Two physical factors combine together to give rise of this phenomenon: one is the much faster heat conduction by FM phonons than that by LM/TM phonons, and the other factor is the strongly temperature-dependent energy exchange rate between FM and LM/TM phonons: 3.7×1010 s at 84 K to 20.3×1010 s at around 510 K.

Zhang, Jingchao; Wang, Xinwei; Xie, Huaqing

2013-03-01

286

Thermodynamics of anisotropic phonon systems in superfluid helium  

Energy Technology Data Exchange (ETDEWEB)

The thermodynamic functions of anisotropic phonon systems in superfluid helium are calculated for all levels of anisotropy. The results show that the thermodynamic functions of strongly anisotropic phonon systems are essentially different from isotropic ones. It is shown that for strongly anisotropic phonon systems, in thermodynamic equilibrium, the energy density of high-energy phonons, {epsilon}/k{sub B}{>=}10 K, is more than ten times higher than in a cone with the same total energy density and with the Bose-Einstein distribution for an isotropic system. The stability curve for anisotropic phonon systems is derived and it is shown that strongly anisotropic phonon systems are thermodynamically stable over a wide temperature range.

Adamenko, I N [Karazin Kharkov National University, Svobody Sq. 4, Kharkov, 61077 (Ukraine); Nemchenko, K E [Karazin Kharkov National University, Svobody Sq. 4, Kharkov, 61077 (Ukraine); Slipko, V A [Karazin Kharkov National University, Svobody Sq. 4, Kharkov, 61077 (Ukraine); Wyatt, A F G [School of Physics, University of Exeter, Exeter EX4 4QL (United Kingdom)

2006-03-15

287

Doped semiconductors as thermal and ballistic phonon detectors  

International Nuclear Information System (INIS)

The possibilities of detecting high-energy phonons with semiconductors are investigated. Hopping conduction is a solution, therefore heavily doped thermistors are efficient at very low temperatures. They are also sensitive to non thermalized phonons and act as 'phono-conductors'. Hopping conduction was utilized in Neutron Transmutation Doped (NTD) germanium thermistors. Preliminary results are presented and discussed on using NTD germanium thermistors for high-energy phonon detection. (R.P.) 25 refs.; 7 figs.

1990-01-01

288

Isotopic effects on the phonon modes in boron carbide.  

UK PubMed Central (United Kingdom)

The effect of isotopes ((10)B-(11)B; (12)C-(13)C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals.

Werheit H; Kuhlmann U; Rotter HW; Shalamberidze SO

2010-10-01

289

Electron-phonon contribution to the thermopower of metals  

Energy Technology Data Exchange (ETDEWEB)

A theorem is proved for the thermopower when limited by the electron-phonon interaction. It is shown for simple metals that the thermopower is given by the Mott formula plus a correction term. The correction term is evaluated and shown to be small for simple metals. Thus we are able to show that Mott's formula is valid for phonon scattering by electrons, even when the energy dependence of the phonons is taken into account. This proof extends our earlier result, which only applied to static impurities, and to phonons in the adiabatic approximation.

Jonson, M.; Mahan, G.D. (Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN (USA) Department of Physics and Astronomy, University of Tennessee, Knoxville, TN (USA))

1990-11-15

290

Theory of thermally weighted electron-phonon transition probabilities  

Energy Technology Data Exchange (ETDEWEB)

We present a refined calculation method for the phonon part (Franck-Condon Overlaps) of the transition probabilities of electron-phonon radiative and non-radiative transitions in crystals. The evaluation of the thermal averaged Franck-Condon integrals is a purely algebraic method and the transition probabilities we use are derived from first principles and completely atomistic. For the electronic transitions we take into account the frequency shift of the lattice and the change of the phonon normal coordinates. Explicit formulae of the phonon parts are derived and it is shown that the common transition probabilities used in literature are special cases of our functional calculation technique.

Schupfner, J.

1980-09-01

291

Phonon anomalies and superconductivity in transition-metal compounds  

International Nuclear Information System (INIS)

[en] We present a physically simple but general argument that explain the phonon anomalies and their interrelation to high T/sub c/'s in transition-metal compounds. It is shown that covalent-bond formation due to hybridization of metal d (T2/sub g/) states and nonmetal p states near E/sub F/ leads to a resonancelike increase of the nonlocal dielectric function. This anomalous increase of the screening produces the phonon softening and explains the interrelation with the high T/sub c/'s as resulting from a simultaneous increase of the electron-phonon matrix elements and a decrease in the phonon energies

1976-12-06

292

Control of Dephasing and Phonon Emission in Coupled Quantum Dots  

CERN Document Server

We predict that phonon subband quantization can be detected in the non-linear electron current through double quantum dot qubits embedded into nano-size semiconductor slabs, acting as phonon cavities. For particular values of the dot level splitting $\\Delta$, piezo-electric or deformation potential scattering is either drastically reduced as compared to the bulk case, or strongly enhanced due to phonon van Hove singularities. By tuning $\\Delta$ via gate voltages, one can either control dephasing, or strongly increase emission into phonon modes with characteristic angular distributions.

Debald, S; Krämer, B

2002-01-01

293

Phonon dynamics of multiferroics: (Er, TM) MnO3  

International Nuclear Information System (INIS)

The phonon dynamics of orthorhombic multiferroic perovskite RMnO3 (R = Er, Tm) using a shell model with pairwise interionic interaction potential has been investigated. The present work includes the computation of the structural parameters, phonon frequencies and the specific heat curves. The symmetry vectors obtained through detailed group - theoretical analysis for Pnma space group at the zone center point were employed to classify the phonon frequencies obtained into their irreducible representations. The evaluated phonon dynamical properties are in good agreement with the available experimental data. (author)

2010-01-01

294

Advances in semiconductor lasers and applications to optoelectronics  

CERN Document Server

This volume includes highlights of the theories underlying the essential phenomena occurring in novel semiconductor lasers as well as the principles of operation of selected heterostructure lasers. To understand scattering processes in heterostructure lasers and related optoelectronic devices, it is essential to consider the role of dimensional confinement of charge carriers as well as acoustical and optical phonons in quantum structures. Indeed, it is important to consider the confinement of both phonons and carriers in the design and modeling of novel semiconductor lasers such as the tunnel

Dutta, Mitra

2000-01-01

295

Plasmonic electron injection drives ultrafast phase transition by catastrophic phonon collapse II: theory  

Science.gov (United States)

The ultrafast photo-induced phase transition in VO2 is promising for data storage and sensing applications. Our experimental work (the previous talk) shows that in a Au/VO2 hybrid nanostructure, electrons excited in the Au photocathode by an ultrafast laser trigger the insulator-to-metal transition in VO2. Here we report first-principles density-functional calculations showing that the collapse of a 6 THz optical phonon, corresponding to a twisting motion of V atoms, is responsible for the ultrafast phase transition. Above a concentration threshold, we find that injected electrons from Au induce collapse of the VO{2 }phonon, which stimulates the monoclinic-to-rutile structural phase transition. We also show that hole-doping can induce the same effect. The abrupt change of the critical phonon results from the weakening of the V-V bonds induced by the combined flux of injected electrons and holes. Thus, our results explain the experimental finding of plasmonic-electron-driven ultrafast phase transition and represent a step towards manipulating the photo-induced phase transition by surface modification.

Wang, Bin; Appavoo, Kannatassen; Brady, Nathaniel; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit; Hilton, David; Haglund, Richard; Pantelides, Sokrates

2013-03-01

296

Evidence for a resonant behavior of the E$_{2g}$ phonon in MgB$_{2}$  

CERN Document Server

Polarized and Resonant Raman scattering (PRS, RRS) have been carried out in microcrystals of MgB$_{2}$ at room temperature in order to study the symmetry of the broad E$_{2g}$ phonon and its coupling to electronic states. We observe a breakdown of the polarization selection rules when the medium is excited with the 2.41 eV laser line. The RRS experiments show that this breakdown is associated to the resonant behavior of the E$_{2g}$ mode. These results may be understood in terms of band structure calculations. These calculations predict a strong coupling between the E$_{2g}$ modes and the B-$% \\sigma $ bands. Unpolarized Raman scattering measurements between 10-300 K in polycrystalline MgB$_{2}$ using the resonant line of 2.41 eV show the expected anharmonic decay of the linewidth for the E$_{2g}$ mode and its energy remains the same below and above the superconducting critical temperature. These results indicate that the E$_{2g}$ phonon may not play an important role in the electron-phonon coupling mechanism...

Martinho, H; Rettori, C; De Lima, O F; Pagliuso, P G; Moreno, N O; Sarrao, J L

2001-01-01

297

Picosecond ultrasonic investigations of phonons in 2D nano-scaled lattices  

International Nuclear Information System (INIS)

We time-resolved the acoustical response of lattices of aluminum nano-dots with a step of a few hundreds nanometers using tunable femtosecond laser pulses in a pump and probe scheme. We detected two kinds of modes, the first being the individual modes of the dots. The other modes are shown to be both dependent on the dot size and on the lattice and are thus interpreted as collective modes. Using several step sizes we show that we can plot the phonon dispersion relation. A simple analytical model very well reproduces the data from which we can describe completely the dependence of the lattice modes on the sample parameters.

2007-01-01

298

Hypersonic modulation of light in three-dimensional photonic and phononic band-gap materials.  

UK PubMed Central (United Kingdom)

The elastic coupling between the a-SiO2 spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves.

Akimov AV; Tanaka Y; Pevtsov AB; Kaplan SF; Golubev VG; Tamura S; Yakovlev DR; Bayer M

2008-07-01

299

Hypersonic modulation of light in three-dimensional photonic and phononic band-gap materials.  

Science.gov (United States)

The elastic coupling between the a-SiO2 spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves. PMID:18764257

Akimov, A V; Tanaka, Y; Pevtsov, A B; Kaplan, S F; Golubev, V G; Tamura, S; Yakovlev, D R; Bayer, M

2008-07-18

300

Phonon Mediated Off-resonant Quantum Dot-Cavity Interaction  

Science.gov (United States)

Optically controlled quantum dot (QD) spins coupled to semiconductor microcavities constitute a promising platform for robust and scalable quantum information processing devices. In recent experiments on coupled QD optical cavity systems a pronounced interaction between the dot and the cavity has been observed even for detunings of many cavity linewidths. This interaction has been attributed to an incoherent cavity enhanced phonon-mediated scattering process and is absent in atomic systems. We demonstrate that despite its incoherent nature, this process preserves the signatures of coherent interaction between a QD and a strong driving laser, which may be observed via the optical emission from the off-resonant cavity. Under bichromatic driving of the QD, the cavity emission exhibits spectral features consistent with optical dressing of the QD transition, namely Rabi side-bands. These cavity emission measurements are more akin to absorption measurements of a strongly driven QD rather than resonance fluorescence measurements. In addition to revealing new aspects of the off-resonant QD-cavity interaction, this result provides a new, simpler means of coherently probing QDs and opens the possibility of employing off-resonant cavities to optically interface QD-nodes in quantum networks.

Majumdar, Arka; Kim, Erik; Bajcsy, Michal; Rundquist, Armand; Vuckovic, Jelena

2012-02-01

 
 
 
 
301

Geometric aspects of phonon polarization transport  

CERN Multimedia

We study the polarization transport of transverse phonons by adopting a new approach based on the quantum mechanics of spin-orbit interactions. This approach has the advantage of being apt for incorporating fluctuations in the system. The formalism gives rise to Berry effect terms manifested as the Rytov polarization rotation law and the polarization-dependent Hall effect. We derive the distribution of the Rytov rotation angle in the presence of thermal noise and show that the rotation angle is robust against fluctuations.

Mehrafarin, Mohammad; 10.1016/j.physleta.2009.04.041

2009-01-01

302

Geometric aspects of phonon polarization transport  

International Nuclear Information System (INIS)

We study the polarization transport of transverse phonons by adopting a new approach based on the quantum mechanics of spin-orbit interactions. This approach has the advantage of being apt for incorporating fluctuations in the system. The formalism gives rise to Berry effect terms manifested as the Rytov polarization rotation law and the polarization-dependent Hall effect. We derive the distribution of the Rytov rotation angle in the presence of thermal noise and show that the rotation angle is robust against fluctuations.

2009-06-01

303

Phonon frequency spectrum in random binary alloys  

International Nuclear Information System (INIS)

Starting from the augmented space formalism (Mookerjee 1973 a,b), a cluster CPA calculation for the phonon density of states is presented for linear chains as well as three-dimensional lattices. Off-diagonal disorder has been taken into account, and a self-consistent medium has been generated. Unlike earlier work, the Green function does not suffer from analytical difficulties in any concentration range. At the same time, the self-consistent medium gives a superior estimate of the band edges and the structures near them. (author)

1979-01-01

304

Phonons in ZrB12  

Science.gov (United States)

The first results of measuring dispersion curves of acoustic phonons in the ZrB12 superconductor are reported. The measurements have been conducted by the inelastic neutron scattering method on an ATOS three-axis spectrometer (IR-8, Russian Research Centre “Kurchatov Institute,” Moscow) at room temperature with a single crystal grown using a 99.5%-enriched 11B isotope. The results obtained have been analyzed in terms of the lattice dynamics model proposed earlier for rare-earth dodecaborides. In this model, the constants of the force interaction of Zr atoms with one another and with the boron framework have been determined.

Rybina, A. V.; Nemkovski, K. S.; Filippov, V. B.; Dukhnenko, A. V.

2010-05-01

305

Spectroscopy of nonequilibrium electrons and phonons  

CERN Multimedia

The physics of nonequilibrium electrons and phonons in semiconductors is an important branch of fundamental physics that has many practical applications, especially in the development of ultrafast and ultrasmall semiconductor devices. This volume is devoted to different trends in the field which are presently at the forefront of research. Special attention is paid to the ultrafast relaxation processes in bulk semiconductors and two-dimensional semiconductor structures, and to their study by different spectroscopic methods, both pulsed and steady-state. The evolution of energy and space distrib

Shank, CV

1992-01-01

306

Localization of Phonons in Two Component Superlattice with Random Thicknesses of the Layers  

CERN Multimedia

Two component superlattice film of 2N layers is considered and dimensionally quantised spectrum of phonon-s is found. The problem of localization of phonon-s in the superlattice with random thicknesses of the layers is investigated. The Landauer resistance of the transport of phonon-s is calculated exactly. For short range disorder the numerical analyses shows, that at frequency ømega=0, there is delocalized state and the correlation length index \

Sedrakian, D G; Sedrakyan, David G.; Sedrakyan, Ara G.

1998-01-01

307

Ground state correlations and the quasiparticle phonon model  

Energy Technology Data Exchange (ETDEWEB)

A method to treat the ground state correlations beyond the RPA is presented. A set of nonlinear equations taking into account effects of the ground state correlations on the pairing and phonon-phonon coupling is derived. The influence of such correlations on properties of the vibrational states in spherical nuclei is studied. (author)

Voronov, V.V. [JINR, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation)

2000-07-01

308

Transverse acoustic phonons in germanium near the melting point  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The transverse acoustic phonon dispersion in germanium has been studied along [111] and [100] up to 935 °C, only 2 degrees below the melting point Tm. No evidence of softening is found, neither near the Brillouin Zone boundary, nor uniformly throughout the BZ. The phonon energies decrease slowly and...

Hennion, B.; Schott, M.

309

Optical phonon lasing in transport through semiconductor double quantum dots  

Science.gov (United States)

We theoretically propose optical phonon lasing for a double quantum dot (DQD) fabricated in a semiconductor substrate. No additional cavity or resonator is required. We show that the DQD couples to only two phonon modes that act as a natural cavity. The pumping to the upper level is realized by an electric current through the DQD under a finite bias. Using the rate equation in the Born-Markov-Secular approximation, we analyze the enhanced phonon emission when the level spacing in the DQD is tuned to the phonon energy. We find the phonon lasing when the pumping rate is much larger than the phonon decay rate, whereas anti-bunching of phonon emission is observed when the pumping rate is smaller. Both effects disappear by an effective thermalization induced by the Franck-Condon effect in a DQD fabricated in a suspended carbon nanotube with strong electron-phonon coupling. ^1 ^1 R. Okuyama, M. Eto, and T. Brandes, arXiv:1205.6955 (2012).

Okuyama, Rin; Eto, Mikio; Brandes, Tobias

2013-03-01

310

Quasiparticle-phonon coupling in inelastic proton scattering  

International Nuclear Information System (INIS)

Multistep-processes in inelastic proton scattering from 89Y 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)

1979-11-30

311

Phonons and charge-transfer excitations in HTS superconductors  

International Nuclear Information System (INIS)

Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs.

1989-01-01

312

X-ray studies of phonon softening in tise2.  

UK PubMed Central (United Kingdom)

The charge-density-wave transition in TiSe (2), which results in a commensurate (2x2x2) superlattice at temperatures below approximately 200 K, presumably involves softening of a zone-boundary phonon mode. For the first time, this phonon-softening behavior has been examined over a wide temperature range by synchrotron x-ray thermal diffuse scattering.

Holt M; Zschack P; Hong H; Chou MY; Chiang TC

2001-04-01

313

Double-[gamma] phonon excitation in the Os nuclei  

Energy Technology Data Exchange (ETDEWEB)

We investigate double-[gamma] phonon excitation in the Os nuclei within the framework of the proton-neutron Interacting Boson Model (IBM-2). We decompose the IBM-2 wave-functions into multiphonon states, and see the contributions of zero, one and two phonon components in the low lying levels of the Os nuclei. (orig.)

Sugita, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Otsuka, T. (Dept. of Physics, Univ. of Tokyo (Japan))

1993-05-31

314

Spin Waves in Terbium : II. Magnon-Phonon Interaction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The selection rules for the linear couplings between magnons and phonons propagating in the c direction of a simple basal-plane hcp ferromagnet are determined by general symmetry considerations. The acoustic-optical magnon-phonon interactions observed in the heavy-rare-earth metals have been explain...

Jensen, J.; Houmann, Jens Christian Gylden

315

Electron-optical phonon coupling in superconductors  

International Nuclear Information System (INIS)

[en] 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] Die Rolle optischer Phononen bei der Supraleitfaehigkeit wird fuer Verbindungen mit verschiedenen atomaren Massen Msub(k) untersucht. Es zeigt sich, dass der Elektronenmassenverstaerkungsfaktor lambda von Msub(k) unabhaengig ist, wenn die Kraftkonstantenmatrix massenunabhaengig ist. Verwendet man jedoch lambda zur Berechnung von Tsub(c), so muss es in seine akustischen und optischen Beitraege zerlegt werden, die beide von Msub(k) abhaengen. Die Interferenzstreuung von einer leichten und einer schweren Masse und ihre Beitraege zu lambda werden innerhalb der freien Elektronennaeherung untersucht. Numerische Ergebnisse fuer Steinsalzstrukturkristall mit naechster und zweitnaechster Nachbarkopplung werden vorgelegt. Diese Ergebnisse deuten darauf hin, dass die Beitraege optischer Phononen zu lambda die Groesse von Tsub(c) betraechtlich erhoehen koennen. (orig./LN)

1975-01-01

316

Phonon induced thermodynamic properties of manganites  

International Nuclear Information System (INIS)

We have investigated the cohesive, elastic, thermal properties of pure and diluted rare earth manganites Re1-xAxMnO3 (where Re is rare earth cation and A is divalent or tetravalent cation) using the Rigid Ion Model (RIM) after modifying its framework to incorporate the van der Waals attraction and the short-range Hafemeister-Flygare type overlap repulsion operative between the first and second neighbour ions. The strong electron phonon interactions are presents in these compounds and the lattice distortions can affect them substantially hence phonon dependent properties deserves proper attention. The specific heat of Re1-xAxMnO3 with rare earth cation (Re = La, Pr, Nd, Sm, Eu, Gd, Th, Dy) at the A site and Ca, Sr, Ba, Pb at the B site has been studied as a function of temperature 10K ? T ? 500K by means of MRIM. We have found that the evaluated cohesive and thermal properties reproduce well the corresponding experimental data implying that the MRIM represent properly the nature of these manganites. Besides, we have reported the elastic properties of some manganites. The results obtained by us are discussed in detail. (author)

2008-01-01

317

Analysis of the absorption spectra and spectral hole burning in zero-phonon lines of F+3 and N1 colour centres in LiF crystals  

International Nuclear Information System (INIS)

The temperature dependences and mechanisms of broadening of zero-phonon lines of F+3 (488 nm) and N1 (523 nm) colour centres in LiF crystals are investigated. The results obtained make it possible to determine the quadratic electronic-vibrational coupling constant for N1 colour centres. The experimental data on the spectral hole burning in zero-phonon lines of F+3 and N1 colour centres indicate that the latter are positively charged. (laser applications and other topics in quantum electronics)

2010-09-10

318

Heterobarrier for converting hot-phonon energy to electric potential  

Science.gov (United States)

We show that hot phonons emitted in energy conversion or resistive processes can be converted to electric potential in heterobarrier structures. Using phonon and electron interaction kinetics and self-consistent ensemble Monte Carlo, we find the favorable conditions for unassisted absorption of hot phonons and design graded heterobarriers for their direct conversion into electric energy. Tandem barriers with nearly optical-phonon height allow for substantial potential gain without current loss. We find that 19% of hot phonons can be harvested with an optimized GaAs/AlxGa1-xAs barrier structure over a range of current and electron densities, thus enhancing the overall energy conversion efficiency and reducing waste heat.

Shin, Seungha; Melnick, Corey; Kaviany, Massoud

2013-02-01

319

Cooling carbon nanotubes to the phononic ground state with constant electron current  

CERN Multimedia

We present a quantum theory of cooling of a mechanical resonator using back-action with constant electron current. The resonator device is based on a doubly clamped nanotube, which mechanically vibrates and acts as a double quantum dot for electron transport. Mechanical vibrations and electrons are coupled electrostatically using an external gate. The fundamental eigenmode is cooled by absorbing phonons when electrons tunnel through the double quantum dot. We identify the regimes in which ground state cooling can be achieved for realistic experimental parameters.

Zippilli, Stefano; Bachtold, Adrian

2008-01-01

320

Search for the 3-phonon state of 40Ca  

International Nuclear Information System (INIS)

[en] 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 40Ca, with the reaction 40Ca + 40Ca 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? array. The analysis confirms the previous results about the GQR and the 2-phonon state in 40Ca. 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 40Ca and 208Pb 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)

2002-01-01

 
 
 
 
321

Quasi-Bound Exiton-LO Phonon Intermediate State in Multi-Phonon Raman Scattering of Semiconductors.  

Science.gov (United States)

A new model is proposed to understand multi-phonon Raman spectrum (MRS) of II-VI semiconductors. A quasibound state of exciton-LO phonon complex (EPQBS) in the intermediate state is shown to be responsible for the observed overtone series. The observation...

K. P. Jain C. S. Jayanthi

1982-01-01

322

Quasi-bound exiton-LO phonon intermediate state in multi-phonon Raman scattering of semiconductors  

International Nuclear Information System (INIS)

A new model is proposed to understand multi-phonon Raman spectrum (MRS) of II-VI semiconductors. A quasibound state of exciton-LO phonon complex (EPQBS) in the intermediate state is shown to be responsible for the observed overtone series. The observation of MRS is a natural consequence of our model in which the EPQBS lies in the absorption continuum. (author)

1982-01-01

323

Application of MIR-FEL irradiation to selectively excite phonons in wide-gap semiconductors  

Energy Technology Data Exchange (ETDEWEB)

A mid-infrared free electron laser (MIR-FEL) (5 - 20 {mu}m) facility (KU-FEL: Kyoto University Free Electron Laser) was constructed to aid various energy science researchers at the Institute of Advanced Energy, Kyoto University. In May 2008, the first power saturation at 13.2 {mu}m was achieved. A pilot application to evaluate selective phonon excitation processes in solid materials by irradiating with MIR-FEL was implemented, and a preliminary experiment without FEL irradiation was conducted. N-doped silicon carbide (SiC) was selected as a sample material due to its unique electrical property where the lattice vibration and the electronic structure are coupled. Two peaks, 1.8 - 2.2 eV and 2.4 - 2.8 eV, which showed strong temperature dependences in both their intensities and peak energies, were observed. These tendencies could be explained by using a donor-acceptor pair luminescence (DAP) model with impurity and defects in the SiC sample. The results imply that we can verify selective phonon excitation by investigating the change in the PL spectrum introduced by MIR-FEL irradiation.

Yoshida, K.; Sonobe, T.; Bakr, M. A. [Kyoto University, Kyoto (Japan); and others

2011-11-15

324

Application of MIR-FEL irradiation to selectively excite phonons in wide-gap semiconductors  

International Nuclear Information System (INIS)

A mid-infrared free electron laser (MIR-FEL) (5 - 20 ?m) facility (KU-FEL: Kyoto University Free Electron Laser) was constructed to aid various energy science researchers at the Institute of Advanced Energy, Kyoto University. In May 2008, the first power saturation at 13.2 ?m was achieved. A pilot application to evaluate selective phonon excitation processes in solid materials by irradiating with MIR-FEL was implemented, and a preliminary experiment without FEL irradiation was conducted. N-doped silicon carbide (SiC) was selected as a sample material due to its unique electrical property where the lattice vibration and the electronic structure are coupled. Two peaks, 1.8 - 2.2 eV and 2.4 - 2.8 eV, which showed strong temperature dependences in both their intensities and peak energies, were observed. These tendencies could be explained by using a donor-acceptor pair luminescence (DAP) model with impurity and defects in the SiC sample. The results imply that we can verify selective phonon excitation by investigating the change in the PL spectrum introduced by MIR-FEL irradiation.

2011-01-01

325

Evidence of strong electron-phonon interaction in iron doped Bi2Sr2Ca1Cu2O8+D  

International Nuclear Information System (INIS)

The authors already shown that infrared laser photo-induced spectra of Bi based ceramic superconductor (n = 2 phase) doped with iron show a highly polarizable environment at about 700 cm-p close to the longitudinal optical mode frequency that we characterize as due to trapped polarons. This modifies the higher frequency side of the Cu-O phonon feature at 630 cm-1 which is currently associated with a stretching mode in the plane. In this paper, the authors report that by increasing the Fe doping up to 25% the authors have succeeded in unveiling an electron-phonon interaction related to that stretching mode. Infrared transmission and reflection spectra show an unusual dip at the longitudinal optical frequency. This feature may with the field that could rise the transverse-longitudinal optical splitting in purely ionic materials. The authors hypothesize that this should lead to a Raman active longitudinal phonon due to the Frolich interaction.

1990-05-04

326

The Phononic Casimir Effect: An Analog Model  

CERN Document Server

We discuss the quantization of sound waves in a fluid with a linear dispersion relation and calculate the quantum density fluctuations of the fluid in several cases. These include a fluid in its ground state. In this case, we discuss the scattering cross section of light by the density fluctuations, and find that in many situations it is small compared to the thermal fluctuations, but not negligibly small and might be observable at room temperature. We also consider a fluid in a squeezed state of phonons and fluids containing boundaries. We suggest that the latter may be a useful analog model for better understanding boundary effects in quantum field theory. In all cases involving boundaries which we consider, the mean squared density fluctuations are reduced by the presence of the boundary. This implies a reduction in the light scattering cross section, which is potentially an observable effect.

Ford, L H

2008-01-01

327

Cavity-type hypersonic phononic crystals  

International Nuclear Information System (INIS)

[en] We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter. (paper)

2012-01-01

328

Zero m phonons in metal chalcogenide nanotubes  

Energy Technology Data Exchange (ETDEWEB)

Phonon dispersions of single-wall MoS{sub 2} and WS{sub 2} nanotubes are calculated within a full symmetry implemented valence force-field model. Tubular structure is found to be characterized by two Raman active modes: by the in-phase breathing modes (in full analogy to carbon nanotubes) with frequency approaching Brillouin scattering domain (as diameter approaches nm), and by the high-energy breathing mode with sulfur shells breathing in phase, but out of phase relative to the Mo/W atoms. Likewise, the longitudinal rigid-shell mode, where sulfur shells vibrate out of phase whilst Mo/W atoms barely move, is predicted to be a fingerprint of the cylindrical configuration in infrared spectra. It is also found that twisting rigid-layer modes characterize chirality of the tubes. Finally, the large diameter limit is discussed and related to the measured Raman and infrared spectra of the layered structures.

Milosevic, I; Dobardzic, E; Dakic, B; Damnjanovic, M [Faculty of Physics, University of Belgrade, Studentski trg 12, POB 368, 11001 Belgrade (Serbia)

2007-12-15

329

The Phononic Casimir effect: An analog model  

Energy Technology Data Exchange (ETDEWEB)

We discuss the quantization of sound waves in a fluid with a linear dispersion relation and calculate the quantum density fluctuations of the fluid in several cases. These include a fluid in its ground state. In this case, we discuss the scattering cross section of light by the density fluctuations, and find that in many situations it is small compared to the thermal fluctuations, but not negligibly small and might be observable at room temperature. We also consider a fluid in a squeezed state of phonons and fluids containing boundaries. We suggest that the latter may be a useful analog model for better understanding boundary effects in quantum field theory. In all cases involving boundaries which we consider, the mean squared density fluctuations are reduced by the presence of the boundary. This implies a reduction in the light scattering cross section, which is potentially an observable effect.

Ford, L H [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Svaiter, N F, E-mail: ford@cosmos.phy.tufts.ed, E-mail: nfuxsvai@cbpf.b [Centro Brasiliero de Pesquisas Fisicas CBPF, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, RJ, 22290 180 (Brazil)

2009-04-01

330

Observation of magnon-phonon interaction at short wavelengths  

International Nuclear Information System (INIS)

[en] Measurements have been made of the magnon and phonon dispersion relations in uranium dioxide at 9oK. 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 ± 1.6oK. Since the Neel temperature is 30.8oK, this coupling constant is of a similar magnitude to the direct magnetic interactions. (author)

1966-01-01

331

Spectroscopic studies of the energy transfer processes important to obtain holmium laser action in the Er:Tm:Ho:YLF; Estudos espectroscopicos dos processos de transferencia de energia relevantes para obtencao de acao laser do holmio no cristal Er:Tm:Ho:YLF  

Energy Technology Data Exchange (ETDEWEB)

There are several processes of energy transfer between Er, Tm and Ho ions in YLF crystal that could be evaluated using the Foerster-Dexter method. Energy transfer processes, important to understand Holmium laser action, were studied, specially involving the energy transfer between the first excited states of Er and Tm donors and Ho acceptor. The back-transfer processes were evaluated too in order to minimize the system losses. Another important process to understand Ho laser action in the host is the energy diffusion mechanism between donor ions due to excitation migration processes which take place before the energy transfer to Ho. The proposed model of energy transfer was developed to include the diffusion mechanism between donors in the absence and presence of the acceptors. The energy transfer probability was evaluated including the back-transfer processes besides the diffusion assistance. A laser medium model based on the fundamental spectroscopic parameters was used in order to determine the ideal donor acceptor concentrations in order to maximize the laser action of Ho at 2,1 {mu}m. (author) 93 refs., 12 tabs., 62 figs.

Tarelho, Luiz Vicente Gomes

1995-12-31

332

OBSERVATION OF STRONGLY FREQUENCY DEPENDENT LIFETIMES OF ACOUSTIC PHONONS IN CaF2  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A strongly frequency dependent lifetime of acoustic phonons in CaF2 at low crystal temperature is observed. The phonon lifetime decreases proportionally to ?-5 indicating spontaneous phonon decay. Furthermore, we report measurements of the spectral distribution of phonons generated by nonradiative t...

Baumgartner, R.; Engelhardt, M.; Renk, K.

333

TWO-MAGNON-ONE-PHONON SCATTERING IN THE LATTICE THERMAL CONDUCTIVITY OF MAGNETIC INSULATORS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A simple, but general model of magnon-phonon scattering as an extension of linear spin-wave theory is presented. Both resonant one-magnon-one-phonon and two-magnon-one-phonon scattering processes are considered. The former are included in the thermal conductivity by diagonalizing the magnon-phonon H...

Dixon, G.

334

Phonons and solid-state qubits for quantum technology  

Science.gov (United States)

Phonons in the context of quantum information processing are traditionally negatives. They induce relaxation or decoherence of or between qubit states. Learning to control phonons for positive purposes, both as supporting technology for quantum information processing, and for other quantum devices is of great possible interest. Already, acoustic waves are used as a supporting technology in microelectronics and optoelectronics (e.g. their slow speed can be useful in certain contexts). Here we consider some methods for making phonons useful and describe the physics of such systems in several potential solid-state systems including silicon. Our results may also be of interest to the optomechanics community.

Soykal, Ö. O.; Ruskov, Rusko; Tahan, Charles

2011-03-01

335

Electron-phonon interaction in proximity of a Mott transition  

International Nuclear Information System (INIS)

The effects of electron-phonon interaction on the electronic properties of a strongly correlated metal on the verge of a Mott metal-insulator transition are studied by means of dynamical mean-field theory. We show that electron-phonon interactions induce a phase separation instability close to the density driven Mott transition, and give rise to significant renormalization of electronic properties like charge susceptibility. Nonetheless, the strong correlation reduces the effectiveness of the electron-phonon coupling in driving a polaronic crossover.

2005-04-30

336

Charge order and phonon renormalizations: Possible implications for cobaltates  

CERN Multimedia

Several experimental and theoretical studies in cobaltates suggest the proximity of the system to charge ordering (CO). We show, qualitatively, in the frame of a $t-V$ model coupled to phonons that optical phonon modes at the $K$ and $M$ points of the Brillouin zone, which involves only $O$-ions displacement around a $Co$-ion, are good candidates to display anomalies due to the CO proximity. If by increasing of $H_2O$ content the system is pushed closer to CO, the mentioned phonon modes should show softening and broadening.

Bejas, M; Foussats, A

2006-01-01

337

Spin-induced variations of phonon frequencies in ferromagnetic metals  

International Nuclear Information System (INIS)

The effects of magnetization on phonon frequencies are investigated for FCC Ni from first principles by combining the fixed spin moment method and density functional perturbation theory (DFPT) as implemented with the all-electron full-potential linearized augmented plane wave (FLAPW) method. We explicitly show that the phonon frequencies change appreciably as the magnetic moment varies, and that the magnetic effect on phonon frequencies comes from the mixed role of the spin-dependent screening, as proposed by Kim, and the effect of magnetostriction.

2007-01-01

338

Electron-phonon interaction in Chevrel-phase compounds  

International Nuclear Information System (INIS)

Experiments on the electron-phonon interaction in Chevrel-phase compounds (CPC) and a theoretical discussion of their results are presented. The authors particularly discuss measurements of the isotope effect of the transition temperature in Mo6Se8 and SnMo6S8 and tunneling spectroscopy experiments on Cu1.8Mo6S8 and PbMo6S8. These investigations have been performed to get information about the strength of the electron-phonon interaction in CPC, and about the question whether there are phonon modes which couple particularly strongly to the electrons in these compounds. (orig./GSCH)

1981-01-01

339

SU(6) limit of the nuclear quasiparticle-phonon model  

International Nuclear Information System (INIS)

It is shown that the Hamiltonian of the quasiparticle-phonon nuclear model has the SU(6) limit. Under some conditions this Hamiltonian can be represented as a rotational invariant which is constructed of the generators of the SU(6) algebra. The collective quadrupole random phase approximation phonon operators and their commutators form a closed algebra. Microscopic expressions for the parameters of the quadrupole phonons for the model are derived. Calculations of maximal numbers of bosons and the test of the conditions giving the SU(6) limit for some Zn isotopes are performed.

1986-01-01

340

Tunneling in suspended carbon nanotubes assisted by longitudinal phonons  

CERN Document Server

Current-voltage characteristics of suspended single-wall carbon nanotube quantum dots show a series of steps equally spaced in voltage. The energy scale of this harmonic, low-energy excitation spectrum is consistent with that of the longitudinal low-k phonon mode (stretching mode) in the nanotube. Agreement is found with a Franck-Condon-based model in which the phonon-assisted tunneling process is modeled as a coupling of electronic levels to underdamped quantum harmonic oscillators. Comparison with this model indicates a rather strong electron-phonon coupling factor of order unity.

Sapmaz, S; Blanter, Y M; Dekker, C; Van der Zant, H S J; Blanter, Ya.M.

2006-01-01

 
 
 
 
341

Bias drop and phonon emission in molecular wires  

Energy Technology Data Exchange (ETDEWEB)

Using the recursion-transfer-matrix (RTM) method combined with the non-equilibrium Green's function (NEGF) method and density-functional theory, we perform ab initio calculations for the electron transport of molecular wires bridged between electrodes. We present an effective potential of molecular wire under a finite bias voltage and discuss the phonon emission and local heating due to inelastic electron-phonon coupling effects. We find that it is strongly dependent on contact conditions. When the contacts to electrodes are bad, excitation phonon modes at contacts become dominant for the energy dissipation.

Hirose, Kenji, E-mail: k-hirose@ak.jp.nec.com [Nano Electronics Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan); Ishii, Hiroyuki; Kobayashi, Nobuhiko [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

2012-01-01

342

Bias drop and phonon emission in molecular wires  

Science.gov (United States)

Using the recursion-transfer-matrix (RTM) method combined with the non-equilibrium Green's function (NEGF) method and density-functional theory, we perform ab initio calculations for the electron transport of molecular wires bridged between electrodes. We present an effective potential of molecular wire under a finite bias voltage and discuss the phonon emission and local heating due to inelastic electron-phonon coupling effects. We find that it is strongly dependent on contact conditions. When the contacts to electrodes are bad, excitation phonon modes at contacts become dominant for the energy dissipation.

Hirose, Kenji; Ishii, Hiroyuki; Kobayashi, Nobuhiko

2012-01-01

343

Coupling of molecular vibrons with contact phonon reservoirs  

International Nuclear Information System (INIS)

In this paper we describe a computational method for coupling localized molecular vibrations with contact phonons using a Green's function formalism. The phonon Green's function is constructed from the dynamical matrix of the contact-molecule-contact coupled system. Within this formalism we identify the imaginary part of the self-energy as the vibron lifetime for decay into contact phonons. This first-principles calculation allows us to compute the microscopic energy dissipation and the heat transport from the molecule to the contacts. This is a fundamental step for the evaluation of the power dissipated in molecular devices and for studying the thermal stability of molecular devices.

2007-05-30

344

Interface Phonons and Polaron Effect in Quantum Wires  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract The theory of large radius polaron in the quantum wire is developed. The interaction of charge particles with interface optical phonons as well as with optical phonons localized in the quantum wire is taken into account. The interface phonon contribution is shown to be dominant for narrow quantum wires. The wave functions and polaron binding energy are found. It is determined that polaron binding energy depends on the electron mass inside the wire and on the polarization properties of the barrier material.

Maslov A; Proshina OV

2010-01-01

345

Phonon-polaritons by two-photon absorption in solids  

International Nuclear Information System (INIS)

A semiclassical theory of the two-photon absorption to phonon polaritons in solids is developed. A 4-band model has been introduced for the phonon-assisted two-photon electronic transitions to polariton states. A numerical calculation is performed for GaP. The results show three different absorption peaks. The first peak, at low energy, corresponds to the phonon polariton band due to transitions through the indirect gap. The other two peaks are associated with transitions across the two lowest gaps of GaP. (author)

1980-01-01

346

Neutron scattering by phonons in quasi-crystals  

Energy Technology Data Exchange (ETDEWEB)

Using the spectral moments method, we studied the inelastic scattering by phonons in very long Fibonacci chains. The results show that the pseudo-acoustic dispersion curves can be associated with Bragg peaks. The intensity of the acoustic phonon lines is proportional to the intensity of the corresponding Bragg peak. A study of disordered Fibonacci chains shows that the intensity of the phonon lines decreases strongly with increasing disorder. These results could explain the difficulties encountered in measurements of the acoustic modes in quasi-crystals. (author).

Benoit, C.; Poussigue, G.; Azougarh, A. (Montpellier-2 Univ., 34 (France))

1990-03-19

347

Proposal for an optomechanical traveling wave phonon-photon translator  

International Nuclear Information System (INIS)

[en] In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.

2011-01-01

348

Proposal for an optomechanical traveling wave phonon-photon translator  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.

Safavi-Naeini, Amir H; Painter, Oskar, E-mail: safavi@caltech.edu, E-mail: opainter@caltech.edu [Thomas J Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125 (United States)

2011-01-15

349

Confined and interface phonons in combined cylindrical nanoheterosystem  

Directory of Open Access Journals (Sweden)

Full Text Available The spectra of all types of phonons existing in a complicated combined nanoheterosystem consisting of three cylindrical quantum dots embedded into the cylindrical quantum wire placed into vacuum are studied within the dielectric continuum model. It is shown that there are confined optical (LO) and interface phonons of two types: top surface optical (TSO) and side surface optical (SSO) modes of vibration in such a nanosystem. The dependences of phonon energies on the quasiwave numbers and geometrical parameters of quantum dots are investigated and analysed.

O.M.Makhanets; O.M.Voitsekhivska; A.M.Gryschyk

2006-01-01

350

Phonon dynamics of orientationally disordered material - RbCN  

International Nuclear Information System (INIS)

An extended three-body force shell model (ETSM) has been developed for the prediction of phonon dynamics of orientatioanally disordered material - RbCN by incorporating the effects of the coupling of translational modes and orientations of cyanide molecules in the framework of TSM. ETSM, has been applied for the first time, for a successful description of the phonon dispersion curves of RbCN along the symmetry directions. The agreement between experimental and present theoretical results is resonably good. This ETSM has a promise to reveal the phonon dynamics and associated properties of other orientationally disordered materials. (author). 18 refs

1991-01-01

351

Isotopic effects on the phonon modes in boron carbide.  

Science.gov (United States)

The effect of isotopes ((10)B-(11)B; (12)C-(13)C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals. PMID:21403227

Werheit, H; Kuhlmann, U; Rotter, H W; Shalamberidze, S O

2010-09-10

352

Phonon softening and superconductivity in tellurium under pressure  

CERN Multimedia

The phonon dispersion and the electron-phonon interaction for the $\\beta$-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\\rm c}$) and confirm the connection between the jump in T$_{\\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Mauri, F; De Gironcoli, S; Louie, S G; Cohen, M L; Mauri, Francesco; Zakharov, Oleg; Gironcoli, Stefano de; Louie, Steven G.; Cohen, Marvin L.

1996-01-01

353

Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors  

Energy Technology Data Exchange (ETDEWEB)

We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.

Leman, S.W.; /MIT, MKI; Cabrera, B.; /Stanford U., Phys. Dept.; McCarthy, K.A.; /MIT, MKI; Pyle, M.; /Stanford U., Phys. Dept.; Resch, R.; /SLAC; Sadoulet, B.; Sundqvist, K.M.; /LBL, Berkeley; Brink, P.L.; Cherry, M.; /Stanford U., Phys. Dept.; Do Couto E Silva, E.; /SLAC; Figueroa-Feliciano, E.; /MIT, MKI; Mirabolfathi, N.; Serfass, B.; /UC, Berkeley; Tomada, A.; /Stanford U., Phys. Dept.

2012-06-04

354

Phonon hardening due to the small-polaron effect  

International Nuclear Information System (INIS)

The influence of the small-polaron effect on the vibrational properties of the strongly coupled electron-phonon system is investigated. It was found that polaron-phonon interaction may cause a noticeable renormalization of the phonon spectra. These changes may be observed by the measurements of the speed of sound for which a very specific dependence on temperature, values of coupling constant and adiabatic parameter is expected. We also found that the rise of the small-polaron effective mass as a function of the coupling constant should be considerably moderated than that anticipated without taking into account the modification of the vibrational spectra.

2005-01-31

355

A new equation for describing heat conduction by phonons  

CERN Multimedia

A new equation, rooted in the theory of Brownian motion, is proposed for describing heat conduction by phonons. Though a finite speed of propagation is a built-in feature of the equation, it does not give rise to an inauthentic wave front that results from the application of the hyperbolic heat equation (of Cattaneo). Even a simplified, analytically tractable version of the equation yields results close to those found by solving, through more elaborate means, the equation of phonon radiative transfer. An explanation is given as to why both Brownian motion and its inverse (radiative transfer) provide equally serviceable paradigms for phonon-mediated heat conduction.

Naqvi, K R

2005-01-01

356

Spin-seebeck effect: a phonon driven spin distribution.  

UK PubMed Central (United Kingdom)

Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.

Jaworski CM; Yang J; Mack S; Awschalom DD; Myers RC; Heremans JP

2011-05-01

357

Heart - Shaped Nuclei: Condensation of Rotational Aligned Octupole Phonons  

CERN Multimedia

The strong octupole correlations in the mass region $A\\approx 226$ are interpreted as rotation-induced condensation of octupole phonons carrying three units of angular momentum aligned with the rotational axis. The condensation represents a quantum phase transition. Discrete phonon energy and parity conservation generate oscillations of the rotational sequences with positive and negative parity. The phonon condensate co-rotates with quadrupole shape forming a rotating heart shape. The coupling between the quadrupole and octupole modes reaches a maximum in the $N\\approx 136$ isotones, approaching the limit of a static heart shape.

Frauendorf, S

2007-01-01

358

Electron-phonon interaction in the t-J model  

CERN Multimedia

We derive a t-J model with electron-phonon coupling from the three-band model, considering modulation of both hopping and Coulomb integrals by phonons. While the modulation of the hopping integrals dominates, the modulation of the Coulomb integrals cannot be neglected. The model explains the experimentally observed anomalous softening of the half-breathing mode upon doping and a weaker softening of the breathing mode. It is shown that other phonons are not strongly influenced, and, in particular, the coupling to a buckling mode is not strong in this model.

Rosch, O

2004-01-01

359

Coherent phonons in pyrochlore titanates A2Ti2O7 (A= Dy, Gd, Tb): A phase transition in Dy2Ti2O7 at 110 K  

Science.gov (United States)

We study the generation of coherent optical phonons in spin-frustrated pyrochlore single crystals Dy2Ti2O7, Gd2Ti2O7, and Tb2Ti2O7 using femtosecond laser pulses (65 fs, 1.57 eV) in degenerate time-resolved transmission experiments as a function of temperature from 4 to 296 K. At 4 K, two coherent phonons are observed at ~5.3 THz (5.0 THz) and ~9.3 THz (9.4 THz) for Dy2Ti2O7 (Gd2Ti2O7), whereas three coherent phonons are generated at ~5.0, 8.6, and 9.7 THz for Tb2Ti2O7. In the case of spin-ice Dy2Ti2O7, a clear discontinuity is observed in the linewidths of both the coherent phonons as well as in the phase of lower-energy coherent phonon mode, indicating a subtle structural change at 110 K. Another important observation is a phase difference of ? between the modes in all the samples, thus suggesting that the driving forces behind the generation of these modes could be different in nature, unlike a purely impulsive or displacive mechanism.

Kamaraju, N.; Kumar, Sunil; Saha, Surajit; Singh, Surjeet; Suryanarayanan, R.; Revcolevschi, A.; Sood, A. K.

2011-04-01

360

Quasiparticle--phonon model of the nucleus. V. Odd spherical nuclei  

Energy Technology Data Exchange (ETDEWEB)

The formalism of the quasiparticle--phonon model of the nucleus for odd spherical nuclei is presented. The exact commutation relations of the quasiparticle and phonon operators together with the anharmonic corrections for the phonon excitations are taken into account in the derivation of equations for the energies and structure coefficients of the wave functions of excited states, which include quasiparticle--phonon and quasiparticle--two-phonon components. The influence of various physical effects and of the dimension of the phonon basis on the fragmentation of the single-quasiparticle and quasiparticle-phonon states is investigated.

Vdovin, A.I.; Voronov, V.V.; Solov' ev, V.G.; Stoyanov, C.

1985-03-01

 
 
 
 
361

Confined optical phonon modes in polar tetrapod nanocrystals detected by resonant inelastic light scattering  

CERN Multimedia

We investigated CdTe nanocrystal tetrapods of different sizes by resonant inelastic light scattering at room temperature and under cryogenic conditions. We observe a strongly resonant behavior of the phonon scattering with the excitonic structure of the tetrapods. Under resonant conditions we detect a set of phonon modes that can be understood as confined longitudinal-optical phonons, surface-optical phonons, and transverse-optical phonons in a nanowire picture.

Krahne, R; Schueller, C; Carbone, L; Kudera, S; Mannarini, G; Manna, L; Heitmannb, D; Cingolani, R; 10.1021/0524492

2006-01-01

362

Improved model of optical phonon confinement in silicon nanocrystals  

Science.gov (United States)

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.

Volodin, V. A.; Sachkov, V. A.

2013-01-01

363

Phonon-assisted decoherence and tunneling in quantum dot molecules  

DEFF Research Database (Denmark)

We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantum kinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual processes with relevant acoustic phonons. We show that the relaxation is dominated by phonon-assisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between the quantum dots is studied in detail. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Grodecka-Grad, Anna; Foerstner, Jens

2011-01-01

364

Phonons in a Nanoparticle Mechanically Coupled to a Substrate  

CERN Multimedia

The discrete nature of the vibrational modes of an isolated nanometer-scale solid dramatically modifies its low-energy electron and phonon dynamics from that of a bulk crystal. However, nanocrystals are usually coupled--even if only weakly--to an environment consisting of other nanocrystals, a support matrix, or a solid substrate, and this environmental interaction will modify the vibrational properties at low frequencies. In this paper we investigate the modification of the vibrational modes of an insulating spherical nanoparticle caused by a weak {\\it mechanical} coupling to a semi-infinite substrate. The phonons of the bulk substrate act as a bath of harmonic oscillators, and the coupling to this reservoir shifts and broadens the nanoparticle's modes. The vibrational density of states in the nanoparticle is obtained by solving the Dyson equation for the phonon propagator, and we show that environmental interaction is especially important at low frequencies. As a probe of the modified phonon spectrum, we co...

Patton, K R; Patton, Kelly R.; Geller, Michael R.

2002-01-01

365

The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals.

D.W. Lynch

2004-09-30

366

Effect of pressure on the phonon properties of europium chalcogenides  

International Nuclear Information System (INIS)

Lattice vibrational properties of europium chalcogenides have been investigated at high pressure by using a simple lattice dynamical model theory viz. the three-body force rigid ion model (TRIM) which includes long range three-body interaction arising due to charge transfer effects. The dispersion curves for the four Eu-chalcogenides agree reasonably well with the available experimental data. Variation of LO, TO, LA and TA phonons with pressure have also been studied at the symmetry points of the Brillouin zone (BZ) for Eu-chalcogenides for the first time by using a lattice dynamical model theory. We have also calculated the one phonon density of states and compared them with the first order Raman scattering results. The calculation of one phonon density of states for Eu-chalcogenides has also been extended up to the phase transition pressure. We observed a pronounced shift in phonon spectrum as pressure is increased. (author)

2000-01-01

367

Empirical potential study of phonon transport in graphitic ribbon  

CERN Document Server

The thermal properties of graphitic ribbon are investigated based on Brenner's empirical potential. The reliability and usefulness of the empirical potential to address the thermal properties of covalent-bonded carbon nanostructures are verified through a comparison of phonon dispersion relations and the density of states of carbon nanotubes with first-principles calculations. The analysis reveals unique edge-phonon states that are highly localized at edge carbon atoms of both armchair and zigzag ribbons. Applying the phonon dispersion relations to the Landauer formula of phonon transport, the quantization and universal features of the low-temperature thermal conductance of graphitic ribbon are elucidated, and it is found that the width of the quantization plateau in the low-temperature region is inversely proportional to the ribbon width.

Yamamoto, T; Watanabe, K; Yamamoto, Takahiro; Mii, Kazuaki; Watanabe, Kazuyuki

2004-01-01

368

Phonon Modes and the Maintenance Condition of a Crystalline Beam  

CERN Document Server

Previously it has been shown that the maintenance condition for a crystalline beam requires that there not be a resonance between the crystal phonon frequencies and the frequency associated with a beam moving through a lattice of N periods. This resonance can be avoided provided the phonon frequencies are all below half of the lattice frequency. Here we make a detailed study of the phonon modes of a crystalline beam. Analytic results obtained in a ?smooth approximation? using the ground-state crystalline beam structure is compared with numerical evaluation employing Fourier transform of Molecular Dynamic (MD) modes. The MD also determines when a crystalline beam is stable. The maintenance condition, when combined with either the simple analytic theory or the numerical evaluation of phonon modes, is shown to be in excellent agreement with the MD calculations of crystal stability.

Wei, Jie; Li, Xiao-Ping; Okamoto, Hiromi; Sessler, Andrew M; Yuri, Yosuke

2005-01-01

369

The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy  

International Nuclear Information System (INIS)

[en] With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals

2004-01-01

370

Confinement of acoustical vibrations in a semiconductor planar phonon cavity  

CERN Document Server

Extending the idea of optical microcavities to sound waves, we propose a {\\it phonon cavity} consisting of two semiconductor superlattices enclosing a spacer with thickness determined by the acoustic wavelength at the center of the first zone-center folded minigap. We show that acoustical phonons can be confined in these layered structures, and propose Raman experiments which are able to probe these novel excitations. The Raman experiments take profit of an optical microcavity scattering geometry that, through the forward-scattering contribution, gives access to the zone-center excitations. We report experimental results of Raman scattering in a structure based in GaAs/AlAs materials that demonstrate unambiguously the observation of phonon cavity confined acoustical vibrations. The experimental results compare precisely with photoelastic model calculations of the Raman spectra of the proposed phonon-cavity embedded optical microcavity.

Trigo, M; Fainstein, A; Jusserand, B; Thierry-Mieg, V

2002-01-01

371

Phonon-assisted tunneling through a double quantum dot system  

International Nuclear Information System (INIS)

Electron transport through a double quantum dot system is studied, taking into account the electron-phonon interaction. The Keldysh nonequilibrium Green function formalism is used to compute the current and transmission coefficient of the system. The influence of the electron-phonon interaction, interdot tunneling and temperature on the density of states and current is analyzed. Results show that the transmission coefficient is a function of the bias in the presence of the electron-phonon interaction. We found that although the electron-phonon interaction results in the appearance of side peaks in the conductance at low temperatures, these disappear at high temperatures. In addition, the temperature influences the shape of the density of the states.

2012-01-01

372

Pauli principle in the quasiparticle-phonon nuclear model  

International Nuclear Information System (INIS)

The influence of ground state correlation in one-and two-phonon states of even-even deformed nuclei is studied in the framework of the semimicroscopic theory. The secular equation for one-phonon excited states is derived, which takes into account the exact commutation relation between the quasiparticle operators on the average. An approach is proposed for transforming the sum over one-phonon space to the integral over parameter. This approach, based on the strength-function method, may be very useful in calculating the average number of quasiparticles in the ground state. It is shown that the ground state correlation can significantly influence on the norm of two-phonon components of the wave function

1980-01-01

373

Quasi-dimensional peculiar features in graphite phonon spectrum  

International Nuclear Information System (INIS)

The phonon spectrum of graphite is analyzed in details on microscopical level and the partial contributions to the density of phonon states from atomic displacements along and normal to the layers are calculated. Quasi-two-dimensional peculiar features of the graphite phonon spectrum are found, in particular the singularity in the spectral density generated by the atomic displacement along the c-axis which is similar to the Dirac peculiarity in the electron spectrum of graphene. Our calculations make it possible to forecast the general properties of graphite phonon and electron spectra in the case of intercalation of graphite by different metals and to explain the change of the superconducting transition temperature in the intercalated graphite.

2009-01-01

374

Fluid phonons, protoinflationary dynamics, and large-scale gravitational fluctuations  

Science.gov (United States)

We explore what can be said on the effective temperature and sound speed of a statistical ensemble of fluid phonons present at the onset of a conventional inflationary phase. The phonons are the actual normal modes of the gravitating and irrotational fluid that dominates the protoinflationary dynamics. The bounds on the tensor-to-scalar ratio result in a class of novel constraints involving the slow roll parameter, the sound speed of the phonons and the temperature of the plasma prior to the onset of inflation. If the current size of the Hubble radius coincides with the inflationary event horizon redshifted down to the present epoch, the sound speed of the phonons can be assessed from independent measurements of the tensor-to-scalar ratio and of the tensor spectral index.

Giovannini, Massimo

2013-07-01

375

Phonons Softening in Tip-Stretched Monatomic Nanowires  

CERN Multimedia

It has been shown in recent experiments that electronic transport through a gold monatomic nanowire is dissipative above a threshold voltage due to excitation of phonons via the electron-phonon interaction. We address that data by computing, via density functional theory, the zone boundary longitudinal phonon frequency of a perfect monatomic nanowire during its mechanical elongation. The theoretical frequency that we find for an ideally strained nanowire is not compatible with experiment if a uniformly distributed stretch is assumed. With the help of a semi-empirical Au-Au potential, we model the realistic nanowire stretching as exerted by two tips. In this model we see that strain tends to concentrate in the junctions, so that the mean strain of the nanowire is roughly one half of the ideal value. With this reduced strain, the calculated phonon softening is in much better agreement with experiment.

Picaud, F; Tosatti, E

2002-01-01

376

Magnons and Magnon-Phonon Interactions in Iron  

Energy Technology Data Exchange (ETDEWEB)

First-principle studies of magnons and magnon-phonon interactions are carried out in bcc and fcc iron in the adiabatic approximation. It is shown that the phonons have a minor effect on magnons in bcc Fe and thus the lattice vibrations make a small contribution to the Curie temperature. fcc Fe is unstable against magnon excitations but the phonons seem to reduce this instability. The magnon-phonon interactions are analyzed in terms of the pair-exchange interaction variations as functions of the interatomic distances. The fcc results suggest that metastable fcc Fe in thin-film or nanostructure form should have interesting magnetic properties. {copyright} {ital 1999} {ital The American Physical Society}

Sabiryanov, R.F.; Jaswal, S.S. [Behlen Laboratory of Physics and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States)

1999-09-01

377

Detection of dark matter particles with low temperature phonon sensors  

Energy Technology Data Exchange (ETDEWEB)

Taking as an example the development effort in Berkeley, the author discusses for nonspecialists (Astronomers and Particle Physicists) the promises of phonon sensing at low temperature for the detection of dark matter particles and the difficulties faced. 31 refs.

Sadoulet, B.

1988-03-01

378

The effect of pulse duration on the interplay of electron heat conduction and electron-phonon interaction: Photo-mechanical versus photo-thermal damage of metal targets  

International Nuclear Information System (INIS)

Here we present a theoretical work on short pulse laser interaction with metal targets. With the help of Two Temperature Model we consider in detail the interplay of two competitive mechanism of the laser deposited energy dissipation: the fast electron heat conduction and the electron-phonon interaction processes. For a range of pulse durations the modelling included a complex description of these processes as the functions of the electron and phonon temperatures. It was shown that for transitional type of metals the maximum surface temperature determined for a range of pulse durations at fixed fluence exhibits peak behavior and the corresponding pulse duration is close to the electron-phonon relaxation time. In contrast, having complex deviation of heat conductivity from its linear growth with the electronic temperature, the group of noble metals shows different behavior in maximum surface temperature depending on the fluence regime. Based on the results, an experimental approach in measuring the electron-phonon relaxation time is suggested and a general tendency of photo-mechanical versus photo-thermal damage of metal targets is deduced.

2009-09-30

379

Basic equations of the nuclear quasiparticle-phonon model  

Energy Technology Data Exchange (ETDEWEB)

A system of basic equations of the nuclear quasiparticle-phonon model for even-even spherical nuclei is derived in the general form. The transition to the approximate system of equations used in numerical calculations is performed. It is demonstrated that a wide class of diagrams can be summed up in the framework of the nuclear quasiparticle phonon model. The model is shown to have large possibilities for a more detailed description of the nuclear characteristics at intermediate and high excitation energies.

Voronov, V.V.; Solov' ev, V.G.

1983-10-01

380

Special phonons and superconductivity in the hexagonal tungsten bronzes  

International Nuclear Information System (INIS)

Neutron scattering measurements on single crystals of hexagonal tungsten bronzes M/sub 0.33/WO3 reveal low-frequency, relatively dispersionless phonon branches which can be associated with the vibrations of the metal atoms M in the large open channels they occupy in the crystal structure. An analysis based on Eliashberg theory shows that the strong dependence of the superconducting transition temperature on the species M arises from these special phonons

1979-11-19

 
 
 
 
381

Nanomechanical vibrating wire resonator for phonon spectroscopy in Helium  

CERN Multimedia

We demonstrate how to build a vibrating wire resonator for phonon excitation in liquid helium. The resonator is designed as a nanoscopic mechanically flexible beam machined out of a semiconductor/metal-hybrid. Quenching of the mechanical resonance around 100 MHz by phonon excitation in liquid ^4He at 4.2 K is shown. First measurements operating the nano-resonator in a dilution of ^3He/^4He at 30 mK are presented.

Kraus, A L; Blick, R H; Kraus, Andreas; Erbe, Artur; Blick, Robert H.

1999-01-01

382

Optomechanical quantum information processing with photons and phonons  

CERN Multimedia

We describe how strong resonant interactions in multimode optomechanical systems can be used to induce controlled nonlinear couplings between single photons and phonons. Combined with linear mapping schemes between photons and phonons, these techniques provide a universal building block for various classical and quantum information processing applications. Our approach is especially suited for nano-optomechanical devices, where strong optomechanical coupling on a single photon level is within experimental reach.

Stannigel, K; Habraken, S J M; Bennett, S D; Lukin, M D; Zoller, P; Rabl, P

2012-01-01

383

Electromagnetic excitation of the two-phonon giant dipole resonance  

International Nuclear Information System (INIS)

The nuclear response of 136Xe and 208Pb to electromagnetic excitation was studied in peripheral, near-relativistic heavy-ion collisions. Large cross sections were observed for the one-phonon and two-phonon isovector giant dipole resonance. The results, in particular the unexpectedly large strength found for the double giant dipole resonance, are discussed and compared to that of other recent measurements. (orig.)

1994-03-07

384

Properties of interface phonon spectra in complicated cylindrical nanosystem  

Directory of Open Access Journals (Sweden)

Full Text Available The spectra of two types of interface phonons (top and side optical) are studied within the framework of dielectric continuum model for combined nanoheterosystems consisting of semiconductor cylindrical quantum dots inside the cylindrical quantum wire placed into dielectric or semiconductor medium. The dependencies of both types of interface phonon energies on the quasiwave numbers and geometric parameters of nanosystem are calculated and analysed.

O.M.Voitsekhivska; A.M.Gryschyk

2007-01-01

385

A quantum simulator for electron-phonon interactions  

CERN Document Server

We propose an approach for quantum simulation of electron-phonon interactions using Rydberg states of cold atoms and ions. We will show how systems of cold atoms and ions can be mapped onto electron-phonon systems of the Su-Schrieffer-Heeger and extended Holstein type. We discuss how properties of the simulated Hamiltonian can be tuned and how to read physically relevant properties from the simulator.

Hague, J P

2011-01-01

386

Electron and Phonon in Neutron Scattering of Semiconductor Crystals  

Science.gov (United States)

An interaction of electron with harmonic, localized and anharmonic fields has been taken to develop the theory of neutron scattering. The Fourier transformed electron Green's function is evaluated by Zubarev equation of motion technique of quantum dynamics and Dyson equation approach. The expression of Debye-Waller factor (DWF) has been obtained from electron phonon linewidth. The study of its (DWF) effect on differential scattering cross-section through temperature, electron phonon coupling constant and excitations has been investigated in this approach.

Gairola, S. C.

2013-08-01

387

Phonon Mediated Transresistivity in a Double Layer Composite Fermion System  

CERN Multimedia

We consider the fractional drag in a double layer system of two-dimensional electrons in the half-filled lowest Landau level. At sufficiently large inter-layer separations the drag is dominated by exchange of acoustic phonons and exhibits novel temperature and inter-layer distance dependences. At low temperatures the phonon mediated drag is strongly enhanced with respect to the case of zero magnetic field.

Khveshchenko, D V

1998-01-01

388

A cryogenic phonon detector to search for dark matter particles  

Energy Technology Data Exchange (ETDEWEB)

The systematic investigation of the thermal and electrical properties of neutron transmutation doped (NTD) Ge at low temperatures and the development of a detector to search for weakly interacting massive particles (WIMP's), predicted by some theories to make up to 90 percent of the matter in the universe, is presented. We have fabricated NTD Ge phonon sensors operated on a dilution refrigerator near 20 mK. The thermal and electrical properties of NTD Ge were investigated first. The zero bias resistance was found to be governed by variable range hopping, but the nonlinearity of the current-voltage characteristics indicated significant hot electron effects near 20 mK. A detailed investigation of hot-electron effects in NTD Ge is described. NTD Ge sensors were found to be very sensitive to high energy phonons generated by interactions of Ge with alpha-particles and photons. The mean absorption length of the high energy phonons in NTD Ge was found to be about 500 microns. In order to use these phonon sensors in conjunction with a target crystal, we developed a bonding technique using a Au-Ge eutectic. The bonds were found to be mechanically strong, thermally cyclable, and more transparent to high energy phonons than conventional silver-filled epoxies. The eutectic bonding technique was also found to leave the thermal and electrical properties of NTD Ge unchanged. We describe ionization signals observed in pure Ge target crystals, generated by the interaction of Ge with alpha-particles and photons; these ionization signals were observed simultaneously with phonon signals from the NTD Ge sensors. Such simultaneous signals can be used to reject unwanted background events, which is an important requirement for a WIMP detector. Finally, we describe the design and testing of a 60 g Ge detector to which six phonon sensors were attached. Simultaneous phonon and ionization signals were observed when irradiating the crystal with photons from Am-241.

Wang, Ning.

1991-01-01

389

Electron-phonon coupling and Peierls transition in metallic nanotubes  

CERN Multimedia

We reexamine the putative Peierls transition in a (5,5) metallic nanotube. We show that the conduction electrons at the Fermi level do not couple to the longitudinal acoustic phonon but rather to a folded-in graphene zone edge phonon having the proper Kekule modulation symmetry. The calculation for the mean-field transition temperature gives 15 K, a value comparable to previous estimates. We discuss the significance of this transition temperature.

Sedeki, A; Bourbonnais, C

1999-01-01

390

X-ray studies of phonon softening in tise2.  

Science.gov (United States)

The charge-density-wave transition in TiSe (2), which results in a commensurate (2x2x2) superlattice at temperatures below approximately 200 K, presumably involves softening of a zone-boundary phonon mode. For the first time, this phonon-softening behavior has been examined over a wide temperature range by synchrotron x-ray thermal diffuse scattering. PMID:11329327

Holt, M; Zschack, P; Hong, H; Chou, M Y; Chiang, T C

2001-04-23

391

Frictional drag between quantum wells mediated by phonon exchange  

DEFF Research Database (Denmark)

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 lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation d. When l(ph) exceeds the critical value, the drag rate is dominated by coupling through an electron-phonon collective mode localized in the vicinity of the electron layers. We argue that the coupled electron-phonon mode may be observable for realistic parameters. Our theory is in good agreement with experimental results for the temperature, density, and d dependence of the drag rate.

BØnsager, M.C.; Flensberg, Karsten

1998-01-01

392

The moment of inertia and energy spectrum for IBM intrinsic ground-state single phonon and double phonon excited-states  

International Nuclear Information System (INIS)

The IBM intrinsic ground-state, single phonon and double phonon excited-states are given, where the double phonon states are different linear combinations of single phonon states. The Hamiltonian is defined as both SU(3) limit and pairing interaction. Using cranking theory, the moment of inertia and energy spectrum for these states are calculated, and rational analytical expressions obtained. As an example, the rationality of these results is also discussed for 168Er.

1993-01-01

393

Size-selective generation of coherent acoustic phonons in semiconductor nanocrystals  

Science.gov (United States)

The propagation of subpicosecond laser pulses generally leads to the production of coherent phonon fields, the amplitude of which is resonantly enhanced when the laser central energy is tuned near an electronic resonance [1]. Here, we describe pump-probe experiments at the absorption edge of CdTexSe1-x nanocrystals revealing a coherent confined acoustic mode with a frequency that varies rapidly with the central wavelength of the laser pulse. The sample consists of nanocrystals of an average radius of 0.4 nm and 10mode frequency increases from 20 cm-1 to 30 cm-1 and its damping from 3 cm-1 to 8 cm-1 as the laser central wavelength moves from 805 nm to 770 nm across the optical gap. Given that the absorption edge of a nanocrystal depends strongly on the particle size, the acoustic mode behavior is attributed to a selective process by which nanocrystals of a particular size are resonantly excited by pulses of a particular central energy. These results are consistent with spontaneous Raman scattering data on similar systems [2]. [1] T. E. Stevens, J. Hebling, J. Kuhl and R. Merlin, Phys. Status Solidi (b) 215, 81 (1999). [2] L. Saviot, B. Champagnon, E. Duval and A. I. Ekimov, Phys. Rev. B 57, 341 (1998). Supported by AFOSR-MURI and NSF.

Bragas, Andrea V.; Aku-Leh, Cynthia; Zhao, Jimin; Merlin, Roberto

2002-03-01

394

Mesoscopic hydro-thermodynamics of phonons  

Directory of Open Access Journals (Sweden)

Full Text Available A generalized Hydrodynamics, referred to as Mesoscopic Hydro-Thermodynamics, of phonons in semiconductors is presented. It involves the descriptions of the motion of the quasi-particle density and of the energy density. The hydrodynamic equations, which couple both types of movement via thermo-elastic processes, are derived starting with a generalized Peierls-Boltzmann kinetic equation obtained in the framework of a Non-Equilibrium Statistical Ensemble Formalism, providing such Mesoscopic Hydro-Thermodynamics. The case of a contraction in first order is worked out in detail. The associated Maxwell times are derived and discussed. The densities of quasi-particles and of energy are found to satisfy coupled Maxwell-Cattaneo-like (hyperbolic) equations. The analysis of thermo-elastic effects is done and applied to investigate thermal distortion in silicon mirrors under incidence of high intensity X-ray pulses in FEL facilities. The derivation of a generalized Guyer-Krumhansl equation governing the flux of heat and the associated thermal conductivity coefficient is also presented.

Aurea R. Vasconcellos; A. R. B. de Castro; C. A. B. Silva; Roberto Luzzi

2013-01-01

395

Light scattering by surface phonons in crystals  

International Nuclear Information System (INIS)

[en] 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] A teoria de espalhamento inelastico de luz por fonons acusticos de superficie num cristal homogeneo, e apresentada. As funcoes de Green sao determinadas atraves do uso de um metodo classico de resposta linear e usado para avaliar a secao de choque de Brillouin. Os modos acusticos sao tirados das solucoes da equacao de onda acustica com condicoes de contorno apropriadas. Sao analizados dois mecanismos de espalhamento de luz: corrugacao da superficie e efeito elasto-optico do nucleo, atraves da derivacao de campos oticos que satisfazem, ambas, as equacoes de onda opto-acustica e as condicoes de contorno eletromagneticas. Nao sao impostas restricoes quanto ao angulo de incidencia da luz. Sao apresentadas tambem algumas linhas representativas de Brillouin e seus comportamentos sao discutidos. (A.C.A.S.)

1980-12-01

396

Structural features of dielectric oxide laser ceramics  

Energy Technology Data Exchange (ETDEWEB)

The relation between the transport characteristics of subterahertz thermal phonons and the structural features of singlephase dielectric crystalline laser ceramics based on cubic oxides synthesised in different technological regimes is studied. The effect of plastic deformation on the formation of the grain structure and intergrain layers (boundaries), as well as on the thermophysical, acoustic, optical, and laser characteristics of the materials is analysed. (active media)

Kaminskii, Alexandr A; Taranov, A V; Khazanov, E N; Akchurin, M Sh

2012-10-31

397

Coherent and phonon-assisted tunnelling in asymmetric double barrier resonant tunnelling structures  

International Nuclear Information System (INIS)

We present a theory for calculating the phonon-assisted tunnelling current in asymmetric double barrier resonant tunnelling structures (DBRTS), in which all of the phonon modes including the interface modes and the confined bulk-like LO phonons and the conduction band nonparabolicity are considered. An important physical picture about coherent and phonon-assisted tunnelling is given. The coherent tunnelling current can be directly determined by both the width of the resonant level and the peak value of the transmission coefficient at the resonant level. The phonon-assisted tunnelling current mainly comes from electron interaction with higher frequency interface phonons (especially the interface phonons localised at either interface of the left barrier). Phonon-assisted tunnelling makes a significant contribution to the valley current. The subband nonparabolicity strongly influences on electron-phonon scattering and current-to-voltage characteristics. A specially designed asymmetric DBRTS may have an improved performance over the symmetric DBRTS. Copyright (2000) CSIRO Australia

1998-12-08

398

Coherent longitudinal acoustic phonons in three-dimensional supracrystals of cobalt nanocrystals.  

UK PubMed Central (United Kingdom)

We use broadband picosecond acoustics to detect longitudinal acoustic phonons with few-gigahertz frequency in three-dimensional supracrystals (with face-centered cubic lattice) of 7 nm cobalt nanocrystal spheres. In full analogy with atomic crystals, where longitudinal acoustic phonons propagate with the speed of sound through coherent movements of atoms of the lattice out of their equilibrium positions, in these supracrystals atoms are replaced by (uncompressible) nanocrystals and atomic bonds by coating agents (carbon chains) that act like mechanical springs holding together the nanocrystals. By repeating the measurements at different laser angles of incidence it was possible to accurately determine both the index of refraction of the supracrystal (n = 1.26 ± 0.03) and the room-temperature longitudinal speed of sound (vs= 1235 ± 12 m/s), which is quite low due to the heavy weight of the spheres (with respect to atoms in a crystal) and the soft carbon chains (with respect to atomic bonds). Interestingly, the speed of sound inside the supracrystal was found to dramatically increase by decreasing the sample temperature due to a change in the stiffness of the dodecanoic acid chains which coat the Co nanocrystals.

Lisiecki I; Polli D; Yan C; Soavi G; Duval E; Cerullo G; Pileni MP

2013-10-01

399

Coherent Longitudinal Acoustic Phonons in Three-Dimensional Supracrystals of Cobalt Nanocrystals.  

UK PubMed Central (United Kingdom)

We use broadband picosecond acoustics to detect longitudinal acoustic phonons with few-gigahertz frequency in three-dimensional supracrystals (with face-centered cubic lattice) of 7 nm cobalt nanocrystal spheres. In full analogy with atomic crystals, where longitudinal acoustic phonons propagate with the speed of sound through coherent movements of atoms of the lattice out of their equilibrium positions, in these supracrystals atoms are replaced by (uncompressible) nanocrystals and atomic bonds by coating agents (carbon chains) that act like mechanical springs holding together the nanocrystals. By repeating the measurements at different laser angles of incidence it was possible to accurately determine both the index of refraction of the supracrystal (n = 1.26 ± 0.03) and the room-temperature longitudinal speed of sound (vs= 1235 ± 12 m/s), which is quite low due to the heavy weight of the spheres (with respect to atoms in a crystal) and the soft carbon chains (with respect to atomic bonds). Interestingly, the speed of sound inside the supracrystal was found to dramatically increase by decreasing the sample temperature due to a change in the stiffness of the dodecanoic acid chains which coat the Co nanocrystals.

Lisiecki I; Polli D; Yan C; Soavi G; Duval E; Cerullo G; Pileni MP

2013-09-01

400

Stress effects on Raman measurements of pulsed laser annealed silicon  

Energy Technology Data Exchange (ETDEWEB)

It has recently been shown that the front surface region of the silicon lattice is severely strained during pulsed laser irradiation. This uniaxial strain reduces the symmetry of the front surface region, resulting in additional shifts and splittings of the phonon frequency and changes in the Raman scattering tensor. It is shown that, for the case of pulsed laser irradiation, the phonon frequency is increased, and the 3-fold degenerate optical phonon is split into a singlet and a doublet. The changes in the Raman scattering tensor make it non-symmetric, and generally invalidate the technique used by Compaan et al. to determine the cross section experimentally. The complications introduced by the presence of stress during pulsed laser annealing, coupled with the temperature dependence of the optical and Raman tensors, make a simple interpretation of the Stokes to anti-Stokes ratio in terms of lattice temperature extremely unreliable. 19 references, 1 figure.

Jellison, G.E. Jr.; Wood, R.F.

1984-01-01

 
 
 
 
401

Laser Refractometry for Biomedical Diagnostics  

International Science & Technology Center (ISTC)

Application of a New Method of Laser Refractometry for Determining the Stimulating Action Mechanisms of Optical Therapy, for Disease Diagnostics and Treatment Efficiency Evaluating of Pneumonia and Helminthosis

402

Intersubband Raman Laser  

Energy Technology Data Exchange (ETDEWEB)

An intersubband Raman laser has been realized in an artificial GaAs/AlGaAs three-level quantum-well structure. A CO{sub 2} laser in resonance with the one-to-three level transition is used as the pump, while the lasing emission occurs via the three-to-two level transition. The one-to-two level spacing is designed to be in resonance with the AlAs-like longitudinal optical phonon mode, favoring the Raman process. This work presents an alternative mechanism for realizing intersubband lasers and opens up new possibilities in reaching the far infrared region and achieving room-temperature operation. {copyright} 2001 American Institute of Physics.

Liu, H. C.; Cheung, Iva W.; SpringThorpe, A. J.; Dharma-wardana, C.; Wasilewski, Z. R.; Lockwood, D. J.; Aers, G. C.

2001-06-04

403

Intersubband Raman Laser  

International Nuclear Information System (INIS)

An intersubband Raman laser has been realized in an artificial GaAs/AlGaAs three-level quantum-well structure. A CO2 laser in resonance with the one-to-three level transition is used as the pump, while the lasing emission occurs via the three-to-two level transition. The one-to-two level spacing is designed to be in resonance with the AlAs-like longitudinal optical phonon mode, favoring the Raman process. This work presents an alternative mechanism for realizing intersubband lasers and opens up new possibilities in reaching the far infrared region and achieving room-temperature operation. [copyright] 2001 American Institute of Physics.

2001-06-04

404

``Q-deformation and energy deficit in liquid helium phonon spectrum``  

Energy Technology Data Exchange (ETDEWEB)

The instability of the phonon spectrum in liquid Helium for T < 1 K is a well established experimental fact. We discuss the role of q-deformation as a possible mechanism to supply the energy deficit that forbidden one-phonon decay into two phonons when the constant {gamma} in the phonon anomalous dispersion relation ({omega}{sup ph} = c{sub 0} p(1 - {gamma}p{sup 2})) is positive, through the analysis of three-phonon processes in a q-phonons gas. (author). 19 refs.

Rodrigues, L.M.C.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]|[Turin Univ. (Iran, Islamic Republic of). Dipt. di Fisica Teorica; Wulck, S. [Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica

1996-09-01

405

Geometry dependence of the phonon modes in CdSe nanorods  

International Nuclear Information System (INIS)

We investigated the geometry dependence of the first-order Raman scattering band of CdSe nanorods experimentally. The band has an asymmetric shape and its position and exact line shape depend on the nanorod diameter and aspect ratio. The band consists of contributions from the longitudinal optical phonon and surface optical phonon modes. While the position of the longitudinal optical phonon related band is purely diameter dependent, the position of the surface optical phonon band depends on the nanorod's aspect ratio. This can be explained by the influence of phonon confinement and a model for surface optical phonons in nanorods.

2009-01-28

406

Phonon spectrum and interaction between nanotubes in single-walled carbon nanotube bundles at high pressures and temperatures  

International Nuclear Information System (INIS)

The Raman spectra of single-walled carbon nanotubes at temperatures up to 730 K and pressures up to 7 GPa have been measured. The behavior of phonon modes and the interaction between nanotubes in bundles have been studied. It has been found that the temperature shift of the vibrational G mode is completely reversible, whereas the temperature shift of radial breathing modes is partially irreversible and the softening of the modes and narrowing of phonon bands are observed. The temperature shift and softening of radial breathing modes are also observed when samples are irradiated by laser radiation with a power density of 6.5 kW/mm2. The dependence of the relative frequency ?/?0 for G+ and G? phonon modes on the relative change A0/A in the triangular lattice constant of bundles of nanotubes calculated using the thermal expansion coefficient and compressibility coefficient of nanotube bundles shows that the temperature shift of the G mode is determined by the softening of the C-C bond in nanotubes. An increase in the equilibrium distances between nanotubes at the breaking of random covalent C-C bonds between nanotubes in bundles of nanotubes is in my opinion the main reason for the softening of the radial breathing modes.

2012-01-01

407

Polarons and bipolarons in strongly interacting electron-phonon systems  

CERN Multimedia

The Holstein Hubbard and Holstein t--J models are studied for a wide range of phonon frequencies, electron--electron and electron--phonon interaction strengths on finite lattices with up to ten sites by means of direct Lanczos diagonalization. Previously the necessary truncation of the phononic Hilbert space caused serious limitations to either very small systems (four or even two sites) or to weak electron--phonon coupling, in particular in the adiabatic regime. Using parallel computers we were able to investigate the transition from `large' to `small' polarons in detail. By resolving the low--lying eigenstates of the Hamiltonian and by calculating the spectral function we can identify a polaron band in the strong--coupling case, whose dispersion deviates from the free--particle dispersion at low and intermediate phonon frequencies. For two electrons (holes) we establish the existence of bipolaronic states and discuss the formation of a bipolaron band. For the 2D Holstein t--J model we demonstrate that the f...

Wellein, G; Fehske, H

1995-01-01

408

Two-octupole-phonon states in 146,148Gd  

International Nuclear Information System (INIS)

The so-called 'two-octupole-phonon states' in 146,148Gd are theoretically analyzed by using the Dyson boson mapping method. In our analyses, the free ground state of 146Gd is treated as doubly closed shell since Z=64 is rather good subshell closure. The starting collective multi-phonon space that we take consists of collective octupole phonons and collective monopole pairing phonons for 146Gd. Additionally correlated particle-pair modes with J?0 are included in the multi-phonon space for 148Gd. The effective Hamiltonian used is constituted by a Woods-Saxon-type single-particle potential, an octupole-octupole force for particle-hole modes and a surface-delta interaction for particle-pair and hole-pair modes. The numerical calculation can considerably well reproduce the octupole collectivity shown by experiments for 146,148Gd. It is shown that the Dyson boson mapping method is useful for such a complicated system as 148Gd. (author).

1996-01-01

409

Phonon Pulse Shape Discrimination in SuperCDMS Soudan  

CERN Document Server

SuperCDMS is the next phase of the Cryogenic Dark Matter Search experiment, which measures both phonon and charge signals generated by particle recoils within a germanium target mass. Charge signals are employed both in the definition of a fiducial volume and in the rejection of electron recoil background events. Alternatively, phonons generated by the charge carriers can also be used for the same two goals. This paper describes preliminary efforts to observe and quantify these contributions to the phonon signal and then use them to reject background events. A simple analysis using only one pulse shape parameter shows bulk electron recoil vs. bulk nuclear recoil discrimination to the level of 1:10^3 (limited by the statistics of the data), with little degradation in discrimination ability down to at least 7 keV recoil energy. Such phonon-only discrimination can provide a useful cross-check to the standard discrimination methods, and it also points towards the potential of a device optimized for a phonon-only ...

Hertel, S A

2011-01-01

410

Nuclear resonant scattering with phonon excitation using synchrotron radiation  

International Nuclear Information System (INIS)

[en] The feasibility of the measurement of phonon energy spectra by utilizing Moessbauer radiation sources was pointed out soon after the discovery of Moessbauer effect, but actually, this measurement was very difficult. The Moessbauer spectroscopy using synchrotron radiation possesses many features, and one of them is the variability of the incident X-ray energy for nuclear excitation. It is considered that the measurement of phonon spectra by utilizing nuclear resonant scattering is feasible by using the synchrotron radiation, for which the spectroscopy to meV with a Si monochromator is performed. By improving the resolution of a Si monochromator, the phonon energy spectra in which elastic and inelastic components were separated were successfully observed for the first time. The measurement of the phonon energy spectra of ?-Fe foils utilizing the nuclear resonant excitation of 57Fe was carried out at the TRISTAN injection storage ring of National Laboratory for High Energy Physics. The experimental setup and the experimental method and the results are reported. It was confirmed that the observed inelastic scattering is due to phonon excitation. (K.I.)

1995-01-01

411

Spin waves in terbium. II. Magnon-phonon interaction  

International Nuclear Information System (INIS)

[en] The selection rules for the linear couplings between magnons and phonons propagating in the c direction of a simple basal-plane hcp ferromagnet are determined by general symmetry considerations. The acoustic-optical magnon-phonon interactions observed in the heavy-rare-earth metals have been explained by Liu as originating from the mixing of the spin states of the conduction electrons due to the spin-orbit coupling. We find that this coupling mechanism introduces interactions which violate the selection rules for a simple ferromagnet. The interactions between the magnons and phonons propagating in the c direction of Tb have been studied experimentally by means of inelastic neutron scatttering. The magnons are coupled to both the acoustic- and optical-transverse phonons. By studying the behavior of the acoustic-optical coupling, we conclude that it is a spin-mixed-induced coupling as proposed by Liu. The coupled magnon--transverse-phonon system for the c direction of Tb is analyzed in detail, and the strengths of the couplings are deduced as a function of wave vector by combining the experimental studies with the theory

1975-07-01

412

Probing thermomechanics at the nanoscale: impulsively excited pseudosurface acoustic waves in hypersonic phononic crystals.  

UK PubMed Central (United Kingdom)

High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system's excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths.

Nardi D; Travagliati M; Siemens ME; Li Q; Murnane MM; Kapteyn HC; Ferrini G; Parmigiani F; Banfi F

2011-10-01

413

Probing thermomechanics at the nanoscale: impulsively excited pseudosurface acoustic waves in hypersonic phononic crystals.  

Science.gov (United States)

High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system's excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426

Nardi, Damiano; Travagliati, Marco; Siemens, Mark E; Li, Qing; Murnane, Margaret M; Kapteyn, Henry C; Ferrini, Gabriele; Parmigiani, Fulvio; Banfi, Francesco

2011-09-22

414

Laser induced luminescence spectroscopy on solid substrates  

International Nuclear Information System (INIS)

This paper provides an overview of the photophysical processes and analytical applications of high-resolution luminescence spectroscopy using solid samples. Experimental results are discussed within the framework of a theoretical model involving isolated guest molecules weakly interacting with the host solid substrate. Examples are given to illustrate the spectral structure of luminescence spectra exhibiting zero-phonon lines and phonon wings. Effects of experimental parameters such as temperature are discussed. Analytical considerations on the various laser-based techniques in fluorescence and phosphorescence analysis are reviewed and discussed in detail.

1988-11-04

415

Ultrafast X-ray diffraction of laser-irradiated crystals  

CERN Document Server

Coherent acoustic phonons have been observed in the X-ray diffraction of a laser-excited InSb crystal. Modeling based on time-dependent dynamical diffraction theory has allowed the extraction of fundamental constants, such as the electron-acoustic phonon coupling time. A dedicated beamline for time-resolved studies has been developed at the Advanced Light Source with special considerations toward high transmission, low scattering and a wide photon energy range. The facility combines a bend magnet beamline, time-resolved detectors and a femtosecond laser system.

Heimann, P A; Kang, I; Johnson, S; Missalla, T; Chang, Z; Falcone, R W; Schönlein, R W; Glover, T E; Padmore, H A

2001-01-01

416

Ultrafast X-ray diffraction of laser-irradiated crystals  

International Nuclear Information System (INIS)

[en] Coherent acoustic phonons have been observed in the X-ray diffraction of a laser-excited InSb crystal. Modeling based on time-dependent dynamical diffraction theory has allowed the extraction of fundamental constants, such as the electron-acoustic phonon coupling time. A dedicated beamline for time-resolved studies has been developed at the Advanced Light Source with special considerations toward high transmission, low scattering and a wide photon energy range. The facility combines a bend magnet beamline, time-resolved detectors and a femtosecond laser system

2001-07-21

417

Phonon coupling of water monomers in a solid nitrogen matrix  

Science.gov (United States)

The infrared absorption spectra of the H2O, HDO, and D2O monomers isolated in solid N2 have been recorded at various temperatures between 4 and 30 K. A study of the absorption features of the ?1, ?2, and ?3 vibrational modes for each monomer shows their optical line shapes to be strongly temperature dependent. For all three modes, a decrease in the absorption amplitude and a proportional broadening of the linewidth was observed with increasing temperature, while the integrated absorbance remained constant. These observations were explained in terms of phonon coupling, by which high frequency intramolecular modes decay by exciting matrix phonons. Fits of the linewidth for the lowest frequency ?2 vibrational mode to the predicted vibrational relaxation rate in a solid medium gave average phonon mode frequencies consistent with the Debye frequency for solid N2.

Wu, L.; Lambo, R.; Tan, Y.; Liu, A.-W.; Hu, S.-M.

2013-03-01

418

Electromagnetic excitation of phonons at C(001) surfaces  

Energy Technology Data Exchange (ETDEWEB)

The photon-phonon coupling at C(001)-(2 x 1) surfaces and its manifestation in far-infrared reflectance anisotropy spectra (FIR-RAS) are theoretically investigated. We solve the coupled system of equations for the electromagnetic field and lattice vibrations, described within the adiabatic bond charge model (ABCM), with the method of expansion into bulk phonon and photon modes. The calculated FIR-RAS exhibit resonances associated with zone-center surface phonons in good agreement with available HREELS experiments and predictions of vibrational modes for diamond (001)-(2 x 1) surfaces from ABCM and ab initio calculations. Interestingly, the reflectance anisotropy spectra for a C(001)-(2 x 1) surface turn out to be qualitatively different from the spectra for a Si(001)-(2 x 1) surface, reported previously.

Perez-Sanchez, F L [Escuela de Ciencias, Universidad Autonoma ' Benito Juarez' de Oaxaca, Avenida Universidad S/N, Ex-Hacienda de Cinco Senores, Ciudad Universitaria, Oaxaca de Juarez, Oaxaca, 68120 (Mexico); Perez-Rodriguez, F, E-mail: fperez@sirio.ifuap.buap.m [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Post. J-48, Puebla 72570 (Mexico)

2009-09-02

419

Phonon coupling of water monomers in a solid nitrogen matrix.  

UK PubMed Central (United Kingdom)

The infrared absorption spectra of the H2O, HDO, and D2O monomers isolated in solid N2 have been recorded at various temperatures between 4 and 30 K. A study of the absorption features of the ?1, ?2, and ?3 vibrational modes for each monomer shows their optical line shapes to be strongly temperature dependent. For all three modes, a decrease in the absorption amplitude and a proportional broadening of the linewidth was observed with increasing temperature, while the integrated absorbance remained constant. These observations were explained in terms of phonon coupling, by which high frequency intramolecular modes decay by exciting matrix phonons. Fits of the linewidth for the lowest frequency ?2 vibrational mode to the predicted vibrational relaxation rate in a solid medium gave average phonon mode frequencies consistent with the Debye frequency for solid N2.

Wu L; Lambo R; Tan Y; Liu AW; Hu SM

2013-03-01

420

Spin-Phonon Coupling in High-Tc Copper Oxides  

Science.gov (United States)

Band calculations on HgBa2CuO4 and La(2-x)SrxCuO4 with phonon and spin-waves within the CuO planes show that partial gaps are created at various energies depending on wavelengths. Spin and phonon gaps appear at different energies when the modulations are along [1,1,0], while they are at the same energy for modulations along [1,0,0]. It is shown that the ability to form gaps and antiferromagnetic waves is correlated with the strength of the interaction parameter ?sf for spin fluctuations. Many unusual properties of the high-TC oxides can be understood from spin-phonon coupling.

Jarlborg, T.

2006-09-01

 
 
 
 
421

Longer InN phonon lifetimes in nanowires.  

UK PubMed Central (United Kingdom)

We present a Raman scattering study of the anharmonic phonon decay of the [Formula: see text], [Formula: see text] and E(1)(LO) phonons in InN nanowires over the 80-400 K temperature range. While the temperature-dependent anharmonic decay in the nanowires is similar to that found for bulk InN, the background contribution to the phonon lifetime is strongly reduced as a result of the improved crystalline quality. High-resolution measurements reveal a remarkably long lifetime of the [Formula: see text] mode. From the comparison between the [Formula: see text] frequencies measured in the nanowires with those of the thin film we obtain the deformation potentials for the [Formula: see text] mode.

Domènech-Amador N; Cuscó R; Artús L; Stoica T; Calarco R

2012-02-01

422

High temperature superconductivity and electron-phonon coupling  

International Nuclear Information System (INIS)

[en] The electron-phonon coupling in a copper oxide based high temperature superconductor has been estimated by taking the anisotropic crystal structure into account. From the Debye temperature of a superconducting material, information about the role of phonons in its superconducting mechanism can be investigated. The void-free acoustic Debye temperature, ?D, of various cuprate high temperature superconductors estimated using the acoustic technique was found to be between 250 and 500 K. The electron-phonon coupling constant was estimated from the transition temperature Tc using the standard BCS theory and also the 2D van Hove scenario with related characteristic temperature. The van Hove scenario seems to explain high temperature superconductivity in the cuprates better than the standard three-dimensional BCS model

2005-01-01

423

Probing confined acoustic phonons in free standing small gold nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Polarized and depolarized spectra from gold (Au) nanoparticles of different sizes are investigated in the small size range, between 3 and 7 nm, using low frequency Raman spectroscopy. Acoustic vibrations of the free-standing Au nanoparticles are demonstrated with frequencies ranging from 5 to 35 cm{sup -1}, opening the way to the development of the acoustic resonators. A blue shift in the phonon peaks along with the broadening is observed with a decrease in particle size. Comparison of the measured frequencies with vibrational dynamics calculation and an examination as from the transmission electron microscopy results ascertain that the low frequency phonon modes are due to acoustic phonon quantization. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar (l = 2) vibrations of the spheroidal mode due to plasmon mediated acoustic vibrations in Au nanoparticles.

Mankad, Venu; Jha, Prafulla K. [Department of Physics, M. K. Bhavnagar University, Bhavnagar 364 001 (India); Ravindran, T. R. [Material Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)

2013-02-21

424

A computer program to calculate phonon shapes using planar dispersion  

International Nuclear Information System (INIS)

[en] A program is written to calculate the shapes of phonons scanned by a triple axis neutron spectrometer. The program takes into account the population factor, 1/omega and (Q.xi) terms of the scattering cross section and the resolution function as formulated by Cooper and Nathans to calculate the intensity at each point of the scan. It is assumed that the dispersion relation does not have a strong curvature so that one can make use of planar dispersion. The fact that the resolution ellipsoid is highly elliptic has been taken care of to speed up the computation of intensity. This computer program has been used to calculate the shapes of phonons in KNO3 for obtaining true phonon frequencies. (auth.)

1979-01-01

425

Anharmonic phonon-electron problem in high temperature superconductors  

International Nuclear Information System (INIS)

[en] Owing to the fact that effects of anharmonicities on the electron-phonon problem in high temperature superconductors are relatively unknown, the problem is solved with the help of double time thermodynamic electron-Green's function theory. The ab initio development of the theory includes a very general and newly formulated Hamiltonian which involves the contributions due to harmonic-, anharmonic-, localized phonons and electron-phonon and electrons. This almost approximation-free technique is capable of automatically predicting the formation and decay of Cooper pairs in the superconducting crystals. Expressions for the life times and density of states of electrons are obtained in the new framework which are responsible to describe a large number of dynamical properties of high temperature superconductors. (author)

2001-01-01

426

Phonons is cage-structured compounds probed by Moessbauer nuclei  

International Nuclear Information System (INIS)

[en] Nuclear resonance inelastic scattering (NRIS) is a unique tool to investigate element-specific phonon density of states by Moessbauer nuclei. This technique enables us to investigate the dynamics of the specific atoms which contain Moessbauer nuclei. For recent times, much attention to the potential of thermoelectricity has been paid in cage-structured compounds such as filled skutterudites, clathrates and so on. Since the proposal of 'phonon-glass-electron-crytal' model, thermal insulation due to phonons has been expected as one of the important parameters in their thermoelectricity. We applied NRIS using several nuclei to the series of cage-structured compounds. We mainly show the recent results of filled skutterudites here. (author)

2010-01-01

427

Electron-phonon interaction in Graphite Intercalation Compounds  

CERN Document Server

Motivated by the recent discovery of superconductivity in Ca- and Yb-intercalated graphite (CaC$_{6}$ and YbC$_{6}$) and from the ongoing debate on the nature and role of the interlayer state in this class of compounds, in this work we critically study the electron-phonon properties of a simple model based on primitive graphite. We show that this model captures an essential feature of the electron-phonon properties of the Graphite Intercalation Compounds (GICs), namely, the existence of a strong dormant electron-phonon interaction between interlayer and $\\pi ^{\\ast}$ electrons, for which we provide a simple geometrical explanation in terms of NMTO Wannier-like functions. Our findings correct the oversimplified view that nearly-free-electron states cannot interact with the surrounding lattice, and explain the empirical correlation between the filling of the interlayer band and the occurrence of superconductivity in Graphite-Intercalation Compounds.

Boeri, L; Giantomassi, M; Andersen, O K; Boeri, Lilia; Bachelet, Giovanni B.; Giantomassi, Matteo; Andersen, Ole K.

2007-01-01

428

Electron-phonon interaction and superconductivity in metallic hydrogen  

International Nuclear Information System (INIS)

[en] The energy bands of face-centered-cubic hydrogen at a r/sub s/ value of 1.64 a.u. were calculated. This corresponds to a density of 3.65 x 1023 hydrogen atoms/cm3 and would require pressures of the order of a megabar to achieve. The electron-phonon matrix element has been calculated using the formalism of Gaspari and Gyorffy and parameters derived from the above calculations. Using various theoretical estimates of the phonon properties of metallic hydrogen the electron-phonon coupling constant or mass enhancement factor, lambda, and the superconducting transition temperature have been calculated. Those calculations indicate that this system would be a superconductor with a transition temperature in excess of 200 K

1976-04-30

429

Spinon-phonon interaction in algebraic spin liquids  

Science.gov (United States)

Motivated by a search for experimental probes to access the physics of fractionalized excitations called spinons in spin liquids, we study the interaction of spinons with lattice vibrations. We consider the case of algebraic spin liquid, when spinons have fermionic statistics and a Dirac-like dispersion. We establish the general procedure for deriving spinon-phonon interactions, which is based on symmetry considerations. The procedure is illustrated for four different algebraic spin liquids: ?-flux and staggered-flux phases on a square lattice, ?-flux phase on a kagome lattice, and zero-flux phase on a honeycomb lattice. Although the low-energy description is similar for all these phases, different underlying symmetry groups lead to a distinct form of spinon-phonon interaction Hamiltonian. The explicit form of the spinon-phonon interaction is used to estimate the attenuation of ultrasound in an algebraic spin liquid. The prospects of the sound attenuation as a probe of spinons are discussed.

Serbyn, Maksym; Lee, Patrick A.

2013-05-01

430

Electron phonon coupling and carrier lifetimes in III-nitride ternary semiconductors  

Science.gov (United States)

III-nitride semiconductors have a large bandgap and find applications in high power devices, in which the thermal management of energy generated becomes a key issue. The transfer of energy from the energetic carriers to the lattice is determined by the electron-phonon coupling for the crystal. In this work, we present our results on the electron-phonon coupling in ternary and quaternary semiconductors. The full phonon dispersion and electron-phonon coupling is determined using ab-initio methods. We then evaluate the carrier lifetimes for the emission of LO phonons by including the full zone and not only the zone center phonons. We expect that the treatment of the electron-phonon coupling effects over the full Brillouin zone could be critical for III-nitride thermal management, and will be directly compared to the results where only the zone center phonons are considered.

Tandon, Nandan; Kassebaum, P. G.; Ram-Mohan, L. R.

2012-02-01

431

Lasing and antibunching of optical phonons in semiconductor double quantum dots  

Science.gov (United States)

We theoretically propose optical phonon lasing in a double quantum dot (DQD) fabricated on a semiconductor substrate. No additional cavity or resonator is required. An electron in the DQD is found to be coupled to only two longitudinal optical phonon modes that act as a natural cavity. When the energy level spacing in the DQD is tuned to the phonon energy, the electron transfer is accompanied by the emission of the phonon modes. The resulting non-equilibrium motion of electrons and phonons is analyzed by the rate equation approach based on the Born-Markov-Secular approximation. We show that lasing occurs for pumping the DQD via electron tunneling at a rate much larger than the phonon decay rate, whereas phonon antibunching is observed in the opposite regime of slow tunneling. Both effects disappear by an effective thermalization induced by the Franck-Condon effect in a DQD fabricated in a suspended carbon nanotube with strong electron-phonon coupling.

Okuyama, R.; Eto, M.; Brandes, T.

2013-08-01

432

Entropy production in hot-phonon energy conversion to electric potential  

Science.gov (United States)

We apply phonon and electron nonequilibrium-population statistical entropy analysis to the recently introduced phonon energy to electric potential conversion heterobarrier with its height optimized for optical phonon absorption under steady electric current. The entropy production rates for phonon and electron subsystems depend on their interaction kinetics and occupancy distributions, indicating the direction of the processes. Under upstream thermal equilibrium among electrons and acoustic and optical phonons, we predict an upper limit of 42% energy conversion for GaAs heterobarrier at 300 K, while the reported Monte Carlo prediction of 19% efficiency is below this limit. We show that for upstream electrons in thermal equilibrium with the acoustic phonons, while under supply of hot optical phonons, the conversion efficiency increases significantly, making integration of the barrier into optical phonon emitting circuits and devices very attractive.

Shin, Seungha; Kaviany, Massoud

2013-08-01

433

Surface lattice dynamics and electron-phonon interaction in ultrathin Bi(111) film.  

UK PubMed Central (United Kingdom)

The surface phonon and electron-phonon interactions in the two-dimensional topological insulator Bi(111) film are calculated, including the spin-orbit coupling from density-functional perturbation theory. By analyzing the zone-center phonons, an anomalous phonon hardening of two Raman modes, Eg and A1g, in ultrathin films is found and is explained by considering the redistribution of the charge density on the surface of the semimetallic Bi. Surface phonon band structures and the surface phonon density of states are given, and we find that softening and hardening of surface phonon modes occur simultaneously in ultrathin Bi film, but the softening may dominate over the hardening. The calculated electron-phonon coupling constant ? for Bi(111) film is much larger than that for the bulk, which might induce surface-localized superconductivity in this two-dimensional topological insulator.

Huang GQ; Yang J

2013-05-01

434

Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3  

Directory of Open Access Journals (Sweden)

Full Text Available A first principles calculation of the lattice dynamical properties of superconducting MgCNi3 has been performed using density functional perturbation theory (DFPT). The calculated phonon dispersion curves and phonon density of states have been compared with inelastic x-ray scattering (IXS) and inelastic neutron scattering (INS) measurements. We show for the first time that phonon dispersion curves for MgCNi3 in whole Brillouin zone are positive (stable phonon modes) and in good agreement with the experimental data. The phonon DOS shows absence of phonon density of states at zero energy unlike earlier calculations. There is a good agreement between calculated and experimental electron-phonon parameter and superconducting transition temperature. The Eliasberg function is quantitatively as well as qualitatively different from the phonon density of states. The lattice specific heat and Debye temperature do not show any anomalous behaviour.

Prafulla K. Jha; Sanjay D. Gupta; Sanjeev K. Gupta

2012-01-01

435

Choosing actions.  

UK PubMed Central (United Kingdom)

Actions that are chosen have properties that distinguish them from actions that are not. Of the nearly infinite possible actions that can achieve any given task, many of the unchosen actions are irrelevant, incorrect, or inappropriate. Others are relevant, correct, or appropriate but are disfavored for other reasons. Our research focuses on the question of what distinguishes actions that are chosen from actions that are possible but are not. We review studies that use simple preference methods to identify factors that contribute to action choices, especially for object-manipulation tasks. We can determine which factors are especially important through simple behavioral experiments.

Rosenbaum DA; Chapman KM; Coelho CJ; Gong L; Studenka BE

2013-01-01

436

Choosing Actions  

Science.gov (United States)

Actions that are chosen have properties that distinguish them from actions that are not. Of the nearly infinite possible actions that can achieve any given task, many of the unchosen actions are irrelevant, incorrect, or inappropriate. Others are relevant, correct, or appropriate but are disfavored for other reasons. Our research focuses on the question of what distinguishes actions that are chosen from actions that are possible but are not. We review studies that use simple preference methods to identify factors that contribute to action choices, especially for object-manipulation tasks. We can determine which factors are especially important through simple behavioral experiments.

Rosenbaum, David A.; Chapman, Kate M.; Coelho, Chase J.; Gong, Lanyun; Studenka, Breanna E.

2013-01-01

437

Band structures and localization properties of aperiodic layered phononic crystals  

International Nuclear Information System (INIS)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

1000-01-00

438

Band structures and localization properties of aperiodic layered phononic crystals  

Energy Technology Data Exchange (ETDEWEB)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

2012-03-15

439

Band structures and localization properties of aperiodic layered phononic crystals  

Science.gov (United States)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Yan, Zhi-Zhong; Zhang, Chuanzeng

2012-03-01

440

Imaging the Electron-Phonon Interaction on the Atomic Scale  

Science.gov (United States)

New STM-based spectroscopic imaging technique, direct real-space imaging of electron-phonon interaction parameter ?, was demonstrated using the combination of STM and inelastic electron tunneling spectroscopy (IETS) for thin Pb islands epitaxially grown on 7x7 reconstructed Si(111). We found that ? increases when the electron scattering at the Pb/Si(111) interface is diffuse and decreases when the electron scattering becomes specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well. Reference: Igor Altfeder, K. A. Matveev, A. A. Voevodin, ``Imaging the Electron-Phonon Interaction on the Atomic Scale'', Physical Review Letters 109, 166402 (2012).

Altfeder, Igor; Matveev, Konstantin; Voevodin, Andrey

2013-03-01

 
 
 
 
441

Impurity Scattering in Luttinger Liquid with Electron-Phonon Coupling  

International Nuclear Information System (INIS)

We study the influence of electron-phonon coupling on electron transport through a Luttinger liquid with an embedded weak scatterer or weak link. We derive the renormalization group (RG) equations which indicate that the directions of RG flows can change upon varying either the relative strength of the electron-electron and electron-phonon coupling or the ratio of Fermi to sound velocities. This results in the rich phase diagram with up to three fixed points: an unstable one with a finite value of conductance and two stable ones, corresponding to an ideal metal or insulator.

2011-03-01

442

Imaging the electron-phonon interaction at the atomic scale.  

Science.gov (United States)

Thin Pb films epitaxially grown on 7×7 reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that ? increases when the electron scattering at the Pb/Si(111) interface is diffuse and decreases when the electron scattering is specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well. PMID:23215098

Altfeder, Igor; Matveev, K A; Voevodin, A A

2012-10-16

443

The inverted pendulum, interface phonons and optic Tamm states  

CERN Multimedia

The propagation of waves in periodic media is related to the parametric oscillators. We transpose the possibility that a parametric pendulum oscillates in the vicinity of its unstable equilibrium positions to the case of waves in lossless unidimensional periodic media. This concept formally applies to any kind of wave. We apply and develop it to the case of phonons in realizable structures and evidence new classes of phonons. Discussing the case of electromagnetic waves, we show that our concept is related to optic Tamm states one but extends it to periodic Optic Tamm state.

Combe, Nicolas

2011-01-01

444

Phase transitions and electron-phonon coupling in platinum hydride.  

UK PubMed Central (United Kingdom)

Structural phase transitions and superconducting properties of platinum hydride under pressure are explored through the first-principles calculations based on the density functional theory. Three new low-pressure phases (Pm3m, Cmmm and P4/nmm) are predicted, and all of them are metallic and stable relative to decomposed cases. The superconducting critical temperature of two high-pressure phases correlates with the electron-phonon coupling. The presence of soft modes induced by Kohn anomalies and the hybridization between H and Pt atoms result in the strong electron-phonon coupling. Our results have major implications for other transition metal hydrides under pressure.

Zhang C; Chen XJ; Lin HQ

2012-01-01

445

Acoustic-phonon-assisted hydrogen diffusion in metal hydrides  

Science.gov (United States)

The theory for acoustic-phonon-induced hydrogen diffusion in model metal hydrides is presented. The general expression for the total transition probability Wpp' is obtained. The analytical expressions for Wpp' are calculated in the high- and low-temperature limits for both the dispersive and nondispersive acoustic phonons and are compared with other calculations. The diffusion rate is found to be temperature independent at low temperature and temperature dependent at higher temperature. Both the phonon emission and absorption processes contribute towards the diffusion rate at high temperature while only emission process contributes at low temperature. The phonon dispersion increases the preexponential factor and decreases the migration energy. The numerical calculations are carried out for PdHx (PdDx) and NbHx (NbDx). The migration energies Em and the preexponential factors D0 are estimated graphically. The diffusion rate increases with increase of temperature up to 170 K for PdHx (PdDx) and up to 100 K for NbHx (NbDx). At higher temperatures the diffusion rate shows an activated behavior. The inverse isotope effect is found for PdHx (PdDx) at low temperature, while it is absent at high temperature. No inverse isotope effect is found for NbHx (NbDx). At low temperature the Em and D0 for H diffusion increase with increase of temperature in both PdHx (PdDx) and NbHx (NbDx). At higher temperatures, Em and D0 become almost constant for PdHx (PdDx), while these again increase with temperature in NbHx (NbDx). It is found that the hydrogen diffuses faster in the bcc matrix than in the fcc matrix. A comparison with the results for optical-phonon-induced diffusion revealed that the acoustic-phonon contribution is larger at low temperature while the contributions of both the acoustic and optical phonons is of the same order at high temperature. The migration energies are also calculated combining the contributions of both the acoustic and optical phonons, and these are found in reasonable agreement with the experimental data.

Dhawan, L. L.; Prakash, S.

1984-03-01

446

Electronic Contributions to the Phonon Damping in Metals  

International Nuclear Information System (INIS)

An imaginary part of the dielectric matrix is derived based on a first order perturbation expansion of the valence electron states in a local potential model of the crystal. The results are used to estimate the electronic contributions to the phonon damping in aluminum and lead. The corrections which have been obtained are of the same order of magnitude at small phonon momenta as the damping earlier calculated for the free electrons. However, the discrepancies between the theoretical and experimental results still remain. The major contribution to damping seems to originate in anharmonic effects, even at 80 deg K

1968-01-01

447

Band gap engineering in simultaneous phononic and photonic crystal slabs  

Energy Technology Data Exchange (ETDEWEB)

We discuss the simultaneous existence of phononic and photonic band gaps in two types of phononic crystals slabs, namely periodic arrays of nanoholes in a Si membrane and of Si nanodots on a SiO{sub 2} membrane. In the former geometry, we investigate in detail both the boron nitride lattice and the square lattice with two atoms per unit cell (these include the square, triangular and honeycomb lattices as particular cases). In the latter geometry, some preliminary results are reported for a square lattice. (orig.)

Djafari Rouhani, B.; Pennec, Y.; Vasseur, J.O.; Hassouani, Y.El; Li, C.; Akjouj, A. [Universite de Lille1 Sciences et Technologies, Cite Scientifique, Institut d' Electronique, de Microelectronique et de Nanotechnologie, UMR CNRS 8520, Villeneuve d' Ascq (France); Boudouti, E.H.El; Bria, D. [Universite de Lille1 Sciences et Technologies, Cite Scientifique, Institut d' Electronique, de Microelectronique et de Nanotechnologie, UMR CNRS 8520, Villeneuve d' Ascq (France); Universite d' Oujda, Laboratoire de Dynamique et d' Optique des Materiaux, Faculte des Sciences, Oujda (Morocco)

2011-06-15

448

Band gap in hypersonic surface phononic lattice of nickel pillars  

Science.gov (United States)

Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed.

Trzaskowska, A.; Mielcarek, S.; Sarkar, J.

2013-10-01

449

Far infrared absorption by acoustic phonons in titanium dioxide nanopowders  

CERN Multimedia

We report spectral features of far infrared electromagnetic radiation absorption in anatase TiO2 nanopowders which we attribute to absorption by acoustic phonon modes of nanoparticles. The frequency of peak excess absorption above the background level corresponds to the predicted frequency of the dipolar acoustic phonon from continuum elastic theory. The intensity of the absorption cannot be accounted for in a continuum elastic dielectric description of the nanoparticle material. Quantum mechanical scale dependent effects must be considered. The absorption cross section is estimated from a simple mechanical phenomenological model. The results are in plausible agreement with the absorption being due to a sparse layer of charge on the nanoparticle surface.

Murray, D B; Saviot, L; Pighini, C; Millot, N; Aymes, D; Liu, H L; Murray, Daniel B.; Netting, Caleb H.; Saviot, Lucien; Pighini, Catherine; Millot, Nadine; Aymes, Daniel; Liu, Hsiang-Lin

2006-01-01

450