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1

By exploiting recent developments associated with coupled microcavities, we introduce the concept of the PT-symmetric phonon laser with balanced gain and loss. This is accomplished by introducing gain to one of the microcavities such that it balances the passive loss of the other. In the vicinity of the gain-loss balance, a strong nonlinear relation emerges between the intracavity-photon intensity and the input power. This then leads to a giant enhancement of both optical pressure and mechanical gain, resulting in a highly efficient phonon-lasing action. These results provide a promising approach for manipulating optomechanical systems through PT-symmetric concepts. Potential applications range from enhancing mechanical cooling to designing phonon-laser amplifiers. PMID:25126921

Jing, Hui; Özdemir, S K; Lü, Xin-You; Zhang, Jing; Yang, Lan; Nori, Franco

2014-08-01

2

Realization of phonon laser with femtosecond technology

One of the most desirable properties of phonon system is sound amplification by stimulated emission of phonon radiation, coined as SASER or called phonon laser or acoustic laser, which is the acoustic counterpart of LASER. Phonon stimulated emission, or sound amplification, has been previously observed fro several occasions in extremely low temperatures, however a lasing behavior of the phonon oscillators has never been established. It is also desirable to build a phonon laser operating at room temperature. Here we present an optically pumped nano-sized phonon laser with an output acoustic wavelength of 9.3 nm, operating at room temperature. The nano phonon laser is composed by InGaN/GaN multiple-quantum-wells (MQWs). By using femtosecond ultraviolet pulses as pumping sources, coherent acoustic phonon amplification with large acoustic gain was observed. When the induced acoustic gain is higher than the acoustic loss due to its traveling nature, a clear laser-like threshold behavior was observed, which resembles a pulsed optical laser. This demonstration will open a new way toward nano-ultrasonics.

Sun, Chi-Kuang; Huang, Yue-Kai; Chern, Gia-Wei

2002-06-01

3

Nonequilibrium phonon effects in midinfrared quantum cascade lasers

We investigate the effects of nonequilibrium phonon dynamics on the operation of a GaAs-based midinfrared quantum cascade laser over a range of temperatures (77-300 K) via a coupled ensemble Monte Carlo simulation of electron and optical-phonon systems. Nonequilibrium phonon effects are shown to be important below 200 K. At low temperatures, nonequilibrium phonons enhance injection selectivity and efficiency by drastically increasing the rate of interstage electron scattering from the lowest injector state to the next-stage upper lasing level via optical-phonon absorption. As a result, the current density and modal gain at a given field are higher and the threshold current density lower and considerably closer to experiment than results obtained with thermal phonons. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.

Shi, Y. B.; Knezevic, I.

2014-09-01

4

Phonon confinement in silicon nanowires synthesized by laser ablation

International Nuclear Information System (INIS)

The phonon confinement effect was investigated by Raman measurements for Si nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) catalyst and for SiNWs thermally oxidized at 700-1000 oC. The Si optical phonon peak for SiNWs, unlike that for bulk Si, showed a downshift and an asymmetric broadening. Thermal oxidation caused a further downshift and broadening. These phenomena can be explained by the phonon confinement effect due to the decrease in the diameter of the Si core of the SiNWs. It was additionally found that excess oxidation caused an upshift of the optical phonon peak due to compressive stress

5

Mode competition and anomalous cooling in a multimode phonon laser.

We study mode competition in a multimode "phonon laser" comprised of an optical cavity employing a highly reflective membrane as the output coupler. Mechanical gain is provided by the intracavity radiation pressure, to which many mechanical modes are coupled. We calculate the gain and find that strong oscillation in one mode suppresses the gain in other modes. For sufficiently strong oscillation, the gain of the other modes actually switches sign and becomes damping, a process we call "anomalous cooling." We demonstrate that mode competition leads to single-mode operation and find excellent agreement with our theory, including anomalous cooling. PMID:25083628

Kemiktarak, Utku; Durand, Mathieu; Metcalfe, Michael; Lawall, John

2014-07-18

6

Mode competition and anomalous cooling in a multimode phonon laser

We study mode competition in a multimode "phonon laser" comprised of an optical cavity employing a highly reflective membrane as the output coupler. Mechanical gain is provided by the intracavity radiation pressure, to which many mechanical modes are coupled. We calculate the gain, and find that strong oscillation in one mode suppresses the gain in other modes. For sufficiently strong oscillation, the gain of the other modes actually switches sign and becomes damping, a process we call "anomalous cooling." We demonstrate that mode competition leads to single-mode operation and find excellent agreement with our theory, including anomalous cooling.

Kemiktarak, Utku; Metcalfe, Michael; Lawall, John

2014-01-01

7

International Nuclear Information System (INIS)

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 radiationseloped free-electron laser radiations

8

Inter-Landau level scattering and LO-phonon emission in Terahertz quantum cascade laser

Digital Repository Infrastructure Vision for European Research (DRIVER)

A Terahertz Quantum Cascade Laser (THz QCL) structure based on a bound to continuum and LO-phonon extraction stage is studied under a strong magnetic field. Two series of power oscillations as a function of magnetic field are observed. Comprehensive simulations of the lifetimes allow the first series to be assigned to interface roughness (elastic) and the second to LO phonon scattering (inelastic) of hot carriers in an excited Landau level, previously unobserved in terahertz QCL. We demonstra...

Pe?re?-laperne, Nicolas; Vaulchier, Louis-anne; Guldner, Yves; Bastard, Ge?rald; Scalari, Giacomo; Giovannini, Marcella; Faist, Je?ro?me; Vasanelli, Angela; Dhillon, Sukhdeep; Sirtori, Carlo

2007-01-01

9

International Nuclear Information System (INIS)

It is experimentally shown for the first time that by the effect of the feed-up laser pulse of 100 fs duration on the silicon target the consecutive structural transitions of the substance into the new crystalline and liquid metallic phase occur both during the laser pulse feed-up and after 0.1-103 ps, depending on the material excitation conditions. The thresholds of the observed structural transitions are determined and the phonon nodes, responsible for therefore, are identified. The structural transitions dynamics in the silicon by the 01.-103 ps times is described within the frames of the model of the phonon modes instability, originating due to the plasma electron-hole effect and also due to the intra- and intermode phonon-phonon anharmonic interactions

10

Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening

Ultrashort optical pulses can be used both to create fundamental quasiparticles in crystals and to change their properties. In noble metals, femtosecond lasers induce bond hardening, but little is known about its origin and consequences. Here we simulate ultrafast laser excitation of silver at high fluences. We compute laser-excited potential-energy surfaces by all-electron ab initio theory and analyze the resulting quantum lattice dynamics. We also consider incoherent lattice heating due to electron-phonon interactions using the generalized two-temperature model. We find phonon hardening, which we attribute to the excitation of s electrons. We demonstrate that this may result in phonon vacuum squeezed states with an optimal squeezing factor of 0.001 at the L-point longitudinal mode. This finding implies that ultrafast laser-induced bond hardening may be used as a tool to manipulate the quantum state of opaque materials, where, so far, the squeezing of phonons below the zero-point motion has only been realized in transparent crystals by a different mechanism. On the basis of our finding, we further propose a method for directly measuring bond hardening.

Cheenicode Kabeer, Fairoja; Grigoryan, Naira S.; Zijlstra, Eeuwe S.; Garcia, Martin E.

2014-09-01

11

Selective cap opening in carbon nanotubes driven by laser-induced coherent phonons

International Nuclear Information System (INIS)

We demonstrate the possibility of a selective nonequilibrium cap opening of carbon nanotubes as a response to femtosecond laser excitation. By performing molecular dynamics simulations based on a microscopic electronic model we show that the laser-induced ultrafast structural changes differ dramatically from the thermally induced dimer emission. Ultrafast bond weakening and simultaneous excitation of two coherent phonon modes of different frequencies, localized in the spherical caps and cylindrical nanotube body, are responsible for the selective cap opening

12

Laser-Ultrasonic Investigation on Lamb Waves in Two-Dimensional Phononic Crystal Plates

In this paper, laser-ultrasonic non-destructive testing is used to investigate the propagation of Lamb waves in two-dimensional phononic crystal plates. The bandgaps are experimentally observed for low-order Lamb wave modes. The influence of crucial parameters such as the periodical arrangement of scatterers on bandgaps is discussed in detail. The finite element simulations further agree well with the results of the laser-ultrasonic investigation.

Wang, Jing Shi; Cheng, Ying; Xu, Xiao Dong; Liu, Xiao Jun

2014-06-01

13

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a theoretical study of the carrier relaxation in a quantum cascade laser (QCL) subjected to a strong magnetic field. Both the alloy (GaInAs) disorder effects and the Frohlich interaction are taken into account when the electron energy differences are tuned to the longitudinal optical (LO) phonon energy. In the weak electron-phonon coupling regime, a Fermi's golden rule computation of LO phonon scattering rates shows a very fast non-radiative relaxation channel for ...

Chen, Yu; Regnault, N.; Ferreira, R.; Zhu, Bang-fen; Bastard, G.

2009-01-01

14

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

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

16

Phonon-assisted upconversion in 1.64-?m Er:YAG lasers

International Nuclear Information System (INIS)

The authors studied the potential capabilities of Er:YAG as a solid-state laser material suitable for diode laser pumping at 1.47 ?m. Their experiments indicate that the laser operation of Er:YAG at 1.64 ?m is severely limited by a competitive deexcitation process and phonon-assisted upconversion, which affects the laser threshold and slope efficiency. The authors measured directly the effect of this upconversion process on the lifetime and population density of the upper laser levels in Er:YAG and have used these values in a cavity rate equation model to predict the laser performance parameters. The predictions agree well with the experimental results

17

Picosecond X-ray diffraction studies of laser-excited acoustic phonons in InSb

International Nuclear Information System (INIS)

We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm2. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak. (orig.)

18

International Nuclear Information System (INIS)

We study the scattering mechanisms driving electron-phonon relaxation in thin gold films via pump-probe time-domain thermoreflectance. Electron-electron scattering can enhance the effective rate of electron-phonon relaxation when the electrons are out of equilibrium with the phonons. In order to correctly and consistently infer electron-phonon coupling factors in films on different substrates, we must account for the increase in steady-state lattice temperature due to laser heating. Our data provide evidence that a thermalized electron population will not directly exchange energy with the substrate during electron-phonon relaxation, whereas this pathway can exist between a non-equilibrium distribution of electrons and a non-metallic substrate

19

Phonon-mediated off-resonant coupling effects in semiconductor quantum-dot lasers

The impact of non-resonant background emitters in semiconductor quantum-dot microcavity lasers is addressed within theoretical investigations based on the solution of the von Neumann equation. Off-resonant coupling between emitter resonances and the cavity mode is enabled via phonons, which are included in the von Neumann dynamics by an effective Lindblad contribution. The results show enhanced coherent emission from non-resonantly coupled quantum dots, while the frequently used phenomenological cavity feeding mechanism only enhances the thermal component of the emission.

Florian, Matthias; Gartner, Paul; Gies, Christopher; Jahnke, Frank

2013-03-01

20

Phonon-mediated off-resonant coupling effects in semiconductor quantum-dot lasers

International Nuclear Information System (INIS)

The impact of non-resonant background emitters in semiconductor quantum-dot microcavity lasers is addressed within theoretical investigations based on the solution of the von Neumann equation. Off-resonant coupling between emitter resonances and the cavity mode is enabled via phonons, which are included in the von Neumann dynamics by an effective Lindblad contribution. The results show enhanced coherent emission from non-resonantly coupled quantum dots, while the frequently used phenomenological cavity feeding mechanism only enhances the thermal component of the emission. (paper)

21

Mid-IR transitions of trivalent neodymium in low phonon laser crystals

Mid-IR Nd 3+ transitions perspective for laser oscillation were analyzed in the CaGa 2S 4, PbGa 2S 4, and PbCl 2 crystals and compared with low phonon fluoride crystals. Fluorescence kinetics decay of the high-lying 4G 7/2 and 4G 5/2; 2G 7/2 and low-lying 4I J levels and its temperature dependence in the range of 13-295 K were measured. For 5 ?m mid-IR transitions of Nd 3+ the radiative relaxation rates are found to be several times higher and multiphonon relaxation (MR) rates are several times lower in lead and calcium thiogallate crystals compared to low phonon fluoride crystals. MR rate dependence on the Nd 3+ to the nearest ligand distance R0 is established experimentally and analyzed in the frame of point-charge model of nonlinear theory of multiphonon relaxation. Mid-IR Nd 3+ 4-5.5 ?m fluorescence spectra of 4I i- 4I j transitions perspective for laser oscillation were measured for the first time in the studied crystals.

Orlovskii, Yurii V.; Basiev, Tasoltan T.; Pukhov, Konstantin K.; Doroshenko, Maxim E.; Badikov, Valery V.; Badikov, Dmitry V.; Alimov, Olimkhon K.; Polyachenkova, Marina V.; Dmitruk, Leonid N.; Osiko, Vyacheslav V.; Mirov, Sergey B.

2007-05-01

22

Extreme ultraviolet laser action in plasmas

International Nuclear Information System (INIS)

The development of a laser operating in the extreme ultraviolet or X-ray spectral regions remains an outstanding problem of current technology. Despite the many proposals, no demonstration of significant gain on a transition in this region has yet been reported. The constraints introduced by decreasing wavelength are increasingly severe, demanding high pump power in a system with a relatively short lifetime. In consequence, much attention has been paid to the use of plasma, often generated by high power laser irradiation, as the gain medium. The various avenues by which laser action in plasmas has been explored is outlined, with a view to identifying those which seem at present to offer promise of success. Particular attention is given to the recombination scheme with an emphasis on a recent demonstration of gain. (author)

23

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have investigated the time resolved backscattering of high frequency phonons (greater-or-equal, slanted 285 GHz) at laser annealed silicon surfaces at low temperatures. It is found that the scattering off the free surface becomes predominantly specular up to frequencies well above 285 GHz and that the anomalous transmission into liquid helium (Kapitza effect) is strongly reduced.

Mok, Erich; Burger, Susanne; Do?ttinger, Siegfried; Lassmann, Kurt; Eisenmenger, Wolfgang

1986-01-01

24

We have investigated terahertz (THz) emission from lithium ternary chalcopyrite crystals LiInSe2, LiGaSe2, LiInS2, and LiGaS2 that were illuminated by 1560 nm femtosecond pump laser pulses. Monocyclic THz emission caused by nonlinear optical effects was initially observed in all the illuminated crystals. Narrow-band THz emission from the coherent phonons were observed in LiInSe2 (2.87 THz) and LiGaSe2 (2.60 and 3.45 THz). These phonon modes were most likely caused by impulsive stimulated Raman scattering.

Takeya, K.; Takemoto, Y.; Kawayama, I.; Murakami, H.; Matsukawa, T.; Yoshimura, M.; Mori, Y.; Tonouchi, M.

2010-07-01

25

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

26

Time-Resolved X-Ray Diffraction from Coherent Phonons during a Laser-Induced Phase Transition

International Nuclear Information System (INIS)

Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion. (c) 1999 The American Physical Society

27

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.

28

Room-temperature laser action at 4.3--4.4 {micro}m in CaGa{sub 2}S{sub 4}:Dy{sup 3+}

Energy Technology Data Exchange (ETDEWEB)

The authors report room-temperature mid-IR laser operation in a new low-phonon-frequency, non-hygroscopic host crystal CaGa{sub 2}S{sub 4} (calcium thiogallate). Laser action at 4.31 {micro}m on the {sup 6}H{sub 11/2} {r_arrow}{sup 6}H{sub 13/2} transition of trivalent dysprosium was achieved with a slope efficiency of 1.6%.

Nostrand, M; Page, R H; Payne, S A; Krupke, W F; Schunemann

1999-04-22

29

International Nuclear Information System (INIS)

We have theoretically and numerically studied nitride-based quantum well (QW) laser structures. More specifically, we have used a QW made with III-nitride where the width of the barrier region is large relative to the electron mean free path, and we have calculated the electron surface capture velocities by considering an electron flux which is captured into the well region. The process is assisted by the emission of the longitudinal optical phonons as predicted by the hybrid (HB) model. The results of surface capture velocities via the emission of HB phonons are compared to the emission of the dielectric continuum phonons (Zakhleniuk et al 1999 Phys. Status Solidi a 176 79). Our investigation shows that the two different phonon models predict almost the same results for the non-retarded limit. Furthermore, the surface capture velocities strongly depend on the size of the structure and the heterostructure materials. Lastly, a comparison to the recent experimental values shows that our model could accurately describe the experimentally measured parameters of the quantum capture processes

30

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

31

The short pulsed, tunable output from the Dutch free electron laser FELIX, coupled with a 45 T pulsed magnet has been used to measure the non-radiative decay rates between Landau levels in n-type InAs/GaSb quantum wells. The decay rate is 2 p/sup -1/ when the cyclotron resonance energy, E/sub CR/ = E/sub LO/ = 30 meV, and only slightly less, 0.8 ps/sup -1/ when E/sub CR/ = 2E/sub LO/ when the principal relaxation pathway is the emission of multiple longitudinal optical (LO) phonons. (12 refs).

Bradley, I V; Murdin, B N; Wells, J P R; Clarke, D G; Stradling, R A; Pidgeon, C R

2001-01-01

32

We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal. PMID:18643683

Kehr, S C; Cebula, M; Mieth, O; Härtling, T; Seidel, J; Grafström, S; Eng, L M; Winnerl, S; Stehr, D; Helm, M

2008-06-27

33

Theory of electron-optical phonon interactions in quantum wells and quantum well laser structures

International Nuclear Information System (INIS)

This thesis is concerned with the study of the quantum processes, including carder transitions and carrier capture, mediated by optical phonons in heterostructure quantum wells based on II-VI and III-V semiconductors and their alloys. The optical phonons are described by three different models namely, a model based on the bulk phonon approximation, the dielectric continuum (DC) model and the hybrid (HB) model. In order to create a discrete energy spectrum for the electrons with energies greater than the barrier energy and in order to reduce electron-phonon scattering rates, we concentrate on the situation in which the heterostructure is confined between metallic barriers. The essential features describing optical phonons are first discussed for the three models. In particular, in the case of the hybrid model we show that the hybridons form an orthogonal set of modes and are characterised by the property of non-locality, which is identified as the source of the mechanical boundary conditions. Calculations are then presented for the intersubband and intrasubband transition rates in the lowest electron subbands by the emission of DC and hybrid phonons in the case of the GaAs/AlAs heterostructure between two metal barriers. The dependence of the transition rates on the distance between the metallic barriers suggests that such, structures could be engineered so as to result in reduced scattering rates. A comparison of the predictions of total scattering rates via the hybrins of total scattering rates via the hybrid model with those via the DC model shows that the DC and the hybrid models are very close in this case. This near-agreement between the two models prompts an investigation on the existence of a sum-rule for the total scattering rates which we discuss in conjunction with a derivation of the rates in terms of Green functions. A sizeable part of this thesis is concerned with the evaluation of electron capture rates for electrons with energies at the bottom of the first and second subbands above the barrier energy which make transitions into the quantum well. We emphasise these calculations for the AlN/GaN quantum well system and for the alloy system GaAs/AlxGa1-xAs. The capture rate within the context of a given model is defined as the transition rate into all available subbands within the quantum well by the emission of either (a) bulk phonons of the well material or (b) the confined and interface phonons of the DC model or (c) the hybridons of the hybrid model (HB). The predictions of the three models are displayed and compared. We find that sharp peaks emerge at regular intervals of increasing well width corresponding to resonances in the electron states as a subband from above the barrier drops into the well. Other peaks arise when the electrons can begin to make transitions into the highest subband in the well. These peaks correspond to optical phonon emission thresholds and so depend on the model used to describe the optical phonon modes. The comparison between the DC model and hybrid model in the case of electron capture shows that the two models are in good agreement with regard to the magnitudes of the electron and phonon resonances and the regular intervals that occur. A different approach is required when the barrier thickness is much larger than the well width. In order to deal with this situation for the process of capture we consider an electron flux injected electrically with energy within the continuum above the barrier. This is subsequently captured into the AlN/GaN and II-VI quantum wells by the emission of bulk and DC phonons. The situation requires the identification of new capture parameters and we show that capture velocity is the appropriate parameter in this case. Calculations of capture velocities against the well width are presented for the DC and bulk phonons. (author)

34

The invention provides an efficient, compact means of generating blue laser light at a wavelength near .about.493+/-3 nm, based on the use of a laser diode-pumped Yb-doped laser crystal emitting on its zero phonon line (ZPL) resonance transition at a wavelength near .about.986+/-6 nm, whose fundamental infrared output radiation is harmonically doubled into the blue spectral region. The invention is applied to the excitation of biofluorescent dyes (in the .about.490-496 nm spectral region) utilized in flow cytometry, immunoassay, DNA sequencing, and other biofluorescence instruments. The preferred host crystals have strong ZPL fluorecence (laser) transitions lying in the spectral range from .about.980 to .about.992 nm (so that when frequency-doubled, they produce output radiation in the spectral range from 490 to 496 nm). Alternate preferred Yb doped tungstate crystals, such as Yb:KY(WO.sub.4).sub.2, may be configured to lase on the resonant ZPL transition near 981 nm (in lieu of the normal 1025 nm transition). The laser light is then doubled in the blue at 490.5 nm.

Krupke, William F. (Pleasanton, CA); Payne, Stephen A. (Castro Valley, CA); Marshall, Christopher D. (Livermore, CA)

2001-01-01

35

Laser air-jet engine: the action of shock waves at low laser pulse repetition rates

International Nuclear Information System (INIS)

The impact and thermal action of laser sparks on the reflector of a laser engine in which the propulsion is produced by repetitively pulsed radiation is estimated. It is shown that for a low pulse repetition rate, the thermal contact of a plasma with the reflector and strong dynamic resonance loads are inevitable. These difficulties can be surmounted by using the method based on the merging of shock waves at a high pulse repetition rate. (laser applications)

36

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

37

Random electric fields and coherent phonon excitation in C60 films by femtosecond laser pulses

The ultrafast relaxation of excitations in a C60 thin film was probed in the energy range 1.6 - 3.4 eV by pump- supercontinuum probe technique with 40 fs time resolution. The relaxation rate shows pronounced spectral dependence with maximum at 2 eV in the region of photoinduced darkening and at 2.4 eV in the region of photoinduced bleaching. It is found that the ultrafast relaxation rate decreases with increasing pumping pulse intensity. The shape of the optical density variation at zero time delay in the region of interband transitions at 2.3 - 3.4 eV is similar to the shape of the second derivative of the stationary absorption spectrum. We propose that this may indicate the creation of a random electric field in the sample during the absorption of the pump pulse. We suggest that the decrease of the relaxation rate with the increase of pumping pulse intensity results from extra-heating of the carriers in hu and t1u bands due to internal conversion from higher excited states, which are populated by two-step photon absorption of the intense pump pulse. Coherent excitation of phonons in the 60 - 300 cm-1 frequency range were detected over a wide spectral probe range. An oscillation with a frequency of 118 cm-1 indicates that the nonequilibrium dimerization of C60 molecules takes place following optical excitation. The full splitting of the Hg(1) intramolecular oscillation mode is observed clearly, which demonstrates that a strong deformation of the molecules upon photon absorption takes place.

Farztdinov, V. M.; Kovalenko, S. A.; Dobryakov, A. L.; Lozovik, Yurii E.; Matveets, Juru A.; Marowsky, Gerd

1998-04-01

38

Nonthermal luminescence of the tungsten surface under the action of pulse laser radiation

International Nuclear Information System (INIS)

Laser-induced radiation outlet of defects on the surface and W surface destruction are studied. Nonthermal luminescence on the samples opposite side terms of laser pulse action has been recorded. Outlet of defects to the surface arising from thermoelastic strain, appearing in laser action area, can be among the reasons of the luminescence

39

Investigation of a cooled electron-beam-controlled CO laser. I. Laser action pure carbon monoxide

Energy Technology Data Exchange (ETDEWEB)

The first experimental investigation was made of the threshold, energy, temporal, and spectral characteristics of a pulsed cooled electron-beam-controlled laser utilizing pure carbon monoxide. The experiments were carried out in a system having an active volume of approx.5 liters at an active gas temperature of approx.100 /sup 0/K and a density up to 1.0 amagat. The excitation duration was varied in the range 30--300 ..mu..sec. Laser action was observed in the spectral range 5.1--5.5 ..mu.. and, as the pump energy was increased, the spectrum broadened into short-wavelength range. It was found that the efficiency of an electron-beam-controlled pure carbon monoxide laser did not exceed 10%. The measured parameters of the electron-beam-controlled carbon monoxide laser did not agree with the results of theoretical calculations.

Basov, N.G.; Danilychev, V.A.; Ionin, A.A.; Kazakevich, V.S.; Kovsh, I.B.; Poletaev, N.L.

1979-06-01

40

International Nuclear Information System (INIS)

Kelvin waves--helical waves on quantized vortex lines--are the normal modes of vortices in a superfluid. At zero temperature, the only dissipative channel of vortex dynamics is phonon emission. Starting with the hydrodynamic action, we derive the Hamiltonian of vortex-phonon interaction, thereby reducing the problem of the interaction of Kelvin waves with sound to inelastic elementary excitation scattering. On the basis of this formalism, we calculate the rate of sound radiation by superfluid turbulence at zero temperature and estimate the value of short-wavelength cutoff of the turbulence spectrum

41

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of phase modulation (resulting in a chirp of an ultrashort laser pulse) on the generation of a coherent A1 phonon in Te was studied. The amplitude of coherent oscillations was found to depend on the sign and value of the pulse chirp: the oscillation amplitude decreases as the chirp increases. For a positive chirp, this effect is twofold stronger than for a negative one. The frequency-resolved response of a bandwidth-limited pulse was studied, which revealed the difference of oscill...

Misochko, Oleg Victor; Andreev, Sergej V.; Kompanets, V. O.; Matveets, Yu A.; Stepanov, A. G.; Chekalin, Sergey V.; Dekorsy, Thomas

2007-01-01

42

Surface temperature evolution in pulsed laser action of millisecond range

Energy Technology Data Exchange (ETDEWEB)

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001-1.573 {mu}m, 50 {mu}s acquisition time for each photodiode, 800 {mu}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{sup -6} transparency at 1.06 {mu}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.

Doubenskaia, M. [DIPI Laboratory, Ecole Nationale d' Ingenieurs de Saint Etienne (ENISE), 58 rue Jean Parot, 42023 St. Etienne (France); Smurov, I. [DIPI Laboratory, Ecole Nationale d' Ingenieurs de Saint Etienne (ENISE), 58 rue Jean Parot, 42023 St. Etienne (France)]. E-mail: smurov@enise.fr

2006-04-30

43

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

44

Excitons, polarons, and laser action in poly(p-phenylene vinylene) films

We have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magnetic resonance, and electroabsorption spectroscopy. We have studied singlet and triplet excitons, polarons, and laser action in PPV films. We found that the lowest-lying absorption band is excitonic in origin. It consists of two absorption components due to a bimodal distribution of the polymer chain conjugation lengths. Electroabsorption spectroscopy unambiguously shows the positions of the lowest-lying odd parity exciton 1Bu at 2.59 eV and two of the higher-lying even-parity excitons, namely, mAg at 3.4 eV and kAg at 3.7 eV. From these exciton energies we obtained a lower bound for the exciton binding energy in PPV, Eb(min)=E(mAg)-E(1Bu)=0.8 eV. The quantum efficiency spectrum for triplet exciton photogeneration consists of two contributions; the intersystem crossing and, at higher energies, singlet fission. From the onset of the singlet fission process at ESF=2ET, we could estimate the energy of the lowest-lying triplet exciton, 1 3Bu, at 1.55 eV, with a singlet-triplet splitting as large as 0.9 eV. From photoinduced absorption spectroscopy we measured the triplet-triplet transition, T?T*, to be 1.45 eV. The quantum efficiency spectrum for polaron photogeneration also consists of two contributions: one extrinsic and the other intrinsic. The latter shows a monotonically increasing function of energy with an energy onset at 3.3 eV. The intrinsic photogeneration process is analyzed with a model of free-electron-hole pair photogeneration, which separate more effectively at higher energy. The carrier generation quantum yield at 3.65 eV is estimated to be 0.5%. The quantum efficiency for photoluminescence, on the other hand, shows one single step-function process, with an onset at 2.4 eV. The photoluminescence spectrum is well structured, showing five phonon side bands with 190 meV separation. We have also studied laser action in PPV thin films and microcavities such as microrings and microdisks. The effective gain spectrum is calculated and the estimated threshold excitation intensity for laser action for the 0-1 transition is found to be in good agreement with the data, with an estimated exciton density of 2×1018 cm-3. Lasing from microring devices shows several narrow waveguide modes, with intermode spacing of 0.45 nm that corresponds to an effective mode refractive index, neff=1.45. The spectral width of the laser modes is resolution limited and gives a lower estimate of the cavity quality factor, Q. For microrings we found Q>5000, which is limited by self-absorption in the polymer film.

Österbacka, R.; Wohlgenannt, M.; Shkunov, M.; Chinn, D.; Vardeny, Z. V.

2003-05-01

45

International Nuclear Information System (INIS)

We have applied femtosecond pump-probe technique with variable pump wavelength to study coherent lattice dynamics in Bi single crystal. Comparison of the coherent amplitude as a function of pump photon energy for two different in symmetry Eg and A1g phonon modes with respective spontaneous resonance Raman profiles reveals that their generation mechanisms are quite distinct. We show that displacive excitation, which is the main mechanism for the generation of coherent A1g phonons, cannot be reduced to the Raman scattering responsible for the generation of lower symmetry coherent lattice modes. - Highlights: ? We have studied coherent phonons of A1g and Eg symmetry in bismuth. ? Amplitudes of both modes were measured in visible and near infrared ranges. ? Obtained data were compared to spontaneous Raman cross sections. ? We show that displacive excitation cannot be reduced for Bi to Raman scattering.

46

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, Săo Carlos, SP, Brazil); B--red laser irradiation (660 nm, Kondortech, Săo Carlos, SP, Brazil); C-- ham irradiation with laser unit off. After laser application, the mice remained immobilized for the injection of 30 microl of 2% formalin in the plantar pad of the irradiated hind pa...

Daniel Pozza; Patricia Fregapani; Joăo Weber; Marília Gerhardt Oliveira; Marcos André de Oliveira; Nelson Ribeiro Neto; Joăo de Macedo Sobrinho

2008-01-01

47

High-resolution laser-based angle-resolved photoemission (ARPES) measurements are carried out on Sb(111) single crystal. Two kinds of Fermi surface sheets are observed, which are derived from the topological surface states: one small hexagonal electron-like Fermi pocket around ? point and the other six elongated lobes of hole-like Fermi pockets around the electron pocket. Clear Rashba-type band splitting due to the strong spin-orbit coupling is observed to be anisotropic in the momentum space. Our super-high-resolution ARPES measurements reveal no obvious kink in the surface band dispersions, indicating a weak electron-phonon interaction in the surface states. In particular, the electron scattering rate for these topological surface states is nearly a constant over a large energy window near the Fermi level that is unusual in terms of the conventional picture.

Xie, Zhuo-Jin; He, Shao-Long; Chen, Chao-Yu; Feng, Ya; Yi, He-Mian; Liang, Ai-Ji; Zhao, Lin; Mou, Dai-Xiang; He, Jun-Feng; Peng, Ying-Ying; Liu, Xu; Liu, Yan; Liu, Guo-Dong; Dong, Xiao-Li; Yu, Li; Zhang, Jun; Zhang, Shen-Jin; Wang, Zhi-Min; Zhang, Feng-Feng; Yang, Feng; Peng, Qin-Jun; Wang, Xiao-Yang; Chen, Chuang-Tian; Xu, Zu-Yan; Zhou, Xing-Jiang

2014-06-01

48

International Nuclear Information System (INIS)

On the basis of a proven design (Liu 2005 et al Appl. Phys. Lett. 87 141102), terahertz quantum cascade laser structures are obtained by altering the GaAs component growth rate to the range of ą10%. The influences of the growth rate on electronic transport and electric output are investigated by an ensemble Monte Carlo simulation, including electronelectron and electronLO phonon scattering. Calculations indicate two important channels for leakage current. One is from upper radiative states to extract states and the other one is from injection states to lower radiative states. With the increase of the GaAs growth rate, the leakage current from the first channel is reduced greatly, resulting in the enhancement of population inversion and the decrease of the current density. The dependence of electric fieldcurrent density characteristics on the GaAs growth rate is in agreement with recent experimental measurement

49

Line-coincidence schemes for producing laser action at soft-x-ray wavelengths

International Nuclear Information System (INIS)

Line-coincidence schemes for producing laser action in the wavelength regime 100-30A are reviewed. Schemes involving pumping of 2?4 transitions in neon-like ions are singled out as particularly attractive

50

Crater formation in a target under the action of a high-power laser pulse

International Nuclear Information System (INIS)

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 1010 to 1014 W/cm2 was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave

51

Raman spectra of SrZrO3 have been successfully obtained at temperatures from 600 °C to 1240 °C by using a new continuous-wave ultraviolet Raman spectroscopic system. The phase transition between cubic and tetragonal phases is due to the collapse of the R25 mode at the R point of the high-temperature cubic Brillouin zone. Two phonon modes observed to soften (decrease) in frequency approach together and their peak intensities continuously decreased with increasing temperature. They disappeared between 1200 °C and 1220 °C. The soft modes remain underdamped, the damping constant of soft modes increased with temperature toward phase-transition temperature satisfying the universal scaling law.

Fujimori, Hirotaka; Yashima, Masatomo; Kakihana, Masato; Yoshimura, Masahiro

2000-02-01

52

Controlling phonon squeezing and correlation via one- and two-phonon interference

International Nuclear Information System (INIS)

When ultrafast laser pulse strikes the crystal with a van Hove singularity in the phonon density of states, it can create a pair of anti-correlated in wave-vector phonons. As a result, the atomic fluctuations in either position or momentum become squeezed in such a way that their size might fall below the vacuum level. The ultrafast pulses can also generate a biphonon state in which the constituent phonons are correlated and/or entangled. Here we show that via the interplay between one- and two-phonon interference the bound and squeezed two-phonon state in (110) oriented ZnTe single crystal can be manipulated. -- Highlights: ? We use a pair of ultrafast laser pulses to manipulate squeezing and correlation of biphonons in ZnTe. ? We demonstrate that the strength of phonon squeezing and correlation can be controlled. ? We observe that a larger correlation comes at expense of a reduced squeezing.

53

Laser device for the protection of biological objects from the damaging action of ionizing radiation

International Nuclear Information System (INIS)

The search for ideal protective agents for use in radiotherapy or post-exposure treatment of victims of radiation accidents is one of the actual problems of radiation protection. Laser irradiation device for the protection of biological objects from the action of ionizing radiation to be used in practice has been manufactured (invention patent RU 2 428 228 C2). This device is used to study the action of various doses of laser radiation and combined irradiation with laser and gamma-radiation, on peripheral blood parameters and number of bone marrow karyocytes of the experimental mice line C57BL/6. The mice were irradiated with ionizing and laser radiation, separately one by one in a special bench. The time interval between two types of irradiation did not exceed 30 min. First, the mice were exposed to ?-radiation then to laser radiation. It was shown that laser radiation can be applied to improve the recovery of hemato genesis after the action of ionizing radiation on biological objects. Then, experiments were conducted to study the action of ?- rays and the combined action of laser radiation and ? -rays on survival, weight and skin of experimental mice. The authors investigated also the action of gamma-rays and combined effects of 650 nm laser radiation and gamma-rays on general mitotic index of bone marrow cells of mice. The method of the laser radiation-protection of biological objects contributes to an increase in the viability of mice, prevents the damages of slity of mice, prevents the damages of skin and also increases the mitotic activity of mice bone marrow cells. (authors)

54

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

55

We investigate spontaneous emission properties and control of the zero phonon line (ZPL) from a diamond nitrogen-vacancy (NV) center coherently driven by a single elliptically polarized control field. We use the Schrödinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization-dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.

Zhang, Duo; Li, Jia-Hua; Yang, Xiao-Xue

2014-04-01

56

Laser Action in Neodymium-Doped Silica Fibre.

Available from UMI in association with The British Library. This thesis describes an investigation into the suitability of neodymium doped monomode optical fibre as a gain medium for miniature laser systems. Characterisation of the material and parameters required for quantitative analysis of such laser systems are presented in a spectroscopic analysis carried out in the first part of the thesis. Measurements performed in this section also indicate that at room temperature the wide fluorescence bands of the neodymium doped silica fibre are spectrally broadened by a homogeneous process. The behaviour of a longitudinally pumped continuous -wave fibre laser is modelled in the next section followed by the design and realisation of a practical system. Efficiencies of approximately 6% and threshold pump powers of 8-12 mW have been obtained, even under narrow linewidth operation. Tunability over ranges of 45-60nm has also been demonstrated. The thesis is concluded by experiments on pulsed fibre lasers. Q-switching the laser has achieved peak powers of several watts in pulses 180ns wide with good agreement between the results obtained and predicted values. Shorter pulses 450ps wide have been realised by mode-locking a fibre laser. Suggestions for reducing the pulse width further and the effects of material dispersion are also given. Finally modulated pump sources have been investigated and it is shown that synchronous pumping with short pulses has limitations due to dispersion, while resonantly pumping relaxation oscillations is a simple means of obtaining a pulsed output.

Alcock, Ian Peter

57

On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity. PMID:22060172

Medvid, Artur; Onufrijevs, Pavels; Mychko, Alexander

2011-01-01

58

Directory of Open Access Journals (Sweden)

Full Text Available Abstract On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity.

Medvid Artur

2011-01-01

59

Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.

El-Kady, Ihab F. (Albuquerque, NM); Olsson, Roy H. (Albuquerque, NM)

2012-01-10

60

Studies of Phonon Anharmonicity in Solids

Today our understanding of the vibrational thermodynamics of materials at low temperatures is emerging nicely, based on the harmonic model in which phonons are independent. At high temperatures, however, this understanding must accommodate how phonons interact with other phonons or with other excitations. We shall see that the phonon-phonon interactions give rise to interesting coupling problems, and essentially modify the equilibrium and non-equilibrium properties of materials, e.g., thermodynamic stability, heat capacity, optical properties and thermal transport of materials. Despite its great importance, to date the anharmonic lattice dynamics is poorly understood and most studies on lattice dynamics still rely on the harmonic or quasiharmonic models. There have been very few studies on the pure phonon anharmonicity and phonon-phonon interactions. The work presented in this thesis is devoted to the development of experimental and computational methods on this subject. Modern inelastic scattering techniques with neutrons or photons are ideal for sorting out the anharmonic contribution. Analysis of the experimental data can generate vibrational spectra of the materials, i.e., their phonon densities of states or phonon dispersion relations. We obtained high quality data from laser Raman spectrometer, Fourier transform infrared spectrometer and inelastic neutron spectrometer. With accurate phonon spectra data, we obtained the energy shifts and lifetime broadenings of the interacting phonons, and the vibrational entropies of different materials. The understanding of them then relies on the development of the fundamental theories and the computational methods. We developed an efficient post-processor for analyzing the anharmonic vibrations from the molecular dynamics (MD) calculations. Currently, most first principles methods are not capable of dealing with strong anharmonicity, because the interactions of phonons are ignored at finite temperatures. Our method adopts the Fourier transformed velocity autocorrelation method to handle the big data of time-dependent atomic velocities from MD calculations, and efficiently reconstructs the phonon DOS and phonon dispersion relations. Our calculations can reproduce the phonon frequency shifts and lifetime broadenings very well at various temperatures. To understand non-harmonic interactions in a microscopic way, we have developed a numerical fitting method to analyze the decay channels of phonon-phonon interactions. Based on the quantum perturbation theory of many-body interactions, this method is used to calculate the three-phonon and four-phonon kinematics subject to the conservation of energy and momentum, taking into account the weight of phonon couplings. We can assess the strengths of phonon-phonon interactions of different channels and anharmonic orders with the calculated two-phonon DOS. This method, with high computational efficiency, is a promising direction to advance our understandings of non-harmonic lattice dynamics and thermal transport properties. These experimental techniques and theoretical methods have been successfully performed in the study of anharmonic behaviors of metal oxides, including rutile and cuprite stuctures, and will be discussed in detail in Chapters 4 to 6. For example, for rutile titanium dioxide (TiO2), we found that the anomalous anharmonic behavior of the B1g mode can be explained by the volume effects on quasiharmonic force constants, and by the explicit cubic and quartic anharmonicity. For rutile tin dioxide (SnO2), the broadening of the B2 g mode with temperature showed an unusual concave downwards curvature. This curvature was caused by a change with temperature in the number of down-conversion decay channels, originating with the wide band gap in the phonon dispersions. For silver oxide (Ag2O), strong anharmonic effects were found for both phonons and for the negative thermal expansion.

Lan, Tian

61

Efficiency of laser action on hemoglobin and oxyhemoglobin in skin blood vessels

The efficiency of light absorption by oxyhemoglobin and deoxyhemoglobin in cutaneous blood vessels in dependence of the radiation wavelength and optical properties of the tissue is investigated. The main goal is to develop the practical application of long pulse flashlamp-pumped dye lasers in the treatment of different cutaneous lesions, based on the selective photothermolysis. The spectra of laser action both on oxyhemoglobin and deoxyhemoglobin of blood vessels at different depths of the tissue layer were calculated using the Kubelka-Munk optical model of the tissue. The obtained results allow to choose the proper wavelength of laser radiation for the selective and efficient influence on the blood chromophores. It is shown that for blood vessels located in tissue up to the depth of 2500 (mu) the action spectra of laser radiation follow the shape of the Q - absorption bands of oxyhemoglobin and deoxyhemoglobin. At deeper layers the action spectra become very narrow ((delta) (lambda) on the order of magnitude 25 - 30 nm) and shift to the long wavelength with maximum at 585 nm and 570 nm for oxyhemoglobin and deoxyhemoglobin, accordingly. The action spectra in the near infrared region remain very broad and cover the range from 600 nm to 1200 nm. It is shown that these bands play the dominant role in the absorption of laser radiation in deeper layers of tissue.

Asimov, Mustafo M.; Asimov, Rustam M.; Rubinov, Anatoly N.

1998-05-01

62

Controlling phonon entanglement and squeezing via one- and two-phonon interference

When ultrafast laser pulse strikes the crystal with a van Hove singularity in the phonon density of states, it creates a pair of anti-correlated in wave vector acoustic phonons. As a result, the atomic fluctuations in either position or momentum become squeezed in such a way that their size might fall below the vacuum level. The ultrafast pulses can also create a two-phonon bound state in which the constituent phonons are entangled. The description of phonon squeezing and/or entanglement requires the quantization since the phenomena come entirely due to the grainy nature of the lattice field. Here we show that via the interplay between one- and two-phonon interference the bound and squeezed two-phonon state in ZnTe can be manipulated. We demonstrate that when two paired-phonon ensembles are overlapped, the strength of phonon squeezing and entanglement can be controlled. However, due to the complementarity of one- and two-phonon interference a larger entanglement comes at expense of a reduced squeezing.

Misochko, Oleg V; Takahashi, Hiroshi; Ohmori, Kenji; Takei, Nobuyuki; Nakamura, Kazutaka G

2010-01-01

63

International Nuclear Information System (INIS)

The wavelength-dependent threshold and power performance of an injectorless quantum cascade laser design using four alloys and the two-phonon-resonance depletion scheme were investigated. A 7 ľm design, which reached threshold current densities as low as 0.45 kA cm?2 at 300 K and overall efficiencies above 2%, was taken as a reference. Variations in layer thickness and composition were applied to study the effects of coupling energy and transition time, increasing the output efficiency up to 5.7%. With regard to the transmission windows from 3 to 5 ľm and 8 to 12 ľm, the design scheme of the reference was also modified to emission wavelengths between 5 and 9 ľm. All devices yield threshold current densities below 1.5 kA cm?2 at 300 K, and at least 550 mW of output power. The characteristic temperatures vary indirectly proportional to the emission wavelength from 100 K at 5 ľm to 300 K at 9 ľm

64

Laser radiation action on the biomedium as nonadiabatic excitation of macromolecules

The extended sphere of the laser successful use at large vagueness of the gear of radiation interaction with biological and biosimilar objects is a main modern paradox in the application of low-intensity coherent radiation in biology and medicine. There are rather regularly, for example, the reasons of immateriality of such parameters as laser radiation coherency degree for biostimulation, but the replacement of semi-conductor lasers by the light diodes isn't observed in medical practice until now. there are also no convincing results on comparative analysis of biostimulated effect under coherent and noncoherent radiation. Action of coherent electromagnetic radiation of the visible and infrared spectral range causes, as appear, the same type structure-optical changes in various objects biological liquids, cells suspensions, model biomolecular solutions, cells of plan, insects and animals. The medicobiologic consequences of laser effect are extremely variable because of the complexity of biological object and sophistication of research techniques and analyses. The energy doze of radiation acting onto a bio-object, as a rule, is extremely small, and hence like the case of extremely high frequency radiation one can to name this action by the 'informative' one, i.e., initiating only biosystem reactions is produced due to its own energy. In connection with the relatively slow biosystem response to the laser radiation action, the nonlocality of this reaction at the local action and large variety of biochemical reactions caused with laser radiation one can assume the existence of uniform physical mechanism realizing the biostimulation effect of laser radiation for various biosystems.

Kompanets, Igor N.; Krasnov, Andrey E.; Malov, A. N.

1996-11-01

65

Subpicosecond Raman study of hot electrons and hot phonons in GaAs

International Nuclear Information System (INIS)

In this paper we will describe in detail the use of Raman scattering with subpicosecond laser pulses for investigating both the Frohlich interactions between electrons and LO phonons and the intervalley electron-phonon interactions. 19 refs., 6 figs

66

Study of Phonon Modes in Germanium Nanowires

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

67

Modification Of Surfaces Under The Action Of UV Laser Radiation

New results on excimer laser application for fine surface structurization are presented. There are considered peculiarities of the UV-photon induced processes of:(i) chemical deposition of carbon and silicon carbide films from CC14 and CH3SiC13vapour precursors onto dielectric substrates,(ii) chemical etching of c-Si in CC14 vapour environment, and (iii) microstructures production by decomposition of organo-metallic (metal resinate) films. The fundamental role of superposition of thermal and photo-stimulated processes is also discussed.

Ageev, Vladimir P.; Konov, Vitaly I.; Kuzmichov, A. V.

1989-05-01

68

Photoexcitation dynamics and laser action in solutions and films of PPE-PPV copolymer

We used a variety of ultrafast and steady-state spectroscopy techniques to study the photoexcitation dynamics and laser action in dilute and concentrated solutions and in thin films of poly(phenylene-ethynylene)/poly(phenylene-vinylene) [PPE-PPV] copolymer. We found that the primary photoexcitations in PPE-PPV solutions are relatively long-lived singlet excitons with lifetime of about 600 ps, consistent with the high-photoluminescence quantum efficiency. The singlet excitons have three distinct photoinduced absorption (PA) bands spanning the mid-IR and near-IR spectral ranges, which are correlated with a strong stimulated emission (SE) band in the blue spectral range. In thin PPE-PPV films, however, the SE band is much weaker because of its overlap with a new PA band that is due to long-lived polaron pairs. As a result we found laser action in dilute PPE-PPV solutions but not in films; this represents the first laser action reported in PPE-type polymers. A study of laser action in solutions of various copolymer concentrations confirms the lack of lasing in concentrated solutions and explains its absence in films. The polaron pair species, triplet excitons that are generated via intersystem crossing, and isolated charged polarons that are generated from polaron pair dissociation are also studied using steady-state spectroscopies.

Tong, M.; Sheng, C. X.; Yang, C.; Vardeny, Z. V.; Pang, Y.

2004-04-01

69

Control of generation regimes of ring chip laser under the action of the stationary magnetic field

Energy Technology Data Exchange (ETDEWEB)

We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)

Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N; Firsov, V V [D.V. Skobel' tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2013-05-31

70

The lasing properties of pyrromethene 567 (PM567) dissolved in solid poly-trimethylsilyl-methacrylate (TMSMA) cross-linked with ethylene glycol dimethacrylate (EGDMA) and copolymerized with methyl methacrylate (MMA) have been investigated. The vol/vol proportion of the different comonomers in each copolymer formulation was systematically varied, and the effect of each composition on the laser action of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5 mJ/pulse from a frequency doubled Q-switched Nd:KGW laser. Lasing efficiencies of up to 14% and good stability with no sign of degradation after 10,000 pump pulses at 1 Hz in the copolymer P(TMSMA:MMA 50:50) were demonstrated. Pumping this sample at 10 Hz, the laser emission of PM567 remained at 45% of its initial value after 40,000 pulses.

Costela, A.; García-Moreno, I.; Carrascoso, M. L.; Sastre, R.

2002-01-01

71

Effect of holmium and erbium laser action on the human lens: an in-vitro study

We investigated the holmium and erbium lasers operating at the medium IR range, used for cataract surgery. The main advantage of these lasers action on biological structures is total absorption of radiation by superficial layers. During the study of the lens emulsification process we found that the mechanical properties of the lens nucleus were of crucial importance for the rate of emulsification. The soft lenses were fragmented and emulsified after 200-700 pulses, while the hard lens required 5000 or more pulses while complete emulsification was not achieved. The results are promising and show that the holmium and erbium lasers can be used for human lens emulsification during ECCE. For clinical purposes, however, it is necessary to construct a suitable fiberoptic tip to be used in cataract removal. It seems that lasers whose beam is in the medium IR range could be used in many ophthalmic operations.

Kasprzak, Jan; Kecik, Dariusz

1997-10-01

72

International Nuclear Information System (INIS)

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

73

Electron scattering and hybrid phonons in low-dimensional laser structures made with GaAs/AlxGa1?xAs

International Nuclear Information System (INIS)

We theoretically and numerically present the hybrid phonon modes for the double heterostructure GaAs/AlxGa1-xAs and their interactions with electrons. More specifically, we have calculated the electron capture within a symmetric quantum well via the emission of hybrid phonons. Our investigation shows that the capture rates via the hybrid phonons are matched to the rates predicted by the dielectric continuum (DC) model and the concentration of aluminium which is an important parameter for controlling the electron capture process in light-emitting diodes (LED)

74

Spatio-temporal evolution of laser-induced air plasma in the stage of laser pulse action

Spatially and temporally resolved emission spectra of laser-induced air plasma in the stage of laser pulse action were studied. Due to the expansion of laser supported detonation wave and shielding effect at the critical surface for CO2 laser radiation, a behavior of spatial separation of the radiative plasma along the radial direction was clearly recognized. Based on the Stark broadening, we investigated the spatio-temporal evolution of the electron density and temperature of the plasma, which was evaluated by fitting the measured spectral profile to the summation of Voigt profiles of all spectral lines in a selected spectral range. The electron density was distributed densely around the focal point and thinly near the plasma edge at early times. On the contrary, the electron temperature around the focal point was a minimum at early times but became a maximum at later times. Unlike the spatio-temporal resolution results of post-pulse in previous work, the results in the present work revealed the information related to the processes of laser energy deposition.

Tang, Jian; Zuo, Duluo; Wu, Tao; Cheng, Zuhai

2013-02-01

75

Phonon lasing in transport through double quantum dots

Energy Technology Data Exchange (ETDEWEB)

An optical phonon laser is proposed using a double quantum dot (DQD) fabricated on semiconductor substrates. The DQD couples to two modes of LO phonons which work as a natural cavity. The pumping is realized by the electric current under a finite bias. We show that lasing takes place when the tunneling rate to external leads is much larger than the decay rate of phonons.

Okuyama, Rin; Eto, Mikio [Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan); Brandes, Tobias [Institut für Theoretische Physik, Technische Universität Berlin, D-10623 Berlin (Germany)

2013-12-04

76

Digital Repository Infrastructure Vision for European Research (DRIVER)

Properties of phonons - quanta of the crystal lattice vibrations - in graphene have attracted strong attention of 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 r...

Nika, Denis L.; Balandin, Alexander A.

2012-01-01

77

Length-scale dependent phonon interactions

This book presents a comprehensive description of phonons and their interactions in systems with different dimensions and length scales. Internationally-recognized leaders describe theories and measurements of phonon interactions in relation to the design of materials with exotic properties such as metamaterials, nano-mechanical systems, next-generation electronic, photonic, and acoustic devices, energy harvesting, optical information storage, and applications of phonon lasers in a variety of fields. The emergence of techniques for control of semiconductor properties and geometry has enabled engineers to design structures in which functionality is derived from controlling electron behavior. As manufacturing techniques have greatly expanded the list of available materials and the range of attainable length scales, similar opportunities now exist for designing devices whose functionality is derived from controlling phonon behavior. However, progress in this area is hampered by gaps in our knowledge of phono...

Srivastava, Gyaneshwar

2014-01-01

78

The Features of Craters Formation on the Target under the Action of Powerful Laser Pulse

International Nuclear Information System (INIS)

The results of experimental and theoretical investigations of craters originating in solid targets of different materials when powerful Nd:glass laser pulse irradiates the surface at flux densities in the range of 1010-1014 W/cm2 are presented. The experimentally observed dependencies of crater depth and ablated mass on laser pulse energy and target material properties are analysed employing the theory of shock wave initiation and propagation under the action of the plasma-producing laser beam. From the comparison of the theoretically deduced and experimentally observed dependencies, a simple formula is derived allowing to determine the pressures in the shock wave and in the plasma corona using the measurements for the crater depth and ablated mass

79

Lanthanide and actinide lasers

International Nuclear Information System (INIS)

Stimulated emission has now been observed from twelve lanthanide ions and one actinide ion. Host media have included crystalline and amorphous solids, metallo-organic and inorganic aprotic liquids, and metal and molecular vapors. Laser action spans a spectral range from approximately 0.3 to 4.0 ?m and involves electronic and phonon-assisted 4f-4f, 5d-4f, and 5f-5f transitions. The lanthanides have enjoyed their greatest utilization in optically-pumped solid-state lasers; sizes range from thin films and small fibers for integrated optics applications to large rods and disks in high-power glass lasers for fusion experiments. The spectroscopic properties which distinguish the operation of lanthanide and actinide lasers in various hosts are reviewed. Recent results and possible future directions to exploit the unique characteristics of lanthanide and actinide elements for lasers are also discussed. 120 references, 7 figures, 4 tables

80

Phonon counting and intensity interferometry of a nanomechanical resonator

Using an optical probe along with single photon detection we have performed effective phonon counting measurements of the acoustic emission and absorption processes in a nanomechanical resonator. Applying these measurements in a Hanbury Brown and Twiss set-up, phonon correlations of the nanomechanical resonator are explored from below to above threshold of a parametric instability leading to self-oscillation of the resonator. Discussion of the results in terms of a "phonon laser", and analysis of the sensitivity of the phonon counting technique are presented.

Cohen, Justin D; MacCabe, Gregory S; Groblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar

2014-01-01

81

Coherent phonon-induced optical modulation in semiconductors at terahertz frequencies

International Nuclear Information System (INIS)

The coherent modulation of electronic and vibrational nonlinearities in atoms and molecular gases by intense few-cycle pulses has been used for high-harmonic generation in the soft x-ray and attosecond regime, as well as for Raman frequency combs that span multiple octaves from the terahertz to petahertz frequency regions. In principle, similar high-order nonlinear processes can be excited efficiently in solids and liquids on account of their high nonlinear polarizability densities. In this paper, we demonstrate the phononic modulation of the optical index of Si and GaAs for excitation and probing near their direct band gaps, respectively at ?3.4 and ?3.0 eV. The large amplitude coherent longitudinal optical (LO) polarization due to the excitation of LO phonons of Si (001) and LO phononplasmon coupled modes in GaAs (001) excited by 10 fs laser pulses induces effective amplitude and phase modulation of the reflected probe light. The combined action of the amplitude and phase modulation in Si and GaAs generates phonon frequency combs with more than 100 and 60 THz bandwidth, respectively. (paper)

82

Long-time correlated quantum dynamics of phonon cooling

We investigate the steady-state cooling dynamics of vibrational degrees of freedom related to a nanomechanical oscillator coupled with a laser-pumped quantum dot in an optical resonator. Correlations between phonon-cooling and quantum-dot photon emission processes occur, respectively, when a photon laser absorption together with a vibrational phonon absorption is followed by photon emission in the optical resonator. Therefore, the detection of photons generated in the cavity mode concomitantly contributes to phonon cooling detection of the nanomechanical resonator.

Carlig, Sergiu; Macovei, Mihai A.

2014-07-01

83

The study of a possible cytotoxic effect of different doses of low-insensitive laser radiation and protective action of low-intensive laser radiation relative to the toxic effect of metals was carried out by means of the alternative method of investigation in vitro on cell cultura Hela. It was established that the investigated doses of low-intensive laser radiation had not produced any toxic effect on cell culture Hela, so the mentioned doses were not cytotoxic. It was revealed that laser radiation reduced the level of the cytotoxic effect of the studied metal salts on the cell culture, and possessed the protective action against the toxic effect of metals. This action has a clear-cut dose- related character.

Dejneka, S. Y.

1997-12-01

84

We have investigated the processes of excitation and ionisation of monomers and clusters of CF3I, IF2CCOF and Fe(CO)5 molecules under the action of femtosecond laser radiation at the wavelengths of 266, 400 and 800 nm. It is concluded that the nature of the excitation of free molecules and clustered molecules by femtosecond pulses is different. The simulation of the ionisation yield of the objects under study has shown that the multiphoton ionisation is the key mechanism in the case of free molecules, while the field ionisation may play a significant role for clusters, in particular, in the case of ionisation at the wavelength of ? = 800 nm.

Apatin, V. M.; Kompanets, V. O.; Lokhman, V. N.; Ogurok, N.-D. D.; Poydashev, D. G.; Ryabov, E. A.; Chekalin, S. V.

2014-05-01

85

Energy Technology Data Exchange (ETDEWEB)

Investigations were made of the threshold, energy, temporal, and spectral characteristics of a cryogenic pulsed electron-beam-controlled CO laser utilizing mixtures of CO with helium and nitrogen. The active volume of the experimental system was approx.5 liters, the excitation duration was 30--300 ..mu..sec, and the active gas density was < or =1.5 amagat. It was shown that cooling the active medium to 80--100 /sup o/K made it possible to increase the gain to 1.5 x 10/sup -2/ cm/sup -1/, the energy output to approx.100 Jxliter/sup -1/xamagat/sup -1/, and the efficiency to 35%. Radiation energies of approx.250 J and 400 J were obtained at densities of 0.5 and 1.5 amagat, respectively. Laser action was observed in the spectral range 4.95--5.5 ..mu... On increasing the pump energy and the buffer gas concentration, the stimulated emission spectrum was shifted toward shorter wavelengths. Decreasing the CO concentration in a nitrogen mixture to 2.5% for a constant exciting pulse duration of approx.100 ..mu..sec increased the radiation pulse duration (at half-height) fromapprox.100 ..mu..sec (pure CO) to approx.3 msec. A comparison was made between the results of theoretical calculations and the experimental data given by other authors.

Basov, N.G.; Danilychev, V.A.; Ionin, A.A.; Kazakevich, V.S.; Kovsh, I.B.; Poletaev, N.L.

1979-06-01

86

Phonon-phonon interactions in transition metals

In this paper the phonon self-energy produced by anharmonicity is calculated using second-order many-body perturbation theory for all bcc, fcc, and hcp transition metals. The symmetry properties of the phonon interactions are used to obtain an expression for the self-energy as a sum over irreducible triplets, very similar to integration in the irreducible part of the Brillouin zone for one-particle properties. The results obtained for transition metals shows that the lifetime is on the order of 10-10 s. Moreover, the Peierls approximation for the imaginary part of the self-energy is shown to be reasonable for bcc and fcc metals. For hcp metals we show that the Raman-active mode decays into a pair of acoustic phonons, their wave vector being located on a surface defined by conservation laws.

Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles

2011-09-01

87

Action of UV excimer laser radiation and fast neutrons on DNA and chromatin proteins of tumour cells

International Nuclear Information System (INIS)

We studied the action on DNA and chromatin proteins from Walker rat tumours of a laser radiation with ? = 248 nm, from an excimer laser, model 1701 - Physical Institute Moscow (0.5-3 MJ/m2 doses) and of a fast neutron beam, produced at the IAP Cyclotron in Bucharest (d(13 MeV) + Be thick target) (5-100 Gy doses). The DNA modifications were established by thermal transitions and by fluorescence properties of complexes with ethidium bromide. The action on chromatin proteins was evaluated by intrinsic fluorescence and by gel electrophoresis. The modifications produced are dose dependent and characteristic of laser radiation and fast neutrons. The complex action includes: the production of DNA strand breaks, protein destruction and chromatin conformation modifications. (Author)

88

Continuous-wave diode-pumped laser action of Ndł?-doped photo-thermo-refractive glass.

Laser action of the photo-thermo-refractive (PTR) glass, which is the photosensitive material for holographic recording of volume Bragg gratings (VBGs), was demonstrated for the first time by introducing Ndł?. Nd:PTR glass has a bandwidth of 27.8 nm and 16.0 nm for luminescence and absorption, respectively. An uncoated 2 mm thick Nd:PTR element generated cw laser output of 124 mW, with a slope efficiency of 25%, by laser diode pumping. This Nd:PTR glass also performed wide bandwidth laser action at 1053.9-1063.3 nm, where the decrease of the pump-absorption efficiency was held off below 30%, even under a 3.5 nm shift of pump wavelength from its absorption center. PMID:21685985

Sato, Yoichi; Taira, Takunori; Smirnov, Vadim; Glebova, Larissa; Glebov, Leonid

2011-06-15

89

International Nuclear Information System (INIS)

An interferometric method is developed and realised using a frequency-modulated pulse for diagnosing a dynamics of fast deformations with a spatial and temporal resolution under the action of a single laser pulse. The dynamics of a free surface of a submicron-thick aluminium film is studied under an action of the ultrashort compression pulse with the amplitude of up to 14 GPa, excited by a femtosecond laser heating of the target surface layer. The spallation strength of aluminium was determined at a record high deformation rate of 3 × 109 s-1. (extreme light fields and their applications)

90

Transverse optical phonon dispersion for multi-layer graphene

The Raman spectra were measured with different wavelength excitation lasers for multi-layer graphene samples obtained by mechanical and electrostatic exfoliation of highly oriented pyrolytic graphite on a silicon substrate. Phonon frequencies depending on the laser energy value are constructed, and the average distance between defects in the resulting multi-layer graphene calculated using G and D lines intensity ratio.

Kurkina, I.; Smagulova, S.

2014-10-01

91

The conference PHONONS 2007 was held 15-20 July 2007 in the Conservatoire National des Arts et Métiers (CNAM) Paris, France. CNAM is a college of higher technology for training students in the application of science to industry, founded by Henri Grégoire in 1794. This was the 12th International Conference on Phonon Scattering in Condensed Matter. This international conference series, held every 3 years, started in France at Sainte-Maxime in 1972. It was then followed by meetings at Nottingham (1975), Providence (1979), Stuttgart (1983), Urbana-Champaign (1986), Heidelberg (1989), Ithaca (1992), Sapporo (1995), Lancaster (1998), Dartmouth (2001) and St Petersburg (2004). PHONONS 2007 was attended by 346 delegates from 37 different countries as follows: France 120, Japan 45, Germany 25, USA 25, Russia 21, Italy 13, Poland 9, UK 9, Canada 7, The Netherlands 7, Finland 6, Spain 6, Taiwan 6, Greece 4, India 4, Israel 4, Ukraine 4, Serbia 3, South Africa 3, Argentina 2, Belgium 2, China 2, Iran 2, Korea 2, Romania 2, Switzerland 2, and one each from Belarus, Bosnia-Herzegovina, Brazil, Bulgaria, Egypt, Estonia, Mexico, Moldova, Morocco, Saudi Arabia, Turkey. There were 5 plenary lectures, 14 invited talks and 84 oral contributions; 225 posters were presented during three poster sessions. The first plenary lecture was given by H J Maris who presented fascinating movies featuring the motion of a single electron in liquid helium. Robert Blick gave us a review on the new possibilities afforded by nanotechnology to design nano-electomechanical systems (NEMS) and the way to use them to study elementary and fundamental processes. The growing interest for phonon transport studies in nanostructured materials was demonstrated by Arun Majumdar. Andrey Akimov described how ultrafast acoustic solitons can monitor the optical properties of quantum wells. Finally, Maurice Chapellier told us how phonons can help tracking dark matter. These 328 presentations gave rise to 185 articles published in the present proceedings. The traditional topics of this conference series (phonons in superconductors and new materials, lattice dynamics, phonons in glasses and disordered materials, phase transitions, light, neutrons and x-ray inelastic scattering) were still very important in the scientific program but an increasing number of contributions occurred in the fields of coherent phonon generation, phonons in nanoscaled structures and nano/micro thermal phonon transport, expressing the growing involvement of condensed matter physicists in nanosciences. Areas like acoustic solitons and phononic crystals are now well established. Two noteworthy contributions have been brought in the long term quest for an operational SASER : one by Harold De Wijn's group from Utrecht in the classical ruby system and another one by Anthony Kent's group from Nottingham, who used semiconductor nanodevices to realize both an amplifying medium and a cavity. With these semiconductor devices the possibility for engineering, generation and detection of THz acoustic phonons are now imminent. By tradition, a prize is awarded every three years at the International Conference on Phonon Scattering in Condensed Matter to honour a scientist for his outstanding contributions to the field of phonon physics. For this twelfth edition, Humphrey Maris has been honoured for his numerous breakthroughs in the physics of phonons and quantum fluids. According to the words of James Wolfe 'Humphrey Maris has delighted and innovated the members of our phonon community with an entertaining style and challenging wit'. Prizes were also awarded for the best presentations during the poster sessions. The two winners were Peter van Capel from Utrecht, Netherlands, ('Simulations of acoustic soliton-induced chirping of exciton resonances') and Patrick Emery from Lille, France, ('Acoustic attenuation in silica in the 100-250 GHz range using coloured picosecond ultrasonics). Both prizes were o

Perrin, Bernard

2007-06-01

92

International Nuclear Information System (INIS)

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

93

Coherent acoustic phonons in nanostructures investigated by asynchronous optical sampling

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new optical pump-probe technique is implemented for the investigation of 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 200 femtoseconds resolution at scan rates of 10 kHz. The generation of coherent acoustic phonons and their propagation ...

Dekorsy, Thomas; Hudert, Florian; Cerna, Roland; Schaefer, Hanjo; Janke, Christof; Bartels, Albrecht; Ko?hler, K.; Braun, Stefan; Wiemer, Maik; Mantl, Siegfried

2006-01-01

94

Phonon-Phonon Interactions in Zinc

International Nuclear Information System (INIS)

Experimental results on the shape of phonon peaks in the neighbourhood of the point of accidental degeneracy of the longitudinal acoustic (LA) and transverse optic (TO/ /)(0, ?, ?, 0) branches polarized in the basal plane of zinc have been recently obtained with the purpose of investigating anharmonic contributions to the potential energy for the motions of the nuclei in this metal. The study has so far been limited to room temperature: particular care is being taken to get adequate instrumental resolution. At present it seems impossible to exclude a slight extra broadening of the phonon lines at ? and q values barely smaller than those corresponding to the point of degeneracy. Further work in this field is under way and will be soon extended to higher and possibly lower temperatures. (author)

95

Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures

We show that large amplitude, coherent acoustic phonon wavepackets can be generated and detected in In$_x$Ga$_{1-x}$N/GaN epilayers and heterostructures in femtosecond pump-probe differential reflectivity experiments. The amplitude of the coherent phonon increases with increasing Indium fraction $x$ and unlike other coherent phonon oscillations, both \\textit{amplitude} and \\textit{period} are strong functions of the laser probe energy. The amplitude of the oscillation is substantially and almost instantaneously reduced when the wavepacket reaches a GaN-sapphire interface below the surface indicating that the phonon wavepackets are useful for imaging below the surface. A theoretical model is proposed which fits the experiments well and helps to deduce the strength of the phonon wavepackets. Our model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refract...

Liu, R; Sanders, G D; Stanton, C J; Yahng, J S; Jho, Y D; Yee, K J; Oh, E; Kim, D S; Liu, Rongliang; Kim, Chang Sub

2003-01-01

96

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

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

97

The temperature dependence of the phonon spectra of ?- uranium has recently been measured by Manley et al.[1] using inelastic neutron scattering and inelastic x-ray scattering techniques. Although there is little evidence of any anharmonicity, the phonon shows some softening in the optic modes at the zone boundary. In a later publication [2], an extra mode was reported to form 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 of mixed electron and phonon character. [1] M. E. Manley, B. Fultz, R. J. McQueeney, C. M. Brown, W. L. Hults, J. L. Smith, D. J. Thoma, R. Osborn, and J. L. Robertson, Phys. Rev. Lett. 86 (2001), p3076. [2] M. E. Manley, M. Yethiraj, H. Sinn, H. M. Volz, A. Alatas, J. C. Lashley, W. L. Hults, G. H. Lander, and J. L. Smith, Phys. Rev. Lett. 96 (2006), p125501.

Yang, Xiaodong; Riseborough, Peter

2007-03-01

98

Phonons in semiconductor nanostructures

Energy Technology Data Exchange (ETDEWEB)

Phonons in semiconductor nanostructures like quantum dots affect the dephasing of optical excitations decisively. In our presented work, the inhomogeneous, atomistic nature of the problem is simulated by employing a valence-force field description. The parameters are taken either directly from experiment or are calculated by density functional theory. The investigated structures include quantum dots of different shapes and alloy compositions. They consist of compounds with either zincblende or wurtzite crystal structure, therefore capturing the equilibrium structures of III-V and group III-nitrides. The phonon density of states is determined by calculating the velocity correlation function in a molecular dynamics simulation. We present also a comparison to continuum elasticity solutions of the wave equation for acoustical phonons.

Knittel, Andreas; Grosse, Frank [Institut fuer Physik der Humboldt- Universitaet zu Berlin, Newtonstr. 15, 12489 Berlin (Germany)

2007-07-01

99

Phonon waveguides for electromechanical circuits

Nanoelectromechanical systems (NEMS), utilizing localized mechanical vibrations, have found application in sensors, signal processors and in the study of macroscopic quantum mechanics. The integration of multiple mechanical elements via electrical or optical means remains a challenge in the realization of NEMS circuits. Here, we develop a phonon waveguide using a one-dimensional array of suspended membranes that offers purely mechanical means to integrate isolated NEMS resonators. We demonstrate that the phonon waveguide can support and guide mechanical vibrations and that the periodic membrane arrangement also creates a phonon bandgap that enables control of the phonon propagation velocity. Furthermore, embedding a phonon cavity into the phonon waveguide allows mobile mechanical vibrations to be dynamically switched or transferred from the waveguide to the cavity, thereby illustrating the viability of waveguide-resonator coupling. These highly functional traits of the phonon waveguide architecture exhibit all the components necessary to permit the realization of all-phononic NEMS circuits.

Hatanaka, D.; Mahboob, I.; Onomitsu, K.; Yamaguchi, H.

2014-07-01

100

Fragmentation of nanoparticles in a liquid under the action of pulsed laser heating is studied theoretically and experimentally. Fragmentation is simulated by solving the kinetic equation for the nanoparticles size distribution function, taking into account the temperature dependence of the thermophysical parameters of the medium. It is shown that fragmentation occurs after separation of smaller fragments from a molten nanoparticle. The simulation results are in good agreement with experimental data obtained in the fragmentation of gold nanoparticles irradiated in water by a copper vapour laser with a peak radiation intensity of about 106 W cm-2.

Kirichenko, N. A.; Sukhov, I. A.; Shafeev, Georgii A.; Shcherbina, M. E.

2012-02-01

101

Spectrum and entanglement of phonons in quantum fluids of light

We study the quantum state of phonons propagating on top of a fluid of light coherently generated in a planar microcavity device by a quasi-resonant incident laser beam. In the steady-state under a monochromatic pump, because of the finite radiative lifetime of photons, a sizable incoherent population of low frequency phonons is predicted to appear. Their mean occupation number differs from a Planck distribution and is independent on the photon lifetime. When the photon fluid is subjected to a sudden change of its parameters, additional phonon pairs are created in the fluid with remarkable two-mode squeezing and entanglement properties. Schemes to assess non-separability of the phonon state from measurements of the correlation functions of the emitted light are discussed.

Busch, Xavier; Parentani, Renaud

2013-01-01

102

Phonons in Ge/Si superlattices with Ge quantum dots

International Nuclear Information System (INIS)

Ge/Si superlattices with Ge quantum dots obtained by means of molecular-beam epitaxy were investigated by means of light Raman scattering under resonance conditions. These structures are shown to have oscillation properties of both two-dimensional and zero-dimensional objects. Within spectrum low-frequency range one observes twisted acoustic phonons (up to 15 order) typical for planar superlattices. Lines of acoustic phonons are overlapped with a wide band of continuous emission. Analysis of frequencies of Ge and Ge-Si optical phonons shows that Ge quantum dots are pseudoamorphous ones and mixing of Ge and Si atoms is a negligible one. One detected low-frequency shift of longitudinal optical phonons at laser excitation energy increase (2.54-2.71 eV)

103

Phonons in Ge/Si superlattices with Ge quantum dots

Ge/Si superlattices with Ge quantum dots obtained by means of molecular-beam epitaxy were investigated by means of light Raman scattering under resonance conditions. These structures are shown to have oscillation properties of both two-dimensional and zero-dimensional objects. Within spectrum low-frequency range one observes twisted acoustic phonons (up to 15 order) typical for planar superlattices. Lines of acoustic phonons are overlapped with a wide band of continuous emission. Analysis of frequencies of Ge and Ge-Si optical phonons shows that Ge quantum dots are pseudoamorphous ones and mixing of Ge and Si atoms is a negligible one. One detected low-frequency shift of longitudinal optical phonons at laser excitation energy increase (2.54-2.71 eV)

Milekhin, A G; Pchelyakov, O P; Schulze, S; Zahn, D R T

2001-01-01

104

Continuous mode cooling and phonon routers for phononic quantum networks

We study the implementation of quantum state transfer protocols in phonon networks, where in analogy to optical networks, quantum information is transmitted through propagating phonons in extended mechanical resonator arrays or phonon waveguides. We describe how the problem of a non-vanishing thermal occupation of the phononic quantum channel can be overcome by implementing optomechanical multi- and continuous mode cooling schemes to create a 'cold' frequency window for transmitting quantum states. In addition, we discuss the implementation of phonon circulators and switchable phonon routers, which rely on strong coherent optomechanical interactions only, and do not require strong magnetic fields or specific materials. Both techniques can be applied and adapted to various physical implementations, where phonons coupled to spin or charge based qubits are used for on-chip networking applications.

Habraken, S J M; Lukin, M D; Zoller, P; Rabl, P

2012-01-01

105

Continuous mode cooling and phonon routers for phononic quantum networks

International Nuclear Information System (INIS)

We study the implementation of quantum state transfer protocols in phonon networks, where, in analogy to optical networks, quantum information is transmitted through propagating phonons in extended mechanical resonator arrays or phonon waveguides. We describe how the problem of a non-vanishing thermal occupation of the phononic quantum channel can be overcome by implementing optomechanical multi- and continuous mode cooling schemes to create a cold frequency window for transmitting quantum states. In addition, we discuss the implementation of phonon circulators and switchable phonon routers, which rely only on strong coherent optomechanical interactions and do not require strong magnetic fields or specific materials. Both techniques can be applied and adapted to various physical implementations, where phonons coupled to spin- or charge-based qubits are used for on-chip networking applications. (paper)

106

Taking into account constraints imposed by the lattice symmetry, the phonon dispersion is calculated for graphene with interactions between first and second nearest neighbors. We show that only five force constants give a very good fitting to elastic constants and Raman frequencies observed in graphite.

Falkovsky, L A

2007-01-01

107

Quantum theory analysis of the action micromechanism exerted on bioparticles from laser microbeams

The effect of laser microbeam trapping the bioparticles has been applied widely in the biology.However the micromechanism of the acting that realizes the laser-microbeam trapping bioparticles is still lacking. In this paper, the act microchenism of the gradiant force of laser microbeam for the bioparticles is analysed by means of quantum theory,The result accords with our experiment.

Yang, Wei-Guo; Zhang, Can-Bang; Xu, Lin; Wen, Yuan-Bin; Wang, Rui-Li; Zhou, Ling-Yun

2008-03-01

108

Phonon Gas Model (PGM) workflow in the VLab Science Gateway

This contribution describes a scientific workflow for first principles computations of free energy of crystalline solids using the phonon gas model (PGM). This model was recently implemented as a hybrid method combining molecular dynamics and phonon normal mode analysis to extract temperature dependent phonon frequencies and life times beyond perturbation theory. This is a demanding high throughout workflow and is currently being implemented in VLab Cyberinfrastructure [da Silveira et al., 2008], which has recently been integrated to the XSEDE. First we review the underlying PGM, its practical implementation, and calculation requirements. We then describe the workflow management and its general method for handling actions. We illustrate the PGM application with a calculation of MgSiO3-perovskite's anharmonic phonons. We conclude with an outlook of workflows to compute other material's properties that will use the PGM workflow. Research supported by NSF award EAR-1019853.

da Silveira, P.; Zhang, D.; Wentzcovitch, R. M.

2013-12-01

109

The influence of composition on the thermal stability of tellurite glasses was investigated by using differential scanning calorimetry (DSC). The studied glasses were synthesized by conventional melting quenching method. The best thermal stability and poor crystallization tendency were obtained for the glass composed of 65TeO2-15ZnO-10Na2O-5BaO-3La2O3 doped with Er2O3 (2 mol %). This glass will be referred, in this article, as TZNBL: Er3+ glass. The spectroscopic properties of the above glass are investigated based on the Judd-Ofelt and McCumber theories. The calculated intensity parameters (?2,4,6) are compared to those obtained for Er3+ in other glasses. The radiative emission rate has been calculated for the different Er3+emitting levels. The high values of ?4 and ?6 confirm the results of the DSC experiment concerning the rigidity of the studied glass. Absorption, emission and gain cross section of the 4I13/2 ? 4I15/2 (Er3+) transition in the studied glass are reported and the results are compared to those of other glasses. The 4I13/2 ? 4I15/2 (Er3+) absorption and emission cross sections derived by the application of the Mc Cumber's theory corroborate the Judd-Ofelt results. The whole of results demonstrate that the new composition leads to good thermal and mechanical properties as well efficient Er3+ absorption, emission cross sections, which make this glass as a promising candidate for laser action and amplification.

Benmadani, Y.; Kermaoui, A.; Chalal, M.; Khemici, W.; Kellou, A.; Pellé, F.

2013-10-01

110

Superconductivity without phonons.

The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material. PMID:18097398

Monthoux, P; Pines, D; Lonzarich, G G

2007-12-20

111

Digital Repository Infrastructure Vision for European Research (DRIVER)

Taking into account the constraints imposed by the lattice symmetry, the phonon dispersion is calculated for graphene with interactions between the first and second nearest neighbors in the framework of the Born-von Karman model. Analytical expressions are obtained for the out-of-plane (bending) modes determined only by two force constants as well as for the in-plane modes with four force constants. Values of the force constants are found in fitting to elastic constants and ...

Falkovsky, L. A.

2007-01-01

112

Berry curvature and the phonon Hall effect

We show that an effective magnetic field acting on phonons naturally emerges in the phonon dynamics of magnetic solids, giving rise to the phonon Hall effect. A general formula for the intrinsic phonon Hall conductivity is derived by using the corrected Kubo formula with the energy magnetization contribution incorporated properly. We thus establish a direct connection between the phonon Hall effect and the intrinsic phonon band structure, i.e., the phonon Berry curvature and phonon dispersion. Based on the formalism, we predict that phonons could also display the quantum Hall effect in certain topological phonon systems. In the low-temperature regime, we predict that the phonon Hall conductivity is proportional to T3 for ordinary phonon systems, while that for the topological phonon system has a linear T dependence with a quantized temperature coefficient.

Qin, Tao; Zhou, Jianhui; Shi, Junren

2012-09-01

113

Thermal plasma irradiation under the action of the microwave-frequency-modulated laser beam

International Nuclear Information System (INIS)

The results of the calculation of the thermal irradiation of the laser plasma formed by a powerful laser beam with the microwave-frequency-modulated intensity are presented. The analytical solution has been obtained for the case of the light detonation regime. It has been shown that the modulation of the gasdynamic parameters due to the absorption of the laser radiation leads to the modulation of the spectral and integral brightness observed from the thermal plasma irradiation.

114

Crater formation in a target under the action of a high-power laser pulse

International Nuclear Information System (INIS)

The results of the experiments and theoretical studies on the craters formation in the targets from different materials under the effect of the powerful neodymium laser within the intensities range from 1010 up to 1014 W/cm2 are presented. The studies on the laser beam interaction with solid targets are carried out with the purpose of determining the efficiency of the materials ablation loading and laser transformation into the shock wave energy

115

Phonon operators in deformed nuclei

International Nuclear Information System (INIS)

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

116

Coherent phonons are collective lattice oscillations which can periodically modulate the physical properties of the crystal. Three kinds of experimentally observed coherent phonons are discussed in this thesis. They are the coherent optical phonons in bulk semiconductors, the coherent acoustic phonons in GaN/InGaN multiple quantum wells and superlattices, and the propagating coherent phonon wavepackets in GaN/InGaN heterostructures and epilayers. A phenomenological oscillator model is presented to explain the oscillating changes in the reflection of bulk semiconductors. The proper definition of the coherent phonon amplitude as the quantum-mechanical average of the phonon creation and annihilation operators constitutes the basis of the microscopic theory of the coherent phonons, which justifies the macroscopic oscillator model. The lattice displacement is related to the coherent phonon amplitude through Fourier transform. Since the laser wavelength is much larger than the lattice constant, the photoexcited carriers distribute uniformly and the carrier density matrix has only the q ? 0 Fourier component. As a result the coupling of the photoexcited carriers to the phonons leads to coherent optical phonons only. The large piezoelectric fields due to the built-in strain in GaN/InGaN semi-conductor superlattices or multiple quantum wells can be partially screened by the photoexcited carriers whose density has the same periodicity of the superlattice. In response the crystal relaxes to a new configuration which triggers the coherent acoustic phonon oscillations. The microscopically derived equation of motion for the coherent phonon amplitude can be mapped onto a one-dimensional wave equation for the lattice displacement which is called the string model. Based on the string model, the coherent control of the coherent acoustic phonons can be carried out theoretically. The last kind is the coherent acoustic phonon wavepackets generated and detected in InGaN/GaN epilayers and heterostructures. We constructed a theoretical model that fits the experiments well and helps to deduce the strength of the coherent phonon wavepackets. This model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refraction, primarily through the Franz-Keldysh effect, and as a result modulate the reflectivity of the probe beam.

Liu, Rongliang

117

Behaviour of neutron irradiated silicon under the action of powerful laser pulses

International Nuclear Information System (INIS)

The behaviour of defects in silicon irradiated by neutrons under the effect of powerful ruby laser pulses (tau approximately 1.0 ms) is studied. Combinations of laser and isochronous annealing at different energies in impulse and annealing temperatures are used. The irradiated layer characteristics are judged by the measurements of electric conductivity and the Hall effe.ct. It is shown that a single laser impulse operating in the regime of free generation can be sufficient for total restoration of the initial crystal properties along the whole depth (300 ?m). It is found that under the laser effect the decay processes and reconstruction of defects have the character different from the case of annealing in a furnace. The conditions for formation of specific defect types are created, annealing of a vacancy nucleus of a disordering region has an explosive character. The great possibilities of utilization of the laser effect in investigation of defect structures are pointed out

118

Optical investigations of powerful laser actions on massive and flyer targets

International Nuclear Information System (INIS)

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 and 11 ?m thick for both cases) placed in front of the massive target at the 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 diameter on the target surface from 70 ?m up to 1200 ?m (moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J always focused on diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. The 3-frame interferometry was employed to investigate the plasma dynamics by means of the electron density distribution time development as well as the disks and foil fragments velocity measurements. Dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. Experimental results were complemented by two-dimensional analytical theory and computer simulations to help their interpretation. 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 macro-particle impact were obtained from measured craters' parameters for both wavelengths of laser radiation. (author)

119

Electron - phonon interaction in strongly correlated systems. Acoustical phonon case

International Nuclear Information System (INIS)

We investigate the interaction of strongly correlated electrons with acoustical phonons in the frame of Hubbard-Holstein model. The electron-phonon interaction and on-site Coulomb repulsion are considered to be strong. By using the Lang-Firsov canonical transformation this problem has been transformed to the problem of mobile polarons. A new diagram technique is used in order to handle the strong Coulomb repulsion of the electrons and the existence of phonon clouds surrounding the electrons. The generalized Wick theorems for chronological products of electron and phonon-clouds operators have been formulated. We have found the collective mode of phonon clouds that surround electrons and discussed the physics of the emission and absorption of this mode by the polarons. We have also discussed the difference in the behaviour of optical and acoustical phonon-clouds surrounding polarons during their movement through the crystal lattice. The aim of the present paper is to gain further insight into the mutual influence of strong on-site Coulomb repulsion and strong electron-phonon interaction using the single band Hubbard-Holstein model and a recently developed diagram approach. We consider now the most interesting case as regards superconductivity of coupling of correlated electrons with dispersion acoustical phonons. (authors)

120

International Nuclear Information System (INIS)

Defects in semiconductors introduce vibrational modes that are distinct from bulk modes because they are spatially localized in the vicinity of the defect. Light impurities produce high-frequency modes often visible by Fourier-transform infrared absorption or Raman spectroscopy. Their vibrational lifetimes vary by orders of magnitude and sometimes exhibit unexpectedly large isotope effects. Heavy impurities introduce low-frequency modes sometimes visible as phonon replicas in photoluminescence bands. But other defects such as surfaces or interfaces exhibit spatially localized modes (SLMs) as well. All of them can trap phonons, which ultimately decay into lower-frequency bulk phonons. When heat flows through a material containing defects, phonon trapping at localized modes followed by their decay into bulk phonons is usually described in terms of phonon scattering: defects are assumed to be static scattering centers and the properties of the defect-related SLMs modes are ignored. These dynamic properties of defects are important. In this paper, we quantify the concepts of vibrational localization and phonon trapping, distinguish between normal and anomalous decay of localized excitations, discuss the meaning of phonon scattering in real space at the atomic level, and illustrate the importance of phonon trapping in the case of heat flow at Si/Ge and Si/C interfaces

121

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 electronicvibrational 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

122

We find that the high thermal conductivity of carbon nanotubes remains intact under severe structural deformations while the corresponding electrical resistance and thermoelectric power show compromised responses. Similar robust thermal transport against bending is found for boron nitride nanotubes. Surprisingly, for both systems the phonon mean free path exceeds the characteristic length of structural ripples induced by bending and approaches the theoretical limit set by the radius of curvature. The robustness of heat conduction in nanotubes refines the ultimate limit that is far beyond the reach of ordinary materials. PMID:17678375

Chang, C W; Okawa, D; Garcia, H; Majumdar, A; Zettl, A

2007-07-27

123

Femtosecond time-resolved x-ray diffraction from optical coherent phonons in CdTe(111) crystal

International Nuclear Information System (INIS)

Coherent phonons excited in a CdTe(111) crystal by 70 fs laser irradiation have been investigated by femtosecond time-resolved x-ray diffraction. The longitudinal optical phonon with a frequency of approximately 5 THz near the Brillouin zone center has been detected as modulation in intensities of x-ray diffraction. Atomic displacement in the [111] direction in the coherent longitudinal optical phonon has been estimated

124

Phonon emission in quasiparticle trapping

International Nuclear Information System (INIS)

Using energy selective S-I-S' tunnel junctions, we have studied the phonons produced by quasiparticle trapping into copper films from single crystal superconducting indium. Excitations in the crystal can be detected both by measuring the increase in the quasiparticle population in the trap and by detecting the relaxation phonons emitted in the trapping process. (orig.)

125

Phonon emission in quasiparticle trapping

Energy Technology Data Exchange (ETDEWEB)

Using energy selective S-I-S' tunnel junctions, we have studied the phonons produced by quasiparticle trapping into copper films from single crystal superconducting indium. Excitations in the crystal can be detected both by measuring the increase in the quasiparticle population in the trap and by detecting the relaxation phonons emitted in the trapping process. (orig.).

Goldie, D.J.; Booth, N.E.; Patel, C.; Salmon, G.L. (Dept. of Physics, Univ. of Oxford, Nuclear Physics Lab. (UK))

1991-02-01

126

Action of low-power laser irradiation on the proliferation of human gingival fibroblasts in vitro

The low level power laser has been used in dental treatments aiming to improve tissue healing. An in vitro study was performed to analyze the laser influence on gingival fibroblast. A human gingival fibroblast culture (LMF) was produced in DME medium with 10% bovine fetal serum (BFS) cells (LMF) were allocated in Petri plates and cultured in different SFB concentrations (0%, 5% e 10%). After 48 hours the plates were divided in 9 groups: 3 control: 3 irradiated by 635 nm laser; and 3 irradiated by 780 nm laser. The cultured cells received 4 applications, in 12 hours intervals, with energy dosage of 2 joules for each plate, by means of a punctual technique. The growth curves showed that the growth levels were lower in low BFS concentrations. The irradiation with laser accelerated the growth rate in all groups. Additionally, the number of cells developed in low BFS concentration (5%) and irradiated was similar to the number of control cells developed in ideal conditions (10% BFS). There was no statistically significant differences between the effects of the two types of laser studied.

Almeida-Lopes, Luciana; Jaeger, Marcia M. M.; Brugnera, Aldo, Jr.; Rigau, Josepa

1998-04-01

127

A calculation of the electron-LA phonon relaxation time of a two dimensional electron gas under the action of a strong magnetic field is performed using a memory function formalism. It is well known that the inverse of the transport relaxation time is the sum of the contributions arising from electron-phonon enteraction and from impurity elastic scattering. In this work we are dealing with the electron-LA phonon scattering contribution, which is the important phonon scattering mechanism at low temperatures. We take into account, through vertex corrections in the diffusive pole approximation, the effect on phonon scattering due to the presence of impurities in the material, which renormalizes the polarization function. The effect of temperature on the renormalized electron-phonon relaxation time is discussed and we show that it yields a non-zero resistivity in the phonon channel scattering at zero temperature.

Leal, C. E.; da Cunha Lima, I. C.; Troper, A.

128

Action of a 904-nm diode laser in orthopedics and traumatology: a clinical study on 447 cases

Objective: The evidence in medical literature is that a beneficial analgesic effect can only be obtained by employing laser radiation of relatively low power density and wavelengths which are able to penetrate tissue. For this reason the semiconductor, or laser diode (GaAs, 904 nm), is the most appropriate choice in pain-reduction therapy. Summary Background Data: Low power laser (or LLL) acts on the Prostaglandins synthesis, increases the endorphins synthesis in the Rolando gelatinous substance and in the dorsal horn of the spinal cord. The L-Arginine, which is the classic substrate of nitric oxide, carries on vasodilatory and anti- inflammatory action. Methods: Treatment was carried out on 447 cases and 435 patients (250 women and 185 men) between 20th May 1987 and 31st December 1999. The patients, whose age ranged from 25 to 70, were suffering from rheumatic, degenerative and traumatic pathologies as well as cutaneous ulcers. The majority of patients had been seen by orthopaedists and rheumatologists and had undergone x-ray, ultrasound scan, etc. All patients had previously received drug-based treatment and/or physiotherapy, with poor results. Two thirds were experiencing acute symptomatic pain, while the others presented a chronic pathology with recurrent crises. We used a pulsed IR diode laser, GaAs emitting at 904 nm. Frequency of treatment: 1 application per day for 5 consecutive days, followed by a 2-day interval. The percentage reduction in symptoms or improvement in functional status were determined on the basis of objective analysis as it happens in the Legal and Insurance Medicine field. Results: Very good results were achieved especially with cases of symptomatic osteoarthritis of the cervical vertebrae, with sport-related injuries, epicondylitis, osteoarthritis of the knee, periarthritis and with cutaneous ulcers. The beneficial action of the LLLT in the latter pathology is linked to the increase in collagen and to fibroblast proliferation. The total relief of the pain was achieved in 80% of acute and 65% of chronic cases. Conclusions: Treatment with 904 nm IR diode laser has substantially reduced the symptoms as well as improved the quality of life of the patient, thus postponing the need for surgery.

Tam, Giuseppe

2001-10-01

129

Bacterial action of carbon dioxide laser radiation in experimental dental root canals

International Nuclear Information System (INIS)

The ability of a carbon dioxide laser to sterilize the root canal of human teeth has been investigated. Three oral bacteria, Streptococcus sanguis, Streptococcus mutans, and Actinomyces viscosus, and three other bacteria, Bacillus cereus, Staphyloccus aureus, and Pseudomonoas aeruginosa were used as experimental organisms. Exposure of cells on glass slides to laser radiation showed there was little difference in the exposure required to kill these six organisms. Complete recovery of bacteria from the root canal was initially a problem and was only achieved when bacterial manipulations and removal were carried out in rapid succession, within 5 min of inoculation. However, the geometry of the instrumented canal and the laser alignment were major factors in achieving consistent cell death of oral bacteria in the root canals. Using sets of 10 teeth, four repeated exposures of 10 W for 1 s was found to sterilize 4 or more of the teeth

130

Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate

We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate RPA ,DA scales with TBGS -1 (S =PA,DA), TBGS being the Block -Gru¨neisen temperature. In the high-T Block -Gru¨neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio RPA/RDA scales with ?1/?n , n being the carrier concentration. We found that only for carrier concentration n ?1010cm-2, RPA/RDA>1. In the low-T Block -Gru¨neisen regime, and for n =1010cm-2, the ratio RPA/RDA scales with TBGDA/TBGPA?7.5 and RPA/RDA>1. In this regime, PA phonon dominates the electron scattering and RPA/RDAgraphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.

Nunes, O. A. C.

2014-06-01

131

Laser action from a terbium beta-ketoenolate at room temperature

Laser activity is achieved in a solution of terbium tris at room temperature in a liquid solvent of acetonitrile or p-dioxane. After precipitation, the microcrystals of hydrated tris chelate are filtered, washed in distilled water, and dried. They show no signs of deterioration after storage.

Bjorklund, S.; Filipescu, N.; Hurt, C. R.; Kellermeyer, G.; Mc Avoy, N.

1969-01-01

132

Phonon dispersion curves and phonon lifetimes in crystalline ammonia

International Nuclear Information System (INIS)

The theory of lattice dynamics of molecular crystals using atom-atom and multipole-multipole potentials developed in previous papers is extended to take account of anharmonic effects. Calculations of the dispersion curves and the density of states for the harmonic phonons in solid ammonia are presented. The finite phonon lifetimes due to anharmonicity are calculated for the zero wave vector modes and compared with experiment. (orig.)

133

Correlated phonons and the Tc-dependent dynamical phonon anomalies

International Nuclear Information System (INIS)

re anomalies observed in the Debye-Waller factor, dynamical pair correlations, and average atomic vibrational energies for a number of high-temperature superconductors. In our approach we do not claim nor believe that the electron-phonon interaction is the primary mechanism leading to high-temperature superconductivity. Nevertheless, our calculations suggest that the dynamically induced low-temperature phonon correlation model can account for these anomalies and illustrates their possible common origin. (Abstract Truncated)

134

Berry Curvature and Phonon Hall Effect

We establish the general phonon dynamics of magnetic solids by incorporating the Mead-Truhlar correction in the Born-Oppenheimer approximation. The effective magnetic-field acting on the phonons naturally emerges, giving rise to the phonon Hall effect. A general formula of the intrinsic phonon Hall conductivity is obtained by using the corrected Kubo formula with the energy magnetization contribution properly incorporated. The resulting phonon Hall conductivity is fully determined by the phonon Berry curvature and the dispersions. Based on the formula, the topological phonon system could be rigorously defined. In the low temperature regime, we predict that the phonon Hall conductivity is proportional to T^3 for the ordinary phonon systems, while that for the topological phonon systems has the linear T dependence with the quantized temperature coefficient. [4pt] [1] Tao Qin and Junren Shi, arXiv:1111.1322 (2011) [0pt] [2] Tao Qin, Qian Niu and Junren Shi, Phys. Rev. Lett., Accepted, (2011).

Qin, Tao; Shi, Junren

2012-02-01

135

Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well

The effect of the acoustic phonons nonequilibrium flux on the photoluminescence of the CdTe/ZnTe thin quantum well, excited quasi-resonantly by the He-Ne-laser is studied. It is established that the phonon flux leads to the change in the form of the quantum well luminescence band even by low generation capacities. It is assumed that the nonequilibrium phonons flux stimulates the excitons migration in the quantum well plane, conditioned by the tunnel transitions between the potential local minima, which are accompanied by the phonons induced emission

Onishchenko, E E; Zajtsev, V V

2001-01-01

136

Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well

International Nuclear Information System (INIS)

The effect of the acoustic phonons nonequilibrium flux on the photoluminescence of the CdTe/ZnTe thin quantum well, excited quasi-resonantly by the He-Ne-laser is studied. It is established that the phonon flux leads to the change in the form of the quantum well luminescence band even by low generation capacities. It is assumed that the nonequilibrium phonons flux stimulates the excitons migration in the quantum well plane, conditioned by the tunnel transitions between the potential local minima, which are accompanied by the phonons induced emission

137

Unconventional plasmon-phonon coupling in graphene

Digital Repository Infrastructure Vision for European Research (DRIVER)

We predict the existence of coupled plasmon-phonon excitations in graphene by using the self-consistent linear response formalism. The unique electron-phonon interaction in graphene leads to unconventional mixing of plasmon and optical phonon polarizations. We find that longitudinal plasmons couple exclusively to transverse optical phonons, whereas graphenes transverse plasmons couple only to longitudinal optical phonons. This coupling can serve as a magnifier for exploring the electron-ph...

Jablan, Marinko; Soljacic, Marin; Buljan, Hrvoje

2011-01-01

138

Picosecond X-ray studies of coherent folded acoustic phonons in a multiple quantum well

International Nuclear Information System (INIS)

Coherent folded acoustic phonons in a multilayered GaSb/InAs epitaxial heterostructure were generated by femtosecond laser pulses and studied by means of ultrafast x-ray diffraction. Coherent phonons excited simultaneously in the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the refractive index due to photogenerated free carriers

139

Spectral Singularities and CPA-Laser Action in a Weakly Nonlinear PT-Symmetric Bilayer Slab

We study optical spectral singularities of a weakly nonlinear PT-symmetric bilinear planar slab of optically active material. In particular, we derive the lasing threshold condition and calculate the laser output intensity. These reveal the following unexpected features of the system: 1. For the case that the real part of the refractive index $\\eta$ of the layers are equal to unity, the presence of the lossy layer decreases the threshold gain; 2. For the more commonly encountered situations when $\\eta-1$ is much larger than the magnitude of the imaginary part of the refractive index, the threshold gain coefficient is a function of $\\eta$ that has a local minimum. The latter is in sharp contrast to the threshold gain coefficient of a homogeneous slab of gain material which is a decreasing function of $\\eta$. We use these results to comment on the effect of nonlinearity on the prospects of using this system as a CPA-laser.

Mostafazadeh, Ali

2014-01-01

140

High efficiency laser action of 1% at. Yb3+:2O3 ceramic.

We report the spectroscopic characteristics and the laser performances of a low-doped 1% at. Yb:Sc(2)O(3) ceramic sample. Under end- pumping at 933 nm and 968 nm in quasi-CW mode, at 1040.5 nm the laser delivers a maximum output power of 4.3 W and 1.77 W, respectively with a corresponding slope efficiency of 74% and 80%, which are, to the best of our knowledge, the highest value reported in literature for ceramics. We explored the tuning range of the sample, which spans from 1005 nm to 1050.5 nm, and finally we characterized the low losses tunable cavity at 1032 nm. PMID:23037362

Pirri, Angela; Toci, Guido; Nikl, Martin; Vannini, Matteo

2012-09-24

141

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Sanders, G. D.; Stanton, C. J.; Kim, Chang-sub

2001-01-01

142

Interaction of optically coherent excited impurity system with heat-pulse ballistic phonons

It is studied the effect of the ballistic phonons of heat pulses of the nanosecond duration on the inverted photon echoes in ruby and in LaF3:Pr3+ for 4777 angstroms (3Po - 3H4) transition at temperature 2 K. The phonon pulses are generated by fast joule heating of thin Cu-film. The photon echo is used as the phonon detector. The decrease in the echo intensity is observed experimentally when ballistic longitudinal phonon pulse was propagated in optically excited volume during photon echo formation. The echo intensity is restored up to initial values by the second ballistic longitudinal phonon pulse in our experiment. In this case the each impurity ion is interacted with two alike phonon pulses after the recording and, accordingly, reading laser pulses. This indicates, that the main effect of the heat ballistic phonon on impurity consists in a shift of the impurity optical frequencies, instead of in relaxation transitions. The energy level shifts are not depended on duration of a pulse in experiment. The effect of the two pulses of the heat ballistic phonons is not additive.

Lisin, V. N.; Shegeda, Anatoly M.; Khabibullin, B. M.; Zuikov, Vladimir A.; Samartsev, Vitaly V.

1999-03-01

143

Dielectricity and Hard Phonons

The maximum value of the superconducting transition temperature Tc due to a phonon-mediated interaction was estimated by Cohen and Anderson in 1972 from ab initio considerations, and found to be about 10 K. McMillan's semi empirical estimate from 1968 gives a value of about 40 K. We consider these estimates on the basis of subsequent theoretical and experimental evidence, and pay attention in particular to the inhomogeneity of the electron gas. This inhomogeneity gives rise to local-field effects, which are mentioned by Cohen and Anderson, however without an explicit estimate of their effect on Tc. They claim that strong local-field effects cause a transition to covalent bonds, which inhibits superconductivity. We consider here strong local-field effects by making use of the inverse dielectric matrix (in reciprocal space), which we review in some detail. We distinguish between the electronic and ionic dielectric matrices, and show that the later can give rise to much stronger local fields, because of the inhe...

Weger, M

2002-01-01

144

Change of vanadium pentoxide optical properties under action of CO2-laser radiation

International Nuclear Information System (INIS)

It is experimentally shown and theoretically based from the point of view of modern representations about solid-state physics that semiconductor oxide capabilities for interaction with reducers (carbon and hydrogen) are shown during heating to such a temperature when they manifest their intrinsic conductivity, i.e. concentration of free electrons in a crystal lattice increases sharply. CO2-laser radiation exciting greatly Me-O lattice vibrations has thermochemical effect, as a result of which partial oxide dissociation takes photochemical process includes vacancy and another crystal defect formation taking place at medium temperatures of a smple, not exceeding 180 K

145

Unprecedented solid-state laser action from BODIPY dyes under UV-pumping radiation

Highly efficient and stable laser emission is demonstrated under drastic UV pumping conditions from recently synthesized BODIPY dye incorporated into polymer host. Under transversal pumping at 355 nm, lasing efficiencies of up to 29%, similar to those obtained in liquid phase, were obtained, with useful lifetimes (drop of the emission by 50%) of 70,000 pulses at 5 Hz repetition rate. The obtained efficiency and photostability are much higher than those obtained with usual commercial dyes emitting in the same spectral region, such as Coumarin 540A, under the same experimental conditions.

Pérez-Ojeda, M. E.; Martín, V.; Costela, A.; García-Moreno, I.; Arroyo Córdoba, I. J.; Peńa-Cabrera, E.

2012-03-01

146

Terahertz emission from target under the action of powerful laser pulses

International Nuclear Information System (INIS)

The target irradiated by high intensity (1018 - 1019 W/cm2) short (10 - 100 ps) laser pulses generates plasma and electron emission from plasma produce virtual cathode. Virtual cathode oscillation leads to power generation in a THz range. This generation mechanism has been studied by numerical simulations using a relativistic electromagnetic PIC code and appears to be very similar to those of usual vircator. However plasma ions result in not only additional electron deceleration but electron focusing. Thereof the efficiency of generation in these radiation sources is several times higher compared to that in the analogous traditional vircators. This mechanism can be used for high power THz range radiation sources creation.

147

This article describes the development of minimally invasive methods in the treatment of lumbar discopathy, with particular attention to percutaneous laser disc decompression (PLDD). The authors discus the therapeutic operating mechanism of PLDD, emphasizing the importance of the thermal characteristics of laser light, which is responsible for the vaporization and ablation of a small amount of tissue from the nucleus pulposus. This causes a significant reduction in pressure in the closed structure of the disc, and consequently reduced compression exerted by the disk on the dural sac and the nerve roots. Improvement in the flow of cerebro-spinal fluid has also been observed on the level at which the operation is performed. On the basis of our own experience and the reports of other authors, we have specified indications and contra-indications for PLDD. Our conclusion is that PLDD is an effective treatment method for low back pain and ischialgia caused by protrusion or herniation of the nucleus pulposus, with elimination or significant reduction in symptoms in over 75% of those treated; reduction or resolution of neurological deficits that arise in the course of lumbar discopathy has also been observed. This method enables one-stage treatment of multi-level degenerative changes in the intervertebral disc. The only absolute contraindications for PLDD are the presence of sequestration, disturbances in blood coagulation, and bacterial infection. PMID:17675991

Maksymowicz, Wojciech; Barczewska, Monika; Sobieraj, Andrzej

2004-06-30

148

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 QDcavity 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 Kćr

2012-01-01

149

Scattering of phonons by dislocations

International Nuclear Information System (INIS)

By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The most basic questions are still debated in the literature. It therefore is pointless to attempt a quantitative comparison between an extensive accumulation of experimental data on the one hand, and the numerous theoretical models on the other. Instead, this chapter will attempt to glean a few qualitative conclusions from the existing experimental data. These results will then be compared with two general models which incorporate, in a qualitative manner, most of the proposed theories of the phonon-dislocation interaction. Until very recently, measurement of thermal conductivity was the only means available to probe the interaction between phonons and defects at phonon frequencies above the standard ultrasonic range of approx. = 109 Hz. The introductory paragraphs provide a brief review of the thermal-conductivity technique and the problems which are encountered in practice. There is also a brief presentation of the theoretical models and the complications that may occur in more realistic situations

150

Demonstration of room-temperature laser action at 2.5 mum from Cr(2+):Cd(0.85)Mn(0.15)Te.

Room-temperature laser action from Cr(2+)-doped Cd(0.85)Mn(0.15)Te has been demonstrated for what is believed to be the first time. We achieved pulsed laser operation centered at ~2.5mu m by pumping into the mid-infrared absorption band of Cr(2+) ions by use of the 1.907- mum output of a H(2) Raman-shifted Nd:YAG laser. The output of the free-running Cr(2+):Cd(0.85)Mn(0.15)Te laser had a width of ~50 nm (FWHM), and the slope efficiency was calculated to be 5.5% under nonoptimum conditions. PMID:18185788

Hömmerich, U; Wu, X; Davis, V R; Trivedi, S B; Grasza, K; Chen, R J; Kutcher, S

1997-08-01

151

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

152

Phonons from neutron powder diffraction

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

153

Nanoscale phononic interconnects in THz frequencies.

Phononic computing is emerging as an alternative computing paradigm to the conventional electronic and optical computing. In this study, we propose and analyze various phononic interconnects, such as nano-scaled phononic resonators, waveguides and switches, on the ?111? surface of 3C-SiC and 3C-GeSi with substitutional and vacancy defects. This is achieved by simultaneously introducing defects of various types, and by varying their specific locations on the surface. To calculate the intrinsic and the defect-induced vibrational properties, such as the phononic bandgap and the variation in the phonon spectra, the total phonon density of states (TPDOS) and the partial phonon density of states (PPDOS) were calculated using molecular dynamics simulations with semi-empirical potentials. The proposed phononic interconnects, in conjunction with electronic and/or photonic interconnects, can be used in the current and future devices. PMID:25260120

Sgouros, Aris P; Neupane, Mahesh R; Sigalas, M M; Aravantinos-Zafiris, N; Lake, Roger K

2014-10-01

154

Structure of the phonon vacuum state

The action of the long-range residual force on the the expectation value of observables in the nuclear ground-states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the (quasi-)particle ground-state. After estimating the improvements over the predictions of the independent particle approximation we compare the ground-state wave functions obtained using the presented approach with those obtained using the conventional random phase approximation (RPA) and its extended version. The problem with overbinding of the nuclear ground state calculated using the RPA is shown to be removed if one sticks to the prescriptions of the present approach. The reason being that the latter conforms to the original variational formulation. Calculations are performed within the two-level Lipkin model in which we present results for the binding energies.

Mishev, S

2012-01-01

155

Phonon creation by gravitational waves

We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique is within experimental reach.

Sabín, Carlos; Ahmadi, Mehdi; Fuentes, Ivette

2014-01-01

156

Phonon dynamics of americium telluride

We report for the first time the complete phonon dispersion curves for Americium telluride (AmTe) using a breathing shell models (BSM) to establish their predominant ionic nature. The results obtained in the present study show the general features of the phonon spectrum. We could not compare our results with the experimental measurements as they are not available so far. We emphasize the need of neutron scattering measurements to compare our results. We also report, for the first time specific heat for this compound.

Arya, B. S.; Aynyas, Mahendra; Ahirwar, Ashok K.; Sanyal, S. P.

2013-06-01

157

Resonances in ferroelectric phononic superlattice

The periodically poled ferroelectric wafer is a two-dimensional phononic superlattice. The important applications of such a solid include ultrasonic transducers at the micro/nano-scale for low intensity ultra-sonography, ferroelectric data storage, and development of very high frequency chips for next generation communication and information technologies, and others. In this work, we show theoretically and experimentally that a ferroelectric phononic superlattice has two distinctive resonances in acousto-electric transformation. They are associated with a split acoustic mode at the boundary between the first and second acoustic Brillouin zone.

Ostrovskii, Igor; Cremaldi, Lucien

2012-10-01

158

Introduction to phonons and electrons

This book focuses on phonons and electrons, which the student needs to learn first in solid state physics. The required quantum theory and statistical physics are derived from scratch. Systematic in structure and tutorial in style, the treatment is filled with detailed mathematical steps and physical interpretations. This approach ensures a self-sufficient content for easier teaching and learning. The objective is to introduce the concepts of phonons and electrons in a more rigorous and yet clearer way, so that the student does not need to relearn them in more advanced courses. Examples are th

Lou, Liang-fu

2003-01-01

159

Phonon creation by gravitational waves

We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique could be, in principle, within experimental reach in a medium-term timescale.

Sabín, Carlos; Bruschi, David Edward; Ahmadi, Mehdi; Fuentes, Ivette

2014-08-01

160

Unconventional plasmon-phonon coupling in graphene

Digital Repository Infrastructure Vision for European Research (DRIVER)

We calculate hybridization of plasmons and intrinsic optical phonons in graphene by using the self-consistent linear response formalism. We find that longitudinal plasmons (transverse magnetic modes) couple exclusively to transverse optical phonons, whereas graphene's transverse plasmons (transverse electric modes) couple only to longitudinal optical phonons. This mixing of polarizations is in contrast to the usual plasmon-phonon coupling in other systems. The resulting chan...

Jablan, M.; Soljac?ic?, M.; Buljan, H.

2010-01-01

161

Ion-phonon interaction in semiconductors

International Nuclear Information System (INIS)

A short review of the experimental results of the infrared luminescence of Co++ impurity centers in II-VI semiconduct ing compounds will be given. These systems show an intermediate ion-phonon interaction which makes it possible to observe both no-phonon and one-phonon structure. Due to extreme simplicity of the electronic structure the interaction of the ionic system with the whole phonon density of states (as a function of temperature) can be interpreted quantitatively

162

Laser phase noise effects on the dynamics of optomechanical resonators

International Nuclear Information System (INIS)

We investigate theoretically the influence of laser phase noise on the cooling and heating of a generic cavity optomechanical system. We derive the back-action damping and heating rates and the mechanical frequency shift of the radiation-pressure-driven oscillating mirror, and derive the minimum phonon occupation number for small laser linewidths. We find that, in practice, laser phase noise does not pose serious limitations to ground-state cooling. Additionally, we explore the regime of parametric amplification where coherent oscillations of the mirror are realizable. It is found that heating from laser phase noise is of significance and can cause the onset of instabilities. We then consider the effects of laser phase noise in a parametric cavity driving scheme that minimizes the back-action heating of one of the quadratures of the mechanical oscillator motion. Laser linewidths, narrow compared to the decay rate of the cavity field, do not pose any significant problems in an experimental setting, but broader linewidths limit the practicality of this back-action evasion method.

163

A study of non-equilibrium phonons in GaAs/AlAs quantum wells

Energy Technology Data Exchange (ETDEWEB)

In this thesis we have studied the non-equilibrium phonons in GaAs/AlAs quantum wells via Raman scattering. We have demonstrated experimentally that by taking into account the time-reversal symmetry relation between the Stokes and anti-Stokes Raman cross sections, one can successfully measure the non-equilibrium phonon occupancy in quantum wells. Using this technique, we have studied the subject of resonant intersubband scattering of optical phonons. We find that interface roughness plays an important role in resonant Raman scattering in quantum wells. The lateral size of the smooth regions in such interface is estimated to be of the order of 100 {Angstrom}. Through a study of photoluminescence of GaAs/AlAs quantum wells under high intensity laser excitation, we have found that band nonparabolicity has very little effect on the electron subband energies even for subbands as high as a few hundred meV above the lowest one. This finding may require additional theoretical study to understand its origin. We have also studied phonon confinement and propagation in quantum wells. We show that Raman scattering of non-equilibrium phonons in quantum wells can be a sensitive measure of the spatial extent of the longitudinal optical (LO) phonons. We deduce the coherence length of LO phonons in GaAs/Al{sub x}Ga{sub 1-x}As quantum wells as a function of the Al concentration x.

Su, Zhenpeng

1996-11-01

164

Coherent longitudinal acoustic phonon approaching THz frequency in multilayer Molybdenum Disulphide.

Coherent longitudinal acoustic phonon is generated and detected in multilayer Molybdenum Disulphide (MoS2) with number of layers ranging from 10 to over 1300 by femtosecond laser pulse. For thin MoS2, the excited phonon frequency exhibits a standing wave nature and shows linear dependence on the sample thickness. The frequency varies from 40 GHz to 0.2 THz (10 layers), which promises possible application in THz frequency mechanical resonators. This linear thickness dependence gradually disappears in thicker samples above about 150 layers, and the oscillation period shows linear dependence on the probe wavelength. From both the oscillation period of the coherent phonon and the delay time of acoustic echo, we can deduce a consistent sound velocity of 7.11*10(3) m/s in MoS2. The generation mechanisms of the coherent acoustic phonon are also discussed through pump power dependent measurement. PMID:25031087

Ge, Shaofeng; Liu, Xuefeng; Qiao, Xiaofen; Wang, Qinsheng; Xu, Zhen; Qiu, Jun; Tan, Ping-Heng; Zhao, Jimin; Sun, Dong

2014-01-01

165

Sound and heat revolutions in phononics.

The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics. PMID:24226887

Maldovan, Martin

2013-11-14

166

Sound and heat revolutions in phononics

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

Maldovan, Martin

2013-11-01

167

Nonlinear phononics using atomically thin membranes

Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic BoseEinstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics.

Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

2014-09-01

168

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 succesfully 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-aulait macules should not be treated as the relaps...

Passeron, Thierry

2012-01-01

169

New facets of quadrupole phonon

International Nuclear Information System (INIS)

A systematic approach to even-even, odd-even, and odd-odd nuclei, based on spherical quadrupole phonons, is discussed. The truncated quadrupole-phonon model (TQM), based on SU(6) symmetry, describes even-even nuclei in the collective approximation. In the particle-TQM interaction model (PTQM), an odd single particle is coupled to the TQM core. In the SU(number) limit of the PTQM, analogs of Nilsson states appear. In the cluster-vibration model, even-even, odd-even, and odd-odd nuclei are described by coupling a few selected shell-model single particles to the quadrupole vibration (harmonic or TQM). The quasicluster-vibration model (QCVM) is an approximation of the CVM in the sense that the cluster consists of a few quasiparticles. Both the diagonalization and the diagrammatic approaches are discussed. The latter leads to generalized vibrational rules (GVR), as a consequence of the nuclear Ward identity. 106 references, 2 tables

170

Phonons from neutron powder diffraction

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 compar...

Dimitrov, D. A.; Louca, D.; Ro?der, H.

1998-01-01

171

This paper reports the first use of a N2O laser for optically pumping vinyl halides, to obtain new cw submillimeter laser lines. Eighteen far-infrared (FIR) emissions have been observed in vinyl chloride, twenty five in vinyl bromide and thirty eight in vinyl flouride.

Gastaud, C.; Redon, M.; Belland, P.; Fourrier, M.

1984-06-01

172

Resonant Enhancement of Coherent Phonons in Carbon Nanotubes Observed with Sub-10fs Time Resolution

Directory of Open Access Journals (Sweden)

Full Text Available Using wavelength-resolved pump-probe spectroscopy with a sub-10-fs laser, we investigated resonant enhancement of radial breathing mode and G-mode coherent phonons in carbon nanotubes (CNTs, and successfully distinguished the electronic states of CNTs with different chiralities.

Yanagi K.

2013-03-01

173

Photon-absorption-induced intersubband optical-phonon scattering of electrons in quantum wells

International Nuclear Information System (INIS)

In the presence of a normally incident intense mid-IR pulsed laser field, both photon-absorption-induced intrasubband and intersubband phonon-scattering of electrons are found by including the photon-assisted phonon-scattering process in a Boltzmann equation for phonon energies that are smaller than the energy separation between two electron subbands in a quantum well. The ultrafast dynamics of the electron distributions for different subbands is studied with various lattice temperatures, photon energies, field strengths, and quantum-well widths. Upward steps found in the differences between the electron distributions with/without the photon-assisted process are attributed to either photon-absorption-induced phonon scattering of electrons via intrasubband transitions or the photon-absorption-induced phonon scattering of electrons via intersubband transitions in quantum wells. The photon-absorption-induced phonon absorption by intersubband transitions of electrons from the first to the second subband is a unique feature in quantum-well systems and is found to have a significant effect on the electron populations in both subbands

174

Observation of coherent phonon generation in C60 films

By studying the temporal behavior of the optical density of C60 thin film with the help of femtosecond laser spectroscopy the coherent phonon oscillations in the frequency region 10 - 400 cm-1 (including with odd symmetry) in the wide spectral region of probing h(omega) pr equals 1.78 divided by 2.34 eV was detected. Spectral dependence of photoinduced response permits to observe selectively the relaxation of electrons in different bands. The possibility of reversible polymerization in excited state is discussed.

Dobryakov, A. L.; Farztdinov, V. M.; Kovalenko, S. S.; Letokhov, Vladilen S.; Lozovik, Yurii E.; Matveets, Juru A.

1996-05-01

175

Electron-phonon interaction effects in tantalum

International Nuclear Information System (INIS)

The results of calculations for a number of electron-phonon interaction effects for tantalum are presented. The calculations are based on Korringa-Kohn-Rostoker energy bands, Born--von Karman phonons, and the rigid-muffin-tin approximation for the electron-phonon matrix element. The calculated Eliashberg spectral function ?2F is compared with the earlier tunneling data of Shen and the proximity tunneling data of Wolf et al. The calculated and tunneling transverse-phonon peaks agree well, but the height of the tunneling longitudinal-phonon peak is smaller than the calculated results. The calculated electron-phonon coupling parameter ? is 0.88, which is larger than the ? determined from superconducting tunneling and superconducting T/sub c/ measurements, but is slightly smaller than the ? determined from electronic specific-heat measurements. Calculated phonon linewidths along various symmetry directions are presented. The temperature dependence of the electrical resistivity due to phonon scattering is calculated in the lowest-order variational approximation and it agrees with experiment. The point-contact spectral function of Kulik, G(?), is determined and compared with ?2F(?). The agreement between calculated and measured electronic specific heat and high-temperature electrical resistivity gives strong support to the validity of the rigid-muffin-tin approximation for electron-phonon matrix elements

176

International Nuclear Information System (INIS)

Calculations of the phonon dispersion curves and the electron-phonon coupling in Nb3Sn are presented, using the non-orthogonal tight-binding method without any adjustable parameter in the theory. The calculations are based on realistic energy bands. The results are in good agreement with the available experimental data. Various anomalous features in the phonon dispersion curves are predicted, especially along the ? direction of the Brillouin zone. The importance of the chain structure for the large electron-phonon coupling is stressed. (orig.)

177

International Nuclear Information System (INIS)

Phonon-induced fluorescence changes have been obtained in the shape of the spectra of selectively laser-excited dye molecules in noncrystalline organic solids, e.g. perylene molecules in Langmuir films of Cd arachidate. The changes in the zero-phonon lines and in the sidebands are observed after heat pulse irradiation (phonon memory), and by realtime phonon detection. The results are explained by electron-phonon interaction and by the model of matrix-shift variations caused by phonon-induced transitions in two-level systems in amorphous solids. (orig.)

178

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.

2006-01-01

179

Phonon-phonon coupling and the stability of the high-temperature bcc phase of Zr

International Nuclear Information System (INIS)

Phonon-phonon coupling strengths have been derived from first-principles total energy calculations for bcc Zr. It is shown that the instability leading to the bcc-hcp first-order phase transition in Zr is overcome at high temperatures by the strong interactions between the T1 N-point phonon and other low-lying (110) T1 vibrational modes

180

In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from 100 to 870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of 15-20 GHz, which is 20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are Al-AlxOy-Al tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the efficiency of their detection by an STJ detector. We demonstrate that the phonons propagate ballistically through a silicon microstructure, and that submicron spatial resolution is realizable in a design such as ours. Spectrally resolved measurements of phonon transport in nanoscale structures and nanomaterials will further the engineering and exploitation of phonons, and thus have important ramifications for nanoscale thermal transport as well as the burgeoning field of nanophononics.

Otelaja, O. O.; Hertzberg, J. B.; Aksit, M.; Robinson, R. D.

2013-04-01

181

International Nuclear Information System (INIS)

In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from ?100 to ?870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of ?1520 GHz, which is ?20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are AlAlxOyAl tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the efficiency of their detection by an STJ detector. We demonstrate that the phonons propagate ballistically through a silicon microstructure, and that submicron spatial resolution is realizable in a design such as ours. Spectrally resolved measurements of phonon transport in nanoscale structures and nanomaterials will further the engineering and exploitation of phonons, and thus have important ramifications for nanoscale thermal transport as well as the burgeoning field of nanophononics. (paper)

182

International Nuclear Information System (INIS)

The collision of two atoms in an external magnetic field and in the field of laser radiation with formation of Fano-Feshbach resonances is investigated. At one-photon resonance of laser radiation with two discrete vibrational states of molecule the dressed states are formed (Autler-Townes effect) which form Fano-Feshbach resonances in interaction with the external magnetic field. In addition, the lower molecular vibrational state is coupled with the continuum of the elastic channel via also LICS (laser-induced continuum structure) forming laser-induced resonance. The cross-sections of elastic and inelastic resonant scattering and expression for the scattering length depending on the external magnetic and laser radiation fields is obtained

183

International Nuclear Information System (INIS)

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 LiNbO3, BaNaNbO5, LiIO3 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 CO2 laser pulses. The analysis of the obtained results with account for the chemical reaction thermodynamics, thermotension and other factors is presented

184

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English 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 fields show oscillations at frequencies characteristic of those of coupled plasmon-phonon modes. Our results are consistent with recent experimental data.

Fabrício M., Souza; J. Carlos, Egues.

185

Size dependence of electron-phonon coupling in ZnO nanowires

Raman spectra of ZnO powder and free-standing nanowires prepared by laser ablation have been studied. All observed vibrational modes in ZnO powder, both first order and higher order scattering, were assigned on the basis of group theoretical analysis. The size dependence of the coupling strength between electron and longitudinal optical (LO) phonon was experimentally estimated. It was found that the coupling strength determined by the ratio of second- to first-order Raman scattering cross sections diminishes with decreasing nanowire diameter, and the Frohlich interaction plays the main role in electron-phonon coupling in ZnO.

Wang, R. P.; Xu, G.; Jin, P.

2004-03-01

186

The effect of pump noise on the synchronisation of selfmodulation oscillations in a solid-state ring laser with periodic pump modulation is studied numerically and experimentally. It is found that, in contrast to desynchronisation that usually occurs under action of noise in the case of 1/1 synchronisation of self-oscillations by a periodic signal, the effect of noise on 1/2 synchronisation may be positive, namely, at a sufficiently low intensity, pump noise is favourable for synchronisation of self-oscillations, for narrowing of their spectrum, and for increasing the signal-to-noise ratio.

Dudetskiy, V. Yu; Lariontsev, E. G.; Chekina, S. N.

2014-09-01

187

Phonon coupling effect upon transport in nanoscale polymers

International Nuclear Information System (INIS)

In an environmental coupled polymer, a variation of the conductivity is evaluated, which results from the external electronphonon interaction coupling with the internal one. A quantized current appears under the external phonon coupling. The resonant tunnelling in the nanoscale polymer driven by the internal electronphonon interaction is enhanced by the external phonon coupling. In addition, the external electronphonon interaction softens the stiffness of the polymer. -- Highlights: ? A quantized current appearing under the external phonon coupling is evaluated. ? The resonant tunnelling is enhanced by the external phonon coupling. ? The external electronphonon interaction softens the stiffness of the polymer.

188

The effect of Landau-Zener dynamics on phonon lasing

Optomechanical systems couple light to the motion of nanomechanical objects. Intriguing new effects are observed in recent experiments that involve the dynamics of more than one optical mode. There, mechanical motion can stimulate strongly driven multi-mode photon dynamics that acts back on the mechanics via radiation forces. We show that even for two optical modes Landau-Zener-Stueckelberg oscillations of the light field drastically change the nonlinear attractor diagram of the resulting phonon lasing oscillations. Our findings illustrate the generic effects of Landau-Zener physics on back-action induced self-oscillations.

Wu, Huaizhi; Heinrich, Georg; Marquardt, Florian

2013-12-01

189

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.

Samoilov V.

2011-01-01

190

Single-phonon X-ray scattering

International Nuclear Information System (INIS)

Determinations of single-phonon diffuse X-ray scattering in lines, areas or volumes of reciprocal space at any temperature, using eigendata given by a lattice dynamical model. Evaluation of contribution to one-phonon scattering from ionic deformations, modelled by a shell model. (orig.)

191

International Nuclear Information System (INIS)

A numerical investigation was made of the structure of thermocapillary convection of a laser melt formed by radiation with various parameters in the specific case of SS304 stainless steel. A critical Reynolds number was found: above this number a single-vortex structure of the melt flow changed to two vortices. A comparison of the shape of the molten pool predicted by numerical calculations with experiments confirmed the existence of a two-vortex structure initiated solely by thermocapillary forces on the melt surface. A correlative dependence was proposed for relating the laser radiation parameters to those of the molten pool when a two-vortex flow structure appeared. (interaction of laser radiation with matter. laser plasma)

192

Sensitivity of the system of cytochrome P-450 of poultry liver to the action of red laser light

International Nuclear Information System (INIS)

It is detected that irradiation of poultry embryos by red laser light (? = 633 nm) at a doze of 1 - 6 mJ can influence a level of the cytochrome P-450 oxidized form in poultry liver. It is supposed that this level is changed due to variations in the content of lipid peroxide compounds in tissue under low-level red laser radiation and is one of the factors of regulation of the intensity of peroxide processes in tissues

193

Propagating phonons coupled to an artificial atom.

Quantum information can be stored in micromechanical resonators, encoded as quanta of vibration known as phonons. The vibrational motion is then restricted to the stationary eigenmodes of the resonator, which thus serves as local storage for phonons. In contrast, we couple propagating phonons to an artificial atom in the quantum regime and reproduce findings from quantum optics, with sound taking over the role of light. Our results highlight the similarities between phonons and photons but also point to new opportunities arising from the characteristic features of quantum mechanical sound. The low propagation speed of phonons should enable new dynamic schemes for processing quantum information, and the short wavelength allows regimes of atomic physics to be explored that cannot be reached in photonic systems. PMID:25213379

Gustafsson, Martin V; Aref, Thomas; Kockum, Anton Frisk; Ekström, Maria K; Johansson, Göran; Delsing, Per

2014-10-10

194

Nonlinear phononics using atomically thin membranes.

Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics. PMID:25204322

Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

2014-01-01

195

Strong squeezing via phonon mediated spontaneous generation of photon pairs

We propose a scheme for generating squeezed light by using a double-cavity optomechanical system driven by a blue detuned laser in one cavity and by a red detuned laser in the other. This double-cavity system is shown to effectively mimic an interaction that is similar to the one for a downconverter, which is known to be a source of strong squeezing for light fields. There are however distinctions, as the phonons which lead to such an interaction can contribute to the quantum noise. We show that squeezing of the output fields, of the order of 10 dB, can be achieved even for an effective mechanical mode occupation number of about 4, which for the chosen parameters corresponds to 10 mK. Our results are generic and applicable to a wide class of electromechanical and optomechanical systems involving the interaction of two electromagnetic modes and one mechanical mode.

Qu, Kenan; Agarwal, G. S.

2014-11-01

196

International Nuclear Information System (INIS)

The paper discusses 1. Classical equations of motion 2. Lattice waves in the crystal 3. State density and Debye spectrum 4. Two - atom linear chain 5. Experimental determination of dispersion corves for simple solid bodies 5.1. Inelastic coherent neutron scattering 5.2. Rare gas crystals 5.3. Alkali halides. (orig.)

197

[LO phonon-plasmon coupled mode in hexagonal IngaN alloy].

Raman scattering spectra of hexagonal InGaN/GaN film, excited with 532 and 488 nm visible laser lines and 325 nm UV laser line, were investigated at room temperature and 78 K. The sample was grown by metalorganic chemical vapor deposition on a sapphire substrate. Excited with 532 and 488 nm visible laser lines, the E2 and A1 (LO) modes were observed at about 571.3 and 736.4 cm(-1), respectively. These scattering signals mainly originate from GaN layer. Excited with 325 nm UV laser line, the E2 mode shifts to 569.7 cm(-1), while A1 (LO) mode shifts to 730.3 cm(-1) and resonance is enhanced. These scattering signals originate from InGaN layer. A broad feature at high frequency of A1 (LO) mode was observed in spectroscopy excited with visible laser line, and was attributed to the LO phonon-plasmon coupled mode of InGaN layer. The electron concentration of InGaN film determined from the frequency of the coupled mode is ne = 1.61 x 10(18) cm(-3). Excited with 325 nm UV laser light, the LO phonon-plasmon coupled mode is absent, and the scattering signal of A1 (LO) mode mainly originates from the surface depletion layer of the sample. The thickness of the surface depletion layer is about 40 nm. Furthermore, the scattering intensities of LO phonon-plasmon coupled mode at room temperature and 78 K were compared and analyzed. The screening wave vectors of plasmon at different temperatures were calculated. At low temperature, the screening wave vector increases, the damping of the plasmon decreases, so the LO phonon-plasmon coupled mode becomes stronger. This work is helpful in understanding the property of InGaN and in developing the optoelectronic devices of nitride. PMID:19385224

Wang, Rui-Min; Chen, Guang-De

2009-01-01

198

Theory for ultrafast dynamics in cuprates: role of electron-phonon coupling

Energy Technology Data Exchange (ETDEWEB)

We present a theory for ultrafast nonequilibrium dynamics in cuprate superconductors. In a typical time-resolved spectroscopy experiment, the sample is exited with an intense laser pulse, creating nonequilibrium quasiparticles which subsequently can relax via various scattering processes, restoring the superconducting state. We use the method of density matrix theory to study the optical excitation and relaxation dynamics in cuprates from a microscopical viewpoint. In particular, we consider scattering with optical phonons, looking at the interplay between relaxation of the excited quasiparticles and the creation of nonequilibrium phonon distributions; the superconducting state is restored on a 10 picosecond timescale, while the phonons have longer relaxation times. Time-resolved pump-probe spectra are calculated and compared both to quasi-equilibrium models and experimental results. (orig.)

Unterhinninghofen, J.; Manske, D. [Max-Planck-Inst. fuer Festkoerperforschung, Stuttgart (Germany); Knorr, A. [Technische Univ., Berlin (Germany)

2007-07-01

199

Theory for ultrafast dynamics in cuprates: role of electron-phonon coupling

International Nuclear Information System (INIS)

We present a theory for ultrafast nonequilibrium dynamics in cuprate superconductors. In a typical time-resolved spectroscopy experiment, the sample is exited with an intense laser pulse, creating nonequilibrium quasiparticles which subsequently can relax via various scattering processes, restoring the superconducting state. We use the method of density matrix theory to study the optical excitation and relaxation dynamics in cuprates from a microscopical viewpoint. In particular, we consider scattering with optical phonons, looking at the interplay between relaxation of the excited quasiparticles and the creation of nonequilibrium phonon distributions; the superconducting state is restored on a 10 picosecond timescale, while the phonons have longer relaxation times. Time-resolved pump-probe spectra are calculated and compared both to quasi-equilibrium models and experimental results. (orig.)

200

Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer.

We report Raman spectra measurements on a MoS(2) monolayer supported on SiO(2) as a function of temperature. Unlike in previous studies, the positions of the two main Raman modes, E(2g)(1) and A(1g) exhibited nonlinear temperature dependence. Temperature dependence of phonon shifts and widths is explained by optical phonon decay process into two acoustic phonons. On the basis of Raman measurements, local temperature change under laser heating power at different global temperatures is derived. Obtained results contribute to our understanding of the thermal properties of two-dimensional atomic crystals and can help to solve the problem of heat dissipation, which is crucial for use in the next generation of nanoelectronic devices. PMID:24897497

Taube, Andrzej; Judek, Jaros?aw; Jastrz?bski, Cezariusz; Duzynska, Anna; ?witkowski, Krzysztof; Zdrojek, Mariusz

2014-06-25

201

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese OBJETIVO: Avaliar a açăo precoce do laser terapęutico e do ultrassom no processo de regeneraçăo de uma lesăo experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesăo do nervo ciático por compressăo, através de uma pinça hemostática acima da fos [...] sa poplítea. Os animais foram divididos em tręs grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervençăo terapęutica. GII: intervençăo terapęutica do laser ArGaAl. GIII: intervençăo terapęutica do ultrassom Pulsado. Iniciamos as intervençőes terapęuticas 24 horas após a lesăo, com aplicaçőes 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 diminuiçăo (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 avaliaçăo final do IFC o GII sobressaiu ao GIII. Quanto a cicatrizaçăo observou-se grande melhora no GII e GIII. CONCLUSĂO: Os resultados evidenciaram que a recuperaçăo nervosa foi maior com a aplicaçăo do laser. Nível de evidęncia II, Estudos terapęuticos - Investigaçăo 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 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 Eugęnio Calçada Dias, Gabriel; Ana Paula Oliveira, Borges.

202

Directory of Open Access Journals (Sweden)

Full Text Available OBJETIVO: Avaliar a açăo precoce do laser terapęutico e do ultrassom no processo de regeneraçăo de uma lesăo experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesăo do nervo ciático por compressăo, através de uma pinça hemostática acima da fossa poplítea. Os animais foram divididos em tręs grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervençăo terapęutica. GII: intervençăo terapęutica do laser ArGaAl. GIII: intervençăo terapęutica do ultrassom Pulsado. Iniciamos as intervençőes terapęuticas 24 horas após a lesăo, com aplicaçőes 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 diminuiçăo (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 avaliaçăo final do IFC o GII sobressaiu ao GIII. Quanto a cicatrizaçăo observou-se grande melhora no GII e GIII. CONCLUSĂO: Os resultados evidenciaram que a recuperaçăo nervosa foi maior com a aplicaçăo do laser. Nível de evidęncia II, Estudos terapęuticos - Investigaçăo 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

2012-01-01

203

International Nuclear Information System (INIS)

The analytical theory for the directivity patterns of ultrasounds emitted from laser-irradiated interface between two isotropic solids is developed. It is valid for arbitrary combinations of transparent and opaque materials. The directivity patterns are derived both in two-dimensional and in three-dimensional geometries, by accounting for the specific features of the sound generation by the photo-induced mechanical stresses distributed in the volume, essential in the laser ultrasonics. In particular, the theory accounts for the contribution to the emitted propagating acoustic fields from the converted by the interface evanescent photo-generated compression-dilatation waves. The precise analytical solutions for the profiles of longitudinal and shear acoustic pulses emitted in different directions are proposed. The developed theory can be applied for dimensional scaling, optimization, and interpretation of the high-pressure laser ultrasonics experiments in diamond anvil cell

204

Energy Technology Data Exchange (ETDEWEB)

The analytical theory for the directivity patterns of ultrasounds emitted from laser-irradiated interface between two isotropic solids is developed. It is valid for arbitrary combinations of transparent and opaque materials. The directivity patterns are derived both in two-dimensional and in three-dimensional geometries, by accounting for the specific features of the sound generation by the photo-induced mechanical stresses distributed in the volume, essential in the laser ultrasonics. In particular, the theory accounts for the contribution to the emitted propagating acoustic fields from the converted by the interface evanescent photo-generated compression-dilatation waves. The precise analytical solutions for the profiles of longitudinal and shear acoustic pulses emitted in different directions are proposed. The developed theory can be applied for dimensional scaling, optimization, and interpretation of the high-pressure laser ultrasonics experiments in diamond anvil cell.

Nikitin, Sergey M., E-mail: sergey.nikitin.Etu@univ-lemans.fr, E-mail: vitali.goussev@univ-lemans.fr [LAUM, UMR-CNRS 6613, Université du Maine, 72085 Le Mans (France); IMMM, UMR-CNRS 6283, Université du Maine, 72085 Le Mans (France); LSPM, UPR-CNRS 3407, Université Paris Nord, 93430 Villetaneuse (France); Tournat, Vincent; Chigarev, Nikolay; Castagnede, Bernard; Gusev, Vitalyi, E-mail: sergey.nikitin.Etu@univ-lemans.fr, E-mail: vitali.goussev@univ-lemans.fr [LAUM, UMR-CNRS 6613, Université du Maine, 72085 Le Mans (France); Bulou, Alain [IMMM, UMR-CNRS 6283, Université du Maine, 72085 Le Mans (France); Zerr, Andreas [LSPM, UPR-CNRS 3407, Université Paris Nord, 93430 Villetaneuse (France)

2014-01-28

205

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

2012-09-01

206

The analytical theory for the directivity patterns of ultrasounds emitted from laser-irradiated interface between two isotropic solids is developed. It is valid for arbitrary combinations of transparent and opaque materials. The directivity patterns are derived both in two-dimensional and in three-dimensional geometries, by accounting for the specific features of the sound generation by the photo-induced mechanical stresses distributed in the volume, essential in the laser ultrasonics. In particular, the theory accounts for the contribution to the emitted propagating acoustic fields from the converted by the interface evanescent photo-generated compression-dilatation waves. The precise analytical solutions for the profiles of longitudinal and shear acoustic pulses emitted in different directions are proposed. The developed theory can be applied for dimensional scaling, optimization, and interpretation of the high-pressure laser ultrasonics experiments in diamond anvil cell.

Nikitin, Sergey M.; Tournat, Vincent; Chigarev, Nikolay; Bulou, Alain; Castagnede, Bernard; Zerr, Andreas; Gusev, Vitalyi

2014-01-01

207

Phonons dispersions in auxetic lattices

Energy Technology Data Exchange (ETDEWEB)

The modes of vibrations in auxetic structures are studied, with models where the two-dimensional lattice is represented by a planar mesh with rod-like particles connected by strings. An auxetic membrane can be obtained modifying a honeycomb one, according to a model proposed by Evans et al. in 1991 and used to explain a negative elastic Poisson's ratio. This property means that auxetic materials have a lateral extension, instead to shrink, when they are stretched. The models here proposed with rod-like particles inserted in the structure have interesting behaviour of acoustic and rotational branches of phonon dispersions. Complete bandgaps of vibrations can be obtained for a proper choice of lattice coupling parameters and distribution of masses in the unit cell of the lattice.

Sparavigna, A [Dipartimento di Fisica, Politecnico di Torino, C.so Duca degli Abruzzi 24, Turin (Italy)

2007-12-15

208

Phonons dispersions in auxetic lattices

International Nuclear Information System (INIS)

The modes of vibrations in auxetic structures are studied, with models where the two-dimensional lattice is represented by a planar mesh with rod-like particles connected by strings. An auxetic membrane can be obtained modifying a honeycomb one, according to a model proposed by Evans et al. in 1991 and used to explain a negative elastic Poisson's ratio. This property means that auxetic materials have a lateral extension, instead to shrink, when they are stretched. The models here proposed with rod-like particles inserted in the structure have interesting behaviour of acoustic and rotational branches of phonon dispersions. Complete bandgaps of vibrations can be obtained for a proper choice of lattice coupling parameters and distribution of masses in the unit cell of the lattice

209

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. PMID:23373951

Fainstein, A; Lanzillotti-Kimura, N D; Jusserand, B; Perrin, B

2013-01-18

210

Phonon frequencies of caesium and metallic hydrogen

International Nuclear Information System (INIS)

The logarithmic plots of measured frequencies for different phonon wave vectors, q, with their atomic numbers, N, are found to give a straight line fit. The relation between the frequency ?sub(N)(q) and the atomic number may be approximated by ?sub(N)(q)=Nsup(-m)C (q,epsilon), where m is found to be a constant equal to 0.75 and C(q,epsilon) is a constant depending on phonon wave-vector and polarization epsilon. This relationship has been used to predict the phonon frequencies of caesium and metallic hydrogen. (Auth.)

211

Electrons and Phonons in Semiconductor Multilayers

Introduction; 1. Simple models of the electron-phonon interaction; 2. Quantum confinement of carriers; 3. Quasicontinuum theory of lattice vibrations; 4. Bulk vibratory modes in an isotropic continuum; 5. Optical modes in a quantum well; 6. Superlattice modes; 7. Optical modes in various structures; 8. Electron-phonon interaction in a quantum well; 9. Other scattering mechanisms; 10. Quantum screening; 11. The electron distribution function; 12. Spin relaxation; 13. Electrons and phonons in the Wurtzite lattice; 14. Nitride heterostructures; 15. Terahertz sources; References; Index.

Ridley, B. K.

2014-08-01

212

Phonon runaway in nanotube quantum dots

We present a formulation of electronic transport in a nanotube quantum dot strongly coupled with vibrations and weakly with leads and the thermal environment. We show that recent observation of anomalous conductance sigatures in single-walled carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms of `hot phonon' using the joint electron-phonon distribution. On the basis of our model, we argue that the variations are indicative of strong electron-phonon coupling requiring an analysis beyond the traditional Tien-Gordon approach.

Siddiqui, L; Datta, S

2006-01-01

213

Positron scattering by phonons in a metal

International Nuclear Information System (INIS)

In the paper one estimated parameters of positron scattering by phonons on the basis of available theoretical models for positron-phonon interaction and of the experimental data on positron energy in a metal. One studied the processes governing positron interaction with a substance. For scattering by phonons dominating at energy values in the neighbourhood of 1 eV one derived formulae for braking ability, length of free run. For tungsten one estimated braking ability, length of free run and run total length for 0,025-10 eV positron energy values

214

Phonon Excitations of Composite Fermion Landau Levels

Phonon excitations of fractional quantum Hall states at filling factors nu = 1/3, 2/5, 4/7, 3/5, 4/3, and 5/3 are experimentally shown to be based on Landau level transitions of Composite Fermions. At filling factor nu = 2/3, however, a linear field dependence of the excitation energy in the high-field regime rather hints towards a spin transition excited by the phonons. We propose to explain this surprising observation by an only partially polarized 2/3-ground-state making the energetically lower lying spin transition also allowed for phonon excitations.

Schulze-Wischeler, F; Zeitler, U; Reuter, D; Wieck, A D; Haug, R J

2004-01-01

215

Anharmonic effects on a phonon-number measurement of a quantum-mesoscopic-mechanical oscillator

International Nuclear Information System (INIS)

We generalize a proposal for detecting single-phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon-number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the read-out oscillator

216

Anharmonic effects on a phonon number measurement of a quantum mesoscopic mechanical oscillator

We generalize a proposal for detecting single phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the readout oscillator.

Santamore, D H; Milburn, G J; Roukes, M L; Goan, Hsi-Sheng

2004-01-01

217

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)

218

International Nuclear Information System (INIS)

The electron machines's development and improvement go through the discovery of new electron sources of high brightness. After reminding the interests in studying silicon cathodes with array of tips as electron sources, I describe, in the three steps model, the main phenomenological features related to photoemission and photoemission and photo-field-emission from a semi-conductor. the experimental set-ups used for the measurements reported in chapter four, five and six are described in chapter three. In chapter three. In chapter four several aspects of photo-field-emission in continuous and nanosecond regimes, studied on the Clermont-Ferrand's test bench are tackled. We have measured quantum efficacies of 0.4 percent in the red (1.96 eV). Temporal responses in the nanoseconds range (10 ns) were observed with the Nd: YLF laser. With the laser impinging at an oblique angle we obtained ratios of photocurrent to dark current of the order of twenty. The issue of the high energy extracted photocurrent saturation is addressed and I give a preliminary explanation. In collaboration with the L.A.L. (Laboratoire de l'Accelerateur Lineaire) some tests with shortened pulsed laser beam (Nd: YAG laser 35 ps) were performed. Satisfactory response times have been obtained within the limitation of the scope (400 ps). (authors). 101 refs. 93 figs., 27 tabs., 3 photos., 1 append

219

Dynamical stabilization of the bcc phase in lanthanum and thorium by phonon-phonon interaction

Digital Repository Infrastructure Vision for European Research (DRIVER)

The recently developed self consistent {\\it ab initio} lattice dynamical method (SCAILD) has been applied to the high temperature bcc phase of La and Th which are dynamically unstable at low temperatures. The bcc phase of these metals is found to be stabilized by phonon-phonon interactions. The calculated high temperature phonon frequencies for La are found to be in good agreement with the corresponding experimental data.

Souvatzis, P.; Bjorkman, T.; Eriksson, O.; Andersson, P.; Rudin, M. I. Katsnelson S- P.

2009-01-01

220

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)

221

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)

222

Energy Technology Data Exchange (ETDEWEB)

Coherent phononic oscillations in Bi and Ag nanowires were studied with a femtosecond pump-probe technique. In Bi nanowires laser pulses of 50 fs excited simultaneously acoustic oscillations at a frequency of about 9.5 GHz and optical phonons in the THz range. The transmission of nanowires on a glass substrate and the light scattered from free standing nanowires were measured. In Ag nanowires laser-induced acoustic oscillations at different excitation levels were studied. The observed reduction of the oscillation frequency at higher pump energy was related to a transient softening of the material. This was directly confirmed for optical phonons by experiments with a pre-pump pulse of variable energy, producing different excitation densities.

Kolomenskii, Alexandre A; Liu Haidong; Zhang Hong; Ye Zuxin; Wu Wenhao; Schuessler, Hans A [Department of Physics, Texas A and M University, College Station, Texas 77843-4242 (United States); Jerebtsov, Sergey N [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching (Germany); Luo Zhiping, E-mail: a-kolomenski@physics.tamu.ed [Microscopy and Imaging Center, Texas A and M University, College Station, Texas 77843-2257 (United States)

2010-03-01

223

International Nuclear Information System (INIS)

Coherent phononic oscillations in Bi and Ag nanowires were studied with a femtosecond pump-probe technique. In Bi nanowires laser pulses of 50 fs excited simultaneously acoustic oscillations at a frequency of about 9.5 GHz and optical phonons in the THz range. The transmission of nanowires on a glass substrate and the light scattered from free standing nanowires were measured. In Ag nanowires laser-induced acoustic oscillations at different excitation levels were studied. The observed reduction of the oscillation frequency at higher pump energy was related to a transient softening of the material. This was directly confirmed for optical phonons by experiments with a pre-pump pulse of variable energy, producing different excitation densities.

224

Constants of Electron-Phonon Interaction for Optical and Intervalley Phonons in n-Ge

Directory of Open Access Journals (Sweden)

Full Text Available The electron scattering in case four-ellipsoidal, two-ellipsoidal and single-ellipsoidal L1-model of conduction band of Germanium is investigated. The constants of electron-phonon interaction for optical ?430 = 4ˇ108 eV/cm and intervalley phonon ?320 = 1,4ˇ108 eV/cm on base of the theory of anisotropy scattering and experimental temperature dependences resistivity are defined. The scattering by optical and intervalley phonon is significant in four-ellipsoidal L1-model of conduction band of n-Ge is shown. The scattering by acoustic phonons is dominated in two and single-valley L1-model.

S.V. Luniov

2014-04-01

225

Toward stimulated interaction of surface phonon polaritons

Energy Technology Data Exchange (ETDEWEB)

Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons.

Kong, B. D.; Trew, R. J.; Kim, K. W., E-mail: kwk@ncsu.edu [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695-7911 (United States)

2013-12-21

226

Acoustic and optical phonons in metallic diamond

Directory of Open Access Journals (Sweden)

Full Text Available The dispersion of acoustic and optical phonons in highly boron-doped diamond has been measured by inelastic X-ray scattering at an energy resolution of 6.4 meV. The sample is doped in the metallic regime and shows superconductivity below 4.2 K (midpoint. The data are compared to pure and nitrogen-doped diamond that represent the non-metallic state. No difference is found for the acoustic phonons in the three samples, while the optical phonons show a shift of the dispersion (softening in qualitative agreement with earlier results from Raman spectroscopy. The presence of boron and nitrogen incorporated into the diamond lattice leads to structural disorder. Evidence for this is found both in the observation of otherwise symmetry-forbidded Bragg intensity at (0 0 2 and intensity from acoustic phonon modes in the vicinity of (0 0 2.

M. Hoesch, T. Fukuda, T. Takenouchi, J.P. Sutter, S. Tsutsui, A.Q.R. Baron, M. Nagao, Y. Takano, H. Kawarada and J. Mizuki

2006-01-01

227

Influence of phonons on semiconductor quantum emission

Energy Technology Data Exchange (ETDEWEB)

A microscopic theory of interacting charge carriers, lattice vibrations, and light modes in semiconductor systems is presented. The theory is applied to study quantum dots and phonon-assisted luminescence in bulk semiconductors and heterostructures. (orig.)

Feldtmann, Thomas

2009-07-06

228

Phonon self energy in transition metals

We present ab initio calculations of the phonon self energy of transition metals obtained using second order many body perturbation theory.ootnotetextS. Narasimhan and D. Vanderbilt, Phys. Rev. B, 43, 4541 (1991) The code we have implementedootnotetextL. Chaput, A. Togo, I. Tanaka and G. Hug, submitted to Phys. Rev. B use the symmetry properties of the phonon-phonon interactions to express the self energy as a sum over irreducible triplets. It is analogous to the reduction of integration to the irreducible part of the Brillouin zone for one particle properties. The self energy of transition metals is then calculated. We show that the Peierls approximationootnotetextR. E. Peierls, Quantum Theory of Solids, Oxford University Press,1964 is in fact reasonable for bcc and fcc metals, but fails for the hcp. The decays paths of phonons producing the self energy is finally analyzed using surfaces of reciprocal space defined by conservation law.

Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles

2011-03-01

229

Phonon density of states of model ferroelectrics

Energy Technology Data Exchange (ETDEWEB)

First principles density functional calculations and inelastic neutron scattering measurements have been used to study the variations of the phonon density of states of PbTiO3 and SrTiO3 as a function of temperature. The phonon spectra of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from those of ferroelectric PbTiO3 and BaTiO3. SrTiO3 has a large 70-90 meV phonon band-gap in both the low temperature antiferrodistortive tetragonal phase and in the high temperature cubic phase. Key bonding changes in these perovskites lead to spectacular differences in their observed phonon density of states.

Choudhury, Narayani [University of Arkansas; Kolesnikov, Alexander I [ORNL; Schober, Helmut [Institut Laue-Langevin (ILL); Walter, Eric J. [College of William and Mary, Williamsburg, VA; Johnson, Mark [Institut Laue-Langevin (ILL); Abernathy, Douglas L [ORNL; Lucas, [ORNL

2010-01-01

230

Phonon Squeezing in a Superconducting Molecular Transistor

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 to the general case by variational analysis. Coherent charge fluctuations are entangled with non-classical phonon states. The Josephson current induces squeezing of the phonon mode, which is controlled by the superc...

Zazunov, A.; Feinberg, Denis; Martin, Thierry

2006-01-01

231

Waveguiding in supported phononic crystal plates

Energy Technology Data Exchange (ETDEWEB)

We investigate, with the help of the finite element method, the existence of absolute band gaps in the band structure of a free-standing phononic crystal plate and of a phononic crystal slab deposited on a substrate. The two-dimensional phononic crystal is constituted by a square array of holes drilled in an active piezoelectric (PZT5A or AlN) matrix. For both matrix materials, an absolute band gap occurs in the band structure of the free-standing plate provided the thickness of the plate is on the order of magnitude of the lattice parameter. When the plate is deposited on a Si substrate, the absolute band gap still remains when the matrix of the phononic crystal is made of PZT5A. The AlN phononic crystal plate losses its gap when supported by the Si substrate. In the case of the PZT5A matrix, we also study the possibility of localized modes associated with a linear defect created by removing one row of air holes in the deposited phononic crystal plate.

Vasseur, J [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Hladky-Hennion, A-C [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Deymier, P [Department of Materials Science end Engineering, University of Arizona, Tucson, Arizona, 85721 (United States); Djafari-Rouhani, B [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Duval, F [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Dubus, B [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Pennec, Y [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France)

2007-12-15

232

Frequency dependence of dispersive phonon images

Scientific Electronic Library Online (English)

Full Text Available SciELO South Africa | Language: English 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 pa [...] per 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 first 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.

K., Jakata; A.G., Every.

233

Frequency dependence of dispersive phonon images

Scientific Electronic Library Online (English)

Full Text Available SciELO South Africa | Language: English 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 pa [...] per 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 first 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.

K., Jakata; A.G., Every.

2008-10-01

234

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Dekorsy, Thomas; Taubert, Richard; Hudert, Florian; Schrenk, Gerhard; Bartels, Albrecht; Cerna, Roland; Kotaidis, Vassilios; Plech, Anton; Ko?hler, Klaus; Schmitz, Johannes; Wagner, Joachim

2007-01-01

235

The effect of NIR laser radiation (808 nm) and gold nanorods on the cells of two strains of Staphylococcus aureus, one of them being methicillin-sensitive and the other being methicillinresistant, is studied. Nanorods having the dimensions 10 × 44 nm with the absorption maximum in the NIR spectral region, functionalised with human immunoglobulins IgA and IgG, are synthesised. It is shown that the use of nanoparticles in combination with NIR irradiation leads to killing up to 97% of the population of microorganisms.

Tuchina, E. S.; Petrov, P. O.; Kozina, K. V.; Ratto, F.; Centi, S.; Pini, R.; Tuchin, V. V.

2014-07-01

236

FY05 LDRD Final Report Mapping Phonons at High-pressure

International Nuclear Information System (INIS)

In order to shed light on the intriguing, and not yet fully understood fcc-isostructural ? ? ? transition in cerium, we have begun an experimental program aimed at the determination of the pressure evolution of the transverse acoustic (TA) and longitudinal acoustic (LA) phonon dispersions up to and above the transition. ?-Ce Crystals of 60-80 mm diameter and 20 mm thickness were prepared from a large ingot, obtained from Ames Lab, using laser cutting, micro-mechanical and chemical polishing techniques. Three samples with a surface normal approximately oriented along the [110] direction were loaded into diamond anvil cells (DAC), using neon as a pressure transmitting medium. The crystalline quality was checked by rocking curve scans and typical values obtained ranged between one and two degrees. Only a slight degradation in the sample quality was observed when the pressure was increased to reach the ?-phase, and data could be therefore recorded in this phase as well. The spectrometer was operated at 17794 eV in Kirkpatrick-Baez focusing geometry, providing an energy resolution of 3 meV and a focal spot size at the sample position of 30 x 60 mm2 (horizontal x vertical, FWHM). Eight to ten IXS spectra were typically recorded per phonon branch. Figure 1 reports the pressure dependence of the LA[100] branch in the ?-phase for pressures of 1, 4 and 6 kbar, together with previous inelastic neutron scattering (INS) results [1] at ambient pressure. A clear decrease of the phonon energies with increasing pressure is observed for 1 and 4 kbar, whereas the phonon energies increase again at 6 kbar, still well within the stability field of the ?-phase. Figure 2 reports the LA dispersion along all three main symmetry directions at 6 kbar (?-phase) and 8 kbar (?-phase), together with the INS results at ambient conditions. Besides the already discussed unusual behavior along the [100] direction, the pressure evolution of the two other longitudinal branches in the ?-phase is quite different. The LA [110] branch displays a downward bending near the zone boundary (ZB), whereas the phonon energies at low reduced momentum transfer remain close to the ones at room pressure. In contrast to this, the LA [111] branch does not display any pressure dependence. The LA phonon energies in the ?-phase at 8 kbar are systematically higher than the corresponding lower pressure phonon energies, consistent with the higher density of the ?-phase and the expected larger elastic constants. We note, however, substantial changes in the lattice dynamics along the [110] direction. While the phonons between ? = 0.4 and 0.6 show a large energy increase with pressure, the phonon energy decreases at the zone boundary, thus leading to a pronounced overbending of the branch. The shape of the LA phonon branches in the ?-phase are close to those measured in thorium at ambient conditions [2] while the ?-phase phonon dispersion resembles fcc metastable lanthanum [3]. This behavior might be a signature of substantial changes in the Fermi surface topology, leading to significant changes in the electron-phonon coupling mechanism. A Born-von Karman fit to the phonon dispersion is currently being performed in order to quantify the changes in the force constant matrix

237

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe2

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

238

Quasiparticle and phonon transport in superconducting indium and quasiparticle trapping

International Nuclear Information System (INIS)

The dynamics of the excess quasiparticles and phonons created in single crystal superconducting indium by pulsed laser irradiation have been investigated at temperatures below 1 K using superconducting tunnel junction detectors. The changes in the time evolution of these excitations have been investigated when quasiparticle trapping occurs from the single crystal into a film of smaller gap superconductor, or of a normal metal where an energy gap is induced by the proximity effect. The experiments deduce a value for the characteristic quasiparticle time in the normal metal film. The phenomenon of trapping has also been investigated for thin film geometries. These experiments identify the mechanisms of the trapping effect and indicate the occurrence of current gain. The characteristic quasiparticle time for the trap material is deduced and is consistent with previous measurements in clean films. (author)

239

International Nuclear Information System (INIS)

The average charge of tungsten ions is revealed to reach 22+ and the maximum one is revealed to reach 29+ when a solid-state tungsten target free from the surface carbon and oxide compound layer is exposed to femtosecond laser radiation the intensity of which is higher than 1016 W/cm2. In this case, the maximum energy of the mentioned ions reaches 1 MeV. The relevant values obtained in case of the target with surface carbon and oxide compound layer under similar parameters of a laser pulse constitute 3+, 5+ and 150 keV. The numerical simulation results show that the mentioned high maximum charge of ions may be ensured due to occurrence of an electrostatic ambipolar field at plasma-vacuum sharp boundary. Collision ionization in the presence of the external quasi-static field is likely to be the key mechanism of ionization of ions with the maximum charges. Besides, the direct over-threshold ionization by the mentioned field may play rather important role. In case of a pure target heavy ions are shown to be efficiently accelerated by hot electrons. It results in production of ions with high energy. One analyzed in detail the effect of recombination on the charge of the recorded ions

240

Investigating the existence of coherent phonon scattering in silicon using phononic crystals

In silicon the majority of heat energy is transported by phonons, which are discrete lattice vibrations. Phonon scattering due to the presence of voids in silicon can further alter the material's thermal conductivity. There is a question about the possibility of some of this scattering being coherent rather than purely incoherent. Coherent phonon scattering is defined as constructive interference of phonons scattered from the inclusions in the phononic crystal. The intent of this work is to investigate the existence of coherent scattering in Si via phononic crystals. A phononic crystal is a periodic array of inclusions inside a host material. The inclusions could be a second material or a void. In this work five different supercell phononic crystals comprised of holes in silicon will be used to investigate the existence of coherent phonon scattering. Each of the supercells had nearly identical critical lengths in order to keep the amount of incoherent scattering equal among all of the PnCs. Porosity differences among the supercells were also minimized. All of the PnCs were fabricated with a focused ion beam (FIB). During fabrication a protective layer of Ti was used to protect the Si from unintentional Ga doping from the FIB. The Ti layer also helped generate voids with more vertical sidewalls. A set of experiments was performed to measure the thermal conductivity of each PnC. Thermal conductivity measurements were carried out on a silicon nitride suspended island platform with platinum resistance temperature detectors and coated with aluminum nitride. A silicon slab was concurrently measured with each PnC, and relative thermal conductivity values were determined. The addition of the PnC decreased Si's thermal conductivity to less than 22% of its original value. An analysis of the results shows there is a reduction in thermal conductivity beyond the effects of porosity and incoherent scattering. This enhanced reduction in thermal conductivity is due to coherent phonon scattering in PnCs.

Goettler, Drew

241

Theoretical study of phonon spectra in ferromagnetic nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Based on the spin-phonon model we analyze the influence of surface and size effects on the phonon properties of ferromagnetic nanoparticles. A Green's function technique in real space enables us to calculate the renormalized phonon energy and its damping depending on the temperature and the anharmonic spin-phonon interaction constants. With decreasing particle size the phonon energy can decrease or increase for different surface spin-phonon interaction constants, whereas the damping increases always. The influence of an external magnetic field is discussed, too. The theoretical results are in reasonable accordance to experimental data.

Wesselinowa, J.M. [University of Sofia, Department of Physics, Blvd. J. Bouchier 5, 1164 Sofia (Bulgaria)], E-mail: julia@phys.uni-sofia.bg; Apostolova, I. [University of Forestry, Faculty of Forest Industry, 10 Kliment Okhridsky Blvd., 1756 Sofia (Bulgaria)

2008-01-14

242

Existence of an independent phonon bath in a quantum device

At low temperatures, the thermal wavelength of acoustic phonons in a metallic thin film on a substrate can widely exceed the film thickness. It is thus generally believed that a mesoscopic device operating at low temperature does not carry an individual phonon population. In this work, we provide direct experimental evidence for the thermal decoupling of phonons in a mesoscopic quantum device from its substrate phonon heat bath at a sub-Kelvin temperature. A simple heat balance model assuming an independent phonon bath following the usual electron-phonon and Kapitza coupling laws can account for all experimental observations.

Pascal, L. M. A.; Fay, A.; Winkelmann, C. B.; Courtois, H.

2013-09-01

243

Coherent acoustic phonon generation in GaAs{sub 1?x}Bi{sub x}

Energy Technology Data Exchange (ETDEWEB)

We have used femtosecond laser pulses to generate coherent acoustic phonons in the dilute Bismide alloy, GaAs{sub 1?x}Bi{sub x}. The observed oscillation periods match well with the oscillation periods calculated using the propagating strain pulse model. We attribute the generation process predominantly to electronic stress due to the absorption of the laser pulse at the surface of the GaAs{sub 1?x}Bi{sub x} layer. Our initial estimates suggest that the incorporation of Bi in GaAs causes an enhancement of the hydrostatic deformation potential because of the resonant state in the valence band due to isolated Bi impurities.

Joshya, R. S.; Kini, R. N., E-mail: rajeevkini@iisertvm.ac.in [Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), CET Campus, Thiruvananthapuram, Kerala 695016 (India); Ptak, A. J.; France, R.; Mascarenhas, A. [National Renewable Energy Laboratory (NREL), 1617 Cole Blvd., Golden, Colorado 80401 (United States)

2014-03-03

244

Coherent phonons in carbon based nanostructures

We have developed a theory for the generation and detection of coherent phonons in carbon based nanotstructures such as single walled nanotubes (SWNTs), graphene, and graphene nanoribbons. Coherent phonons are generated via the deformation potential electron/hole-phonon interaction with ultrafast photo-excited carriers. They modulate the reflectance or absorption of an optical probe pules on a THz time scale and might be useful for optical modulators. In our theory the electronic states are treated in a third nearest neighbor extended tight binding formalism which gives a good description of the states over the entire Brillouin zone while the phonon states are treated using valence force field models which include bond stretching, in-plane and out-of-plane bond bending, and bond twisting interactions up to fourth neighbor distances. We compare our theory to experiments for the low frequency radial breathing mode (RBM) in micelle suspended single-walled nanotubes (SWNTs). The analysis of such data provides a wealth of information on the dynamics and interplay of photons, phonons and electrons in these carbon based nanostructures.

Sanders, G. D.; Nugraha, A. R. T.; Sato, K.; Kim, J.-H.; Lim, Y.-S.; Kono, J.; Saito, R.; Stanton, C. J.

2014-06-01

245

Cryogenic phonon-mediated particle detectors for dark matter searches and neutrino physics

International Nuclear Information System (INIS)

asiparticles which diffuse in the Al pad until they are trapped in the lower gap Tl links. The sensitivity of the detector was found to be increased by this open-quotes funnelingclose quotes action. A second detector was built that incorporates 0.25 ?m wide lines defined by direct electron-beam exposure of the photoresist. If the superconducting line is sufficiently narrow, single phonons are capable of driving sections normal which should improve the sensitivity and linearity of the detector

246

Phonons and Lattice Dielectric Properties of Zirconia

We have performed a first-principles study of the structural and vibrational properties of the three low-pressure (cubic, tetragonal, and especially monoclinic) phases of ZrO2, with special attention to the computation of the zone-center phonon modes and related dielectric properties. The calculations have been carried out within the local-density approximation using ultrasoft pseudopotentials and a plane-wave basis. The fully relaxed structural parameters are found to be in excellent agreement with experimental data and with previous theoretical work. The total-energy calculations correctly reproduce the energetics of the ZrO2 phases, and the calculated zone-center phonon frequencies yield good agreement with the infrared and Raman experimental frequencies in the monoclinic phase. The Born effective charge tensors are computed and, together with the mode eigenvectors, used to decompose the lattice dielectric susceptibility tensor into contributions arising from individual infrared-active phonon modes. This w...

Zhao, X; Zhao, Xinyuan; Vanderbilt, David

2001-01-01

247

International Nuclear Information System (INIS)

The phonon dispersion in CsBr was determined at room temperature by inelastic neutron scattering. A time-of-flight apparatus was used with a pseudostatic chopper. In a large number of experiments, over 800 phonons could be measured in the planes (100) and (110). The results are in very good agreement with comparable data from other investigations. The results were compared with various model calculations. It was thus clear that by considering the polarizability, it is possible to make considerably better predictions on the course of dispersion than can be made with simpler models. By adapting the breathing shell model, in which even photons outside the main symmetry directions were considered, a parametric law could be found enabling the model calculation to well describe the data. The adapted breathing shell model was used to calculate the state density of the phonons. (orig./LH)

248

Phonon dispersion of ice under pressure.

We report measurements of the phonon dispersion of ice Ih under hydrostatic pressure up to 0.5 GPa, at 140 K, using inelastic neutron scattering. They reveal a pronounced softening of various low-energy modes, in particular, those of the transverse acoustic phonon branch in the [100] direction and polarization in the hexagonal plane. We demonstrate with the aid of a lattice dynamical model that these anomalous features in the phonon dispersion are at the origin of the negative thermal expansion (NTE) coefficient in ice below 60 K. Moreover, extrapolation to higher pressures shows that the mode frequencies responsible for the NTE approach zero at approximately 2.5 GPa, which explains the known pressure-induced amorphization (PIA) in ice. These results give the first clear experimental evidence that PIA in ice is due to a lattice instability, i.e., mechanical melting. PMID:15601100

Strässle, Th; Saitta, A M; Klotz, S; Braden, M

2004-11-26

249

Observation of phonon frequency thresholds in the anomalous Kapitza resistance

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Phonons emitted by superconducting tunneling junctions into insulator crystal substrates exhibit a sharp amplitude reduction above 85 GHz if the tunneling diodes are covered by 4He. This is attributed to the onset of an enhanced phonon transport into helium.

Koblinger, Otto; Heim, Ulrich; Welte, Michael; Eisenmenger, Wolfgang

1983-01-01

250

The phonon vacuum state in a Lipkin model

The action of the long-range residual force on the expectation value of observables in the nuclear ground states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the independent-particle ground-state using the two-level Lipkin-Meshkov-Glick (LMG) model. After estimating the improvements over the predictions of the independent-particle approximation we compare the ground and first excited states wave functions, obtained using the presented approach, with those, obtained using the conventional random phase approximation (RPA) and its extended version. The problem with overbinding of the nuclear ground state calculated using the RPA is shown to be removed if one sticks to the prescriptions of the present approach. The reason being that the latter conforms to the original variational formulation.

Mishev, S.

2014-09-01

251

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe$_2$

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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}. Renormalized phonon energies are observed over a large wavevector range $(0.3, 0, 0.5) \\le \\mathbf{q} \\le (0.5, 0, 0.5)$. Detailed ab-initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative ag...

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

2011-01-01

252

Phonon softening and electron-phonon-coupling in the superconducting Ta-Zr system

International Nuclear Information System (INIS)

Measurements of the phonon density of states DOS for Ta75Zr25 are presented, obtained from inelastic neutron scattering experiments. A comparison with the DOS of Ta displays a pronounced phonon softening below 11 meV on alloying Zr. Further we performed tunneling experiments on Ta70Zr30 and Ta80Zr20 from which the Eliashberg functions ?2F((h/2?)?) were derived. In comparison to the DOS of Ta75Zr25, below 11 meV both spectra are strongly shifted to lower frequencies indicating a strong enhancement of the electron-phonon-coupling. (orig.)

253

Phonon-Mediated Anomalous Dynamics of Defects

Dynamics of an array of line defects interacting with a background elastic medium is studied in the linear regime. It is shown that the inertial coupling between the defects and the ambient phonons leads to an anomalous response behavior for the deformation modes of a defect-lattice, in the form of anisotropic and anomalous mass and elastic constants, resonant dissipation through excitation of phonons, and instabilities. The case of a single fluctuating line defect is also studied, and it is shown that it could lead to formation of shock waves in the elastic medium for sufficiently high frequency deformation modes.

Najafi, A; Najafi, Ali; Golestanian, Ramin

2002-01-01

254

Monochromatic phonon generation by superconducting tunnel junctions

International Nuclear Information System (INIS)

Superconducting tunneling junctions are metal-oxide-metal structures where the insulating oxide is thin enough so that electrons can tunnel quantum mechanically from one side to the other. The devices are used for fast switching computer elements, low noise microwave mixers, ultra sensitive magnetic flux detectors, and highly reproducible voltage standards. The junctions are also well suited for the generation and the detection of phonons. Two different ways of tunable monochromatic phonon generation by superconducting tunnel junctions are discussed. Examples of each method are presented

255

Kinetic formula for estimating resistive phonon lifetimes

International Nuclear Information System (INIS)

An improved kinetic formula which can be used to estimate the average phonon resistive lifetime ?R from thermal conductivity data is presented. The relation is ?=Cc22?R, where ? is the thermal conductivity, C is the specific heat, and c2 is the second sound velocity. At very low temperatures c2?cD/ ?3 , where cD is the Debye velocity, and the result reduces to the standard kinetic formula. However, above about 0.02FTHETAD c2 undergoes a rapid decrease. As a consequence, phonon lifetimes estimated by the modified formula are considerably longer than those obtained from the standard kinetic formula

256

Cosmic acceleration with cosmological soft phonons

The dark energy scalar field is here presented as a mean-field effect arising from the collective motion of interacting structures on an expanding lattice. This cosmological analogue to solid-state soft phonons in an unstable crystal network is shown to produce cosmic acceleration while mimicking phantom equation of state. From an analysis of the Hubble diagram of type Ia supernovae, we present constraints on the parameters of the cosmic Lagrange chain, as well as on time-variation of the soft phonon equation of state, before we conclude on new phenomenology associated to this interpretation.

Rekier, J

2012-01-01

257

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

258

Phonon spectra in one-dimensional quasicrystals

International Nuclear Information System (INIS)

The propagation of phonons in one-dimensional quasicrystals is investigated. The authors use the projection method which has been recently proposed to generate almost periodic tilings of the line. They define a natural Laplace operator on these structures which models phonon (and also tight-binding electron) propagation. The self-similarity properties of the spectrum are discussed, as well as some characteristic features of the eigenstates, which are neither extended nor localized. The long-wavelength limit is examined in more detail; it is argued that one is the lower critical dimension for this type of models

259

Surface-phonon instabilities of W(001)

Tight-binding calculations of the surface-phonon dispersion curves for unreconstructed p(1×1) W(001) reveal a whole region of soft surface modes at the boundary of the surface Brillouin zone, caused by interactions with electronic surface states around EF. An interplay of Fermi-surface nesting features and real-space d-orbital interactions leads to the maximum instability of the MŻ5 phonons, the basis of the observed c(2×2) reconstruction patterns. For small H coverages the electronic surface states are not removed but modified, probably in such a way as to produce incommensurate reconstructions.

Wang, X. W.; Weber, W.

1987-04-01

260

Phonon interference effects in molecular junctions

International Nuclear Information System (INIS)

We study coherent phonon transport through organic, ?-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features very analogous to those observed theoretically and experimentally for electron transport in similar molecules. The destructive interference features observed in four different cross-conjugated molecules significantly reduce the thermal conductance with respect to linear conjugated analogues. Such control of the thermal conductance by chemical modifications could be important for thermoelectric applications of molecular junctions

261

Interaction of magnetic ions with phonons

International Nuclear Information System (INIS)

The magnetoelastic interaction leads to shifts in equilibrium positions of the ions for the static part of the interaction and to magnetic ion-phonon effects for the dynamic part. The various effects which result from this interaction are discussed. The author shows how this interaction leads to changes in the phonon and magnon spectra in the case of magnetically ordered materials, how it can give rise to structural transitions in the case of strong magnetoelastic coupling, how it can lead to critical effects for sound propagation near phase transitions and to various other effects. (Auth.)

262

Phonon polariton modes in semiconductor superlattices

International Nuclear Information System (INIS)

Phonon polariton modes in semiconductor superlattices are studied. Polariton electric fields and the dispersion relation are derived by electromagnetic theory, and due to periodicity in the direction normal to the superlattice layers, Bloch's theorem is applied. Polariton modes are found to exist between the TO and LO phonon frequencies, and approach the surface polariton frequency in the limit of large tangential wave vectors. The frequencies are also strongly dependent on the ratio of the layer thicknesses. Results are illustrated by a GaAs-GaP superlattice. (author)

263

Neutron-Phonon Interaction in Neutron Star Crusts

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The phonon spectrum of Coulomb lattice in neutron star crusts above the neutron drip density is affected by the interaction with the ambient neutron Fermi-liquid. For the values of the neutron-phonon coupling constant in the range $0.1 \\le \\lambda \\le 1$ an appreciable renormalization of the phonon spectrum occurs which can lead to a lattice instability manifested in an exponential growth of the density fluctuations. The BCS phonon exchange mechanism of superconductivity lea...

Sedrakian, Armen

1998-01-01

264

Band structure characteristics of T-square fractal phononic crystals

International Nuclear Information System (INIS)

The T-square fractal two-dimensional phononic crystal model is presented in this article. A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal. We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method. The fractal design has an important impact on the band structures of the two-dimensional phononic crystals

265

Optical phonons in Ge quantum dots obtained on Si(111)

The light combination scattering on the optical phonons in the Ge quantum dots, obtained on the Si surface of the (111) orientation through the molecular-beam epitaxy, is studied. The series of lines, connected with the phonon spectrum quantization, was observed. It is shown, that the phonon modes frequencies are well described by the elastic properties and dispersion of the voluminous Ge optical phonons. The value of the Ge quantum dots deformation is determined

Talochkin, A B

2002-01-01

266

Size-dependent phonon transmission across dissimilar material interfaces

International Nuclear Information System (INIS)

In this paper, we study the size effects on the phonon transmission across material interfaces using the atomistic Greens 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 Greens function method and the phonon transmission is calculated through the obtained Greens 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. (paper)

267

Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

International Nuclear Information System (INIS)

The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ? We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ? The results show the first PBGs start with zero Hz with low modes. ? Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.

268

Synthetic thermoelectric materials comprising phononic crystals

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

269

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

2012-12-01

270

Generalized Kinetic Theory of Electrons and Phonons

A Generalized Kinetic Theory was proposed in order to have the possibility to treat particles which obey a very general statistics. By adopting the same approach, we generalize here the Kinetic Theory of electrons and phonons. Equilibrium solutions and their stability are investigated.

Rossani, A

2002-01-01

271

Electron-phonon interaction in Hubbard systems

The renormalization of the electron-phonon interaction in a Hubbard system due to the electronic correlations is investigated using different slave-boson mean-field approximations. We find that the renormalization depends strongly on the doping but also on the slave-boson method which is used to describe the correlations.

Keller, J.; Leal, C. E.; Forsthofer, F.

1995-02-01

272

Kohn anomaly in phonon driven superconductors

Anomalies often occur in the physical world. Sometimes quite unexpectedly anomalies may give rise to new insight to an unrecognized phenomenon. In this paper we shall discuss about Kohn anomaly in a conventional phonon-driven superconductor by using a microscopic approach. Recently Aynajian et al.'s experiment showed a striking feature; the energy of phonon at a particular wave-vector is almost exactly equal to twice the energy of the superconducting gap. Although the phonon mechanism of superconductivity is well known for many conventional superconductors, as has been noted by Scalapino, the new experimental results reveal a genuine puzzle. In our recent work we have presented a detailed theoretical analysis with the help of microscopic calculations to unravel this mystery. We probe this aspect of phonon behaviour from the properties of electronic polarizability function in the superconducting phase of a Fermi liquid metal, leading to the appearance of a Kohn singularity. We show the crossover to the standard Kohn anomaly of the normal phase for temperatures above the transition temperature. Our analysis provides a nearly complete explanation of this new experimentally discovered phenomenon. This report is a shorter version of our recent work in JPCM.

Das, M. P.; Chaudhury, R.

2014-08-01

273

Phonon dispersion curves of fcc La

International Nuclear Information System (INIS)

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

274

Dispersion Relations for Phonons in Magnesium

International Nuclear Information System (INIS)

The dispersion relation for acoustic phonons hose wave vectors lie in the basal plane have been measured by neutron spectrometry. A triple axis spectrometer has been used both in the conventional method and 'constant Q-bar' method. The results are compared ith calculations based on two-neighbour central forces. (author)

275

LOW FREQUENCY PHONONS IN SINTERED COPPER

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Measurements of Young's Modulus and sound velocity of a range of sintered copper powder samples have demonstrated the existence of low frequency soft phonon modes that could explain the low temperature anomaly in the Kapitza resistance between liquid 3He and sintered metal heat exchangers below 10 mK.

Frisken, B.; Guillon, F.; Harrison, J.; Page, J.

1981-01-01

276

Digital Repository Infrastructure Vision for European Research (DRIVER)

We generalize the momentum average (MA) approximation to study the properties of models with momentum-dependent electron-phonon coupling. As in the case of the application of the original MA to the Holstein model, the results are analytical, numerically trivial to evaluate, exact for both zero bandwidth and for zero electron-phonon coupling, and are accurate everywhere in parameter space. Comparison with available numerical data confirms this accuracy. We then show that furt...

Goodvin, Glen L.; Berciu, Mona

2008-01-01

277

Illustrative numerical comparisons between phonon mean free paths and phonon thermal conductivity

International Nuclear Information System (INIS)

Measurements of thermal conductivity are often used as an interrogative technique to learn about phonon scattering processes in solids. In general the relationship between thermal conductivity lambda and a phonon mean free path l is complex and it is therefore necessary to make some simplifying assumptions in order to make this relationship tractable. These assumptions may lead to erroneous conclusions, many of which have appeared in the published literature. An intuitive insight is provided to the relationship between lambda and l

278

We present a theory of phonon-assisted photoluminescence from a semiconductor quantum dot (QD) whose electron and phonon subsystems are resonantly coupled via the polar electron-phonon interaction. We show that the resonance-induced renormalization of the QD energy spectrum, leading to the formation of the polaron-like states, can be performed exactly in terms of the arbitrarily degenerate states of electron-hole pairs and the phonon modes of equal energies. Using the model of QDs with finite potential barriers for electron and holes leads to new selection rules of interband optical transitions and the three-particle interaction describing simultaneous absorption and/or emission of a photon and a phonon. We also derive a simple expression for the differential cross section of the stationary, low-temperature photoluminescence, which allows the fundamental parameters of the polaron-like excitations to be readily extracted from the frequency-resolved experimental spectra. In particular, the energies of the excitations and the coherence relaxation rates of the optical transitions resulting in their generation and recombination are shown to be directly given by the positions and widths of the photoluminescence peaks. The developed theory complements the existing experimental techniques of studying the phonon-assisted photoluminescence from individual nanocrystals. PMID:25321054

Baimuratov, Anvar S; Rukhlenko, Ivan D; Leonov, Mikhail Yu; Shalkovskiy, Alexey G; Baranov, Alexander V; Fedorov, Anatoly V

2014-08-11

279

Unified theory of electron-phonon renormalization and phonon-assisted optical absorption

We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron-phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally leads to the Allen-Heine theory of temperature-dependent energy levels, the Franck-Condon principle, the Herzberg-Teller effect and to phonon-assisted optical absorption in indirect band gap materials. In addition, our theory predicts sub-gap phonon-assisted optical absorption in direct gap materials, as well as an exponential edge which we tentatively assign to the Urbach tail. We also consider a semiclassical approach to the calculation of optical absorption spectra which simultaneously captures energy-level renormalization and phonon-assisted transitions and is especially suited to first-principles electronic structure calculations. We demonstrate this approach by calculating the phonon-assisted optical absorption spectrum of bulk silicon.

Patrick, Christopher E.; Giustino, Feliciano

2014-09-01

280

Unified theory of electron-phonon renormalization and phonon-assisted optical absorption.

We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron-phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally leads to the Allen-Heine theory of temperature-dependent energy levels, the Franck-Condon principle, the Herzberg-Teller effect and to phonon-assisted optical absorption in indirect band gap materials. In addition, our theory predicts sub-gap phonon-assisted optical absorption in direct gap materials, as well as an exponential edge which we tentatively assign to the Urbach tail. We also consider a semiclassical approach to the calculation of optical absorption spectra which simultaneously captures energy-level renormalization and phonon-assisted transitions and is especially suited to first-principles electronic structure calculations. We demonstrate this approach by calculating the phonon-assisted optical absorption spectrum of bulk silicon. PMID:25134725

Patrick, Christopher E; Giustino, Feliciano

2014-09-10

281

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

2011-12-01

282

Observation of the full exciton and phonon fine structure in CdSe/CdS dot-in-rod heteronanocrystals.

Light emission of semiconductor nanocrystals is a complex process, depending on many factors, among which are the quantum mechanical size confinement of excitons (coupled electron-hole pairs) and the influence of confined phonon modes and the nanocrystal surface. Despite years of research, the nature of nanocrystal emission at low temperatures is still under debate. Here we unravel the different optical recombination pathways of CdSe/CdS dot-in-rod systems that show an unprecedented number of narrow emission lines upon resonant laser excitation. By using self-assembled, vertically aligned rods and application of crystallographically oriented high magnetic fields, the origin of all these peaks is established. We observe a clear signature of an acoustic-phonon assisted transition, separated from the zero-phonon emission and optical-phonon replica, proving that nanocrystal light emission results from an intricate interplay between bright (optically allowed) and dark (optically forbidden) exciton states, coupled to both acoustic and optical phonon modes. PMID:24861569

Granados Del Águila, Andrés; Jha, Bhawana; Pietra, Francesca; Groeneveld, Esther; de Mello Donegá, Celso; Maan, Jan C; Vanmaekelbergh, Daniël; Christianen, Peter C M

2014-06-24

283

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

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

284

Using time resolved ultrafast spectroscopy, we have demonstrated that the far infrared (FIR) excitations in ferroelectric crystals may be modified through an arsenal of control techniques from the fields of guided waves, geometrical and Fourier optics, and optical pulse shaping. We show that LiNbO3 and LiTaO3 crystals of 10-250 micron thickness behave as slab waveguides for phonon-polaritons, which are admixtures of electromagnetic waves and lattice vibrations, when the polariton wavelength is on the order of or greater than the crystal thickness. Furthermore, we show that ferroelectric crystals are amenable to processing by ultrafast laser ablation, allowing for milling of user-defined patterns designed for guidance and control of phonon-polariton propagation. We have fabricated several functional structures including THz rectangular waveguides, resonators, splitters/couplers, interferometers, focusing reflectors, and diffractive elements. Electric field enhancement has been obtained with the reflective stru...

Ward, D W; Feurer, T; Nelson, K A; Osgood, R M; Roth, R M; Statz, E R; Stoyanov, N; Beers, Jaime D.; Feurer, Thomas; Nelson, Keith A.; Osgood, Richard M.; Roth, Ryan M.; Statz, Eric; Stoyanov, Nikolay; Ward, David W.

2004-01-01

285

Molecular dynamics study of phonon screening in graphene

Phonon interaction with electrons or phonons or with structural defects result in a phonon mode conversion. The mode conversion is governed by the frequency wave-vector dispersion relation. The control over phonon mode or the screening of phonon in graphene is studied using the propagation of amplitude modulated phonon wave-packet. Control over phonon properties like frequency and velocity opens up several wave guiding, energy transport and thermo-electric applications of graphene. One way to achieve this control is with the introduction of nano-structured scattering in the phonon path. Atomistic model of thermal energy transport is developed which is applicable to devices consisting of source, channel and drain parts. Longitudinal acoustic phononmode is excited fromone end of the device. Molecular dynamics based time integration is adopted for the propagation of excited phonon to the other end of the device. The amount of energy transfer is estimated from the relative change of kinetic energy. Increase in the phonon frequency decreases the kinetic energy transmission linearly in the frequency band of interest. Further reduction in transmission is observed with the tuning of channel height of the device by increasing the boundary scattering. Phonon mode selective transmission control have potential application in thermal insulation or thermo-electric application or photo-thermal amplification.

Javvaji, Brahmanandam; Roy Mahapatra, D.; Raha, S.

2014-04-01

286

Terahertz emission spectroscopy of coherent phonons in semiconductors

We investigate infrared-active coherent phonons excited in Te, PbTe (un-doped, n-type and p-type), and CdTe by observing the terahertz (THz) emission from these samples. Coherent THz emission corresponding to the longitudinal- optical (LO)-phonon frequency has been observed for all the samples, while no significant THz emission is observed at the transverse-optical (TO)-phonon frequency even at high carrier densities (> 1018 cm-3). The absence of THz emission at the TO-phonon frequency strongly contradicts the observation in the transient reflectivity measurements, where the signal oscillations at the TO-phonon frequencies arising from the LO-phonon-plasmon coupling (L_ mode) have been observed at high carrier densities. It is found from a model calculation that for a dipole oscillator on a sample surface the THz emission around the TO-phonon frequency is strongly suppressed due to the large dielectric constant near this frequency.

Tani, Masahiko; Fukasawa, Ryoichi; Herrmann, Michael; Sakai, Kiyomi; Nakashima, Shin-ichi; Yoshioka, Nobuya; Ishida, Akihiro; Fujiyasu, Hiroshi

1999-05-01

287

The article presents the current perspective on the nature of photoexcited states in semiconductor quantum dots (QDs). The focus is on multiple excitons and photo-induced electron-phonon dynamics in PbSe and CdSe QDs, and the advocated view is rooted in the results of ab initio studies in both energy and time domains. As a new type of material, semiconductor QDs represent the borderline between chemistry and physics, exhibiting both molecular and bulk-like properties. Similar to atoms and molecules, the electronic spectra of QD show discrete bands. Just as bulk semiconductors, QDs comprise multiple copies of the elementary unit cell, and are characterized by valence and conduction bands. The electron-phonon coupling in QDs is weaker than in molecules, but stronger than in bulk semiconductors. Unlike either material, the QD properties can be tuned continuously by changing QD size and shape. The molecular and bulk points of view often lead to contradicting conclusions. For example, the molecular view suggests that the excitations in QDs should exhibit strong electron-correlation (excitonic) effects, and that the electron-phonon relaxation should be slow due to the discrete nature of the optical bands and the mismatch of the electronic energy gaps with vibrational frequencies. In contrast, a finite-size limit of bulk properties indicates that the kinetic energy of quantum confinement should be significantly greater than excitonic effects and that the electron-phonon relaxation inside the quasi-continuous bands should be efficient. Such qualitative differences have generated heated discussions in the literature. The great potential of QDs for a variety of applications, including photovoltaics, spintronics, lasers, light-emitting diodes, and field-effect transistors makes it crutual to settle the debates. By synthesizing different viewpoints and presenting a unified atomistic picture of the excited state processes, our ab initio analysis clarifies the controversies regarding the phonon bottleneck and the generation of multiple excitons in semiconductor QDs. Both the electron-hole and charge-phonon interactions are strong and, therefore, optical excitations can directly generate multiple excitons, while the electron-phonon relaxation exhibits no bottlenecks, except at low excitation energies and in very small QDs.

Prezhdo, Oleg V.

2008-07-01

288

Photoemission and phonon spectroscopies have yielded widely varying estimates of the electron-phonon coupling parameter ? on the surfaces of topological insulators, even for a particular material and technique. We connect the results of these experiments by determining the Dirac fermion quasiparticle spectral function using information from measured spectra of a strongly interacting, low-lying optical surface phonon band. The manifest spectral features resulting from the coupling are found to vary on energy scales acoustic phonons in metals. We explore different means of determining ? from the electron perspective and identify definitions that yield values consistent with phonon spectroscopy.

Howard, Colin; El-Batanouny, M.

2014-02-01

289

Establishment of correlated states in a quantum dot interacting with an acoustic-phonon reservoir

We investigate the effects of a low-frequency (acoustic) phonon bath on the dynamics of a quantum dot modeled as a cascade three-level system. We show that the phonon bath appears to the upper transition of the cascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators. The action of the annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usual harmonic oscillator that it serves as a linear amplifier to the system, and thereby gives rise to unusual features in the dynamics of the quantum dot. We find that the phonon bath, although being in a thermal state, affects the quantum dot as a correlated-type reservoir which results in the decay of the system to a correlated two-photon state with the population distribution no longer obeying a Boltzmann distribution. It is particularly interesting that even for a zero-temperature phonon reservoir, the steady state is a correlated state which, under appropriate conditions on the Rabi frequencies and the damping rates, can reduce to a strongly correlated pure state. It is shown that the two-photon correlations result in a significant squeezing and strong two-photon correlations in the radiation field emitted by the quantum dot. The presence of the correlations in the system is manifest in the presence of quantum beats in the time evolution of the populations and the radiation intensity. The effect of the ordinary spontaneous emission on the features induced by the phonon bath is also discussed.

Huang, Hui; Li, Gao-xiang; Gu, Wen-ju; Ficek, Zbigniew

2014-08-01

290

Scattering of thermal phonons by extended defects in dielectric crystals

Energy Technology Data Exchange (ETDEWEB)

The scattering of thermal phonons by extended defects in dielectric crystals has been observed through measurements of thermal conductivity and ballistic heat pulse propagation. The thermal conductivities of LiF and NaCl conatining 500 low-angle grain boundaries per cm were measured in the range 0.08-5 K. The measurements gave little or no evidence for phonon scattering from the grain boundaries. Measurements of phonon scattering at a 10 deg. grain boundary in silicon using direct generation and detection of ballistically propagating heat pulses were made over an effective phonon temperature range of 2 to 20 K. The grain boundary reflection coefficient was determined to be < 2%. The thermal conductivities of LiF crystals containing 5 x 10/sup 6/ - 3 x 10/sup 7/ dislocations per square cm were measured over the temperature range 0.1 to 10 K. The measurements of the sheared crystal indicated that the slow transverse phonon mode was strongly scattered by a dynamic phonon-dislocation interaction at T approximately < 2 K, while the remaining modes were scattered primarily by the boundaries. The measurements of the bent crystals indicated that, for T approximately < 2 K, the slow transverse and possibly the longitudinal phonons were strongly scattered by a dynamic phonon-dislocation interaction. For T approximately > 2 k, some fraction of the phonons (at least the slow transverse mode) were still strongly scattered, even after long exposure to ..gamma.. irradiation, while the remaining phonons were scattered primarily by the boundaries.

Roth, E. P.

1975-01-01

291

From Planck's quanta to phonon in solids

International Nuclear Information System (INIS)

Planck's 1900 published results on the black body radiation had the first application in the quantification of radiation. This quantum hypothesis explained several noteworthy light- matter interaction effects in 1905. These were the electron emission, Stokes law and gas ionization. As soon as two years later, A. Einstein derived an expression for the specific heat of solids, applying the quantum hypothesis to the mechanical oscillation of the atoms. In the present work, the main ideas which led to the concept of phonon are discussed. From an historical point of view, the developments due to Einstein, Born, Debye, among others are analyzed and most important properties of the phonons are presented. Finally, the importance of this entity in the theory of solids is explained, in particular regarding the thermal and optical properties as well as the electrical conductivity

292

Electron-phonon superconductivity beyond Migdal's theorem

International Nuclear Information System (INIS)

One of the common elements between the various high Tc superconductors, cuprates and C60 compounds, is the very small value of the Fermi energy, comparable with the Debye phonon frequencies. This situation implies a breakdown of Migdal's theorem for the electron-phonon many body problem and leads to important nonadiabatic effects. We have generalized Eliashberg equations to include vertex corrections and other nonadiabatic effects in a perturbative scheme. This leads to a rather complex situation in which the critical temperature for superconductivity can be strongly enhanced if the el-ph scattering involves mainly small momenta. Recent studies show that this situation can be naturally realized in view of electronic correlations. ((orig.))

293

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

294

Phonon affected transport through molecular quantum dots.

To describe the interaction of molecular vibrations with electrons at a quantum dot contacted to metallic leads, we extend an analytical approach that we previously developed for the many-polaron problem. Our scheme is based on an incomplete variational Lang-Firsov transformation, combined with a perturbative calculation of the electron-phonon self-energy in the framework of generalized Matsubara functions. This allows us to describe the system at weak-to-strong coupling and intermediate-to-large phonon frequencies. We present results for the quantum dot spectral function and for the kinetic coefficient that characterizes the electron transport through the dot. With these results we critically examine the strengths and limitations of our approach, and discuss the properties of the molecular quantum dot in the context of polaron physics. We place particular emphasis on the importance of corrections to the concept of an anti-adiabatic dot polaron suggested by the complete Lang-Firsov transformation. PMID:21832393

Loos, J; Koch, T; Alvermann, A; Bishop, A R; Fehske, H

2009-09-30

295

Structural Properties and Phonon dispertion of NACl

Directory of Open Access Journals (Sweden)

Full Text Available Although many phenomena in condensed matter Physics can be understood on the basis of a model, there are also considerable number of physical properties of solid which can not be explained except in the framework of lattice dynamics. We have calculated the phonon frequencies of Na Cl, using an approach which is a combination of frozen phonon and force constants methods in the framework of density functional pseudopotential theory. The dispersion relation curves, were calculated along symmetry direction ?, ? and Ů. We also calculated Grunesein parameters for all modes at X and L points in Brillion zone. The calcutions are made in the framework of density functional and pseudopotential theory, using super cell method, with the valence orbitals expanded in plane waves.

R. Khoda-Bakhsh

2001-06-01

296

Vacuum Phonon Tunneling in Variable Temperature STM

We demonstrate that the temperature of the terminating atom of STM tip can be directly measured by inelastic electron tunneling spectroscopy. A previously unknown mechanism of interfacial thermal transport, field-induced phonon tunneling, has been revealed by ultrahigh vacuum scanning tunneling microscopy. Using thermally broadened Fermi-Dirac distribution in the STM tip as in-situ atomic scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric fields and thermally vibrating image charges, "thermal mirages". By comparing experimental data and theory, we show that the thermal energy transmitted through atomically narrow vacuum gap due to thermal vibration of image charges exceeds, by ten orders of magnitude, the Planck's thermal radiation energy. Reference: I. Altfeder, A. A. Voevodin, A. K. Roy, PRL 105, 166101 (2010)

Altfeder, Igor; Voevodin, Andrey; Roy, Ajit

2011-03-01

297

Scattering of phonons by cluster defects

International Nuclear Information System (INIS)

The scattering of phonons in crystals containing defect aggregates of spherical shape has been studied. An expression is obtained for the phonon mean free path in the form of a series in ascending powers of the wave vector q. The wave vector dependence of the scattering can be satisfactorily represented by qsup(4)(qsup(3) + (qsub(o)sup(3))/qsup(3)+qsub(o)sup(3)), where C and qsub(o) are constants depending on the defect diameter (C>> 1). It is observed that the scattering is of the qsup(4) type for wavelengths small compared with the defect size. For wave-lengths comparable to and smaller than the defect size, the mean free path exhibits a weak dependence on the wave vector. The result is at variance with the wave-vector-independent geometrical scattering often assumed for small wave-lengths. Thermal conductivity measurements on irradiated crystals can be consistently explained by the present results. (auth.)

298

Interaction of Thermal Phonons with Interfaces

Energy Technology Data Exchange (ETDEWEB)

In this chapter we will first explore the connection between interface scattering and thermal transport using the Boltzmann transport equation (BTE). It will be shown that Boltzmann transport provides a convenient method for considering boundary scattering in nanochannel structures. For internal interfaces such as grain boundaries found in polycrystals, it is more natural to consider transmission and reflection across a single boundary. In this regard we will discuss theories related to interface thermal resistance. Our qualitative discussion of the theories of phonon transport will be followed by a discussion of experimental techniques for measuring thermal transport. We end this chapter by giving a detailed description of two complimentary experimental techniques for measuring the influence of interfaces on thermal phonon transport.

David H. Hurley; Subhash Shinde; Edward Piekos

2013-11-01

299

Phonons as building blocks in nuclear structure

International Nuclear Information System (INIS)

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

300

Signal of high-energy phonons created by low-energy phonons in superfluid helium

International Nuclear Information System (INIS)

Starting from the solution of the kinetic equation, we have calculated the distribution function for the high-energy phonons, which are created by a short pulse of low-energy phonons moving in superfluid helium. This enables an explicit expression for the energy density flux to be derived. Hence we find the amplitude of the high-energy phonon signal as a function of time on a bolometer. We divide this signal into two halves: the 'head' and 'tail' which arrive before and after the peak signal, respectively. We analyze which high-energy phonons form the head and tail of the signal. The half-widths of head and tail are calculated and approximate formulas which describe the shapes of them are obtained. The partial contribution of high-energy phonons, with different momenta, to the total signal at different times is determined. These results are compared with the experimental results given in the preceding paper [R. V. Vovk, C. D. H. Williams, and A. F. G. Wyatt, Phys. Rev. B 69, 144524 (2004)

301

Phonon focussing in high Tc superconductors

International Nuclear Information System (INIS)

The phonon enhancement factor is the ratio of energy flux for a particular polarisation and propagation direction to the corresponding flux in the isotropic case. Mathematically, it is the ratio of the solid angle in the wave vector space to the corresponding solid angle in the group velocity space. Plots of enhancement factors for the shear mode of the phase and group velocity surface for the superconductors YBCO, BSCCO and LSCO using the elastic constant data are given

302

Phonon-Drag Thermopower at High Temperatures

Digital Repository Infrastructure Vision for European Research (DRIVER)

The adiabatic cristal model is offered. It is shown that springy nuclei oscillations relatively electronic envelops and waves of such oscillations (inherent oscillations and waves) may exist in crystals. The analysis of experimental temperature dependencies of resistivity in semiconductors with electron-vibrational centres has shown that inherent oscillations effectively interact with crystalline phonons as well as with electrons and holes, creating powerful interaction of e...

Vdovenkov, V. A.

1999-01-01

303

Soft phonon anomalies in relaxor ferroelectrics

International Nuclear Information System (INIS)

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

304

Soft phonons in the relaxor ferroelectric PMN

A review is given of recent neutron scattering results of soft phonons for prototypical relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O3 (PMN). PMN shows a ``diffuse" ferroelectric transition at around Tm 265 K, remaining in the cubic phase down to the lowest temperature. One of the important clues for relaxor behavior is the formation of ``polar nanoregions" (PNR) below Td suggested by Burns and Dacol[1]. From the recent series of inelastic neutron scattering experiments, Gehring et al.[2] observed a dramatic change of the transverse optic (TO) phonon dispersion from normal one to the ``waterfall"-type one across T_d. Also, Hirota et al. proposed a simple model to resolve the puzzling problem of diffuse scattering for PMN by introducing ``condensed soft mode with phase shift." We have extensively investigated the TO and the transverse acoustic (TA) modes down to 11 K. The soft mode, overdamped by polar nanoregions below Td recovers dramatically below 220 K. The square of the soft phonon energy E_ph^2 increases linearly with decreasing temperature and E_ph reaches 11 meV at T=11 K. The TA phonon line broadening starts at Td and disappears at 220 K, coincident with the recovery of the TO mode. This research is being carried out with many collaborators, including W. Chen, P. M. Gehring, K. Hirota, G. Shirane, C. Stock, and Z.-G. Ye. [1] G. Burns et al., Solid State Commun. 48, 853 (1983). [2] P. M. Gehring et al., cond-mat/0108170. [3] K. Hirota et al., cond-mat/0109386.

Wakimoto, Shuichi

2002-03-01

305

Soft Phonon Anomalies in Relaxor Ferroelectrics

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

Shirane, G

2000-01-01

306

Nonharmonic phonons in ?-iron at high temperatures

Phonon densities of states (DOS) of bcc ?-Fe57 were measured from room temperature through the 1044 K Curie transition and the 1185 K fcc ?-Fe phase transition using nuclear resonant inelastic x-ray scattering. At higher temperatures all phonons shift to lower energies (soften) with thermal expansion, but the low transverse modes soften especially rapidly above 700 K, showing strongly nonharmonic behavior that persists through the magnetic transition. Interatomic force constants for the bcc phase were obtained by iteratively fitting a Born-von Kármán model to the experimental phonon spectra using a genetic algorithm optimization. The second-nearest-neighbor fitted axial force constants weakened significantly at elevated temperatures. An unusually large nonharmonic behavior is reported, which increases the vibrational entropy and accounts for a contribution of 35 meV/atom in the free energy at high temperatures. The nonharmonic contribution to the vibrational entropy follows the thermal trend of the magnetic entropy, and may be coupled to magnetic excitations. A small change in vibrational entropy across the ?-? structural phase transformation is also reported.

Mauger, L.; Lucas, M. S.; Muńoz, J. A.; Tracy, S. J.; Kresch, M.; Xiao, Yuming; Chow, Paul; Fultz, B.

2014-08-01

307

Phonon effects in molecular conduction junctions

This talk will give an overview of our work on effects of electron-phonon coupling on molecular conduction, including dephasing, dissipation and heating, then describe some recent observations, interpretations and predictions on three phenomena involving phonons in molecular junctions: (a) Heat conduction and its rectification by molecular wires^1,2; (b) inelastic electron tunneling spectroscopy^3-5 and (c) phonon-induced multi-stability, hysteresis and negative differential resistance in molecular conduction.^6 ^1 D. Segal, A. Nitzan and P. Hä'nggi, J. Chem. Phys. 119, 6840-6855 (2003) ^2 D. Segal and A. Nitzan, cond-mat/0405472 ^3 M. Galperin, M. Ratner and A. Nitzan, J. Chem. Phys. 121, 11965-11979 (2004) ^4 M. Galperin, M. Ratner and A. Nitzan, Nano Lett., 4, 1605-1611 (2004) ^5 M. Galperin, A. Nitzan, M. A. Ratner and D. R. Stewart, to be published http://atto.tau.ac.il/nitzan/253.pdf ^6 M. Galperin, M. A.Ratner and A. Nitzan, Nano Letters, in press http://atto.tau.ac.il/nitzan/254.pdf

Nitzan, Abraham

2005-03-01

308

Disruption of superlattice phonons by interfacial mixing

Molecular dynamics simulations and lattice dynamics calculations are used to study the vibrational modes and thermal transport in Lennard-Jones superlattices with perfect and mixed interfaces. The secondary periodicity of the superlattices leads to a vibrational spectrum (i.e., dispersion relation) that is distinct from the bulk spectra of the constituent materials. The mode eigenvectors of the perfect superlattices are found to be good representations of the majority of the modes in the mixed superlattices for up to 20% interfacial mixing, allowing for extraction of phonon frequencies and lifetimes. Using the frequencies and lifetimes, the in-plane and cross-plane thermal conductivities are predicted using a solution of the Boltzmann transport equation (BTE), with agreement found with predictions from the Green-Kubo method for the perfect superlattices. For the mixed superlattices, the Green-Kubo and BTE predictions agree for the cross-plane direction, where thermal conductivity is dominated by low-frequency modes whose eigenvectors are not affected by the mixing. For the in-plane direction, mid-frequency modes that contribute to thermal transport are disrupted by the mixing, leading to an underprediction of thermal conductivity by the BTE. The results highlight the importance of using a dispersion relation that includes the secondary periodicity when predicting phonon properties in perfect superlattices and emphasize the challenges of estimating the effects of disorder on phonon properties.

Huberman, Samuel C.; Larkin, Jason M.; McGaughey, Alan J. H.; Amon, Cristina H.

2013-10-01

309

Phonon Knudsen flow in nanostructured semiconductor systems

We determine the size effect on the lattice thermal conductivity of nanoscale wire and multilayer structures formed in and by some typical semiconductor materials, using the Boltzmann transport equation and focusing on the Knudsen flow effect. For both types of nanostructured systems we find that the phonon transport is reduced significantly below the bulk value by boundary scattering off interface defects and/or interface modes. The Knudsen flow effects are important for almost all types of semiconductor nanostructures but we find them most pronounced in Si and SiC systems due to the very large phonon mean-free paths. We apply and test our wire thermal-transport results to recent measurements on Si nanowires. We further investigate and predict size effects in typical multilayered SiC nanostructures, for example, a doped-SiC/SiC/SiO$_2$ layered structure that could define the transport channel in a nanosize transistor. Here the phonon-interface scattering produces a heterostructure thermal conductivity smalle...

Ziambaras, E; Ziambaras, Eleni; Hyldgaard, Per

2005-01-01

310

Phonon-lifetimes in demixing systems.

The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolved, stroboscopic measurements. Complementary to the study of long wavelength acoustic phonons, as studied previously, we extended these investigations to Brillouin-zone boundary modes that are particularly sensitive to variations of the local structure. Starting from the homogeneous mixed phase the behaviour of these modes during demixing is observed in real-time. A simple dynamical model based on local structure variants helps to interpret the results. It is shown that the phonon lifetimes vary strongly during the phase separation and increase drastically during the coarsening process. Up to a critical size of precipitates of about 10 nm, zone-boundary modes are found to be strongly damped, while beyond the line widths are reduced to the experimental resolution. This finding leads to the conclusion that the typical mean free path of these modes is of the order of 10 nm, which corresponds to 20 unit cells. PMID:22634583

Davaasambuu, J; Güthoff, F; Petri, M; Hradil, K; Schober, H; Ollivier, J; Eckold, G

2012-06-27

311

Optimization of phononic filters via genetic algorithms

International Nuclear Information System (INIS)

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 filteringand vibration filtering

312

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

313

International Nuclear Information System (INIS)

The arrays of the silicon nanocrystals in the boron-doped amorphous silicon films are studied by the method of the light combined scattering spectroscopy. The nanocrystals were formed in the initial amorphous films under the pulse effect of the excimer laser. The effects of the electron-phonon interaction were experimentally identified in the silicon nanocrystal/amorphous matrix heterostructure. These effects may be described within the frames of the known Fano interference model

314

Multi-phonon dynamics of the ultra-fast photoinduced transition of (EDO-TTF)2SbF6

International Nuclear Information System (INIS)

We report here the first observation of the photoinduced insulating-to-metal phase transition in the (EDO-TTF)2SbF6 salt, which occurs on the picosecond time-scale. The time-resolved optical experiments performed with 80 fs time-resolution demonstrate that the dynamical process involves several low-frequency phonons, as the crystalline structure is destabilized upon laser excitation.

315

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

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

316

Magnetic-Field-Assisted Terahertz Quantum Cascade Laser Operating up to 225 K

Advances in semiconductor bandgap engineering have resulted in the recent development of the terahertz quantum cascade laser1. These compact optoelectronic devices now operate in the frequency range 1.2-5 THz, although cryogenic cooling is still required2.3. Further progress towards the realization of devices operating at higher temperatures and emitting at longer wavelengths (sub-terahertz quantum cascade lasers) is difficult because it requires maintaining a population inversion between closely spaced electronic sub-bands (1 THz approx. equals 4 meV). Here, we demonstrate a magnetic-field-assisted quantum cascade laser based on the resonant-phonon design. By applying appropriate electrical bias and strong magnetic fields above 16 T, it is possible to achieve laser emission from a single device over a wide range of frequencies (0.68-3.33 THz). Owing to the suppression of inter-landau-level non-radiative scattering, the device shows magnetic field assisted laser action at 1 THz at temperatures up to 215 K, and 3 THz lasing up to 225 K.

Wade, A.; Fedorov, G.; Smirnov, D.; Kumar, S.; Williams, B. S.; Hu, Q.; Reno, J. L.

2008-01-01

317

Non-equilibrium phonon generation and detection in microstructure devices

We demonstrate a method to excite locally a controllable, non-thermal distribution of acoustic phonon modes ranging from 0 to 200 GHz in a silicon microstructure, by decay of excited quasiparticle states in an attached superconducting tunnel junction (STJ). The phonons transiting the structure ballistically are detected by a second STJ, allowing comparison of direct with indirect transport pathways. This method may be applied to study how different phonon modes contribute to the thermal conductivity of nanostructures.

Hertzberg, J. B.; Otelaja, O. O.; Yoshida, N. J.; Robinson, R. D.

2011-10-01

318

Phonon transmission through solid-liquid helium interfaces

International Nuclear Information System (INIS)

The previously reported technique for measuring phonon emission at a solid/4He boundary as a function of angle has been extended. A new technique is described whereby such angular measurements can be performed using superconducting tunnel junctions as frequency selective phonon detectors. Measurements of the angular emission from an atomically flat NaF sample into liquid 4He have been carried out using both bolometers and tunnel junctions as phonon detectors. (author)

319

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

320

Strong coupling superconductivity mediated by three-dimensional anharmonic phonons

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate three dimensional anharmonic phonons in tetrahedral symmetry and superconductivity mediated by these phonons. Three dimensional anharmonic phonon spectra are calculated directly by solving Schr\\"odinger equation and the superconducting transition temperature is determined by using the theory of strong coupling superconductivity assuming an isotropic gap function. With increasing the third order anharmonicity $b$ of the tetrahedral ion potential, we find a cros...

Hattori, Kazumasa; Tsunetsugu, Hirokazu

2010-01-01

321

Phonon Hall thermal conductivity from Green-Kubo formula

Digital Repository Infrastructure Vision for European Research (DRIVER)

We derive a formula for the thermal conductivity tensor of a ballistic phonon Hall model. It is found that, although the diagonal elements of the conductivity tensor diverge to infinite, the off-diagonal elements are finite,antisymmetric, and odd in magnetic field. The off-diagonal elements are non-zero only if the dynamic matrix of the phonon system breaks mirror reflection symmetry. The results are obtained without perturbative assumptions about the spin-phonon interactions.

Wang, Jian-sheng; Zhang, Lifa

2009-01-01

322

Isotopic effects on the phonon modes in boron carbide

International Nuclear Information System (INIS)

The effect of isotopes (10B-11B; 12C-13C) 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.

323

Plasmon-phonon Strongly-Coupled Mode in Epitaxial Graphene

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the dispersion measurements, using angle-resolved reflection electron-energy-loss-spectroscopy (AREELS), on two-dimensional (2D) plasmons in single and multilayer graphene which couple strongly to surface optical phonon (FK phonon) modes of silicon carbide substrate. The coupled modes show discrete dispersion behaviors in the single and bilayer graphene. With increasing graphene layers on SiC(0001), a transition from plasmon-like dispersion to phonon-like dispersio...

Liu, Yu; Willis, Roy F.

2009-01-01

324

Size-dependent hot-phonon dynamics in graphene flakes

We examine the ultrafast carrier phonon dynamics in graphene flakes with different lateral sizes. By using a size-selective centrifugation technique, we create graphene films with graphene flake sizes in the region of 120-450 nm. The transient transmission exhibits two-step relaxation, which are attributed to carrier thermalization followed by hot phonon cooling. We find that the cooling of the hot phonons proceeds faster, by a factor of three, for the smallest graphene flakes.

Cunning, Benjamin V.; Ishioka, Kunie; Brown, Christopher L.; Kielpinski, Dave

2014-05-01

325

Graphene-to-substrate energy transfer through out-of-plane longitudinal acoustic phonons.

Practically, graphene is often deposited on substrates. Given the major substrate-induced modification of properties and considerable energy transfer at the interface, the graphene-substrate interaction has been widely discussed. However, the proposed mechanisms were restricted to the two-dimensional (2D) plane and interface, while the energy conduction in the third dimension is hardly considered. Herein, we disclose the transfer of energy perpendicular to the interface of the combined system of the 2D graphene and the 3D base. More precisely, our observation of the energy dissipation of optically excited graphene via emitting out-of-plane longitudinal acoustic phonon into the substrate is presented. By applying nanoultrasonic spectroscopy with a piezoelectric nanolayer embedded in the substrate, we found that under photoexcitation by a femtosecond laser pulse graphene can emit longitudinal coherent acoustic phonons (CAPs) with frequencies over 1 THz into the substrate. In addition, the waveform of the CAP pulse infers that the photocarriers and sudden lattice heating in graphene caused modification of graphene-substrate bond and consequently generated longitudinal acoustic phonons in the substrate. The direct observation of this unexplored graphene-to-substrate vertical energy transfer channel can bring new insights into the understanding of the energy dissipation and limited transport properties of supported graphene. PMID:24559107

Chen, I-Ju; Mante, Pierre-Adrien; Chang, Cheng-Kai; Yang, Szu-Chi; Chen, Hui-Yuan; Huang, Yu-Ru; Chen, Li-Chyong; Chen, Kuei-Hsien; Gusev, Vitalyi; Sun, Chi-Kuang

2014-03-12

326

An impact of different doses (10-500 kGy) of ?-irradiation on electron-phonon coupling in Ge-doped CdTe (CdTe:Ge) single crystals was investigated via low-temperature (T=5 K) photoluminescence (LTPL) and resonant Raman scattering (RRS). In the present work electron-phonon coupling concerns longitudinal optical (LO) phonons and was described in terms of Huang-Rhys factor. It was obtained ?-irradiation in such dose range leads to the increases in the value of Huang-Rhys factor. At high doses (equal to 200 kGy) the saturation of the increased at low doses Huang-Rhys factor was observed. Based on the features of radiation-stimulated changes in LTPL, increasing of electron-LO-phonon coupling can be explained by radiation-induced defect compensation process involving, with the great probability, Ge dopant atoms filling of native cadmium vacancies (VCd) and by other related mechanisms such as radiation-induced Ge clusters dissociation. Such compensation is resulted in the proving of the crystalline perfection of irradiated crystals. The latter was confirmed by resonant Raman scattering measurements. Resonant Raman conditions for near E0+?0 gap (2,54 eV at 80 K) were obtained by temperature tuning of the band gap keeping the excitation energy fixed for laser excitation energies near E0+?0. It was found good agreement in the dose dependencies of the values of Huang-Rhys factors and 2LO/1LO phonon modes ratio obtained from resonant Raman spectra. The increasing in the intensity of Fröhlich-induced 2LO-phonon modes with the increase of the irradiation dose and decreasing in impurity-induced 1LO-phonon intensity indicates about decreasing in the defect concentration in studied crystals. Relatively high saturation dose corresponding to the 2LO/1LO phonon modes ratio indicates high radiation strength of studied material.

Nasieka, Iu.; Boyko, M.; Strelchuk, V.; Danilchenko, B.; Rashkovetskyi, L.; Fochuk, P.

2014-10-01

327

Self-consistent calculation of electron-phonon couplings

International Nuclear Information System (INIS)

An approach is described in which the electron-phonon coupling is evaluated by using the change in the self-consistent crystal potential caused by a ''frozen-phonon'' distortion of the lattice. Both the vibrational and electronic properties of the solid are computed directly and used for the electron-phonon coupling calculation. The method can be used to examine electron-phonon interactions without any empirical information about the electronic or vibrational states of the material. Recent applications of the method include the successful prediction of superconductivity in highly compressed silicon

328

Theory of the phonon Hall effect in paramagnetic dielectrics.

Based upon Raman spin-lattice interaction, we propose a theoretical model for the phonon Hall effect in paramagnetic dielectrics, which was discovered recently in an experiment [C. Strohm, G. L. J. A. Rikken, and P. Wyder, Phys. Rev. Lett. 95, 155901 (2005).]. The phonon Hall effect is revealed to be a phonon analogue to the anomalous Hall effect in electron systems. The thermal Hall conductivity is calculated by using the Kubo formula. Our theory reproduces the essential experimental features of the phonon Hall effect, including the sign, magnitude, and linear magnetic field dependence of the thermal Hall conductivity. PMID:16712169

Sheng, L; Sheng, D N; Ting, C S

2006-04-21

329

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)

330

Phonon bandgap engineering of strained monolayer MoS2

The phonon band structure of monolayer MoS2 is characteristic of a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes. Therefore, the phonon bandgap engineering is of practical significance for the manipulation of phonon-related mechanical or thermal properties in monolayer MoS2. We perform both phonon analysis and molecular dynamics simulations to investigate the tension effect on the phonon bandgap and the compression induced instability of the monolayer MoS2. Our key finding is that the phonon bandgap can be narrowed by the uniaxial tension, and is completely closed at ? = 0.145; while the biaxial tension only has a limited effect on the phonon bandgap. We also demonstrate the compression induced buckling for the monolayer MoS2. The critical strain for buckling is extracted from the band structure analysis of the flexure mode in the monolayer MoS2 and is further verified by molecular dynamics simulations and the Euler buckling theory. Our study illustrates the uniaxial tension as an efficient method for manipulating the phonon bandgap of the monolayer MoS2, while the biaxial compression as a powerful tool to intrigue buckling in the monolayer MoS2.

Jiang, Jin-Wu

2014-06-01

331

Proposal for an Optomechanical Traveling Wave Phonon-Photon Translator

In this article 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 formed from coupled photonic and phononic crystal planar circuits. Applications of the phonon-photon translator 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 are considered.

Safavi-Naeini, Amir H

2010-01-01

332

Phonon Cooling in a Superconductor - Normal Metal - Superconductor Tunnel Junction

We present evidence for the cooling of normal metal phonons by electron tunneling in a Superconductor - Normal metal - Superconductor tunnel junction. The normal metal electron temperature is extracted by comparing the device current-voltage characteristics to the theoretical prediction. We use a quantitative model for the phonon cooling that includes the electron-phonon coupling in the normal metal and the Kapitza resistance between the substrate and the metal. It gives an excellent fit to the data and enables us to extract an effective phonon temperature in the normal metal.

Rajauria, S; Fournier, T; Hekking, F W J; Courtois, H; Pannetier, B; Rajauria, Sukumar

2006-01-01

333

Phononic glass: a robust acoustic-absorption material.

In order to achieve strong wide band acoustic absorption under high hydrostatic pressure, an interpenetrating network structure is introduced into the locally resonant phononic crystal to fabricate a type of phononic composite material called "phononic glass." Underwater acoustic absorption coefficient measurements show that the material owns high underwater sound absorption coefficients over 0.9 in 12-30 kHz. Moreover, the quasi-static compressive behavior shows that the phononic glass has a compressive strength over 5 MPa which is crucial for underwater applications. PMID:22894191

Jiang, Heng; Wang, Yuren

2012-08-01

334

Phonon softening and failure of graphene under tensile strain

Phonon softening of graphene under tensile strain is investigated based on ab initio density functional theory calculations. We demonstrate that, over a wide range of tensile strain directions, the strain-induced enhancement of phonon softening can give rise to phonon instabilities resulting in a mechanical failure of graphene. It is shown that there are two types of instabilities associated with phonons near K and ? points, respectively, which induce symmetry-breaking structural distortions, and both of them lead to mechanical failure prior to the elastic failure commonly expected when the structural symmetry is retained.

Hwang, Jeongwoon; Ihm, Jisoon; Kim, Kyung-Suk; Cha, Moon-Hyun

2014-12-01

335

Specular scattering probability of acoustic phonons in atomically flat interfaces.

We report a direct determination of the specular scattering probability of acoustic phonons at a crystal boundary by observing the escape of incident coherent phonons from the coherent state during reflection. In the sub-THz frequency range where the phonon wavelength is much longer than the lattice constant, the acoustic phonon-interface interaction is found to agree well with the macroscopic theory on wave scattering from rough surfaces. This examination thus quantitatively verifies the dominant role of atomic-scale corrugations in the Kapitza anomaly observed at 1-10 K and further opens a new path to nondestructively estimate subnanoscale roughness of buried interfaces. PMID:20366314

Wen, Yu-Chieh; Hsieh, Chia-Lung; Lin, Kung-Hsuan; Chen, Hung-Pin; Chin, Shu-Cheng; Hsiao, Ching-Lien; Lin, Yuan-Ting; Chang, Chia-Seng; Chang, Yuan-Chih; Tu, Li-Wei; Sun, Chi-Kuang

2009-12-31

336

A quantum formalism for a terahertz acoustic laser

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The aim of this work is to improve the study of a phonon laser (saser) proposed by us several years ago[1]. This is a device capable to generate an intense coherent beam of acoustical phonons. Our acoustic laser consists in a double barrier heterostructure tailored such the energy difference between [...] the ground and the first excited state in the well is close to the energy of the LO phonon. The electrons are directly injected into the excited level. Therefore they decay producing a high rate of LO phonons. These phonons are confined inside the well and decay into a pair of phonons[2]: LO -> + TA. The TA phonons escape the well in the [111] direction constituting an intense coherent beam. Recently were studied (and sometimes realized experimentally) several kinds of phonon lasers. Up to our knowledge our saser is the only that has a very short wavelength (smaller than 25 Ĺ) and a very long range (greater than 1000 mum). Because of that, such beam could have applications to acoustic nanoscopy, acoustic nanolithography and phonoelectronics. In early articles[1, 3, 4, 5, 6] we get the kinetic equations for the averaged electron and phonon populations. Quantum fluctuations were not taken into account. The system Hamiltonian is H = He + Hph + He-ph + Hph-ph + He-e. To solve this Hamiltonian we expand their eigenfunctions in the basis of the eigenstatesŚjn1n2n3ń of the single particle part of it. We obtain a set of coupled equations for the expansion coefficients that can be solved with some approximations. The results are qualitatively similar to those obtained previously.

Ihosvany, Camps Rodríguez; Sergio Saul, Makler; Enrique Victoriano, Anda.

337

Ab initio calculation of the thermodynamic properties of InSb under intense laser irradiation

International Nuclear Information System (INIS)

In this paper, phonon spectra of InSb at different electronic temperatures are presented. Based on the phonon dispersion relationship, we further perform a theoretical investigation of the thermodynamic properties of InSb under intense laser irradiation. The phonon entropy, phonon heat capacity, and phonon contribution to Helmholtz free energy and internal energy of InSb are calculated as functions of temperature at different electronic temperatures. The abrupt change in the phonon entropy- temperature curve from Te = 0.75 to 1.0 eV provides an indication of InSb undergoing a phase transition from solid to liquid. It can be considered as a collateral evidence of non-thermal melting for InSb under intense electronic excitation effect

338

International Nuclear Information System (INIS)

In this paper, we introduce an improvement of the Debye model for the phonon spectrum in a quantum box at low temperatures. This improvement is a direct consequence of the consideration of the discrete phonon spectrum in some special quantum boxes, names in this paper, quantum cubic cells (QCC in which the highest significant level, qT, is smaller than 100). We show that a discrete Planck spectrum may occur in nanometric QCC around the temperature 1K. Furthermore, we demonstrate that the total energy density and the heat capacity become functions of the product of cell size by temperature Pq, which are clear and measurable quantum effects in solid QCC. The limits of this quantum regime of the cubic cell are set as Pq is an element of [0.1, 1] and a reciprocity rule for the cell size and temperature is given. The thermodynamic functions for the phonon gas in QCC are recalculated taking into account their dependency on Pq. The calculation of the phonon average velocity, which plays a key role in the Debye model, is also reconsidered and simplified for quasi-isotropic cubic crystals. Finally, the theoretical formula of the Debye temperature for quasi-isotropic cubic solids is corrected (at low temperatures) and put in a form which depends on a single elastic constant. We show that this correction reduces the errors between the calculated and experimental Debye temperatures of some elements which crystallize in the cubic system. (author)

339

Phonon propagation in liquid 4He

International Nuclear Information System (INIS)

A system is described which has been successfully used to study the propagation of high-frequency phonons in liquid 4He at T = 0.1 K and pressures up to 24 bar. The properties of superconducting tunnel junction detectors are discussed in some detail and the various contributions to the received signal shape are considered. The paper describes a reliable and accurate method of linearly translating specimens in 3He- 4He refrigerators which does not give an excessive heat load. Examples of received signals are presented which show the difference between the frequency-selective tunnel junction detectors and the broad band graphite bolometers. (author)

340

Phonon modes in LPCMO thin films

Energy Technology Data Exchange (ETDEWEB)

We report a study of the infrared properties of a series of (La{sub 1-y}Pr{sub y}){sub 0.67}Ca{sub 0.33}MnO{sub 3} (y=0, 0.5, 0.6) thin films. The samples, grown on NdGaO{sub 3} substrates, showed optically active phonons corresponding to external, bending and stretching modes with no significant temperature shifts. The effective spectral weight, given by N{sub eff}({omega}=0.5 eV) of these films is seen to follow scaling behavior similar to polycrystalline samples.

Margankunte, Naveen [Department of Physics, University of Florida (United States)], E-mail: naveen@phys.ufl.edu; Dhakal, Tara; Tanner, D.B.; Biswas, Amlan [Department of Physics, University of Florida (United States)

2008-04-01

341

Light scattering by surface phonons in crystals

International Nuclear Information System (INIS)

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)

342

Low temperature phonon anomalies in cuprates

International Nuclear Information System (INIS)

The inelastic neutron scattering measurement on La1.85Sr.15CuO4 single crystals shows that the in-plane LO phonon dispersion at low temperature is incompatible with the current view on the dynamic charge stripes, which for this composition should have the periodicity of 4a. Instead the results are consistent with the dynamic stripes with the periodicity of 2a, half of what is expected and a quarter of the magnetic periodicity. Calculations with the two-band t-t'-J model suggest that such 2a stripe charge ordering may help hole pairing

343

Phonon scattering in graphene over substrate steps

DEFF Research Database (Denmark)

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

Sevincli, Haldun; Brandbyge, Mads

2014-01-01

344

Energy Technology Data Exchange (ETDEWEB)

The electron-phonon and vibronic couplings governing the spectral properties have been studied in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll a (BChl a)-protein complex at 4.5 K using a spectrally selective difference fluorescence line-narrowing technique. The complex is a part of the light-harvesting system of green photosynthetic bacteria. Its lowest-energy absorption band, peaking at 826 nm and responsible for the fluorescence, is believed to be due to Q{sub y} transitions of largely isolated molecules. One of the main merits of the used method compared with the more common fluorescence line narrowing is that the zero-phonon lines (ZPL) resonant with the excitation laser can be accurately measured, allowing precise determination of the Huang-Rhys (HR) factors, the main characteristics of the linear electron-phonon and vibronic coupling strengths. Over 60 individual vibrational modes of intra- and intermolecular origin have been resolved in the energy range of 45-1600 cm{sup -1}. The small HR factors for these modes, ranging between 0.001 and 0.018, add up to a value of S {sub vib}=0.38{+-}0.07. The effective HR factor for the phonons, S {sub ph}, was found clearly wavelength-dependent, varying from {approx}0.7 at short wavelengths to {approx}0.3 at the long-wavelength tail of the absorption spectrum. Coupling between the BChl a molecules is likely responsible for this wavelength dependence.

Raetsep, Margus [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Freiberg, Arvi [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia) and Institute of Molecular and Cell Biology, University of Tartu, Tartu (Estonia)]. E-mail: arvi.freiberg@ut.ee

2007-11-15

345

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

346

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

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

347

Oscillation of the transport lifetime due to LO phonon scattering in quasi-one-dimensional channels

The transport properties of quantum wires (QW's), mainly under the action of strong magnetic field, have been studied both theoretically and experimentally. In this report we use the memory-function projection-operator theory to obtain the resistivity of a QW built by structural and electric confinement and show that, in the absence of a magnetic field, oscillations in the transport lifetime appear due to scattering by LO phonons. These oscillations describe the harmonic confinement and are weakly dependent on the carrier concentration in the quantum limit. We suggest that this could be an easy way to characterize that structure using dc transport.

Baldan, M. R.; Leal, C. E.; da Cunha Lima, I. C.

1992-05-01

348

Electron-phonon interaction on optical spectra of nanoelectronic devices

Information obtained on the solid-state lattice dynamics by electron-phonon interaction between lattice phonons and electrons could open up to learn more about lattice dynamics and to apply it in nanoelectronic devices including software reliability, nano-size capacitors, master clock sources, as well as non-contact temperature probes on nano-electronic and photonicdevices.

Kim, Q.

2002-01-01

349

Phonons and charge-transfer excitations in HTS superconductors

Energy Technology Data Exchange (ETDEWEB)

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.

Bishop, A.R.

1989-01-01

350

Phonon thermal transport through tilt grain boundaries in strontium titanate

In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO3. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO3 contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.

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

2014-08-01

351

Variational Monte Carlo method for electron-phonon coupled systems

We develop a variational Monte Carlo (VMC) method for electron-phonon coupled systems. The VMC method has been extensively used for investigating strongly correlated electrons over the last decades. However, its applications to electron-phonon coupled systems have been severely restricted because of its large Hilbert space. Here, we propose a variational wave function with a large number of variational parameters, which is suitable and tractable for systems with electron-phonon coupling. In the proposed wave function, we implement an unexplored electron-phonon correlation factor, which takes into account the effect of the entanglement between electrons and phonons. The method is applied to systems with diagonal electron-phonon interactions, i.e., interactions between charge densities and lattice displacements (phonons). As benchmarks, we compare VMC results with previous results obtained by the exact diagonalization, the Green function Monte Carlo method and the density matrix renormalization group for the Holstein and Holstein-Hubbard model. From these benchmarks, we show that the present method offers an efficient way to treat strongly coupled electron-phonon systems.

Ohgoe, Takahiro; Imada, Masatoshi

2014-05-01

352

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)

353

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

354

International Nuclear Information System (INIS)

By inelastic neutron scattering the phonon dispersion curves in YBa2Cu3O7 and YBa2Cu3O6 were investigated. Based on these results, the differences in the phonon densities of states of the two compounds are analyzed

355

Multiple interruption of optically generated acoustic phonons in ruby

International Nuclear Information System (INIS)

This thesis clarifies the rate-determining processes which tend to equilibrate the bottlenecked 29 cm-1 phonons with the temperature bath in stationary experiments. In addition, the direct relaxation between the Zeeman components of E is measured, revealing at high pumping, both continuous and time-resolved, a strong phonon bottleneck. (Auth.)

356

Rigid-plane phonons in layered crystals

Energy Technology Data Exchange (ETDEWEB)

The determination of the layer number N in nanoscale thin layered crystals is a challenging problem of technological relevance. In addition to innovative experimental techniques, a thorough knowledge of the underlying lattice dynamics is required. Starting from phenomenological atomic interaction potentials we have carried out an analytical study of the low-frequency optical phonon dispersions in layered crystals. At the gamma point of the two-dimensional Brillouin zone the optical phonon frequencies correspond to rigid-plane shearing and compression modes. We have investigated graphene multilayers (GML) and hexagonal boron-nitride multilayers (BNML). The frequencies show a characteristic dependence on N. The results which are represented in the form of fan diagrams are very similar for both materials. Due to charge neutrality within layers Coulomb forces play no role, only van der Waals forces between nearest neighbor layers are relevant. The theoretical results agree with recent low-frequency Raman results on rigid-layer modes [Tan et al., Nature Mater. 11, 294 (2012)] in GML and double-resonant Raman scattering data on rigid-layer compression modes [Herziger et al., Phys. Rev. B 85, 235447 (2012)] in GML. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Michel, K.H. [Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerpen (Belgium); Verberck, B. [Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerpen (Belgium); Institut fuer theoretische Physik und Astrophysik, Universitaet Wuerzburg, Am Hubland, 97074 Wuerzburg (Germany)

2012-12-15

357

Rigid-plane phonons in layered crystals

International Nuclear Information System (INIS)

The determination of the layer number N in nanoscale thin layered crystals is a challenging problem of technological relevance. In addition to innovative experimental techniques, a thorough knowledge of the underlying lattice dynamics is required. Starting from phenomenological atomic interaction potentials we have carried out an analytical study of the low-frequency optical phonon dispersions in layered crystals. At the gamma point of the two-dimensional Brillouin zone the optical phonon frequencies correspond to rigid-plane shearing and compression modes. We have investigated graphene multilayers (GML) and hexagonal boron-nitride multilayers (BNML). The frequencies show a characteristic dependence on N. The results which are represented in the form of fan diagrams are very similar for both materials. Due to charge neutrality within layers Coulomb forces play no role, only van der Waals forces between nearest neighbor layers are relevant. The theoretical results agree with recent low-frequency Raman results on rigid-layer modes [Tan et al., Nature Mater. 11, 294 (2012)] in GML and double-resonant Raman scattering data on rigid-layer compression modes [Herziger et al., Phys. Rev. B 85, 235447 (2012)] in GML. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

358

Carrier dynamics and coherent acoustic phonons in nitride heterostructures

We model generation and propagation of coherent acoustic phonons in piezoelectric InGaN/GaN multi-quantum wells embedded in a \\textit{pin} diode structure and compute the time resolved reflectivity signal in simulated pump-probe experiments. Carriers are created in the InGaN wells by ultrafast pumping below the GaN band gap and the dynamics of the photoexcited carriers is treated in a Boltzmann equation framework. Coherent acoustic phonons are generated in the quantum well via both deformation potential electron-phonon and piezoelectric electron-phonon interaction with photogenerated carriers, with the latter mechanism being the dominant one. Coherent longitudinal acoustic phonons propagate into the structure at the sound speed modifying the optical properties and giving rise to a giant oscillatory differential reflectivity signal. We demonstrate that coherent optical control of the differential reflectivity can be achieved using a delayed control pulse.

Sanders, G D

2006-01-01

359

Phonon thermal conductivities of multi-layered graphene

Using an exact numerical solution of the phonon Boltzmann equation, we show that the intrinsic lattice thermal conductivities, ?, of N-layer graphene (N=1-5) are dominated by contributions from out-of-plane, flexural (ZA) phonon modes contrary to previous theories based on the relaxation time approximation, which assumed this contribution to be negligible [1, 2]. We find a reduction of ? with increasing N due to interlayer coupling, which: 1) lifts the degeneracy of the flexural acoustic mode frequencies, 2) makes the ZA phonon branch become linear near the zone-center, and 3) breaks a selection rule for anharmonic phonon-phonon scattering in two-dimensional systems. [4pt] [1] P. G. Klemens and D. F. Pedraza, Carbon vol. 32, pp. 735-741 (1994). [0pt] [2] B. D. Kong, S. Paul, M. B. Nardelli and K. W. Kim, Phys. Rev. B 80, 033406 (2009).

Lindsay, Lucas; Broido, David

2011-03-01

360

Doped semiconductors as thermal and ballistic phonon detectors

The use of doped semiconductors to detect phonons is discussed, emphasizing the use of neutron transmutation doped (NTD) germanium as well as the available data regarding high energy phonons. Hopping conduction is described as the object of experiments with NTD germanium, and NTD germanium is described in terms of its qualities as a thermistor and as a phono-conductor. The semiconductor is concluded to be a good sensor for phonon which leads to discussions of the necessary interface between the thermistor and the crystal and of dealing with the long decay times of the pulses. The detection of ionization is also reviewed, suggesting that pure germanium allows the detection at very low electric fields. Highly doped germanium is concluded to be an effective phonon sensor, and the use of gold-germanium eutectic permits the necessary transparency for observing some ballistic phonons.

Sadoulet, B.; Shutt, T.; Wang, N.; Cummings, A.; Barnes, P.; Beeman, J.; Emes, J.; Haller, E. E.; Lange, A.; Giraud-Heraud, Y.

361

Influence of Phonon dimensionality on Electron Energy Relaxation

We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor (NIS) tunnel junction thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to clearly see the onset of the effects of two-dimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the lowest temperatures below 0.5 K for the 30 nm membranesootnotetextJ. T. Karvonen and I. J. Maasilta, Phys. Rev. Lett. 99, 145503 (2007)..

Maasilta, Ilari; Karvonen, Jenni

2008-03-01

362

Surface anharmonicity: Temperature dependence of phonon energies on Cu(110)

International Nuclear Information System (INIS)

The temperature dependence of surface phonons on Cu(110) has been determined with high resolution electron energy loss spectroscopy between 21 and 766 K. Phonons at bar ? and at bar Y, both with atomic motion perpendicular to the surface, have been examined to assess the importance of anharmonicity at the surface. As the temperature is increased the observed phonon energies decrease and the linewidths increase. The same percentage decrease is observed at bar ? and bar Y. A simple model using an anharmonic potential can reproduce the magnitude and shape of the temperature dependence of the phonon at bar ?. Direct comparison with bulk phonon studies shows that the anharmonicity at the surface is 4.1--4.8 times greater. 18 refs., 5 figs

363

Bulk and surface phonon-polaritons in ternary mixed crystals

International Nuclear Information System (INIS)

The bulk and surface phonon-polaritons in ternary mixed crystals are investigated in the random-element-isodisplacement model and Born-Huang approximation. The numerical results of the polariton frequencies and oscillator strengths as functions of the wavevector and the composition for ternary mixed crystals AlxGa1-xAs, ZnxCd1-xS, and GaxIn1-xN are obtained and discussed. It is shown that there are three propagated bands separated by two forbidden bands for the phonon-polaritons in bulk materials and two branches of surface phonon-polaritons in semi-infinite systems. The 'two-mode' and 'one-mode' behaviours of phonon-polaritons are also shown in the dispersion curves of bulk and surface phonon-polaritons

364

Search for the 3-phonon state of 40Ca

International Nuclear Information System (INIS)

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)

365

Energy Technology Data Exchange (ETDEWEB)

We report results of first-principles calculations for structural properties, electronic structure, phonon spectrum and electron-phonon interaction for the antiperovskite compound AlCNi{sub 3}. The structural properties are calculated using a plane-wave-pseudopotential method and the density functional theory within the generalised gradient approximation. The electronic structure and density of states for AlCNi{sub 3} are presented and compared with previous theoretical calculations. Our structural and electronic results are used, within the implementation of a linear response technique, for calculations of phonon states. We have observed that all phonon modes are stable along the [100] direction while unstable phonon modes are found in the [110] and [111] symmetry directions. At the Brillouin zone edge point X, the electron-phonon coupling parameters for phonon modes in AlCNi{sub 3} are calculated to be smaller than their corresponding values for MgCNi{sub 3}. This result indicates that the electron-phonon interaction is not very strong in AlCNi{sub 3}.

Tuetuencue, H M [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Duman, S [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Bagci, S [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Srivastava, G P [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)

2007-12-15

366

International Nuclear Information System (INIS)

We describe a general method to determine the relative phase difference between the complex components of a phononic Raman tensor from the measured angular dependence of the intensity of light scattered inelastically by the phonon in a Raman process. The method is applied to Raman spectra of a (110)-oriented SmBa2Cu3O7-? thin film obtained at room temperature. From our spectra we derive for the A1g-like phonons the anisotropy ratio and the relative phase difference between the two independent components of the Raman tensor as a function of laser energy ??. We point out that our results can be used to verify theoretical calculations of Raman tensors and compare our data with values calculated for the related compound YBa2Cu4O8. copyright 1998 The American Physical Society

367

International Nuclear Information System (INIS)

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)

368

Frozen phonon calculations for the L(2/3, 2/3, 2/3) phonon of niobium and molybdenum

International Nuclear Information System (INIS)

Materials with high superconducting transition temperatures frequently exhibit anomalous features in their phonon dispersion curves. The origin of these anomalies and their significance for superconductivity has been the subject of much debate. Two seemingly different models have been proposed to explain these anomalies in terms of the electron-phonon interaction. The first model focuses on real space charge-density distortions (CDD's), while the second emphasizes the states in reciprocal space near the Fermi energy. To test the assumptions in these models and to better understand the details of the electronic response to lattice vibrations in transition metals self-consistent frozen phonon calculations were performed for the (2/3, 2/3, 2/3) phonon in Nb and Mo. Initial results are reported for the CDD's associated with this phonon and discuss the differences between Nb and Mo

369

Energy Technology Data Exchange (ETDEWEB)

We investigate femtosecond laser ablation of metals using a hybrid simulation scheme. Two equations are solved simultaneously: one for the electronic system, which accounts for laser energy absorption and heat conduction, the other for the dynamics of the lattice where the ablation process takes place. For the electron temperature a generalized heat conduction equation is solved by applying a finite difference scheme. For the lattice properties, e.g. pressure, density or temperature, we use common molecular dynamics. Energy transfer between the subsystems is allowed by introducing an electron-phonon coupling term. This combined treatment of the electronic and atomic systems is an extension of the well known two-temperature model. Atomic scale images of the ablation process are shown. The dependence of ablation and melting depth on characteristic parameters, such as the pulse duration and the laser fluence is discussed.

Sonntag, Steffen; Roth, Johannes; Gaehler, Frank; Trebin, Hans-Rainer [Institut fuer Theoretische und Angewandte Physik, Universitaet Stuttgart, 70550 Stuttgart (Germany)

2008-07-01

370

Phonons and electron-phonon coupling in YNi2B2C

Energy Technology Data Exchange (ETDEWEB)

We present a combined density functional perturbation theory and inelastic neutron scattering study of the lattice dynamical properties of YNi2B2C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to the presence of large displacements of the light atoms, i.e., B and C, which is unusual in view of the rather low phonon energies. Specific modes exhibiting a strong coupling to the electronic quasiparticles were investigated as a function of temperature. Their energies and line widths showed marked changes on cooling from room temperature to just above the superconducting transition at Tc = 15.2 K. Calculations simulating the effects of temperature allow us to model the observed temperature dependence qualitatively.

Weber, Frank [Karlsruher Institut fur Technologie; Pintschovius, L. [Karlsruher Institut fur Technologie; Reichardt, W. [Karlsruher Institut fur Technologie; Heid, R. [Karlsruher Institut fur Technologie; Bohnen, K.-P. [Karlsruher Institut fur Technologie; Kreyssig, Andreas [Ames Laboratory; Reznik, D. [Technische Universitat Dresden; Hradil, K. [Institut fur physikalische Chemie

2014-03-04

371

We derive the frequency shifts and the broadening of ?-point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic spectrum, induced by the strain, results in a polarization dependence of the LO and TO modes. This dependence is in agreement with the experimental results showing a periodic modulation of the Raman intensity of the split G peak. Moreover, the anomalous behavior of the frequency shift reported in undeformed graphene is found to be robust under strain.

Assili, M.; Haddad, S.

2014-09-01

372

Electron-phonon heat transfer in monolayer and bilayer graphene

We calculate the heat transfer between electrons to acoustic and optical phonons in monolayer and bilayer graphene (MLG and BLG) within the quasiequilibrium approximation. For acoustic phonons, we show how the temperature-power laws of the electron-phonon heat current for BLG differ from those previously derived for MLG and note that the high-temperature (neutral-regime) power laws for MLG and BLG are also different, with a weaker dependence on the electronic temperature in the latter. In the general case we evaluate the heat current numerically. We suggest that a measurement of the heat current could be used for an experimental determination of the electron-acoustic-phonon coupling constants, which are not accurately known. However, in a typical experiment heat dissipation by electrons at very low temperatures is dominated by diffusion and we estimate the crossover temperature at which acoustic-phonon coupling takes over in a sample with Joule heating. At even higher temperatures optical phonons begin to dominate. We study some examples of potentially relevant types of optical modes, including, in particular, the intrinsic in-plane modes and additionally the remote surface phonons of a possible dielectric substrate.

Viljas, J. K.; Heikkilä, T. T.

2010-06-01

373

Bulk viscosity coefficients due to phonons in superfluid neutron stars

International Nuclear Information System (INIS)

We calculate the three bulk viscosity coefficients as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system. The solution of the dynamical evolution of the phonon number density allows us to calculate the bulk viscosity coefficients as function of the phonon collisional rate and the phonon dispersion law, which depends on the neutron pairing gap. Our method of computation is rather general, and could be used for different superfluid systems, provided they share the same underlying symmetries. We find that the behavior with temperature of the bulk viscosity coefficients is dominated by the contributions coming from the collinear regime of the 2?3 phonon processes. For typical star radial pulsation frequencies of ? ? 104s?1, we obtain that the bulk viscosity coefficients at densities n?>4n0 are within 10% from its static value for T?9 K and for the case of strong neutron superfluidity in the core with a maximum value of the 3P2 gap above 1 MeV, while, otherwise, the static solution is not a valid approximation to the bulk viscosity coefficients. Compared to previous results from Urca and modified Urca reactions, we conclude that at T ? 109K phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ? 2n0 when the opening of the Urca processes takes place

374

Point source in a phononic grating: stop bands give rise to phonon-focusing caustics

International Nuclear Information System (INIS)

We use locally-excited gigahertz surface phonon wavepackets in microscopic line structures of different pitches to reveal profound anisotropy in the radiation pattern of a point source in a grating. Time-domain data obtained by an ultrafast optical imaging technique and by numerical simulations are Fourier transformed to obtain frequency-filtered real-space acoustic field patterns and k-space phononic band structure. The numerically-obtained k-space images are processed to reveal an intriguing double-horn structure in the lowest-order group-velocity surface, which explains the observed non-propagation sectors bounded by caustics, noted at frequencies above the bottom of the first stop band. We account for these phonon-focusing effects, analogous to collimation effects previously observed in two- and three-dimensional lattices, with a simple analytical model of the band structure based on a plane wave expansion. As the frequency is increased, a transition to dominant waveguiding effects along the lines is also documented. (paper)

375

Influence of phonon emission on intersubband lifetimes in wide GaAs/AlGaAs and Si/SiGe quantum wells

Energy Technology Data Exchange (ETDEWEB)

We have previously used the picosecond far-infrared free electron laser FELIX, at Rijnhuizen, to make the first direct excite-probe determination of the intersubband relaxation rate in wide GaAs/AlGaAs quantum wells with the subband separation smaller than the optical phonon energy. This measurement yielded short (40ps) lifetimes while acoustic phonon emission occurs on a 200ps scale. This is also in contrast with, among others, saturation measurements of swide wells with the UCSB FEL which gave lifetimes of 600ps. We discuss here the interpretation of the range of published results by calculation of the LO-phonon scattering rate, including the effects of finite electron temperature, T{sub e}. We have shown that relaxation can be dominated by LO-phonon emission even in wide wells, through the high energy tail of the distribution. The rate is very sensitive to T{sub e} between 30-70K, and also to carrier concentration, making it possible to account for the wide variety of published results with a single mechanism. We have extended our measurements to wide Si/SiGe quantum Wells, and find similarly short times (20-30ps). However, in non-polar materials such as SiGe the deformation potential scattering is much weaker and acoustic phonon emission (order 10ps in n-silicon) is expected to dominate.

Murdin, B.N. [FOM-Institute Rijnhuizen (Netherlands); Pidgeon, C.R.; Lee, S.C. [Heriot-Watt Univ., Edinburgh (United Kingdom)] [and others

1995-12-31

376

Construction of Wannier functions in phononic structures

The modelling and simulation of periodic structures with defects define boundary value problems (BVPs) which are conceptually and numerically difficult to solve. Innovative and problem-tailored analysis methods need to be devised to solve defect problems efficiently and accurately. One possible attractive method is based on the ideas related to the construction of Wannier functions. Wannier functions constitute a complete sequence of localised orthogonal functions which are derived from associated periodic versions of defect problems. In this paper we review general properties of Wannier functions from a linear algebra point of view, introduce an easy-to-use symbolic notation for the diagonalisation of the governing equations and construct the Wannier functions for a variety of phononic devices. Using certain distinguished properties inherent in the wavenumber-dependence of the eigenvalues we prove the orthogonality and completeness of the Wannier functions in a conceptually novel way.

Muradoglu, M. S.; Baghai-Wadji, Alireza R.

2008-12-01

377

Phonon-induced artificial magnetic fields

We investigate the effect of a rotating Bose-Einstein condensate on a system of immersed impurity atoms trapped by an optical lattice. We analytically show that for a one-dimensional, ring-shaped setup the coupling of the impurities to the Bogoliubov phonons of the condensate leads to a non-trivial phase in the impurity hopping. The presence of this phase can be tested by observing a drift in the transport properties of the impurities. These results are quantitatively confirmed by a numerically exact simulation of a two-mode Bose-Hubbard model. We also give analytical expressions for the occurring phase terms for a two-dimensional setup. The phase realises an artificial magnetic field and can for instance be used for the simulation of the quantum Hall effect using atoms in an optical lattice.

Klein, Alexander

2008-01-01

378

Engineering surface waves in flat phononic plates

Surface acoustic-wave phenomena span a wide range of length scales going from the devastation of earthquakes down to image reconstruction of buried nanostructures. In solid-fluid systems, the so-called Scholte-Stoneley waves (SSWs) dominate the scene at the interface with their evanescent fields decaying away into both media. Understanding and manipulating these waves in patterned surfaces would enable new applications of sound to be devised for imaging and acoustic signal processing, although this task has so far remained elusive. Here, we report SSW modes displaying directional gaps and band folding in fluid-loaded solid phononic plates. The plates are inhomogeneously patterned with in-plane periodic modulations of the elastic constants, but present flat surfaces free of corrugations. We experimentally demonstrate control of SSWs, which opens a promising route toward acoustic fluid sensing, microscopy, and signal processing.

Estrada, Héctor; Candelas, Pilar; Belmar, Francisco; Uris, Antonio; García de Abajo, F. Javier; Meseguer, Francisco

2012-05-01

379

The phonon theory of liquid thermodynamics

Heat capacity of matter is considered to be its most important property because it holds information about system's degrees of freedom as well as the regime in which the system operates, classical or quantum. Heat capacity is well understood in gases and solids but not in the third state of matter, liquids, and is not discussed in physics textbooks as a result. The perceived difficulty is that interactions in a liquid are both strong and system-specific, implying that the energy strongly depends on the liquid type and that, therefore, liquid energy can not be calculated in general form [1]. Here, we develop a phonon theory of liquids where this problem is avoided. We demonstrate good agreement of calculated heat capacity of important monatomic, molecular and hydrogen-bonded network liquids such as H2O in a wide range of pressure and temperature.

Bolmatov, Dima; Trachenko, Kostya

2012-01-01

380

The phonon theory of liquid thermodynamics.

Heat capacity of matter is considered to be its most important property because it holds information about system's degrees of freedom as well as the regime in which the system operates, classical or quantum. Heat capacity is well understood in gases and solids but not in the third main state of matter, liquids, and is not discussed in physics textbooks as a result. The perceived difficulty is that interactions in a liquid are both strong and system-specific, implying that the energy strongly depends on the liquid type and that, therefore, liquid energy can not be calculated in general form. Here, we develop a phonon theory of liquids where this problem is avoided. The theory covers both classical and quantum regimes. We demonstrate good agreement of calculated and experimental heat capacity of 21 liquids, including noble, metallic, molecular and hydrogen-bonded network liquids in a wide range of temperature and pressure. PMID:22639729

Bolmatov, D; Brazhkin, V V; Trachenko, K

2012-01-01

381

Structure and Phonon Dispersionof Bi(111) from He Atom Scattering

International Nuclear Information System (INIS)

Full text: As a material with significant differences in bulk and surface properties, bismuth (Bi) has attracted renewed interest among researchers. The presence of metallic surface states is unusual for a bulk semimetal and provides the playground for ideas related to the electronic response of the surface and even the possibility of two-dimensional superconductivity. With regard to phonon states, calculations of the bulk phonon dispersion are consistent with experimental data only when spin-orbit interaction is taken into account. Recently, squeezed bulk phonon states were measured with femtosecond x-ray diffraction. In contrast to phonons in the bulk and the electronic surface structure nothing is known about the surface phonons of the Bi(111) surface. They are in a low energy region of meV and therefore not accessible with satisfying resolution for most scattering techniques, but with experiments using helium atom scattering (HAS) surface phonons can be investigated successfully. We have used elastic and inelastic HAS to study the Bi(111) surface therefore we are able to present the first report on phonon creation and annihilation events on this surface. The surface phonon dispersion relation has been determined from measured time-of-flight spectra of inelastically scattered He atoms. The obtained group velocity lies somewhat above the bulk group velocity. Elastic HAS experiments reveal rather large diffraction peaks in comparison to other metals. A first comparismparison to other metals. A first comparison between theoretical (eikonal approximation, GR-method) and measured diffraction peak intensities yields a surface charge density corrugation of 16% of the surface unit cell. This value is surprisingly large since the reported metallic character of the Bi(111) surface would imply a nearly flat corrugation. The observed surface corrugation and the steep slope in the phonon dispersion may both point to the important role of the strong covalent bonds at the surface. (author)

382

International Nuclear Information System (INIS)

The working parts of a flowing gas laser are enclosed within a pressurized housing. An ionizer is mounted in proximity to the working region such that generated electrons pass into the working region wherein lasing action occurs

383

The influence of phonons on quantum diffusion in superconductors

Energy Technology Data Exchange (ETDEWEB)

The hopping motion of charged light particles coupled to superconducting electrons as well as to phonons is investigated within the framework of a two-state model. Sufficiently far below the transition temperature T[sub c] the hopping rate is dominated by one-phonon processes if the static energy shifts between the particle ground states are finite but smaller than twice the BCS energy gap. In the opposite limit of large energy asymmetries phonon coupling does not crucially influence the jump rates. The role of nonlinear lattice coupling is investigated. (orig.)

Regelmann, T. (Max-Planck-Inst. fuer Metallforschung, Inst. fuer Physik, Stuttgart (Germany)); Fritzsche, A. (Max-Planck-Inst. fuer Metallforschung, Inst. fuer Physik, Stuttgart (Germany)); Schimmele, L. (Max-Planck-Inst. fuer Metallforschung, Inst. fuer Physik, Stuttgart (Germany)); Seeger, A. (Max-Planck-Inst. fuer Metallforschung, Inst. fuer Physik, Stuttgart (Germany) Univ. Stuttgart, Inst. fuer Theoretische und Angewandte Physik (Germany))

1994-07-01

384

The influence of phonons on quantum diffusion in superconductors

International Nuclear Information System (INIS)

The hopping motion of charged light particles coupled to superconducting electrons as well as to phonons is investigated within the framework of a two-state model. Sufficiently far below the transition temperature Tc the hopping rate is dominated by one-phonon processes if the static energy shifts between the particle ground states are finite but smaller than twice the BCS energy gap. In the opposite limit of large energy asymmetries phonon coupling does not crucially influence the jump rates. The role of nonlinear lattice coupling is investigated. (orig.)

385

Electron Transport and Hot Phonons in Carbon Nanotubes

We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, that we validate by accurate first principles calculations on (6,6) and (11,11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a non-equilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.

Lazzeri, M; Mauri, F; Ferrari, A C; Robertson, J

2005-01-01

386

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

387

Electron-phonon coupling in suspended graphene: supercollisions by ripples.

Using electrical transport experiments and shot noise thermometry, we find strong evidence that "supercollision" scattering processes by flexural modes are the dominant electron-phonon energy transfer mechanism in high-quality, suspended graphene around room temperature. The power law dependence of the electron-phonon coupling changes from cubic to quintic with temperature. The change of the temperature exponent by two is reflected in the quadratic dependence on chemical potential, which is an inherent feature of two-phonon quantum processes. PMID:24842236

Laitinen, Antti; Oksanen, Mika; Fay, Aurélien; Cox, Daniel; Tomi, Matti; Virtanen, Pauli; Hakonen, Pertti J

2014-06-11

388

Phonon detection in single crystalline silicon with superconducting tunneling junctions

International Nuclear Information System (INIS)

Recent experimental results on phonon detection with Sn/SnOx/Sn superconducting tunneling junctions (STJ) are reported. Phonons are generated in a single-crystalline Si substrate by means of ?-radiation. Two STJ's, evaporated on top of the substrate, are used as detectors. At low temperatures (T<0.9K) a strong correlation is found between the energies deposited in both junctions. Marked differences are observed between frontside and backside irradiation of the substrates. Phonon focusing, due to the anisotropic elastic constants of Si, is held responsible for the observed energy correlations. (author) 9 refs.; 4 figs

389

Lifetimes of confined acoustic phonons in ultrathin silicon membranes.

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures. PMID:23496722

Cuffe, J; Ristow, O; Chávez, E; Shchepetov, A; Chapuis, P-O; Alzina, F; Hettich, M; Prunnila, M; Ahopelto, J; Dekorsy, T; Sotomayor Torres, C M

2013-03-01

390

Tunneling in suspended carbon nanotubes assisted by longitudinal phonons

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

391

Phonon softening and superconductivity in tellurium under pressure

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

392

Magnetic field induced thermal effect of phonons in graphene

Energy Technology Data Exchange (ETDEWEB)

We investigate the effect of a magnetic field on the thermal properties of phonons in graphene. We calculate the heat capacity of the phonons using a generating functional technique, and find a new phenomenon that a staircase-like behaviour appears in the change of the phonon heat capacity as well as the thermal conductivity with the temperature. The width and height of each step are related to the magnetic field and the temperature. This may provide a scheme of controlling the thermal properties of graphene by a weak magnetic field. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Peng, Feng [Physics Department, Beijing University of Science and Technology, Beijing 100083 (China)

2011-06-15

393

Phonons in Ta-D and Ta-H alloys

International Nuclear Information System (INIS)

The acoustical phonon frequencies for Ta alloyed with 22% D and with 18% H have been measured at room temperature. For comparison the phonon dispersion curves of pure Ta (including previously unknown [110] T1 mode) have also been determined. The observed frequency shifts are qualitatively the same as those for the system Nb-D. For the optical branches in Ta-D two energy levels could be found at 20.3 THz and at 28.5 THz independent of the phonon wavevector. (author)

394

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)

395

Interaction of phonons at superfluid helium-solid interfaces

Directory of Open Access Journals (Sweden)

Full Text Available New method to obtain the interaction Hamiltonian of phonons at superfluid helium-solid interface is proposed in the work. Equations of hydrodynamic variables are obtained in terms of second quantization if helium occupies a half-space. The contributions of all processes to the heat flux from solid to superfluid helium are calculated based on obtained Hamiltonian. The angular distribution of phonons that are emitted by solid are found in different processes. It is shown, that all of exit angles of superfuild helium phonons are allowed. The obtained results are compared with experimental data and with previous theoretical works.

I.N. Adamenko

2014-03-01

396

Phonon Transport through Point Contacts between Graphitic Nanomaterials

Measurements of thermal transport through contacts between individual multiwall carbon nanotubes show that, contrary to common expectation, the normalized contact thermal conductance per unit area depends linearly on the tube diameter. The result is corroborated with and extended to multilayer graphene nanoribbons through molecular dynamics simulations. Semiquantitative analyses show that these intriguing observations are consistent with an explanation based on an unexpectedly large phonon mean free path in the c-axis direction of graphite, phonon reflection at free surfaces, and phonon focusing in highly anisotropic graphitic materials.

Yang, Juekuan; Shen, Meng; Yang, Yang; Evans, William J.; Wei, Zhiyong; Chen, Weiyu; Zinn, Alfred A.; Chen, Yunfei; Prasher, Ravi; Xu, Terry T.; Keblinski, Pawel; Li, Deyu

2014-05-01

397

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

398

Optical phonon lifetimes in sputtered AlN thin films

International Nuclear Information System (INIS)

We study the vibrational properties of AlN thin films deposited on silicon (100) substrates by the reactive DC-pulsed magnetron sputtering. The frequencies and lifetimes of the E1(TO) and A1(LO) optical phonons are calculated from Fourier transform infrared spectra using the factorized model of a damped oscillator. We analyze the structural properties by the x-ray diffraction technique to correlate the elongation of phonon lifetimes with increasing film thickness. The lifetimes of the phonon modes in AlN thin films are compared to the values in a single crystal.

399

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)

400

Isotopic effects on the phonon modes in boron carbide.

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

2010-10-01

401

PHONON SOFTENING IN INTERMEDIATE VALENT SmB6

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have measured the Raman spectrum of a SmB6 single crystal and compared it to LaB6 and EuB6. Beside the three high energy Raman active phonons we found additional excitations in these compounds. Most prominent is a peak at 172 cm-1 for SmB6, 214 cm-1 for LaB6 and 220 cm-1 for EuB6. The spectra are analysed in terms of defect induced phonon scattering. The softening of the line in intermediate valent (IV) SmB6 is explained in analogy with the phonon anomalies found in other IV compounds.

Mo?rke, I.; Wachter, P.

1981-01-01

402

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

403

Optomechanical photon detection and enhanced dispersive phonon readout

In cavity optomechanics, nanomechanical motion couples to a localized optical mode. The regime of single-photon strong coupling is reached when the optical shift induced by a single phonon becomes comparable to the cavity linewidth. We consider a setup in this regime comprising two optical modes and one mechanical mode. For mechanical frequencies nearly resonant to the optical level splitting, we find the photon-phonon and the photon-photon interactions to be significantly enhanced. In addition to dispersive phonon detection in a novel regime, this offers the prospect of optomechanical photon measurement. We study these QND detection processes using both analytical and numerical approaches.

Ludwig, Max; Painter, Oskar; Marquardt, Florian

2012-01-01

404

Proposal for an optomechanical traveling wave phonon-photon translator

International Nuclear Information System (INIS)

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.

405

Phonons in crystals using inelastic X-ray scattering

International Nuclear Information System (INIS)

The use of Inelastic X-ray Scattering (IXS) to investigate phonons and phonon dispersion in crystals opens the field of phonon spectroscopy, allowing measurements on tiny samples: micrograms of material, or single crystals ?10 to 100 micron diameter, are sufficient. Here we review the technique as it is practiced at BL35XU of SPring-8, in Hyogo prefecture. An introduction is provided that is aimed at potential IXS users, highlighting the unique and advantageous aspects of the technique. Present work, including several example experiments, and future directions, are discussed. (author)

406

Entangled phonons in atomic Bose-Einstein condensates

We theoretically propose the measurement of phonon entanglement as a tool to study the quantum dynamics of atomic Bose-Einstein condensates. In particular, we show that nonseparability of the phonon modes offers a unambiguous signature of the quantum origin of the phonon emission by analog Hawking and dynamical Casimir processes. The method is numerically validated by applying a generalized Peres-Horodecki criterion to a truncated Wigner description of the condensate. Viable strategies to implement the proposed scheme in state-of-the-art experiments are discussed.

Finazzi, Stefano; Carusotto, Iacopo

2014-09-01

407

Bias drop and phonon emission in molecular wires

International Nuclear Information System (INIS)

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.

408

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

409

Electron-Phonon Correlation Effects in Molecular Transistors

The effects of electron-phonon interactions in molecular transistors are studied analytically in the Kondo regime. We show that a Holstein electron-phonon coupling can explain the weak gate voltage dependence of the Kondo temperature observed experimentally in some of these devices. A molecular center-of-mass mode opens a new channel for charge and spin fluctuations and in the antiadabatic limit the latter are described by an asymmetric two-channel Kondo model. Below the Kondo temperature the system develops a dynamical Jahn-Teller distortion and a low energy peak emerges in the phonon spectral density that could be observed in Raman microscopy experiments.

Balseiro, C A; Grempel, D R

2006-01-01

410

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere

Directory of Open Access Journals (Sweden)

Full Text Available An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL in a Yb3+ doped silica microsphere (YDSM with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 ?W, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials.

Yantang Huang

2014-02-01

411

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere

International Nuclear Information System (INIS)

An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL) in a Yb3+ doped silica microsphere (YDSM) with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 ?W, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials

412

We investigated the optical properties of Ge1- x Se x and Ge1- x- y Se x As y amorphous films by using spectroscopic ellipsometry and Raman spectroscopy. The dielectric functions and absorption coefficients ( ?) of the amorphous films were determined from the measured ellipsometric angles (?,?). We obtained the optical gap energies and the Urbach energies from the absorption coefficients and found a strong bowing effect in the optical gap energy of Ge1- x- y Se x As y , where the endpoint binaries were Ge0.50Se0.50 and Ge0.31As0.69. Based on the correlation between the optical gap energies and the Urbach energies, we attributed the large bowing parameter to electronic disorder. Using Raman spectroscopy, we measured the phonon modes and discussed the composition dependence of the phonon peak frequencies and lineshapes in terms of structural units. Based on the composition dependence of the phonons in Ge1- x- y Se x As y , we identified the phonon modes of Ge0.31As0.69. A resonant Raman phenomenon was observed in Ge0.40Se0.60 at a laser excitation of 514 nm (2.41 eV). We verified that this laser energy corresponded to the transition energy of Ge0.40Se0.60 by using the second derivative of the dielectric function of Ge0.40Se0.60.

Lee, Hosuk; So, Hyeon Seob; Lee, Hosun; Shin, Hae-Young; Yoon, Seokhyun; Ahn, Hyung-Woo; Kim, Su-Dong; Lee, Suyoun; Jeong, Doo-Seok; Cheong, Byung-ki

2014-06-01

413

Theoretical study of the phonon spectra of hexagonal multiferroics RMnO3

International Nuclear Information System (INIS)

The phonon properties of hexagonal multiferroic RMnO3 materials are studied using a Green's function technique. The calculations are performed on the basis of the Heisenberg and the transverse Ising model taking into account anharmonic spin-phonon and phonon-phonon interaction terms. The strong spin-phonon interaction leads to an anomaly in the phonon energy and the damping around the magnetic and ferroelectric phase transitions. The phonon spectrum is discussed for different exchange, magnetoelectric and spin-phonon interaction constants. It is shown that the phonon energy depends on the radius of the rare earth ion rR. The influence of an applied magnetic field on the phonon spectrum is studied, too. The predictions are consistent with experimental results

414

Theoretical study of the phonon spectra of multiferroic BiFeO{sub 3} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

The phonon properties of multiferroic BiFeO{sub 3} (BFO) nanoparticles are studied using a Green's function technique on the basis of the Heisenberg and the transverse Ising models, taking into account anharmonic spin-phonon and phonon-phonon interaction terms. The phonon spectrum is obtained for different exchange, magnetoelectric, and spin-phonon interaction constants. The influence of temperature, surface and size effects on the phonon energy and damping is discussed. The phonon energy and damping in BFO nanoparticles are greater in comparison to those in bulk BFO. The strong spin-phonon interactions lead to anomalies in the phonon spectrum around the magnetic and ferroelectric phase transitions. The influence of an applied magnetic field is studied, too. The predictions are consistent with experimental results.

Apostolova, I [Faculty of Forest Industry, University of Forestry, Boulevard Kliment Okhridsky 10, 1756 Sofia (Bulgaria); Apostolov, A T [Department of Applied Physics, Technical University, Boulevard Kliment Okhridsky 8, 1000 Sofia (Bulgaria); Wesselinowa, J M [Department of Physics, University of Sofia, Boulevard J. Bouchier 5, 1164 Sofia (Bulgaria)

2009-01-21

415

Theoretical study of the phonon spectra of multiferroic BiFeO3 nanoparticles

International Nuclear Information System (INIS)

The phonon properties of multiferroic BiFeO3 (BFO) nanoparticles are studied using a Green's function technique on the basis of the Heisenberg and the transverse Ising models, taking into account anharmonic spin-phonon and phonon-phonon interaction terms. The phonon spectrum is obtained for different exchange, magnetoelectric, and spin-phonon interaction constants. The influence of temperature, surface and size effects on the phonon energy and damping is discussed. The phonon energy and damping in BFO nanoparticles are greater in comparison to those in bulk BFO. The strong spin-phonon interactions lead to anomalies in the phonon spectrum around the magnetic and ferroelectric phase transitions. The influence of an applied magnetic field is studied, too. The predictions are consistent with experimental results.

416

Laser Processing and Chemistry

This book gives an overview of the fundamentals and applications of laser-matter interactions, in particular with regard to laser material processing. Special attention is given to laser-induced physical and chemical processes at gas-solid, liquid-solid, and solid-solid interfaces. Starting with the background physics, the book proceeds to examine applications of lasers in standard laser machining and laser chemical processing (LCP), including the patterning, coating, and modification of material surfaces. This fourth edition has been enlarged to cover the rapid advances in the understanding of the dynamics of materials under the action of ultrashort laser pulses, and to include a number of new topics, in particular the increasing importance of lasers in various different fields of surface functionalizations and nanotechnology. In two additional chapters, recent developments in biotechnology, medicine, art conservation and restoration are summarized. Graduate students, physicists, chemists, engineers, a...

Bäuerle, Dieter

2011-01-01

417

Directory of Open Access Journals (Sweden)

Full Text Available Biochemical changes in oral fluid of patients with chronic generalized parodontitis were investigated; the most informative indices were found out, they were used for estimating complex therapy effectiveness by means of low intensive helium neon laser radiation and alternating running magnetic field

O.Yu. Guseva

2009-09-01

418

Ultrafast X-ray diffraction of laser-irradiated crystals

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

419

Phonon Modes and the Maintenance Condition of a Crystalline Beam

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

420

Two-phonon ?-vibrational states in 170Er

International Nuclear Information System (INIS)

Two phonon ?-vibrational states in the nucleus 170Er have been investigated by Coulomb excitation. The experiments were carried out at the Laboratori Nazionali di Legnaro (LNL) using the GASP array coupled to the new Lund Silicon Array (LuSiA) detector system for charged particle detection. LuSiA consists of four square double-sided silicon-strip detectors mounted in a box surrounding the target position. The two-phonon ?-vibrational states were populated using the 32S +170Er reaction at a ''safe'' beam energy of 117 MeV. Along with the excitation energies of the states, of particular interest is the B(E2) ratio between the transitions from the two-phonon and one-phonon states which is predicted to have a specific value at the critical point Y(5). Preliminary results from the experiment are presented.

421

Phonons Softening in Tip-Stretched Monatomic Nanowires

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

422

Generation of coherent acoustic phonons in piezoelectric semiconductor heterostructures

We review some experimental and theoretical aspects of coherent acoustic phonon generation in piezoelectric semiconductor multiple quantum wells. In order to model more advanced and complicated nano-acoustic devices, a macroscopic continuum theory for the generation and propagation of coherent acoustic phonons in piezoelectric semiconductor heterostructures is presented. The macroscopic approach is applicable in the coherent regime, and can be easily utilized to study coherent acoustic devices based on piezoelectric semiconductor heterosutructures. For each phonon mode, the corresponding coherent acoustic field obeys a loaded string equation. The driven force has contributions from the piezoelectric and deformation potential couplings. We applied the theory to model the generation of coherent longitudinal acoustic phonons in (0001)-oriented InGaN/GaN multiple quantum wells. The numerical results are in good agreement with the experimental ones. By using the macroscopic theory, we also investigated the crystal...

Chern, G W; Huang, Y K; Lin, K H; Chern, Gia-Wei; Sun, Chi-Kuang; Huang, Yue-Kai; Lin, Kung-Hsuan

2003-01-01

423

Phononics and Micromechanics of Bio-Colloidal Wiseana Iridovirus.

By using Brillouin Light Scattering (BLS), we have investigated phononic properties of Wiseana iridovirus (WIV) assemblies and dispersed individual viruses at hypersonic frequency window. Propagating modes in virus assemblies and localized vibrational eig...

A. Kisliuk, H. Xiong, J. Neiswinger, R. D. Hartschuh, S. P. Wargacki

2008-01-01

424

Exact numerical methods for electron-phonon problems

We present the basic principles of exact diagonalization and (dynamical) density-matrix renormalization-group approaches to the calculation of ground state and dynamical properties in electron-phonon systems.

Jeckelmann, E; Jeckelmann, Eric; Fehske, Holger

2006-01-01

425

Phonon density of states of ?-Fe precipitates in Cu

The phonon density of states of ?-Fe precipitates in a Cu matrix were studied as a function of particle size by using nuclear resonant inelastic scattering of synchrotron radiation. The host metal affects the phonon density of states of the precipitates up to 30 nm in diameter. Larger precipitates are free from the influence of the host metal and show rather similar phonon density of states to those of fcc-Fe alloy bulk specimens such as stainless steel (310ss) and Fe70Ni30 at room temperature although ?-Fe is unstable at room temperature under an atmospheric condition. Careful observation, however, yields characteristics of ?-Fe precipitates in the phonon density of states.

Tsunoda, Y.; Kurimoto, Y.; Seto, M.; Kitao, S.; Yoda, Y.

2002-12-01

426

Phonon-assisted decoherence in coupled quantum dots

We analyse various phonon-assisted mechanisms which contribute to the decoherence of excitonic qubits in quantum dot systems coupled by the F\\"orster-type transfer process. We show the significant loss of coherence accompanied by dissipation due to charge carrier oscillations between qubit states by using a model of one-phonon assisted F\\"orster-type transfer process. We obtain explicit expressions for the relaxation and dephasing times for excitonic qubits interacting with acoustic phonons via both deformation potential and piezoelectric coupling. We compare the decoherence times of the GaAs/AlGaAs material system with half times of concurrence decay in a 2$\\otimes$2 bipartite mixed excitonic qubit system. We extend calculations to determine the influence of phonon mediated interactions on the non-unitary evolution of Berry phase in quantum dot systems.

Thilagam, A

2007-01-01

427

The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy

International Nuclear Information System (INIS)

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

428

Charge tuning of nonresonant magnetoexciton phonon interactions in graphene.

Far from resonance, the coupling of the G-band phonon to magnetoexcitons in single layer graphene displays kinks and splittings versus filling factor that are well described by Pauli blocking and unblocking of inter- and intra-Landau level transitions. We explore the nonresonant electron-phonon coupling by high-magnetic field Raman scattering while electrostatic tuning of the carrier density controls the filling factor. We show qualitative and quantitative agreement between spectra and a linearized model of electron-phonon interactions in magnetic fields. The splitting is caused by dichroism of left- and right-handed circular polarized light due to lifting of the G-band phonon degeneracy, and the piecewise linear slopes are caused by the linear occupancy of sequential Landau levels versus ?. PMID:24580621

Rémi, Sebastian; Goldberg, Bennett B; Swan, Anna K

2014-02-01

429

Phonon localization in cubic GaN/AlN superlattices

To enhance the devices performance a better understanding of the confinement of polar optical-phonons in the heterostructures should be achieved. In this work, we investigated a set of three cubic GaN/AlN superlattices (SL) grown by plasma-assisted Molecular Beam Epitaxy (MBE) on 3C-SiC substrates by structural and optical measurements. Reciprocal Space Mapping (RSM) at the (113) reflections revealed the SL satellite peaks and the strain in the structures as well photoluminescence spectra evidence the quantum confinement. Different line broadenings in the Raman spectra measured in each heterostructure indicate that the longitudinal optical phonons of GaN describe different localization lengths. Through the application of the spatial correlation model we have quantified the localization length of these phonons and established a correlation with the GaN layer thicknesses. For the first time it is presented localized optical phonons (LO) in cubic GaN layers.

Rodrigues, A. D.; de Godoy, M. P. F.; Mietze, C.; As, D. J.

2014-05-01

430

Phonon excitation and instabilities in biased graphene nanoconstrictions

DEFF Research Database (Denmark)

We investigate how a high current density perturbs the phonons in a biased graphene nanoconstriction coupled to semi-infinite electrodes. The coupling to electrode phonons, electrode electrons under bias, Joule heating, and current-induced forces is evaluated using first principles density functional theory and nonequilibrium Green's function calculations. We observe a strongly nonlinear heating of the phonons with bias and breakdown of the harmonic approximation when the Fermi level is tuned close to a resonance in the electronic structure of the constriction. This behavior is traced back to the presence of negatively damped phonons driven by the current. The effects may limit the stability and capacity of graphene nanoconstrictions to carry high currents.

Gunst, Tue; Lu, Jing Tao

2013-01-01

431

Molecular transistor coupled to phonons and Luttinger-liquid leads

We study the effects of electron-phonon interactions on the transport properties of a molecular quantum dot coupled to two Luttinger-liquid leads. In particular, we investigate the effects on the steady state current and DC noise characteristics. We consider both equilibrated and unequilibrated on-dot phonons. The density matrix formalism is applied in the high temperature approximation and the resulting semi-classical rate equation is numerically solved for various strengths of electron-electron interactions in the leads and electron-phonon coupling. The current and the noise are in general smeared out and suppressed due to intralead electron interaction. On the other hand, the Fano factor, which measures the noise normalized by the current, is more enhanced as the intralead interaction becomes stronger. As the electron-phonon coupling becomes greater than order one, the Fano factor exhibits super-Poissonian behaviour.

Takei, S; Mitra, A; Takei, So; Kim, Yong Baek; Mitra, Aditi

2004-01-01

432

Phonon-assisted tunneling regimes in diatomic molecules

Electronic transport in diatomic molecules (two-level systems) connected to metallic contacts is analyzed in the presence of competing electron-electron and electron-phonon interactions. We show that phonon emission and absorption processes are strongly modified when a Coulomb energy $U$ is included, as the phonons open channels that can result in destructive or constructive interference effects. Resonance conditions for these processes produce dramatic effects both in the density of states at the molecular sites, as well as in the conductance through the system. We find in particular an enhanced {\\it Rabi-assisted tunneling} due to phonons, as the resonance conditions are met, which is made more evident for increasing temperatures. These effects are controllable by voltage gating of the molecular sites, and should be accessible in current experiments.

Vernek, E; Ulloa, S E; Sandler, N

2007-01-01

433

Interatomic potential for accurate phonons and defects in UO2

We have developed an improved uranium dioxide interatomic potential by fitting to forces, energies, and stresses of first principles molecular dynamics calculations via a genetic algorithm approach called Iterative Potential Refinement (IPR). We compare the defect energetics and vibrational properties of the IPR-fit potential with other interatomic potentials, density functional theory calculations, and experimental phonon dispersions. We find that among previously published potentials examined, there is no potential that simultaneously yields accurate defect energetics and accurate vibrational properties. In contrast, our IPR-fit potential produces both accurate defects and the best agreement with the experimental phonon dispersion and phonon density of states. This combination of accurate properties makes this IPR-fit potential useful for simulating UO2 in high temperature, defect-rich environments typical for nuclear fuel. Additionally, we verify that density functional theory with a Hubbard U correction accurately reproduces the experimentally derived UO2 phonon density of states.

Thompson, Alexander E.; Meredig, Bryce; Stan, Marius; Wolverton, C.

2014-03-01

434

Mapping gigahertz vibrations in a plasmonicphononic crystal

International Nuclear Information System (INIS)

We image the gigahertz vibrational modes of a plasmonicphononic crystal at sub-micron resolution by means of an ultrafast optical technique, using a triangular array of spherical gold nanovoids as a sample. Light is strongly coupled to the plasmonic modes, which interact with the gigahertz phonons by a process akin to surface-enhanced stimulated Brillouin scattering. A marked enhancement in the observed optical reflectivity change at the centre of a void on phononic resonance is likely to be caused by this mechanism. By comparison with numerical simulations of the vibrational field, we identify resonant breathing deformations of the voids and elucidate the corresponding mode shapes. We thus establish scanned optomechanical probing of periodic plasmonicphononic structures as a new means of investigating their coupled excitations on the nanoscale. (paper)

435

Forward Electron-Phonon Scattering in Normal and Superconducting States

The sharp forward electron-phonon $(FEP)$ and impurity $(FIS)$ scattering change the normal and superconducting properties significantly. The pseudo-gap like features are present in the density of states for $\\omega <\\Omega $, where $T_c$, due to the $FEP$ pairing, is linear with respect to the electron-phonon coupling constant. The $FIS$ impurities are pair weakening for $s-$ and $d-wave$ pairing.

Dolgov, O V; Kulic, M L; Oudovenko, V S

1998-01-01

436

Pressure-stiffened Raman Phonons in Group III Nitrides

Digital Repository Infrastructure Vision for European Research (DRIVER)

It has long been puzzling regarding the atomistic origin of the pressure-induced Raman phonon stiffening that generally follows a polynomial expression with coefficients needing physical indication. Here we show that an extension of the bond-order-length-strength (BOLS) correlation mechanism to the pressure domain has led to an analytical solution to connect the pressure-induced Raman phonon stiffening directly to the bonding identities of the specimen and the response of th...

Sun, Chang Q.

2008-01-01

437

Optomechanical quantum information processing with photons and phonons

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

438

Optomechanical quantum information processing with photons and phonons.

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 interactions on a single photon level are within experimental reach. PMID:23031105

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

2012-07-01

439

Phonon-induced Quantum Entanglement in Diamond Nanostructures

We consider the quantum entanglement such as spin squeezing and the reciprocal of the mean quantum Fisher information per particle(RMQFIP) resulted from the phonon-induced spin-spin interactions in diamond nanoresonator. The entangled state can be generated by adjusting the near-resonant coupling and the single phonon coupling strength and the better entanglement and a longer entangled time interval can be achieved by increasing the number of charged nitrogen-vacancy (NV) centers.

Xia, Qi-Guo; Liu, Li-Shu

2014-08-01

440

Phonon effect on an optically driven quantum dots device

Energy Technology Data Exchange (ETDEWEB)

The quantum oscillations of population in an optically driven asymmetrical double quantum dot device coupled to phonons are investigated theoretically and an analytical result is obtained. It shows that, even at zero temperature, the phonon effect is considerable. The Rabi frequency and tunneling rate between two dots are renormalized by a factor and its square, respectively. The ideal Rabi oscillation is changed into a beat pattern.

Wu Zhuojie [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China)]. E-mail: wuzj@sjtu.edu.cn; Zhu Kadi [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Yuan Xiaozhong [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Jiang Yiwen [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Yao Ming [School of Physics and Electrical Information Science, Ning Xia University, Yinchuan 75000 (China)

2005-12-05

441

Phonon effect on an optically driven quantum dots device

International Nuclear Information System (INIS)

The quantum oscillations of population in an optically driven asymmetrical double quantum dot device coupled to phonons are investigated theoretically and an analytical result is obtained. It shows that, even at zero temperature, the phonon effect is considerable. The Rabi frequency and tunneling rate between two dots are renormalized by a factor and its square, respectively. The ideal Rabi oscillation is changed into a beat pattern

442

Band gap engineering in simultaneous phononic and photonic crystal slabs

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 SiO2 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 re...

Djafari Rouhani, Bahram; Pennec, Yan; Elboudouti, Eh; Vasseur, J.; Elhassouani, Y.; Li, Chanseng; Akjouj, A.; Bria, D.

2010-01-01

443

Phonons and Solitons in 1D Mott Insulators

We study the problem of one-dimensional (1D) Luttinger liquids in the insulating Mott-Hubbard phase in the presence of acoustic phonons in the semiclassical limit. We show that solitonic excitations can propagate freely in the system and the energy required to produce a soliton is reduced by a polaronic effect. We find a critical value of the electron-phonon coupling constant for which this energy vanishes.

Chang, C M; Bishop, A R; Chang, Chun-Min

2000-01-01

444

Nanomechanical vibrating wire resonator for phonon spectroscopy in Helium

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, Andreas; Erbe, Artur; Blick, Robert H.

1999-01-01

445

A cryogenic phonon detector to search for dark matter particles

International Nuclear Information System (INIS)

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 a 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

446

d-wave superconductivity from electron-phonon interactions

Digital Repository Infrastructure Vision for European Research (DRIVER)

I examine electron-phonon mediated superconductivity in the intermediate coupling and phonon frequency regime of the quasi-2D Holstein model. I use an extended Migdal-Eliashberg theory which includes vertex corrections and spatial fluctuations. I find a d-wave superconducting state that is unique close to half-filling. The order parameter undergoes a transition to s-wave superconductivity on increasing filling. I explain how the inclusion of both vertex corrections and spati...

Hague, J. P.

2007-01-01

447

Theory of Phonon Hall Effect in Paramagnetic Dielectrics

Based upon spin-lattice interaction, we propose a theoretical model for the phonon Hall effect in paramagnetic dielectrics. The thermal Hall conductivity is calculated by using the Kubo formula. Our theory reproduces the essential experimental features of the phonon Hall effect discovered recently in ionic dielectric Tb$_3$Ga$_5$O$_{12}$, including the sign, magnitude and linear magnetic field dependence of the thermal Hall conductivity.

Sheng, L; Ting, C S

2006-01-01

448

X-ray studies of phonon softening in tise2.

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

449

Coupled Spin-Phonon Excitations in Helical Multiferroics

Digital Repository Infrastructure Vision for European Research (DRIVER)

Both the Dzyaloshiskii-Moriya interaction and the exchange-striction are shown to affect dynamically the magnetoelectric excitations in the perovskite multiferroic RMnO3. The exchange-striction results in a biquadratic interaction between the spins and the transverse phonons, giving rise to quantum fluctuations of the ferroelectric polarization P. This leads to low-lying phonon modes that are perpendicular to P and to the helical spins at small wave vector but are parallel t...

Jia, Chenglong; Berakdar, Jamal

2010-01-01

450

Phonon-assisted tunneling in asymmetric resonant tunneling structures

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on the dielectric continuum model, we calculated the phonon assisted tunneling (PAT) current of general double barrier resonant tunneling structures (DBRTSs) including both symmetric and antisymmetric ones. The results indicate that the four higher frequency interface phonon modes (especially the one which peaks at either interface of the emitter barrier) dominate the PAT processes, which increase the valley current and decrease the PVR of the DBRTSs. We show that an a...

Shi, Jun-jie; Sanders, Barry C.; Pan, Shao-hua

1998-01-01

451

Phonon softening in Ni-Mn-Ga alloys

Digital Repository Infrastructure Vision for European Research (DRIVER)

The TA2 phonon dispersion curves of Ni-Mn-Ga alloys with different compositions which transform to different martensitic structures have been measured over a broad temperature range covering both paramagnetic and ferromagnetic phases. The branches show an anomaly (dip) at a wave number that depends on the particular martensitic structure, and there is softening of these anomalous phonons with decreasing temperature. This softening is enhanced below the Curie point, as a consequence of spin-ph...

Man?osa, Llui?s; Planes Vila, Antoni; Zarestky, Jerel L.; Lograsso, T. A.; Schlagel, D. L.; Stassis, C.

2001-01-01

452

The inverted pendulum, interface phonons and optic Tamm states

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Combe, Nicolas

2011-01-01