Physical mechanisms of coherent acoustic phonons generation by ultrafast laser action.
Ruello, Pascal; Gusev, Vitalyi E
2015-02-01
In this review we address the microscopic mechanisms that are involved in the photogeneration processes of GHz-THz coherent acoustic phonons (CAP) induced by an ultrafast laser pulse. Understanding and describing the underlying physics is necessary indeed for improving the future sources of coherent acoustic phonons useful for the non-destructive testing optoacoustic techniques. Getting more physical insights on these processes also opens new perspectives for the emerging field of the opto-mechanics where lattice motions (surface and/or interfaces ultrafast displacements, nanostructures resonances) are controlled by light. We will then remind the basics of electron-phonon and photon-phonon couplings by discussing the deformation potential mechanism, the thermoelasticity, the inverse piezoelectric effect and the electrostriction in condensed matter. Metals, semiconductors and oxide materials will be discussed. The contribution of all these mechanisms in the photogeneration process of sound will be illustrated over several examples coming from the rich literature. PMID:25038958
Self-organization in a phonon laser
Camps, I
2000-01-01
We make an adaptation of laser modelling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (TA) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO_1) into secondary (LO_2) and TA (LO_1 -> LO_2 + TA) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a ph...
Photon-phonon laser on crystalline silicon: a feasibility study
Zadernovsky, A. A.
2015-03-01
We discuss a feasibility of photon-phonon laser action in bulk silicon with electron population inversion. It is well known, that only direct gap semiconductors are used as an active medium in optical lasers. In indirect gap semiconductors, such as crystalline silicon, the near-to-gap radiative electron transitions must be assisted by emission or absorption of phonons to conserve the momentum. The rate of such two-quantum transitions is much less than in direct gap semiconductors, where the similar radiative transitions are single-quantum. As a result, the quantum efficiency of luminescence in silicon is too small to get it as a laser material. Numerous proposals to overcome this problem are aimed at increasing the rate of radiative recombination. We suggest enhancing the quantum efficiency of luminescence in silicon by stimulating the photon part of the two-quantum transitions by light from an appropriate external laser source. This allows us to obtain initially an external-source-assisted lasing in silicon and then a true photon-phonon lasing without any external source of radiation. Performed analysis revealed a number of requirements to the silicon laser medium (temperature, purity and perfection of crystals) and to the intensity of stimulating radiation. We discuss different mechanisms that may hinder the implementation of photon-phonon lasing in silicon.
A phonon laser using quantum dot spin states
Khaetskii, Alexander; Hu, Xuedong; Zutic, Igor
2013-03-01
Sound analog of laser (saser) has not yet been realized experimentally, though some steps in this direction have been made recently [1]. As is known, the main reason impeding coherent generation of phonons in solid state is high density of phonon states [2]. We suggest a particular realization of saser, which consists of an ensemble of quantum dots and uses the Zeeman-split spin levels of the ground orbital state in the quantum dot. We develop a complete set of saser equations taking into account the Coulomb blockade conditions for a quantum dot, and evaluate all the parameters such as the threshold, output power and efficiency of the device. Supported by NSF-ECCS and US ONR, NSF PIF,and US ARO. [1]. R.P. Beardsley et al., PRL 104, 085501 (2010). [2]. J. Chen and J.B. Khurgin, IEEE Journal of Quantum Electronics, 39, 600 (2003) .
Simulation of Confined and Interface Phonons Scattering in Terahertz Quantum Cascade Laser
He, Xiao-Yong; Cao, Jun-Cheng; Lü, Jing-Tao; Feng, Song-Lin
2005-12-01
We have performed the calculation of resonant-phonon transition in a terahertz quantum cascade laser. The electron wavefunctions and energy levels are obtained by solving the Schrödinger and Poisson equations self-consistently. The scattering rates of the confined, interface, and bulk phonons are calculated by using the Fermi golden rule. It has been shown that the confined phonon scattering is comparable to the interface phonon scattering and should be taken into consideration in the calculation.
Dynamics of a vertical cavity quantum cascade phonon laser structure
Maryam, W.; Akimov, A. V.; Campion, R. P.; Kent, A. J.
2013-01-01
Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325?GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic output of the device as a function of time after applying electrical pumping. The emission builds in intensity reaching a steady state on a timescale of order 0.1??s. We show that the results are consistent with a model of the dynamics of a saser cavity exactly analogous to the models used for describing laser dynamics. We also obtain estimates for the gain coefficient, steady-state acoustic power output and efficiency of the device. PMID:23884078
Khurgin, Jacob B
2014-01-01
Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.
Mode competition and anomalous cooling in a multimode phonon laser
Kemiktarak, Utku; Metcalfe, Michael; Lawall, John
2014-01-01
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.
Non-thermal processes of coherent acoustic phonons generation in semiconductors by femtosecond laser
Ruello, P.; Gusev, V.; Babilotte, P.; Pezeril, T.; Vaudel, G.; Mounier, D.
2012-03-01
Seeking for the new opportunities to efficiently excite GHz-THz coherent acoustic phonons by femtosecond lasers is an active field of research. Several fundamental objectives have to be addressed in order to achieve this acoustic phonons manipulation by femtosecond laser. Among them, the understanding of femtosecond generation of coherent acoustic phonons remains a key route. Several electron-phonon, photon-phonon and phonon-phonon interaction mechanisms are involved in the processes of generation and remain only partially understood up to now. In this paper, we will present a survey of ultrafast photo-generation of coherent acoustic phonon in semiconductors. We will focus first on the generation of the phonons by fs-laser excitation through the photoinduced modifications of nanoscopic internal electric fields (deformation potential) in non-piezo-active [100] GaAs semiconductor. We will show secondly how it is possible to develop more efficient sources by using piezo-active [111], [-1-1-1] and [411] GaAs semiconductors. In that case, generation of GHz acoustic phonon due to inverse piezoelectrical effect is based on ultrafast light-induced screening of the near surface built-in electric field.
Doping dependence of LO-phonon depletion scheme THz quantum-cascade lasers
International Nuclear Information System (INIS)
The effect of doping on terahertz quantum-cascade lasers (QCL) utilizing the longitudinal-optical (LO)-phonon depletion scheme of the lower laser state is investigated. Five identical 2.8 THz samples were grown with 2D equivalent doping ranging from 4.3 x 109 to 3.9 x 1010 cm-2. A linear dependence on doping is observed for both the threshold current density Jth and maximum current density Jmax. Only the sample doped to 3.9 x 1010 cm-2 shows the effects of free-carrier absorption with a nonlinear increase in Jth, while the Jmax remained linear. Since the applied field determines when the lasing action takes place, linearity is expected when the losses are independent of doping. All samples showed a similar Tmax of 140 K and T0 of 30 K
Phonon-mediated back-action of a charge readout on a double quantum dot.
Gasser, U; Gustavsson, S; Küng, B; Ensslin, K; Ihn, T
2010-07-01
Quantum point contacts are in use as an on-chip capacitative readout for the charge state of quantum dot systems. Here we investigate experimentally the back-action of quantum point contacts (QPCs) on a nearby double quantum dot (DQD). Driving current through a QPC influences the DQD state and leads to a measurable current flow in the DQD circuit with no bias voltage applied. The responsible mechanism is an indirect back-action process due to ohmic heating of the phonon bath. The system behaves like a thermoelectric engine, where a temperature gradient between the phonon bath and the electronic bath generates work observable as a measurable current flowing through the DQD. PMID:20571190
Phonon-mediated back-action of a charge readout on a double quantum dot
International Nuclear Information System (INIS)
Quantum point contacts are in use as an on-chip capacitative readout for the charge state of quantum dot systems. Here we investigate experimentally the back-action of quantum point contacts (QPCs) on a nearby double quantum dot (DQD). Driving current through a QPC influences the DQD state and leads to a measurable current flow in the DQD circuit with no bias voltage applied. The responsible mechanism is an indirect back-action process due to ohmic heating of the phonon bath. The system behaves like a thermoelectric engine, where a temperature gradient between the phonon bath and the electronic bath generates work observable as a measurable current flowing through the DQD.
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The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)
Effect of Pulse Width and Fluence of Femtosecond Laser on Electron—Phonon Relaxation Time
International Nuclear Information System (INIS)
The electron-phonon relaxation time as functions of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The two-temperature model is solved using a finite difference method for copper target. The temperature distribution of the electron and the lattice along with space and time for a certain laser fluence is presented. The time-dependence of lattice and electron temperature of the surface for different pulse width and different laser fluence are also performed, respectively. Moreover, the variation of heat-affected zone per pulse with laser fluence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the electron-phonon relaxation time is reasonably accurate with the influences of pulse width and fluence of femtosecond laser
Effect of pulse width and fluence of femtosecond laser on electron-phonon relaxation time
International Nuclear Information System (INIS)
The electron-phonon relaxation time as functions of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The two-temperature model is solved using a finite difference method for copper target. The temperature distribution of the electron and the lattice along with space and time for a certain laser fluence is presented. The time-dependence of lattice and electron temperature of the surface for different pulse width and different laser fluence are also performed, respectively. Moreover, the variation of heat-affected zone per pulse with laser fluence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the electron-phonon relaxation time is reasonably accurate with the influences of pulse width and fluence of femtosecond laser. (authors)
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The authors present a simulation and experimental study on the effect of phonon extraction level separation on the performance of GaAs-based three-well resonant-phonon terahertz quantum-cascade lasers (QCLs). The phonon extraction level separation is varied from 30 to 42 meV. Because of the efficient longitudinal-optical phonon scattering, the 36 meV QCL shows the largest gain, the best temperature performance and the highest output power. As for the lower (30 meV) or higher (42 meV) energy separation QCLs, the electron–longitudinal-optical phonon interaction still works by involving a transfer of in-plane momentum. The measured lasing characteristics are in qualitative agreement with simulation
Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening
Cheenicode Kabeer, Fairoja; Grigoryan, Naira S.; Zijlstra, Eeuwe S.; Garcia, Martin E.
2014-09-01
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.
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The operation of state-of-the-art optoelectronic quantum devices may be significantly affected by the presence of a nonequilibrium quasiparticle population to which the carrier subsystem is unavoidably coupled. This situation is particularly evident in new-generation semiconductor-heterostructure-based quantum emitters, operating both in the mid-infrared as well as in the terahertz (THz) region of the electromagnetic spectrum. In this paper, we present a Monte Carlo-based global kinetic approach, suitable for the investigation of a combined carrier–phonon nonequilibrium dynamics in realistic devices, and discuss its application with a prototypical resonant-phonon THz emitting quantum cascade laser design. (paper)
Wilson, T.; Kasper, E.; Oehme, M.; Schulze, J.; Korolev, K.
2014-11-01
We report on the direct excitation of 246 GHz longitudinal acoustic phonons in silicon doping superlattices by the resonant absorption of nanosecond-pulsed far-infrared laser radiation of the same frequency. A longitudinally polarized evanescent laser light field is coupled to the superlattice through a germanium prism providing total internal reflection at the superlattice interface. The ballistic phonon signal is detected by a superconducting aluminum bolometer. The sample is immersed in low-temperature liquid helium.
Random laser action in bovine semen
Smuk, Andrei; Lazaro, Edgar; Olson, Leif P.; Lawandy, N. M.
2011-03-01
Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination.
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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
Energy Technology Data Exchange (ETDEWEB)
Shimada, Toru [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Hirosaki University, 1 Bunkyo-cho, Hirosaki, Aomori 036-8152 (Japan); Kamaraju, N., E-mail: nkamaraju@lanl.gov [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Los Alamos National Laboratory, Center for Integrated Nanotechnologies, Los Alamos, New Mexico 87545 (United States); Frischkorn, Christian [Department of Physics, Free University of Berlin, Arnimallee 14, 14195 Berlin (Germany); Wolf, Martin; Kampfrath, Tobias [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)
2014-09-15
We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80?MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6?THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material.
Shimada, Toru; Kamaraju, N.; Frischkorn, Christian; Wolf, Martin; Kampfrath, Tobias
2014-09-01
We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80 MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6 THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material.
Energy Technology Data Exchange (ETDEWEB)
Ivanov, Dmitry; Rethfeld, Baerbel [Technical University Kaiserslautern, Physics Department (Germany)
2009-07-01
In this work we demonstrate the generation of phononic temperature waves in short pulse (pico- and femto-seconds) laser nanostructuring experiments on a metal surface. The existence of such waves was predicted based on numerical calculations with the atomistic-continuum model. This model describes the kinetics of transient nonequilibrium laser-induced processes at the atomic level and fast electron heat conduction in continuum. The analysis of obtained numerical data allowed to deduce the macroscopic parameters of observed thermal waves. The description of wave-like behavior within the frames of the diffusion equation is considered and the comparative analyzes between the continuum and the atomistic-continuum calculations is presented. The characteristic time of thermal wave relaxation was found to be on the level of 50 ns.
Mid-IR transitions of trivalent neodymium in low phonon laser 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
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.
Tb3+-doped KPb2Br5: Low-energy phonon mid-infrared laser crystal
Roy, U. N.; Hawrami, R. H.; Cui, Y.; Morgan, S.; Burger, A.; Mandal, Krishna C.; Noblitt, Caleb C.; Speakman, S. A.; Rademaker, K.; Payne, S. A.
2005-04-01
Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5mol% TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21/c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256°C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ˜0.4?mto25?m and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5?m, 3?m, 2.3?m, and 2?m corresponding to F67-F?7 transitions, for ? =2-5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134cm-1 from Raman scattering spectrum.
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The terahertz (THz) frequency quantum cascade laser (QCL) is a semiconductor heterostructure laser that has attracted much research interest over the past decade. We report on the high performance of THz QCLs based on a three-well resonant-phonon (RP) depopulation active region (AR) and operating in the frequency range 2.7 THz to 4.0 THz. Devices, processed into surface-plasmon waveguides, lased up to 116 K in pulsed mode with threshold current densities as low as 840 Acm?2. The effects of the design frequency and laser cavity length on performance are discussed. We also report on the operation of QCLs with reduced AR thicknesses, and show, for the first time, that the AR thickness of RP QCLs processed in a surface plasmon waveguide can be reduced to as little as 5 µm. Finally, we demonstrate the use of an electrically tuneable THz QCL, based on a heterogeneous AR, for spectroscopic imaging of the high-explosive pentaerythritol tetranitrate. (paper)
Optically pumped mid-infrared laser action in the monohaloacetylenes
Rutt, H. N.
1995-02-01
Strong optically pumped laser action excited by a TEA carbon dioxide laser has been obtained from monofluoro-acetylene in the 560-610 cm -1 region with outputs of up to 25 mJ and superfluorescent operation readily achieved without optimisation. These result from excitation of a combination of the two bending modes v4+v5. Laser action was also obtained with 9 ?m excitation of the v3 C?F stretch, on a difference band terminating in v4, with similar properties. Lasers of this type are rare. As well as being a potentially useful laser source in a region sparsely populated with good lasers, the results are of interest in the context of on going investigations of the spectroscopy of HCCF. Most, but not all lines are assigned. Very weak, erratic laser action was observed from chloro- and bromo-acetylene.
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Mode-selective phonon excitation by a mid-infrared laser (MIR-FEL) is demonstrated via anti-Stokes Raman scattering measurements of 6H-silicon carbide (SiC). Irradiation of SiC with MIR-FEL and a Nd-YAG laser at 14 K produced a peak where the Raman shift corresponds to a photon energy of 119 meV (10.4 ?m). This phenomenon is induced by mode-selective phonon excitation through the irradiation of MIR-FEL, whose photon energy corresponds to the photon-absorption of a particular phonon mode
Energy Technology Data Exchange (ETDEWEB)
Yoshida, Kyohei; Hachiya, Kan; Okumura, Kensuke; Mishima, Kenta; Inukai, Motoharu; Torgasin, Konstantin; Omer, Mohamed [Graduate School of Energy Science, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Sonobe, Taro [Kyoto University Research Administration Office, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Zen, Heishun; Negm, Hani; Kii, Toshiteru; Masuda, Kai; Ohgaki, Hideaki [Institute of Advanced Energy, Kyoto University, Gokasyo, Uji, Kyoto 611-0011 (Japan)
2013-10-28
Mode-selective phonon excitation by a mid-infrared laser (MIR-FEL) is demonstrated via anti-Stokes Raman scattering measurements of 6H-silicon carbide (SiC). Irradiation of SiC with MIR-FEL and a Nd-YAG laser at 14 K produced a peak where the Raman shift corresponds to a photon energy of 119 meV (10.4 ?m). This phenomenon is induced by mode-selective phonon excitation through the irradiation of MIR-FEL, whose photon energy corresponds to the photon-absorption of a particular phonon mode.
Makovetskii, D N
2011-01-01
This is a part of an overview of my early studies on nonlinear spin-phonon dynamics in solid state optical-wavelength phonon lasers (phasers) started in 1984. The main goal of this work is a short description and a qualitative analysis of experimental data on low-frequency nonlinear resonances revealed in a nonautonomous ruby phaser. Under phaser pumping modulation near these resonances, an unusual kind of self-organized motions in the ruby spin-phonon system was observed by me in 1984 for the first time. The original technique of optical-wavelength microwave-frequency acoustic stimulated emission (SE) detection and microwave-frequency power spectra (MFPS) analysis was used in these experiments (description of the technique see: D.N.Makovetskii, Cand. Sci. Diss., Kharkov, 1983). The real time evolution of MFPS was studied using this technique at scales up to several hours. The phenomenon of the self-organized periodic alternation of SE phonon modes was experimentally revealed at hyperlow frequencies from abou...
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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
Makovetskii, D N
2004-01-01
Two qualitatively different kinds of resonant destabilization of phonon stimulated emission (SE) are experimentally revealed for periodically forced multimode ruby phaser (phonon laser) operating at SE frequencies about 9 GHz, i.e. at microwave acoustic wavelengths of 1 micron. The inversion state of Cromium(3+) spin-system in ruby was created by electromagnetic pump at 23 GHz. Under deep modulation of pump power at low frequencies OMEGA_m = 70-200 Hz deterministic chaotic reconfigurations of the acoustic microwave power spectra (AMPS) were observed. This range of SE destabilization corresponds to the relaxational resonance that is well known for optical class-B lasers. Outside the relaxational resonance range, namely at ultra-low (infrasonic) frequencies OMEGA_m about 10 Hz, the other type of resonant destabilization of stationary phonon SE was observed by us for the first time. This new nonlinear resonance (we call it lambda-resonance) manifests itself as very slow and periodically repeated self-reconfigura...
Ultrafast dynamics and laser action of organic semiconductors
Vardeny, Zeev Valy
2009-01-01
Spurred on by extensive research in recent years, organic semiconductors are now used in an array of areas, such as organic light emitting diodes (OLEDs), photovoltaics, and other optoelectronics. In all of these novel applications, the photoexcitations in organic semiconductors play a vital role. Exploring the early stages of photoexcitations that follow photon absorption, Ultrafast Dynamics and Laser Action of Organic Semiconductors presents the latest research investigations on photoexcitation ultrafast dynamics and laser action in pi-conjugated polymer films, solutions, and microcavities.In the first few chapters, the book examines the interplay of charge (polarons) and neutral (excitons) photoexcitations in pi-conjugated polymers, oligomers, and molecular crystals in the time domain of 100 fs-2 ns. Summarizing the state of the art in lasing, the final chapters introduce the phenomenon of laser action in organics and cover the latest optoelectronic applications that use lasing based on a variety of caviti...
Phoenix's Laser Beam in Action on Mars
2008-01-01
[figure removed for brevity, see original site] Click on image to view the animation The Surface Stereo Imager camera aboard NASA's Phoenix Mars Lander acquired a series of images of the laser beam in the Martian night sky. Bright spots in the beam are reflections from ice crystals in the low level ice-fog. The brighter area at the top of the beam is due to enhanced scattering of the laser light in a cloud. The Canadian-built lidar instrument emits pulses of laser light and records what is scattered back. The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.
Quantum Dot Array Energy Spectrum Tuning With Laser Pulse Action
Dvurechenskii, A. V.; Yakimov, A. I.; Volodin, V. A.; Efremov, M. D.; Nikiforov, A. I.; Mikhalyov, G. Yu.; Gatskevich, E. I.; Ivlev, G. D.
2007-04-01
Space-charge spectroscopy has been used to study the hole energy spectrum of array of Ge quantum dots (QD's) coherently embedded in a Si matrix and subjected ex situ to a ruby laser (? = 694 nm) nanosecond pulsed action. The obtained results give evidence for a substantial reduction of the QD's size dispersion and for a narrowing distribution of the hole energy levels stimulated by nanosecond laser irradiation.
Energy Technology Data Exchange (ETDEWEB)
Stanton, N.M.; Martinez, C.E.; Kent, A.J.; Novikov, S.V.; Foxon, C.T. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham (United Kingdom)
2004-11-01
We have used bolometric detection techniques to study the phonons generated by ultrafast optical excitation of a gallium nitride/aluminium nitride superlattice (SL) structure. For excitation wavelengths shorter than 435 nm, we observe a strong longitudinal acoustic phonon signal. Angular dependence measurements show that this signal enhancement becomes channelled closer to the SL growth direction for excitation wavelengths shorter than the peak photoluminescence wavelength. The results are consistent with similar measurements using GaAs/AlAs SL's, where ultrafast optical excitation resulted in the generation of monochromatic phonons when the structure was resonantly excited. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Studies of random laser action in ?-conjugated polymers
International Nuclear Information System (INIS)
Laser action usually occurs within carefully configured resonant cavities. However, stimulated emission in disordered systems may also lead to coherent laser action above a certain threshold excitation intensity, Ith, which was dubbed as 'random lasing'. In random lasing a sequence of spectrally narrow emission lines, which are characteristic of laser modes, is superimposed on the amplified spontaneous emission band. We studied the statistical threshold distribution function, F(Ith) of Ith, of random lasers in ?-conjugated polymer films and its evolution with respect to the excitation area. The measurements were supported by pictures of the excited area taken while lasing occurs. We found that random lasing is accompanied by the appearance of lasing random cavities in the pictures, indicating that the sharp lines in the emission spectrum are, in fact, laser modes related to the random cavities formed in the disordered gain medium. Moreover a correlation exists between the cavity size extracted from the Fourier transform of the random lasing emission spectra and the size of the random resonators in the pictures obtained. In addition we also found that the measured F(Ith) has a marked asymmetry with respect to the average threshold, (Ith)ave, which decreases with the excitation area. An existing theoretical model based on random resonators in the polymer film is found to be in good agreement with the obtained F(Ith) function
Phonon engineering for nanostructures.
Energy Technology Data Exchange (ETDEWEB)
Aubry, Sylvie (Stanford University); Friedmann, Thomas Aquinas; Sullivan, John Patrick; Peebles, Diane Elaine; Hurley, David H. (Idaho National Laboratory); Shinde, Subhash L.; Piekos, Edward Stanley; Emerson, John Allen
2010-01-01
Understanding the physics of phonon transport at small length scales is increasingly important for basic research in nanoelectronics, optoelectronics, nanomechanics, and thermoelectrics. We conducted several studies to develop an understanding of phonon behavior in very small structures. This report describes the modeling, experimental, and fabrication activities used to explore phonon transport across and along material interfaces and through nanopatterned structures. Toward the understanding of phonon transport across interfaces, we computed the Kapitza conductance for {Sigma}29(001) and {Sigma}3(111) interfaces in silicon, fabricated the interfaces in single-crystal silicon substrates, and used picosecond laser pulses to image the thermal waves crossing the interfaces. Toward the understanding of phonon transport along interfaces, we designed and fabricated a unique differential test structure that can measure the proportion of specular to diffuse thermal phonon scattering from silicon surfaces. Phonon-scale simulation of the test ligaments, as well as continuum scale modeling of the complete experiment, confirmed its sensitivity to surface scattering. To further our understanding of phonon transport through nanostructures, we fabricated microscale-patterned structures in diamond thin films.
Metal fusion by laser radiation action in an oxidizing medium
International Nuclear Information System (INIS)
Interaction of concentrated heat fluxes with metals is found in various scientific and technological applications. In previous studies the process of laser heating of a massive copper target in an oxidizing atmosphere was considered. In this situation an oxide film was formed on the irradiated metal surface, which leads to an intense change in the absorption capability of the target. In the models considered the temperatures were limited to values below the fusion point of copper. In the present study the investigation of laser radiation interaction with a two layer oxide-metal system will be extended in temperature through the point of target fusion to the point of commencement of fusion of the zirconium dioxide layer using the example of zirconium. Results are presented from a calculation of fusion of a massive zirconium plate under the action of laser radiation with consideration of simultaneous surface oxidation. 8 refs., 2 figs
Energy Technology Data Exchange (ETDEWEB)
Li Simian [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Hebei Key Laboratory of Optoelectronic Information and Geo-detection Technology Shijiazhuang University of Economics, Shijiazhuang 050031 (China); Huang Huan; Wang Yang; Wu Yiqun; Gan Fuxi [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhu Weiling; Wang Wenfang; Chen Ke; Yao Daoxin; Lai Tianshu [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)
2011-09-01
A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb{sub 2}Te{sub 3} film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb{sub 2}Te{sub 3} film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A{sub 1g}{sup 1} and E{sub g}) of crystalline Sb{sub 2}Te{sub 3} enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb{sub 2}Te{sub 3} film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb{sub 2}Te{sub 3}-like topological insulators.
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
Laser action in pi-conjugated polymers and photonic crystals
Shkunov, Maxim N.
2000-10-01
Laser action properties of highly luminescent ?- conjugated polymers and organic molecules were studied in thin films, microcavities, highly scattering media and three-dimensional photonic crystals. The experiments employed ultrafast laser amplifiers as high-intensity excitation sources. Under intense laser excitation a dramatic spectral narrowing (SN) and lifetime shortening were discovered in thin films of conjugated polymers. SN was achieved at several wavelengths in the visible spectral range between 420 and 630 nm. Ultrafast measurements of emission lifetime in poly(2,5-dioctyloxy-p-phenylenevinylene) (DOO-PPV) revealed ~240 ps and ~10 ps decay dynamics for photoluminescence and amplified spontaneous emission regimes. A two-color femtosecond pump-probe technique demonstrated a highly intensity dependent photoinduced absorption (PA) decay dynamics in DOO-PPV with characteristic decay times of ~240 ps and ~4 ps for low and high excitation intensities. A highly monochromatic laser-like emission without a cavity was demonstrated in polymer films at very high excitation intensities (10-90 MW/cm 2) and was shown to be caused by amplified Raman scattering. Multimode laser emission was observed in cylindrical polymer microcavities, including self-assembled microrings on optical fibers and patterned microdisks. In the absence of a laser cavity, inhomogeneous films of DOO-PPV, as well as solutions infiltrated into opal crystals, exhibited an unusual stimulated emission behavior when very narrow lines appeared in the emission spectrum. This regime was associated with random lasing, in which optical feedback is induced by random light scattering by inhomogeneities within the amplification medium. Scanning Electron Microscope (SEM) imaging of opal single crystals demonstrated an fcc crystalline structure with silica spheres ~290 nm in diameter. Optical transmission and reflectivity measurements along the [111] direction showed a well-defined photonic stop band in the red region of the spectrum. Three-dimensional photonic crystal lasers based on opal single crystals infiltrated with laser dye solutions were demonstrated in the blue and red regions of the spectrum. Optical feedback was provided via Bragg scattering of light from (220) and (111) opal crystalline planes. This discovery revealed a possibility of simultaneous lasing in three dimensions from the same crystalline structure.
Annealing of implanted silicon under the action of microsecond pulsed TEA-CO2 laser radiation
International Nuclear Information System (INIS)
Results of annealing of boron implanted silicon under the action of microsecond pulsed CO2 laser radiation are presented. The time dependence of sample surface temperature for different energy densities of laser pulse are shown. Reflection high energy electron diffraction evidences an amorphous layer on the sample top surface before laser irradiation. Following laser annealing a complete epitaxy was evidenced
Quenching of laser action in cresyl violet by 6943 A radiation
International Nuclear Information System (INIS)
Complete quenching of laser action in the dye when pumped by the second harmonic of a ruby laser is achieved in the presence of light of wavelength 6943 A. It is believed that the quenching is due to depletion of the upper laser level population by stimulated emission, and further that the unsatisfactory performance of flash-pumped cresyl violet rhodamine 6G lasers may stem from the quenching action of a red component in the pump light. (U.S.)
Wette, Frederik
1991-01-01
In recent years substantial progress has been made in the detection of surface phonons owing to considerable improvements in inelastic rare gas scattering tech niques and electron energy loss spectroscopy. With these methods it has become possible to measure surface vibrations in a wide energy range for all wave vectors in the two-dimensional Brillouin zone and thus to deduce the complete surface phonon dispersion curves. Inelastic atomic beam scattering and electron energy loss spectroscopy have started to play a role in the study of surface phonons similar to the one played by inelastic neutron scattering in the investigation of bulk phonons in the last thirty years. Detailed comparison between experimen tal results and theoretical studies of inelastic surface scattering and of surface phonons has now become feasible. It is therefore possible to test and to improve the details of interaction models which have been worked out theoretically in the last few decades. At this point we felt that a concise, co...
Melnikov, A A; Chekalin, S V
2010-01-01
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
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
Self-seeded forward lasing action from a femtosecond Ti:sapphire laser filament in air
International Nuclear Information System (INIS)
428 nm forward lasing action was observed from a femtosecond laser filament in air created by Ti:sapphire laser pulses. The 800 nm femtosecond laser filament not only provides a source for population inversion between two vibrational levels (B2?u+(0) and X2?g+(1)) of N2+ but also generates a 428 nm seed from filament-induced white light. This simple technique will find more applications in standoff spectroscopy. (letter)
Strong far-infrared laser action in carbonyl fluoride and vinyl fluoride
International Nuclear Information System (INIS)
Intense far-infrared laser action is reported for carbonyl fluoride and vinyl fluoride. Eleven new lines with wavelengths between 339 ?m 2 laser. Twenty-three lines with wavelengths in the range 172 ?m, <= lambda <= 783 ?m were detected when pumping the recently discovered efficient FIR laser molecule vinyl fluoride. In addition, three very weak new lines were found using 1.1-difluorethylen. (orig.)
Electron-Phonon and Phonon-Phonon Interactions
International Nuclear Information System (INIS)
1. Form of crystal Hamiltonian. 1.1. Adiabatic approximation and electron-phonon, interaction. 1.2. Harmonic approximation and phonon-phonon interaction. 1.3. Crystal momentum conservation. 2. Electron-phonon interaction in metals. 2.1. Real-time Green functions. Migdal's theorem. 2.2. Renormalization effects in normal state. 2.3. Pair interaction and superconductivity. 2.4. Hydro- dynamical limit and transport equation. 3. Phonon-phonon interaction in insulators. 3.1. Imaginary- time Green functions and perturbation theory. 3.2. Thermal and elastic properties. 3.3. Phonon renormalization effects. 3.4. Heat propagation and second sound. (author)
Generation of electromagnetic radiation in laser action with solids
International Nuclear Information System (INIS)
A new effect of electromagnetic pulse generation in solids, exposed to laser irradiation was revealed experimentally. The ruby laser with 694.36 nm wave length was used in the experiments. Monocrystals of Si, GaAs, KCl, LiF, polycrystals of Cu, Al, metals, the rocks-calcite, marble, natural quartz, feldspar - were used as samples. The effect of electromagnetic pulse generation, which is characterized by sharp threshold dependence on the density of laser radiation power, as well as on the type of material and its characteristics was observed for each material. The possibility of using the method of electromagnetic pulse detection during laser irradiation for evaluation of defectiveness degree and strength characteristics of investigated materials was shown
SPALLATION UNDER THE ACTION OF A LASER INDUCED SHOCK WAVE
Cottet, F.; Ng, A.; Da Silva, L.; Marty, L.
1988-01-01
The conditions of laser-driven shock wave loading leads to study the dynamic fracture in an unusual range of stress and strain rates : 0.2-2 Mbar and more than 107s-1. A cumulative damage criteria for spallation process has been included in a one-dimensional finite difference hydrodynamic code. This program correctly fits spallation experiments on aluminum targets of various thicknesses irradiated by 2 ns laser pulse of 1012W/cm2 incident intensity.
Phonon localization in ultrathin layered structures
Döring, F.; Eberl, C.; Schlenkrich, S.; Schlenkrich, F.; Hoffmann, S.; Liese, T.; Krebs, H. U.; Pisana, S.; Santos, T.; Schuhmann, H.; Seibt, M.; Mansurova, M.; Ulrichs, H.; Zbarsky, V.; Münzenberg, M.
2015-02-01
An efficient way for minimizing phonon thermal conductivity in solids is to nanostructure them by means of reduced phonon mean free path, phonon scattering and phonon reflection at interfaces. A sophisticated approach toward this lies in the fabrication of thin multilayer films of different materials. In this paper, we show by femtosecond-pump-probe reflectivity measurements that in different multilayer systems with varying acoustic mismatch (consisting of metals, semiconductors, oxides and polymers), oscillations due to phonon localization can be observed. For the growth of multilayer films with well-defined layer thicknesses, we used magnetron sputtering, evaporation and pulsed laser deposition. By altering the material combinations and reducing the layer thicknesses down to 3 nm, we observed different mechanisms of phonon blocking, reaching in the frequency regime up to 360 GHz.
Biological Effects of Contact Action of 1470 vs. 810 nm Semiconductor Lasers in vitro
Directory of Open Access Journals (Sweden)
N.A. Schumilova
2015-01-01
Full Text Available The aim of the investigation is to identify the character of biological effects of contact action of semiconductor laser with a wavelength of 1470 nm on the tissues with different optical and mechanical properties compared to the exposure to laser radiation with a wavelength of 810 nm. Materials and Methods. The study was performed on a chicken muscle tissue, liver of the cattle, nasal polyp, removed nasal septum cartilage. While making a linear incision of the tissues by the laser with a speed of 2 mm/s assessment of the width of ablation and coagulation zones, and the crater depth with the following measurement under the microscopy conditions were carried on. Weighing of the tissue specimens before and after the spot action was performed. Standardization of the operating speed was achieved by using uniformly moving recorder chart. Results. Radiation power increment of 1470 nm wavelength laser contributes to the increase of the ablation and coagulation zone width to a greater degree compared to 810 nm laser. Exposure to 1470 nm laser with a power of 1 W causes the tissue to stick to the fiber. When power is 2 W, coagulation zone of soft tissues is comparable, and in some cases exceeds it after treatment by 810 nm laser. In relation to the crater depth, 1470 nm radiation is inferior to 810 nm radiation, but is superior in relation to vaporization abilities. Conclusion. For tissue ablation with 1470 nm laser a power of 2 W is optimal, as it provides a sparing superficial effect, and in a number of cases exceeds the action of 810 nm 7 W laser by its coagulation properties. Generation of a crater with a less depth after application of 1470 nm laser allows it to be recommended for superficial coagulation of vascular lesions.
Study on modes of energy action in laser-induction hybrid cladding
International Nuclear Information System (INIS)
The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.
Study on modes of energy action in laser-induction hybrid cladding
Energy Technology Data Exchange (ETDEWEB)
Huang Yongjun, E-mail: huangyj@mail.hzau.edu.cn [College of Engineering and Technology, Huazhong Agricultural University, Wuhan 430070 (China); Zeng Xiaoyan [Division of Laser Science and Technology, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)
2009-11-15
The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.
Study on modes of energy action in laser-induction hybrid cladding
Huang, Yongjun; Zeng, Xiaoyan
2009-11-01
The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.
Phonon manipulation with phononic crystals.
Energy Technology Data Exchange (ETDEWEB)
Kim Bongsang; Hopkins, Patrick Edward; Leseman, Zayd C.; Goettler, Drew F.; Su, Mehmet F. (University of New Mexico, Albuquerque, NM); El-Kady, Ihab Fathy; Reinke, Charles M.; Olsson, Roy H., III
2012-01-01
In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power 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.
Synthesis of nanoporous structures in metallic materials under laser action
Kazanskiy, N. L.; Murzin, S. P.; Osetrov, Ye. L.; Tregub, V. I.
2011-11-01
We defined conditions of the laser-aided formation of nanoporous structures with nanopores ranging in size from 40 to 50 nm using laser pulses of 10.6 ?m wavelength at a pulse-repetition rate of up to (4-5)×10 3 Hz for a model metallic material (a two-component alloy "brass of 62%"). It has been established that the exposure to a uniform laser light at depths of up to 25-30 ?m results in the formation of nanopores with a relatively uniform distribution across the surface. The resulting pattern contains both solitary pores and ramified porous channels. The nanopores are uniformly distributed within a subgrain, being fairly stable in size and shape. The nanopore size and shape feature larger non-uniformity on the subgrain boundary. The resulting metallic structures show promise for use as catalysts and ultrafiltration membranes.
International Nuclear Information System (INIS)
The dynamics of coherent phonons in fluorine-containing crystals under plasma formation were studied using a nonlinear pump–probe technique based on third harmonic generation. In LiF crystal more than one phonon mode was observed. The modes are the overtones of a fundamental wave with a frequency of 0.38 THz. In CaF2 crystal phonons with frequencies of 1 and 0.1 THz were observed. In BaF2 crystal, in addition to coherent phonons with frequencies of 1 THz and 67 GHz, a significant increase of amplitude in the phonon modes with a time delay of 15 ps was detected. (letter)
Efficiency of laser action on hemoglobin and oxyhemoglobin in skin blood vessels
Asimov, Mustafo M.; Asimov, Rustam M.; Rubinov, Anatoly N.
1998-05-01
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.
Whispering-gallery mode resonators for highly unidirectional laser action.
Wang, Qi Jie; Yan, Changling; Yu, Nanfang; Unterhinninghofen, Julia; Wiersig, Jan; Pflügl, Christian; Diehl, Laurent; Edamura, Tadataka; Yamanishi, Masamichi; Kan, Hirofumi; Capasso, Federico
2010-12-28
Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (? ? 10 ?m) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of ?5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers. PMID:21149678
Whispering-gallery mode resonators for highly unidirectional laser action
Wang, Qi Jie; Yan, Changling; Yu, Nanfang; Unterhinninghofen, Julia; Wiersig, Jan; Pflu?gl, Christian; Diehl, Laurent; Edamura, Tadataka; Yamanishi, Masamichi; Kan, Hirofumi; Capasso, Federico
2010-01-01
Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with...
Study on laser action from UV-curable chiral nematic liquid crystals
International Nuclear Information System (INIS)
This paper describes the study on laser action from UV-curable chiral nematic liquid crystals (CLCs) doped with a fluorescent dye before and after photopolymerization of CLC host. When an optically active agent without crosslinkable moiety was doped in a UV-curable nematic liquid crystal, the laser action from the CLC cell was quite different before and after photopolymerization. Before the polymerization, optically pumping of dye-doped CLC cells with a linearly polarized laser beam gave rise to the laser emission with circular polarization at the band edge of CLC reflection as a consequence of the internal distributed feedback effect. Successively, photopolymerization of the CLC with 365 nm light brought about the thorough disappearance of the CLC reflection band probably due to the phase separation leading to the emergence of amplified spontaneous emission of fluorescent dye by optically pumping. In contrast, the dye-doped CLC cell including a crosslinkable agent with a cholesteryl residue enabled the mirrorless laser action after photopolymerization. This is because the selective reflection band of CLC host was retained by the planar structure of cholesteric polymer network
Electron Scattering and Hybrid Phonons in Low Dimensional Laser Structures made with GaAs/AlxGa1-xAs
Stavrou, V. N.; Veropoulos, G. P.
2009-01-01
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 ...
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 µm 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 µm and 8 to 12 µm, the design scheme of the reference was also modified to emission wavelengths between 5 and 9 µm. 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 µm to 300 K at 9 µm
Energy Technology Data Exchange (ETDEWEB)
Rademaker, K; Heumann, E; Payne, S A; Huber, G; Krupke, W F; Isaenko, L I; Burger, A
2004-09-15
For the first time laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2} + {sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. Rare earth- doped MPb{sub 2}Br{sub 5} (M=K, Rb) is a promising candidate for long wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd{sup 3+}:MPb{sub 2}Br{sub 5} has high potential for laser operation at new wavelengths as well as for the realization of short-wavelength lasing due to upconversion processes.
Costela, A.; García-Moreno, I.; Carrascoso, M. L.; Sastre, R.
2002-01-01
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.
Decoherence measurement of single phonons using spectral interference
Waldermann, F C; Nunn, J; Surmacz, K; Lee, K H; Jaksch, D; Walmsley, I A; Spizziri, P; Olivero, P; Prawer, S
2008-01-01
We present a novel technique to measure the decoherence characteristics of optical phonons in a solid. Coherent phonons are excited by ultrafast laser pulses by spontaneous, transient Raman scattering. Pulse pair excitation leads to an interference pattern in the excitation and Stokes spectrum. The visibility of the spectral interference is used to determine the degree of phase coherence of the optical phonons. The scheme operates at excitation levels of much less than one phonon per mode. It can be realized using laser sources two orders of magnitude slower than existing schemes. This technique can be applied to measure the phonon lifetime in any Raman active solid. We apply this scheme to measure the phonon lifetime of diamond.
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Nonlinear-laser properties of crystals of non-centrosymmetric orthorhombic semi-organic tris(glycine) zinc chloride Gly3?ZnCl2 are reported in this paper. Under one-micron picosecond pumping many-phonon high-order SRS, a more than two-octaves Stokes and anti-Stokes lasing frequency comb, ''Cherenkov''-type SHG, THG, and several cascaded parametric self-sum-frequency generation processes were observed. All recorded Raman-induced laser wavelengths were identified and attributed to the ?(3)-promoting vibration modes of the crystal. A brief review of nonlinear-laser properties of known SRS-active heterodesmic semi-organic crystals with partially ionic bonding character between structural units is given as well
Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback
Energy Technology Data Exchange (ETDEWEB)
Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatüre, Mete [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)
2014-10-27
We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191?Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.
Spontaneous emission of phonons by coupled quantum dots
Brandes, Tobias; Kramer, Bernhard
1999-01-01
We find an interference effect for electron-phonon interactions in coupled semiconductor quantum dots that can dominate the nonlinear transport properties even for temperatures close to zero. The intradot electron tunnel process leads to a `shake up' of the phonon system and is dominated by a double-slit-like interference effect of spontaneously emitted phonons. The effect is closely related to subradiance of photons (Dicke effect) in a laser-trapped two-ion system and expla...
Nika, Denis L.; Balandin, Alexander A.
2012-01-01
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...
Coherent longitudinal acoustic phonons in pyrite
International Nuclear Information System (INIS)
We have studied the coherent longitudinal acoustic (LA) phonon in a single crystal of pyrite (FeS2) by femtosecond pump and probe spectroscopy. The coherent LA phonon signal is observed as a very clear oscillatory structure in the reflection type pump and probe measurement. The amplitude, decay rate, frequency and phase of the signal show large changes as the wavelength of the laser is varied. By applying a wave-packet model to the analysis of the coherent LA phonon signal, it is found that the refractive index, the extinction coefficient and the longitudinal sound velocity are obtained from the coherent LA phonon signal without need for any other material parameters. From the experimental result, we precisely determine these values for the pyrite sample. The wavelength dependence of the change of the complex dielectric constant is also obtained
Non-equilibrium Phonons in CaWO4: Issues for Phonon Mediated Particle Detectors
Msall, Madeleine; Head, Timothy; Jumper, Daniel
2009-03-01
The CRESST experiment looks for evidence of dark matter particles colliding with nuclei in CaWO4, using cryogenic bolometers sensitive to energy deposition ˜ 10 keV with a few percent accuracy. Calibration of the energy deposited in the phonon system depends upon the details of the evolution of the non-equilibrium energy in the CaWO4 absorber. Our phonon images sensitively measure variations in angular phonon flux, providing key information about the elastic constants and scattering rates that determine the energy evolution. Phonon pulses, created by focused photoexcitation of a 150 nm Cu film, are detected after propagation through 3 mm of CaWO4. The 20 ns Ar-ion laser pulse creates a localized (10-3 mm^2) source of 10-20 K blackbody phonons. The sample is at 2 K. Our images show that the elastic constants derived from ultrasonic velocities along high symmetry axes do not accurately predict the total phonon flux along non-symmetry directions. We present new data on the dependence of phonon flux on excitation level and discuss the influence of isotope and anharmonic decay on the shape of phonon pulses in these ultrapure samples. Thanks to J.P. Wolfe and the Frederick Seitz Materials Research Laboratory, Urbana, IL, for partial support of this work.
Non-equilibrium phonon dynamics
International Nuclear Information System (INIS)
This book presents information on the following topics: studies of nonequilibrium dynamics in the time domain; studies on nonequilibrium phonons by optical techniques; generation, propagation and detection of terahertz phonons in gallium arsenide; monochromatic phonon generation by superconductiong tunnel junctions; phonon imaging-theory and applications; an introduction to crossing effects in phonon scattering; phonon echoes, polarization echoes, and acoustic phase conjugation in solids; introduction to phonon hydrodynamics; electron-phonon interacti, screening and phonon-generation; surface acoustic waves; vibrational energy exchange between gases and solids; and the gas/phonon interface - desorption and other phenomena
Phonon counting and intensity interferometry of a nanomechanical resonator
Cohen, Justin D; MacCabe, Gregory S; Groblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar
2014-01-01
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.
Room temperature visible laser action of F aggregated centers in LiF:Mg, OH crystals
International Nuclear Information System (INIS)
A color center laser based on F center emission in LiF monocrystals doped with Mg and OH- was operated at room temperature. The Li monocrystals were grown under dry N2 atmosphere by a modified Czochralski technique and irradiated with 50 keV X-rays or 1 MeV electrons in order to produce F centers, F aggregates, and hole centers. F2 center action was observed at 690 nm with about 250 W of peak output power and 10 ns pulse width
Dispersive effect on dual-color laser action from one-dimensional scattering gain media
International Nuclear Information System (INIS)
The dual-color laser action from the Rh6G solution with TiO2 scattering particles is investigated by solving Maxwell’s equations and rate equations of electronic population simultaneously. A one-dimensional (1D) dispersive model is proposed to explain the experiment results. The results indicate that, although the dispersion in optical domain is relatively small, the dispersion for both gain materials and scattering particles has significant influence on modes of random lasing, which lead to more lasing modes and lower spectral intensity. (paper)
Damage to the surface of silicon in the solid phase by the action of Nd:YAG laser pulses
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An investigation was made of solid-phase damage to the surface of silicon by Nd:YAG laser pulses. The results made it possible to postulate particle emission when the surface of silicon was subjected to laser pulses with the threshold power density Imelt corresponding to the onset of surface melting. Such emission was attributed to the formation of surface microcracks as a result of condensation of nonequilibrium defects under the action of elastic stresses. (interaction of laser radiation with matter. laser plasma)
Phonon - mediated particle detection
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When an incident particle collides with an electron or nucleus in an insulating crystal, the recoil kinetic energy is converted rapidly into a burst of low-energy phonons. If the crystal is very pure and free of defects, and if it is very cold, (T--0.1K), the phonons will propagate ballistically for distances of several centimeters. The authors report on experiments with two types of superconducting phonon sensors being considered for use on a new kind of particle detector, called a Silicon Crystal Acoustic Detector (SiCAD), which reads out phonons generated by particle scattering events
Zazhogin, A. P.; Umreiko, D. S.; Patapovich, M. P.; Fadaeian, A. R.; Komyak, A. I.; Umreiko, S. D.
2011-07-01
Spectroscopic studies of the surface laser plasma formed by the action of sequential high-power double laser pulses close to a porous body containing microquantities of ammonium polyuranates showed that the intensities of uranium spectral lines that are proportional to the elemental content in the plasma depend significantly on the physicochemical properties of the uranium compounds. The line intensities increase by several times with almost the same increase in the formation enthalpy of the compounds.
International Nuclear Information System (INIS)
We discovered several new nonlinear-laser ?(3)-properties in tetragonal YVO4 vanadate, which is well-known birefringent optical material, host-crystal for lanthanide lasant ions, and attractive gain media for Raman laser converters. We hope that observed many-phonon SRS, almost sesqui-octave Stokes and anti-Stokes lasing comb, cascaded self-frequency ''tripling'' and self-sum-frequency generation in the blue spectral range could significantly enriche applied potential of this crystal
Microscopic model of a phononic refrigerator
Arrachea, Liliana; Chamon, Claudio; Capaz, Rodrigo
2012-01-01
We analyze a simple microscopic model to pump heat from a cold to a hot reservoir in a nanomechanical system. The model consists of a one-dimensional chain of masses and springs coupled to a back gate through which a time-dependent perturbation is applied. The action of the gate is to modulate the coupling of the masses to a substrate via additional springs that introduce a moving phononic barrier. We solve the problem numerically using non-equilibrium Green function techniques. For low driving frequencies and for sharp traveling barriers, we show that this microscopic model realizes a phonon refrigerator.
Myasnikov, D. V.; Konyashkin, A. V.; Ryabushkin, O. A.
2011-02-01
A model of nonlinear-optical crystal heating is proposed that enables one to determine temperature distribution inside the sample under action of laser radiation from the measurements of internal crystal temperature. Absorption and heat transfer coefficient at crystal-air boundary are also determined. Crystal temperature is measured by analyzing changes of piezoelectric resonance frequencies of the sample.
Recombination of electron-hole plasma in silicon under action of femtosecond laser impulse
International Nuclear Information System (INIS)
The experimental data on the dynamics of the conductivity electrons relaxation at the stage, preceding the silicon surface layer melting, are obtained. The energy of the sounding radiation quantum is lesser than the forbidden zone width, which makes it possible to obtain information on the electron-phonon relaxation processes by the electrons concentration on the conductivity zone ? 1021 cm-3
Phonon Thermal Conduction in Graphene
Nika, D. L.; Pokatilov, E. P.; Askerov, A. S.; Balandin, A. A.
2008-01-01
We investigated theoretically the phonon thermal conductivity of single layer graphene. The phonon dispersion for all polarizations and crystallographic directions in graphene lattice was obtained using the valence-force field method. The three-phonon Umklapp processes were treated exactly using an accurate phonon dispersion and Brillouin zone, and accouting for all phonon relaxation channels allowed by the momentum and energy conservation laws. The uniqueness of graphene wa...
Optomechanics: Photons refrigerating phonons
Cleland, Andrew
2009-07-01
Optomechanics is a promising route towards the observation of quantum effects in relatively large structures. Three papers, each discussing a different implementation, now combine optical sideband and cryogenic cooling to refrigerate mechanical resonators to fewer than 60 phonons.
Birefringent phononic structures
Directory of Open Access Journals (Sweden)
I. E. Psarobas
2014-12-01
Full Text Available Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.
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Large single crystals of the compound LaBO2MoO4, undoped and doped with Nd3+ ions, were grown. Their multi-wavelength Stokes and anti-Stokes picosecond generation, nonlinear-laser effects, and neodymium IR luminescence were investigated. We classify these crystals as a promising material for Raman frequency converters and gain medium for solid-state lasers
Phonon-Assisted Incoherent Excitation of a Quantum Dot and its Emission Properties
Weiler, S; Roy, C; Ulrich, S M; Richter, D; Jetter, M; Hughes, S; Michler, P
2012-01-01
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.
Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene
Araujo, Paulo T.; Mafra, Daniela L.; Sato, Kentaro; Saito, Riichiro; Kong, Jing; Dresselhaus, Mildred S.
2012-01-01
In this letter, we present a step towards understanding the bilayer graphene (2LG) interlayer (IL)-related phonon combination modes and overtones as well as their phonon self-energy renormalizations by using both gate-modulated and laser-energy dependent inelastic scattering spectroscopy. We show that although the IL interactions are weak, their respective phonon renormalization response is significant. Particularly special, the IL interactions are mediated by Van der Waals forces and are fun...
Phonon waveguides for electromechanical circuits
Hatanaka, D.; Mahboob, I.; Onomitsu, K.; Yamaguchi, H.
2014-07-01
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.
Phonon waveguides for electromechanical circuits.
Hatanaka, D; Mahboob, I; Onomitsu, K; Yamaguchi, H
2014-07-01
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. PMID:24929340
PHONONS IN INTRINSIC JOSEPHSON SYSTEMS
Energy Technology Data Exchange (ETDEWEB)
C. PREIS; K. SCHMALZL; ET AL
2000-10-01
Subgap structures in the I-V curves of layered superconductors are explained by the excitation of phonons by Josephson oscillations. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted.
PHONONS IN INTRINSIC JOSEPHSON SYSTEMS
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Subgap structures in the I-V curves of layered superconductors are explained by the excitation of phonons by Josephson oscillations. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted
Phonon dispersion in hypersonic two-dimensional phononic crystal membranes
Graczykowski, B.; Sledzinska, M.; Alzina, F.; Gomis-Bresco, J.; Reparaz, J. S.; Wagner, M. R.; Sotomayor Torres, C. M.
2015-02-01
We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes.
Spectrum and entanglement of phonons in quantum fluids of light
Busch, Xavier; Parentani, Renaud
2013-01-01
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.
Continuous mode cooling and phonon routers for phononic quantum networks
Habraken, S. J. M.; Stannigel, K.; Lukin, M. D.; Zoller, P.; Rabl, P.
2012-11-01
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.
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)
Continuous mode cooling and phonon routers for phononic quantum networks
Habraken, S J M; Lukin, M D; Zoller, P; Rabl, P
2012-01-01
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.
Xie, Hongqiang; chu, Wei; Zeng, Bin; Yao, Jinping; Jing, Chenrui; Li, Ziting; Cheng, Ya
2015-01-01
We experimentally investigate generation of backward 357 nm N2 laser in a gas mixture of N2/Ar using 800-nm femtosecond laser pulses, and examine the involved gain dynamics based on pump-probe measurements. Our findings show that a minimum lifetime of population inversion in the excited N2 molecules is required for generating intense backward nitrogen lasers, which is ~0.8 ns under our experimental conditions. The results shed new light on the mechanism for generating intense backward lasers from ambient air, which are highly in demand for high sensitivity remote atmospheric sensing application.
Laser action in Rhodamine 6G doped titania-containing ormosils
Hu, Lili; Jiang, Zhonghong
1998-03-01
A new titania-containing ormosil xerogel derived from 80 mol% glycidoxypropyltrimethoxysilane (GPTMS) and 20 mol% titanum alkoxide (Ti(OBu) 4) modified by methyl methacrylate (MMA) was synthesized via the sol-gel method as dye laser host. Two kinds of matrices, one without initiator for the polymerization of MMA and another with benzoyl peroxide initiator, were prepared. Their optical properties, microstructure characteristics and surface laser damage thresholds are reported. Laser oscillation was easily achieved in all hand-polished Rhodamine 6G doped titania-containing ormosil xerogels. The effects of dye concentration and dye-matrix combination on the fluorescent emission, slope efficiency, photostability and tunable bandwidth were examined. Benzoyl peroxide is confirmed to be effective in improving the matrix density, but it is harmful to the laser behavior of Rhodamine 6G dye. A laser efficiency of 13% and photostability of 12 GJ/mol were obtained in a 2×10 -4 M Rhodamine 6G doped dye laser. A brief comparison of laser performance and matrix properties of Rhodamine 6G doped dye lasers based on the present matrix and PMMA, ormosil and sol-gel silica glass is made.
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)
Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon
Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin
2015-02-01
Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.
Generation of radicals in hard biological tissues under the action of laser radiation
Sviridov, Alexander P.; Bagratashvili, Victor N.; Sobol, Emil N.; Omelchenko, Alexander I.; Lunina, Elena V.; Zhitnev, Yurii N.; Markaryan, Galina L.; Lunin, Valerii V.
2002-07-01
The formation of radicals upon UV and IR laser irradiation of some biological tissues and their components was studied by the EPR technique. The radical decay kinetics in body tissue specimens after their irradiation with UV light were described by various models. By the spin trapping technique, it was shown that radicals were not produced during IR laser irradiation of cartilaginous tissue. A change in optical absorption spectra and the dynamics of optical density of cartilaginous tissue, fish scale, and a collagen film under exposure to laser radiation in an air, oxygen, and nitrogen atmosphere was studied.
Vasil'chenko, Zh V.; Azharonok, V. V.; Filatova, I. I.; Shimanovich, V. D.; Golubev, V. S.; Zabelin, A. M.
1996-09-01
Emission spectroscopy methods were used in an investigation of thermodynamic parameters of a surface plasma formed by the action of cw CO2 laser radiation of (2-5)×106 W cm-2 intensity on stainless steel in a protective He or Ar atmosphere. The spatiotemporal structure and pulsation characteristics of the plasma plume were used to determine the fields of the plasma electron density and temperature.
Laser phase noise effects on the dynamics of optomechanical resonators
Phelps, Gregory; Meystre, Pierre
2011-06-01
We present a theoretical analysis of the effects of laser phase noise on the sideband cooling of opto-mechanical oscillators, demonstrating how it limits the minimum occupation number of the phonon mode being cooled and how it modifies optical cooling rate and mechanical frequency shift of the mechanical element. We also comment on the effects of laser phase noise on coherent oscillations of the mechanical element in the blue detuned regime and on the back-action evasion detection method where an additional drive is used to prevent heating of one quadrature of motion of the oscillator.
International Nuclear Information System (INIS)
The dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature is investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti, for the conditions of strong electron-phonon nonequilibrium. These conditions are characteristic of metal targets subjected to energetic ion bombardment or short-pulse laser irradiation. Computational analysis based on first-principles electronic structure calculations of the electron density of states predicts large deviations (up to an order of magnitude) from the commonly used approximations of linear temperature dependence of the electron heat capacity and a constant electron-phonon coupling. These thermophysical properties are found to be very sensitive to details of the electronic structure of the material. The strength of the electron-phonon coupling can either increase (Al, Au, Ag, Cu, and W), decrease (Ni and Pt), or exhibit nonmonotonic changes (Ti) with increasing electron temperature. The electron heat capacity can exhibit either positive (Au, Ag, Cu, and W) or negative (Ni and Pt) deviations from the linear temperature dependence. The large variations of the thermophysical properties, revealed in this work for the range of electron temperatures typically realized in femtosecond laser material processing applications, have important implications for quantitative computational analysis of ultrafast processes associated with laser interaction with metalsiated with laser interaction with metals
Makovetskii, D N
2012-01-01
A problem of self-organized motions in solid-state nonequilibrium media has been studied experimentally using methods of quantum acoustics. Generalized Poincare cross-sections of microwave power spectra (MPS) have been obtained in an optical-wavelengths acoustic laser (paramagnetic phaser) based on ruby crystal. Considerable narrowing of MPS and their autowave-like superslow motion have been observed under conditions of periodical pump modulation beyond the region of the phaser relaxation resonance. Some preliminar experimental results of this work were published in: Solid State Communications, Vol.90, No.8, P.501 (1994). An interpretation of the experimental data see arXiv:1101.0482v1 ; arXiv:cond-mat/0410460v1 ; arXiv:cond-mat/0303188v1 .
Phonons in Twisted Bilayer Graphene
Cocemasov, Alexandr I.; Nika, Denis L.; Balandin, Alexander A.
2013-01-01
We theoretically investigated phonon dispersion in AA-stacked, AB-stacked and twisted bilayer graphene with various rotation angles. The calculations were performed using the Born-von-Karman model for the intra-layer atomic interactions and the Lennard-Jones potential for the inter-layer interactions. It was found that the stacking order affects the out-of-plane acoustic phonon modes the most. The difference in the phonon densities of states in the twisted bilayer graphene a...
Action of a 904-nm diode laser in orthopedics and traumatology: a clinical study on 447 cases
Tam, Giuseppe
2001-10-01
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.
Nanoscale coherent acoustic phonon imaging
Daly, Brian C.; Klein, Julien; Norris, Theodore B.; Pau, Stanley; Tennant, Donald M.; Taylor, Joseph A.; Bower, John E.
2006-02-01
An ultrafast optical pump and probe technique known as picosecond ultrasonics is used to generate and detect coherent acoustic phonon pulses in nanostructured films grown on Si wafers. By detecting the phonons after they have diffracted across a millimeter thick wafer, it is possible to measure the scattered phonons in the acoustic far field. Numerical backpropagation algorithms can then be used in order to reconstruct the object which scattered the acoustic phonon pulses. We describe measurements and simulations of experiments performed on surface and sub-surface nanostructures. Results with ~500 nm image resolution are shown, and plans for improving that resolution by an order of magnitude will be described.
Coherent-phonon vibronic sideband
International Nuclear Information System (INIS)
We present the theory of vibronic sideband spectra due to coherent phonon modes using the conventional model of linear electron-phonon coupling and displaced equilibrium positions of the oscillators in the exited and final electronic states. Unlike in the conventional theory the initial state of the oscillator is taken as a coherent phonon state and not as a thermalized one. Under these conditions we got an exact analytical solution for the lineshape of the vibronic sideband. The sideband is determined by two parameters, the Huang-Rhys parameter S and the coherence parameter ? of the phonon state. For ?=0 the lineshape converts into the standard Pekarian form for T=0
Analysis of the stress raising action of flaws in laser clad deposits
International Nuclear Information System (INIS)
Highlights: ? Laser clad defects are 0D-pores/inclusions, 1D-clad waviness or 2D-planar defects. ? Surface pore of laser clad bar initiates fatigue cracks. ? Side edge surface pores are more critical than in-clad surface pores. ? Smaller notch radius and angle of as-laser clad surface raises stress significantly. ? Planar inner defects grow faster towards surface. - Abstract: Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations
Accelerating piston action and plasma heating in high-energy density laser plasma interactions
Levy, M. C.; Wilks, S. C.; Baring, M. G.
2013-03-01
In the field of high-energy density physics (HEDP), lasers in both the nanosecond and picosecond regimes can drive conditions in the laboratory relevant to a broad range of astrophysical phenomena, including gamma-ray burst afterglows and supernova remnants. In the short-pulse regime, the strong light pressure (>Gbar) associated ultraintense lasers of intensity I > 1018 W/cm2 plays a central role in many HEDP applications. Yet, the behavior of this nonlinear pressure mechanism is not well-understood at late time in the laser-plasma interaction. In this paper, a more realistic treatment of the laser pressure 'hole boring' process is developed through analytical modeling and particle-in-cell simulations. A simple Liouville code capturing the phase space evolution of ponderomotively-driven ions is employed to distill effects related to plasma heating and ion bulk acceleration. Taking into account these effects, our results show that the evolution of the laser-target system encompasses ponderomotive expansion, equipartition, and quasi-isothermal expansion epochs. These results have implications for light piston-driven ion acceleration scenarios, and astrophysical applications where the efficiencies of converting incident Poynting flux into bulk plasma flow and plasma heat are key unknown parameters.
Studies on laser action from polymeric matrices doped with coumarin 503
Costela, A.; García-Moreno, I.; Barroso, J.; Sastre, R.
1998-08-01
The lasing properties of coumarin 503 (C503) dissolved in pure poly(methyl methacrylate) homopolymer and in copolymers of methyl methacrylate with 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and styrene have been investigated. The laser samples were transversely pumped at 337 nm with 1.2-mJ pulses from a nitrogen laser. The influence on the C503 laser performance of parameters such as dye concentration, viscoelasticity of the matrix, and degree of crosslinking of the polymeric chains were examined. Lasing efficiencies of up to 19% and lifetimes (defined as a 90% efficiency drop) of 2600 pulses at 2 Hz repetition rate were demonstrated. Conditions that could result in an increase of dye photostability by the addition of 1,4-diazobicyclo[2.2.2]octane or cyclooctatetraene are discussed.
Spectroscopy and laser action of Cr3+, Nd3+ codoped crystal with Ca-Gallogermanate structure
Azkargorta, J.; Iparraguirre, I.; Balda, R.; Ferna?ndez, J.; Kaminskii, A.
1994-01-01
Energy transfer between Cr3+ and Nd3+ ions has been investigated in the 4.2K-300K temperature range by using steady-state and time-resolved laser spectroscopy. Nonradiative energy transfer has been studied from the time-resolved emission spectra and the donor fluorescence decays. The transfer efficiency was calculated as a function of temperature by using the Cr3+ lifetimes of the single doped and codoped samples. Laser experiments were carried out in a diffusive cavity by pumping with Xenon ...
International Nuclear Information System (INIS)
A new approach is proposed for correcting the eye refraction by controlled variation of the mechanical properties of the sclera and cornea upon nondestructive laser heating. Experimental ex vivo studies of rabbit and pig eyes show that laser-induced local denaturation of the sclera changes the refraction of the cornea by 3 diopters on the average, and the subsequent nondestructive irradiation of the cornea increases its plasticity, which leads to a further increase in its radius of curvature and a decrease in refraction down to 7 diopters.
International Nuclear Information System (INIS)
Formation of a liquid phase with a transition to a homogeneous amorphous state under the surface layer solidification is detected under picosecond laser pulse effect on the microcrystalline graphite. A periodic surface structure is produced in the heating region with the period of the order of the length of the heating pulse wave, its strokes following the direction of this pulse polarization. Study of the probing laser pulse reflection kinetics has shown, that the typical time of liquid phase and solidification life makes up ? 10-10 s
THz electromagnetic emission by coherent infrared-active phonons
Dekorsy, Thomas; Auer, Holger; Bakker, Huib J.; Roskos, Hartmut G.; Kurz, Heinrich
1996-01-01
Coherent phonons are excited in single-crystal tellurium by above-band-gap excitation with femtosecond laser pulses. Coherent infrared-active lattice vibrations give rise to the emission of electromagnetic waves at the phonon frequency. The excitation mechanism is based on the ultrafast buildup of a photo-Dember field and the coupling of a polar lattice mode to this field. The dynamics of the Dember field is obtained from a numerical simulation of the electron-hole plasma dynamics close to th...
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)
Energy Technology Data Exchange (ETDEWEB)
Estreicher, S. K., E-mail: Stefan.Estreicher@ttu.edu; Gibbons, T. M.; Kang, By.; Bebek, M. B. [Physics Department, Texas Tech University, Lubbock, Texas 79409-1051 (United States)
2014-01-07
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.
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
International Nuclear Information System (INIS)
Trigonal Na3Li(MoO4)2?6H2O was found to be an attractive, simultaneously ?(2)- and ?(3)-active nonlinear optical crystal. We investigated its basic optical properties and observed several nonlinear effects, namely many-phonon SRS, almost two-octave Stokes and anti-Stokes lasing combs, SHG, THG, and efficient cascaded (?(3) ? ?(2))-generation, as well as SRS arising from nonlinear interaction of two different ?(3)-active vibrations. All recorded nonlinear-lasing components were identified and attributed to SRS-promoting vibration modes. A short review of nonlinear-laser molybdates is given
Acoustic Metamaterials and Phononic Crystals
2013-01-01
This comprehensive book presents all aspects of acoustic metamaterials and phononic crystals. The emphasis is on acoustic wave propagation phenomena at interfaces such as refraction, especially unusual refractive properties and negative refraction. A thorough discussion of the mechanisms leading to such refractive phenomena includes local resonances in metamaterials and scattering in phononic crystals.
New superconducting scanning phonon spectroscopy
International Nuclear Information System (INIS)
A new phonon-detection technique utilizing superconducting tunnel junctions is introduced. In this technique the high-frequency phonons emitted from a generator are detected by a superconducting sensor placed apart from it by a thin layer (< or approx. =100 ?m) of liquid helium. The sensor is either a single-tunnel junction or a double-tunnel junction. The phonon signal increases nonlinearly with an increase of generator current. In the case that a double-tunnel-junction sensor is used, the information on the energy spectrum of the transmitted phonons is obtained by varying the detectable phonon cutoff energy by quasiparticle injection. For the phonons emitted from a superconducting tunnel junction, a clear change at the phonon cutoff energy equal to the generator gap is observed. The spatial scanning spectroscopy with a spatial resolution of 20 ?m is performed by moving a sensor relative to the generator. The observed phonon spatial distribution has a periodically modulated structure for the superconducting tunnel generator accompanying a diffusive instability. The limits and applications of this technique are also discussed
Theory of phonon dynamics in an ion trap
Dutta, T; Sengupta, K
2015-01-01
We develop a theory to address the non-equilibrium dynamics of phonons in a one-dimensional trapped ion system. We elaborate our earlier results obtained in Phys. Rev. Lett. {\\bf 111}, 170406 (2013) to chart out the mechanism of dynamics-induced cooling and entanglement generation between phonons in these systems when subjected to a linear ramp protocol inducing site-specific tuning of on-site interactions between the phonons. We further extend these studies to non-linear ramps and periodic drive protocols and identify the optimal ramp protocol for minimal cooling and entanglement generation time. We qualitatively address the effect of noise arising out of fluctuation of the intensity of the laser used to generate entanglement and provide a detailed discussion of a realistic experimental setup which may serve as a test bed for our theory.
Strong coupling and laser action of ladder-type oligo(p-phenylene)s in a microcavity.
Höfner, Michael; Kobin, Björn; Hecht, Stefan; Henneberger, Fritz
2014-12-01
We investigate the coupling of ladder-type quarterphenyl to the photon modes of a dielectric ZrOx /SiOx microcavity at ultraviolet wavelengths. For a relatively long cavity (?10 ?m) with high-reflectivity mirrors (0.998), optically pumped laser action is demonstrated in the weak-coupling regime. We observe single-mode operation with a threshold of 0.4 mJ?cm(-2) . Strong coupling is achieved by using a short ?/2 cavity. We find pronounced anti-crossing features of the molecular (0,0) and (0,1) vibronic transitions and the cavity mode in angle-dependent reflectivity measurements providing Rabi splittings of (90±10) meV. All these features occur spectrally resonant to the exciton transition of ZnO demonstrating the potential of ladder-type oligo(p-phenylene)s for the construction of inorganic/organic hybrid microcavities. PMID:25234768
Nemtsev, I Z; Luzhnikov, E A; Lapshin, V P; Gol'dfarb, Iu S; Badalian, A V
1997-01-01
Extracorporeal exposure to LG-79 He-Ne laser of 12 mWt power was used in 57 patients hospitalized at the intoxication reanimation department with acute poisonings with psychotropic drugs. The clinical result was a decrease of the incidence of pneumonia in the patients with x-ray signs of venous congestion from 52% among those administered to physiochemotherapy to 24% after this treatment modality. Laser hemotherapy brought about a temporary normalization of the erythrocyte membrane permeability, which was changed biophysically by means of a diffractometer. Red cell aggregation was approximating the norm, decreasing by 20%, and platelet aggregation decreased by 17%. Analysis of the results brought as to a conclusion that He-Ne laser exposure is an effective source of singlet stimulation of molecular O2 evenly dissolved in the blood, which causes resonance oscillations of water difields. This leads to membrane depolarization, which is probably responsible for purification of polarized membranes from toxic agents fixed by them. PMID:9382223
Correlated phonons and the Tc-dependent dynamical phonon anomalies
International Nuclear Information System (INIS)
Anomalously large low-temperature phonon anharmonicities can lead to static as well as dynamical changes in the low-temperature properties of the electron-phonon system. We focus our attention on the dynamically generated low-temperature correlations in an interacting electron-phonon system using a self-consistent dynamical approach in the intermediate coupling range. The polaron correlations are produced by the charge-density fluctuations which are generated dynamically by the electron-phonon coupling. Conversely, the latter is influenced in the presence of the former. The purpose of this work is to examine the dynamics of this dual mechanism between the two using the illustrative Froehlich model. In particular, the influence of the low-temperature phonon dynamics on the superconducting properties in the intermediate coupling range is investigated. The influence on the Holstein reduction factor as well as the enhancement in the zero-point fluctuations and in the electron-phonon coupling are calculated numerically. We also examine these effects in the presence of superconductivity. Within this model, the contribution of the electron-phonon interaction as one of the important elements in the mechanisms of superconductivity can reach values as high as 15 endash 20% of the characteristic scale of the lattice vibrational energy. The second motivation of this work is to understand the nature of the Tc-dependent temperature anomalies observed in the Debye-Waller 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)
Phonon Linewidths and Electron Phonon Coupling in Nanotubes
Lazzeri, M; Mauri, F; Ferrari, A C; Robertson, J; Lazzeri, Michele; Mauri, Francesco
2006-01-01
We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G- peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G- linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G- peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G+ and G- peaks to TO (tangential) and LO (axial) modes.
Spectral self-action of THz emission from ionizing two-color laser pulses in gases
Cabrera-Granado, Eduardo; Chen, Yxing; Babushkin, Ihar; Bergé, Luc; Skupin, Stefan
2015-02-01
The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and numerical simulations in 1D, 2D and 3D geometries taking into account propagation effects of both pump and THz fields. We show that produced THz signals interact with free electron trajectories and thus significantly influence further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action contributes to the observed strong spectral broadening of the generated THz field. We show that diffraction of the generated THz radiation is the limiting factor for the co-propagating low frequency amplitudes and thus for the self-action mechanism in 2D and 3D geometries.
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.
Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well
Onishchenko, E E; Zajtsev, V V
2001-01-01
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
Spectral self-action of THz emission from ionizing two-color laser pulses in gases
Cabrera-Granado, Eduardo; Babushkin, Ihar; Bergé, Luc; Skupin, Stefan
2014-01-01
The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and finite-difference-time-domain simulations in 1D and 2D geometries. We show that produced THz signals interact with free electron trajectories and thus influence significantly further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action plays a key role in the observed strong spectral broadening of the generated THz field. Diffraction limits the achievable THz bandwidth by efficiently depleting the low frequency amplitudes in the propagating field.
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
Jet formation in spallation of metal film from substrate under action of femtosecond laser pulse
Inogamov, N. A.; Zhakhovskii, V. V.; Khokhlov, V. A.
2015-01-01
It is well known that during ablation by an ultrashort laser pulse, the main contribution to ablation of the substance is determined not by evaporation, but by the thermomechanical spallation of the substance. For identical metals and pulse parameters, the type of spallation is determined by film thickness d f . An important gauge is metal heating depth d T at the two-temperature stage, at which electron temperature is higher than ion temperature. We compare cases with d f F m, gold film deposited on the glass target acquires a cupola-shaped blister with a miniature frozen nanojet in the form of a tip on the circular top of the cupola ( F abs and F m are the absorbed energy and the melting threshold of the film per unit surface area of the film). A new physical mechanism leading to the formation of the nanojet is proposed.
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
Sanders, G. D.; Stanton, C. J.; Kim, Chang-sub
2001-01-01
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 ...
Coherent Longitudinal Acoustic Phonon Approaching THz Frequency in Multilayer Molybdenum Disulphide
Shaofeng Ge; Xuefeng Liu; Xiaofen Qiao; Qinsheng Wang; Zhen Xu; Jun Qiu; Ping-Heng Tan; Jimin Zhao; Dong Sun
2014-01-01
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 di...
Phonon Raman scattering in superconductors
International Nuclear Information System (INIS)
If a superconductor has a Raman-active phonon mode of low frequency (larger but of the order of magnitude of the superconducting energy gap 2?), we show that electron-phonon coupling leads to a complex bound excitation, also Raman active, with a discrete frequency lower than 2? and with intensity which can be appreciable. We propose that these are the lines found by Sooryakumar and Klein at approximately the energy-gap frequency in superconducting 2H-NbSe2
PHONON DISPERSIONS IN CALCIUM TUNGSTATE
Krishnamurthy, N.; Kesavasamy, K.
1981-01-01
External mode formalism is applied to study phonons in CaWO4. The effective ionic charges of the Coulomb interactions and the effective ionic radii of Born-Mayer shortrange potential are determined so that the dynamical equilibrium conditions are satisfied and lattice energy is of right order in comparison with other complex ionic crystals. The calculated phonon dispersion relations along [001] and [110] directions are in reasonable agreement with the neutron data. The generalised LST relatio...
Phononics in Low-Dimensions: Engineering Phonons in Nanostructures and Graphene
Balandina, Alexander A.; Nika, Denis L.
2012-01-01
Phonons - quanta of crystal lattice vibrations - reveal themselves in all electrical, thermal and optical phenomena in materials. Nanostructures open exciting opportunities for tuning the phonon energy spectrum and related properties of materials for specific applications. The possibilities for controlled modification of the phonon transport and phonon interactions - referred to as phonon engineering or phononics - increase even further with the advent of graphene and two-di...
New Mid-IR Lasers Based on Rare-Earth-Doped Sulfide and Chloride Materials
International Nuclear Information System (INIS)
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 ? 4 (micro)m. Traditional oxide and fluoride hosts have effective phonon energies in the neighborhood of 1000 cm-1 and 500 cm-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, CaGa2S4 and KPb2Cl5. The CaGa2S4:Dy3+ laser operating at 4.3 (micro)m represents the first sulfide laser operating beyond 2 (micro)m. The KPb2Cl5:Dy3+ 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 CaGa2S4:Dy3+ at 2.4 (micro)m, CaGa2S4:Dy3+ at 1.4 (micro)m, and KPb2Cl5:Nd3+ 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.ios, 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 CaGa2S4 and KPb2Cl5, direct generation of mid-IR laser radiation in a solid-state host has been demonstrated. In KPb2Cl5, predictions indicate that laser operation to 9 (micro)m may be possible, a wavelength previously considered unreachable in a room-temperature, solid-state host
New Mid-IR Lasers Based on Rare-Earth-Doped Sulfide and Chloride Materials
Energy Technology Data Exchange (ETDEWEB)
Nostrand, M
2000-09-01
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.
Energy Technology Data Exchange (ETDEWEB)
Leal, C.E. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Sensores e Materiais]|[Universidade do Estado, Rio de Janeiro, RJ (Brazil); Cunha Lima, I.C. da [Universidade do Estado, Rio de Janeiro, RJ (Brazil)]|[Universidade Sao Francisco, Itatiba, SP (Brazil). Faculdade de Engenharia; Baldan, M.R. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Sensores e Materiais; Troper, A. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]|[Universidade do Estado, Rio de Janeiro, RJ (Brazil)
1996-03-01
A calculation of the electron-LA phonon scattering contribution for an electron gas under the action of strong magnetic field is performed using memory function formalism. We take into account, through vertex corrections in the diffusive pole approximation, the combined effect due to the presence of impurities in the material, which renormalizes the polarization function. The renormalized electron-phonon interaction is discussed and we calculate, in the low temperature regime, the dependence of the phonon channel resistivity in terms of the strength of magnetic field. (author). 7 refs.
International Nuclear Information System (INIS)
A calculation of the electron-LA phonon scattering contribution for an electron gas under the action of strong magnetic field is performed using memory function formalism. We take into account, through vertex corrections in the diffusive pole approximation, the combined effect due to the presence of impurities in the material, which renormalizes the polarization function. The renormalized electron-phonon interaction is discussed and we calculate, in the low temperature regime, the dependence of the phonon channel resistivity in terms of the strength of magnetic field. (author). 7 refs
Energy Technology Data Exchange (ETDEWEB)
Gilman, J.J. [Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering
1996-12-31
In crystals (and/or glasses) with localized sp{sup 3} or spd-bonding orbitals, dislocations have very low mobilities, making the crystals very hard. Classical Peierls-Nabarro theory does not account for the low mobility. The breaking of spin-pair bonds which creates internal free-radicals must be considered. Therefore, a theory based on quantum mechanics has been proposed (Science, 261, 1436 (1993)). It has been applied successfully to diamond, Si, Ge, SiC, and with a modification to TiC and WC. It has recently been extended to account for the temperature independence of the hardness of silicon at low temperatures together with strong softening at temperatures above the Debye temperature. It is quantitatively consistent with the behaviors of the Group 4 elements (C, Si, Ge, Sn) when their Debye temperatures are used as normalizing factors; and appears to be consistent with data for TiC if an Einstein temperature for carbon is used. Since the Debye temperature marks the approximate point at which phonons of atomic wavelengths become excited (as contrasted with collective acoustic waves), this confirms the idea that the process which limits dislocation mobility is localized to atomic dimensions (sharp kinks).
DEFF Research Database (Denmark)
Nysteen, Anders; Nielsen, Per Kær
2012-01-01
It is well-known that decoherence deteriorates the efficiency of cavity QED systems containing quantum dots (QDs), and that a major contribution stems from the coupling between the electrical carriers in the QD and acoustic phonons [1]. Employing a recently published model [2], we demonstrate how a proper matching between the electronic wavefuntion and the phonon-induced energy shift of valence and conduction band may be exploited to change the decoherence and decay properties of the QD by suppressing the phonon-induced processes. This effect may be addressed in a photoluminescence experiment, where a CW laser excites a two-level QD which interacts with a non-Markovian reservoir of acoustical phonons, see Fig. 1a. We assume a simple harmonic confinement of the electronic carriers, resulting in Gaussian wavefunctions, (r) / exp[?r2/(2W2 )], withWe (Wg) being the width of the electron (hole) wavefunction. In Fig. 1b we plot the stationary QD population vs. the laser frequency. We observe that for non-equal electron and hole wavefunction, the phonon-induced effect on the population surprisingly is fully suppressed at specific detunings. In a coupled QD–cavity system [2, 3], see Fig. 2a, this effect causes the QD lifetime to be unaffected by phonon processes at specific QD-cavity detunings. Furthermore, as shown in Fig. 2b, a proper choice of the QD wavefunction minimizes the phonon-induced pure dephasing rate, both in terms of the short-time magnitude and the long-time constant value. Furthermore we show, that even for realistic QDs, where We and Wg are determined by the QD shape and material composition, a significant suppression of phonon-induced processes is possible. Thus, more efficient quantum systems may be obtained if the QD wavefunctions are properly matched with the phononic properties of the surroundings.
Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang
2015-01-01
A new approach is proposed to light up band-edge stimulated emission arising from a semiconductor with dipole-forbidden band-gap transition. To illustrate our working principle, here we demonstrate the feasibility on the composite of SnO2 nanowires (NWs) and chicken albumen. SnO2 NWs, which merely emit visible defect emission, are observed to generate a strong ultraviolet fluorescence centered at 387?nm assisted by chicken albumen at room temperature. In addition, a stunning laser action is further discovered in the albumen/SnO2 NWs composite system. The underlying mechanism is interpreted in terms of the fluorescence resonance energy transfer (FRET) from the chicken albumen protein to SnO2 NWs. More importantly, the giant oscillator strength of shallow defect states, which is served orders of magnitude larger than that of the free exciton, plays a decisive role. Our approach therefore shows that bio-materials exhibit a great potential in applications for novel light emitters, which may open up a new avenue for the development of bio-inspired optoelectronic devices. PMID:25758749
Phononics in low-dimensional materials
Directory of Open Access Journals (Sweden)
Alexander A. Balandin
2012-06-01
Full Text Available Phonons – quanta of crystal lattice vibrations – reveal themselves in all electrical, thermal, and optical phenomena in materials. Nanostructures open exciting opportunities for tuning the phonon energy spectrum and related material properties for specific applications. The possibilities for controlled modification of the phonon interactions and transport – referred to as phonon engineering or phononics – increased even further with the advent of graphene and two-dimensional van der Waals materials. We describe methods for tuning the phonon spectrum and engineering the thermal properties of the low-dimensional materials via ribbon edges, grain boundaries, isotope composition, defect concentration, and atomic-plane orientation.
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
Phonons do not harm some ion-trap quantum simulators
Wang, C.-C. Joseph; Freericks, James
2010-03-01
Ion-trap quantum simulators can be used to simulate simple spin Hamiltonians. In this talk, we focus on applying driving laser fields in the transverse direction, detuned from phonon resonances and in the Lamb-Dicke limit. The interaction of the light with the hyperfine states of the ion can cause the system to feel a spin-dependent force, which, in turn, results in an effective spin-spin coupling of the system, one of the simplest spin Hamiltonians to simulate is the transverse field Ising model. For this Hamiltonian, one can show, via an explicit factorization of the evolution operator for the spin and the phonon degrees of freedom, that the phonons completely decouple from the problem and do not affect the time-dependent dynamics of the spins, even if one moves near resonance with a normal mode of the ion chain. This implies that one need not worry about any decoherence effects arising from the phonons, and it implies that the spin Hamiltonian simulation is less susceptible to noise than previously thought. We also discuss how general these results are when one considers other spin Hamiltonians or when one goes beyond the Lamb-Dicke limit.
Coherent LO phonons in optically excited double quantum wells
Energy Technology Data Exchange (ETDEWEB)
Papenkort, Thomas; Kuhn, Tilmann [Institut fuer Festkoerpertheorie, Universitaet Muenster (Germany); Axt, Vollrath Martin [Institut fuer Theoretische Physik III, Universitaet Bayreuth (Germany)
2009-07-01
In a double quantum well with a sufficiently thin barrier between the wells the two wells couple, i.e. the subbands are no longer localized in one of the wells but extend over both. By optically exciting such a double well under the influence of a static electric field an electron density can be obtained which is localized in one of the two wells. Because of tunneling the electrons oscillate between the two wells with the frequency of the subband splitting. This causes an oscillating polarization which couples strongly to a polar lattice, thereby creating coherent LO phonons. We present numerical calculations of this efficient phonon generation process in an AlGaAs-GaAs double quantum well. Using a quantum kinetic approach we calculate both the dynamics of the electronic subsystem driven by a semi-classical laser field and of the phonons created via the Froehlich interaction. We study the coherent amplitude and the fluctuations of the generated phonon states. They depend on the subband structure, which is defined by the dimensions of the double quantum well and the strength of the electric field, as well as on the exact excitation conditions.
Structure of the phonon vacuum state
Mishev, S
2012-01-01
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.
Phonon spectra in quantum wires
Directory of Open Access Journals (Sweden)
Ili? Dušan
2007-01-01
Full Text Available Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most important feature is that, beside the allowed energy zones (which are continuous as in the bulk structure, zones of forbidden states appear. Different values of the boundary parameters lead to the appearance of lower and upper energy gaps, or dispersion branches spreading out of the bulk energy zone. The spectra of phonons in corresponding unbound structures were correlated to those in bound structures.
Nanoscale phononic interconnects in THz frequencies.
Sgouros, Aris P; Neupane, Mahesh R; Sigalas, M M; Aravantinos-Zafiris, N; Lake, Roger K
2014-11-14
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
High-energy phonon creation from cold phonons in pulses of different length in He II
International Nuclear Information System (INIS)
We have carried out a theoretical investigation of the experimentally observed phenomenon that long-lived high-energy (h) phonons are generated by a moving cloud of low-energy (l) phonons. The h phonons are created from the l phonons by four phonon processes (4pp) and they are lost from the trailing edge of the l phonon cloud, because they have a lower velocity than the l phonons, and form the h phonon cloud. We obtain a set of equations which completely describe these phenomenon. The solution of these equations accounts for the high efficiency of the conversion process: a major part of the energy in the l phonons can be converted to h phonons within the propagation time of the pulse (-4 s). In short pulses (-7 s) the h phonons escape as soon they are created, but in long pulses the h phonon density increases within the l cloud. It is shown that in long phonon pulses there can be a suprathermal number of h phonons within the l cloud. The theory describes the cooling of pulses of different length due to energy being transformed into h phonons. It also accounts well for the important characteristics of h phonon generation which is an unusual example of energy transferring from low-energy to high-energy states
A study of non-equilibrium phonons in GaAs/AlAs quantum wells
Energy Technology Data Exchange (ETDEWEB)
Su, Zhenpeng
1996-11-01
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.
Phonon dynamics of americium telluride
Arya, B. S.; Aynyas, Mahendra; Ahirwar, Ashok K.; Sanyal, S. P.
2013-06-01
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.
Introduction to phonons and electrons
Lou, Liang-fu
2003-01-01
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
Electron-phonon coupling deduced from phonon line shapes
International Nuclear Information System (INIS)
We investigate the Fano-type line shape of the Ba mode of Y1-xCaxBa2Cu3O6+y films observed in Raman spectra with A1g symmetry. The line shape is described with an extended Fano formula that allows us to obtain the bare phonon parameters and the self-energy effects based on a phenomenological description of the real and imaginary part of the low-energy electronic response. It turns out that the phonon intensity originates almost entirely from a coupling to this electronic response with negligible contributions from interband (high-energy) electronic excitations. In the normal state we obtain a measure of the electron-phonon coupling via the mass-enhancement factor ?. We find anti ? = 6.8 ± 0.5% around optimum doping and only weak changes of the self-energy in the superconducting state. With increased disorder at the Ba site we find a decreased intensity of the Ba mode which we can relate to a decreased electron-phonon coupling. (orig.)
Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene
Araujo, Paulo; Mafra, Daniela; Sato, Kentaro; Saito, Richiiro; Kong, Jing; Dresselhaus, Mildred
2013-03-01
In this work, we present a step towards further understanding of the bilayer graphene (2LG) interlayer (IL)-related phonon combination modes and overtones as well as their phonon self-energy renormalizations by using both gate-modulated and laser-energy dependent inelastic scattering spectroscopy. We show that although the IL interactions are weak, their respective phonon renormalization response is significant. Particularly special, the IL interactions are mediated by Van der Waals forces and are fundamental for understanding low-energy phenomena such as transport and infrared optics. Our approach opens up a new route to understanding fundamental properties of IL interactions which can be extended to any graphene-like material, such as MoS2, WSe2, oxides and hydroxides. Furthermore, we report a previously elusive crossing between IL-related phonon combination modes in 2LG, which might have important technological applications.
Coherent Longitudinal Acoustic Phonon Approaching THz Frequency in Multilayer Molybdenum Disulphide
Ge, Shaofeng; Liu, Xuefeng; Qiao, Xiaofen; Wang, Qinsheng; Xu, Zhen; Qiu, Jun; Tan, Ping-Heng; Zhao, Jimin; Sun, Dong
2014-07-01
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*103 m/s in MoS2. The generation mechanisms of the coherent acoustic phonon are also discussed through pump power dependent measurement.
Phononic Frequency Combs through Nonlinear Resonances
Cao, L. S.; Qi, D. X.; Peng, R. W.; Wang, Mu; Schmelcher, P.
2014-02-01
We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems.
Li, Chen; Delaire, Olivier; Chen, Xin; Singh, David; May, Andrew; Ma, Jie; McGuire, Michael; Ehlers, Georg; Christianson, Andrew; Huq, Ashfia
2013-03-01
Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rocksalt tellurides in general.
The graphene phonon dispersion with C{sup 12} and C{sup 13} isotopes
Energy Technology Data Exchange (ETDEWEB)
Whiteway, Eric; Bernard, Simon; Yu, Victor; Hilke, Michael [Department of Physics, McGill University, Montréal H3A 2T8 (Canada); Austing, D. Guy [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)
2013-12-04
Using very uniform large scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D+D' peak corresponding to a double phonon process involving both an inter- and intra-valley phonon. In order to both eliminate substrate effects and to probe large areas, we undertook to study Raman scattering for large scale chemical vapor deposition (CVD) grown graphene using two different isotopes (C12 and C13) so that we can effectively exclude and subtract the substrate contributions, since a heavier mass downshifts only the vibrational properties, while keeping all other properties the same.
The graphene phonon dispersion with C12 and C13 isotopes
International Nuclear Information System (INIS)
Using very uniform large scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D+D' peak corresponding to a double phonon process involving both an inter- and intra-valley phonon. In order to both eliminate substrate effects and to probe large areas, we undertook to study Raman scattering for large scale chemical vapor deposition (CVD) grown graphene using two different isotopes (C12 and C13) so that we can effectively exclude and subtract the substrate contributions, since a heavier mass downshifts only the vibrational properties, while keeping all other properties the same
Heralded Single-Phonon Preparation, Storage, and Readout in Cavity Optomechanics
Galland, Christophe; Sangouard, Nicolas; Piro, Nicolas; Gisin, Nicolas; Kippenberg, Tobias J.
2014-04-01
We show how to use the radiation pressure optomechanical coupling between a mechanical oscillator and an optical cavity field to generate in a heralded way a single quantum of mechanical motion (a Fock state). Starting with the oscillator close to its ground state, a laser pumping the upper motional sideband produces correlated photon-phonon pairs via optomechanical parametric down-conversion. Subsequent detection of a single scattered Stokes photon projects the macroscopic oscillator into a single-phonon Fock state. The nonclassical nature of this mechanical state can be demonstrated by applying a readout laser on the lower sideband to map the phononic state to a photonic mode and performing an autocorrelation measurement. Our approach proves the relevance of cavity optomechanics as an enabling quantum technology.
Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate
Energy Technology Data Exchange (ETDEWEB)
Nunes, O. A. C., E-mail: oacn@unb.br [Institute of Physics, University of Brasilia, Brasilia, 70910-900 DF (Brazil)
2014-06-21
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 R{sup PA,DA} scales with T{sub BG}{sup S?1} (S=PA,DA), T{sub BG}{sup S} being the Block?Gru{sup ¨}neisen temperature. In the high-T Block?Gru{sup ¨}neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio R{sup PA}/R{sup DA} scales with ?1/?(n), n being the carrier concentration. We found that only for carrier concentration n?10{sup 10}cm{sup ?2}, R{sup PA}/R{sup DA}>1. In the low-T Block?Gru{sup ¨}neisen regime, and for n=10{sup 10}cm{sup ?2}, the ratio R{sup PA}/R{sup DA} scales with T{sub BG}{sup DA}/T{sub BG}{sup PA}?7.5 and R{sup PA}/R{sup DA}>1. In this regime, PA phonon dominates the electron scattering and R{sup PA}/R{sup DA}<1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.
Energy Technology Data Exchange (ETDEWEB)
Sardar, D.K.; Yow, R.M.; Sayka, A. [Div. of Earth and Physical Sciences, The Univ. of Texas at San Antonio, San Antonio, TX (United States)
2001-02-01
The inter-Stark energy levels due to crystal-field splittings within the {sup 1}D{sub 2} {yields} {sup 3}H{sub 4} intermanifold transition of Pr{sup 3+} in calcium fluorapatite, Ca{sub 5}(PO{sub 4}){sub 3}F, have been characterized using the fluorescence spectrum at 10 K. The temperature effects of the spectral width and position of the 623.1 (R{sub 2} {yields} X{sub 4}) nm line within the {sup 1}D{sub 2} {yields} {sup 3}H{sub 4} intermanifold of Pr{sup 3+} in this host have also been investigated. The linewidth of this transition was found to increase with increasing temperature. The emission line shifted toward the shorter wavelength (blue shift). The experimental result of the temperature-dependent widths of this emission line is explained using the phonon-ion interaction theory based on the Debye model for phonons in crystalline solids. (orig.)
Phonon-phonon interaction in gadolinium-gallium garnet crystals
International Nuclear Information System (INIS)
Propagation velocity and temperature dependence of the sound wave attenuation coefficient in gadolinium-gallium garnet crystals are measured. The measurements are carried out in the frequency range 0.4 to 2.0 GHz and temperature range 77 to 293 K. On the basis of the measurements Debye temperature, specific heat of crystal as a function of temperature, and the temperature dependence of thermal phonon lifetime are determined. For calculation it is assumed that the examined material is isotropic. (author)
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
Phonon anharmonicity of iron monosilicide
Povzner, A. A.; Filanovich, A. N.
2015-01-01
A self-consistent thermodynamic model of the crystal lattice of FeSi is developed. In the framework of this model calculations of the heat capacity, coefficient of thermal expansion and bulk modulus of FeSi in a wide temperature range are carried out. On the basis of comparison with the experimental data, electronic contribution to the heat capacity of FeSi is obtained, the temperature dependence of which is caused by the insulator to metal transition, accompanied by disappearance of the energy gap in the electronic spectrum. We have found strong phonon anharmonicity of FeSi, which is manifested in substantial reduction of the Debye temperature and Gruneisen parameter with increasing temperature. The obtained values for the Gruneisen parameter of the crystal lattice of FeSi correlate with the estimations of the Gruneisen parameters for individual branches of the phonon spectrum of FeSi measured in neutron and synchrotron experiments.
Quasiparticle-phonon nuclear model
International Nuclear Information System (INIS)
Basic assumption of the quasiparticle-phonon nuclear model (QPNM) and its two applications are presened. The introduction of tensor forces in the QPNM is described and the results of studying the fragmentation of charge-exchange resonances in spherical nuclei are given. The low-lying Ksup(?)=0sup(+), 2+, 3+ and 4+ states in doubly even deformed nuclei are described. The results calculated in the QPNM are compared with those obtained in the interacting boson model
Control of Coherent Acoustic Phonons
Ozgur, Umit; Lee, Chang-won; Everitt, Henry O.
2000-01-01
Using sub-picosecond optical pump-probe techniques, coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were generated and controlled in an InGaN multiple quantum well structure. A one-pump, one-probe differential transmission technique revealed that carriers injected near the barrier band edge were quickly captured into the quantum wells and generated strong coherent ZFLAP oscillations. Two-pump differential transmission was used to generate and control coherent ZFL...
Phonons from neutron powder diffraction
Dimitrov, D. A.; Louca, D.; Ro?der, H.
1998-01-01
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...
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.)
Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs
Basak, Amlan Kumar; Petek, Hrvoje; Ishioka, Kunie; Thatcher, Evan M.; Stanton, Christopher J.
2015-03-01
We present a joint experimental theoretical study of the coupling of coherent phonons in bulk GaAs with a nonequilibrium electron-hole plasma following photoexcitation at the E1 gap by ultrafast laser pulses. In contrast to prior coherent phonon experiments where photoexcitation across the E0 gap generated electrons in the ? valley, for the E1 gap excitation, the majority of the electrons are generated in the satellite L valleys. This leads to a drastically different situation from the previous studies because the damping of electrons is now faster due to the higher scattering rates in the L valley, and, in addition, the diffusion of carriers has a significant effect on the plasma response due to the shorter optical absorption depth of the pump-probe light. Reflectivity measurements show coherent phonon-plasmon oscillations, whose frequencies lie between the transverse and longitudinal optical phonon frequencies due to the heavy damping and change with time due to the diffusion of the plasma. We analyze the experimental data with a theoretical model that describes the time and density-dependent coupling of the coherent phonon and the electron-hole plasma as the photoexcited carriers diffuse into the sample on a subpicosecond time scale. The calculated phonon-plasmon dynamics qualitatively reproduce the experimentally observed time-dependent frequency.
Interconversion of photon-phonon in a silica optomechanical microresonator
Dong, ChunHua; Shen, Zhen; Zou, ChangLing; Guo, GuangCan
2015-03-01
In an optomechanical resonator, the optical and mechanical excitations can be coherently converted, which induces a transparency window for a weak probe laser beam. Here, we report an experimental study of transient optomechanically induced transparency (OMIT) using the silica microsphere with the breathing modes. The transient OMIT behavior obtained are in good agreement with theoretical calculations. In addition, the coherent interconversion between optical and mechanical excitations that can be used for light storage and readout has also been studied here. Our experimental results indicate that the light storage is closely related to the process of OMIT, and the photon-phonon conversion can be further applied to optical wavelength or optical mode conversion.
Phononic Frequency Combs via Nonlinear Resonances
Cao, Lushuai; Peng, Ruwen; Wang, Mu; Schmelcher, Peter
2013-01-01
We study the analogue of optical frequency combs in driven nonlinear phononic systems, and present a new generation mechanism for phononic frequency combs via nonlinear resonances. The nonlinear resonance refers to the simultaneous excitation of a set of phonon modes by the external driving, and thereby generated frequency combs are characterized by an array of equidistant spectral lines in the spectrum of each nonlinearly excited phonon mode. Frequency combs via nonlinear resonance of different orders are investigated, and particularly we reveal the possibility for correlation tailoring in higher order cases. The investigation contributes to potential applications in various nonlinear acoustic processes, such as harvesting phonons and generating phonon entanglements, and can also be generalized to other nonlinear systems.
Phonons in Yukawa lattices and liquids
International Nuclear Information System (INIS)
The understanding of the theoretical structure of phonon dispersion in Yukawa lattices and the relationship between these perfect lattice phonons on the one hand, and the excitations in the disordered and liquid states on the other, is an important issue in analysing experimental and simulation results on plasma crystals. As the first step in this programme, we have numerically calculated the full phonon spectrum for 2D triangular Yukawa lattices, for a wide range of ?-bar (screening parameter) values and along different propagation angles. Earlier calculations of the excitation spectra of the 2D and 3D Yukawa liquids were based on the quasilocalized charge approximation (QLCA), whose implicit premise is that the spectrum of an average distribution (governed by the isotropic liquid pair correlation function) is a good representation of the actual spectrum. To see the implications of this model more clearly, we compare the high ? (near crystallization) QLCA phonon spectra with the angle-averaged phonon spectra of the lattice phonons
Room temperature laser action and Q-switching of F-aggregate color centers in LiF
International Nuclear Information System (INIS)
The authors have verified room temperature operation of F/sub 2/ and F/sub 2//sup +/ color center lasers in LiF heavily irradiated with gamma rays. The F/sub 2//sup -/ centers in their samples exhibit exceptional stability and can be used as solid state passive Q-switches for Nd:YAG lasers. The authors have presented a preliminary picture which helps to explain the origin of unusual behavior in the F/sub 2/ and F/sub 2//sup +/ lasers. Larger doses of gamma radiation, antireflection coatings, and a longitudinal pumping geometry should provide higher efficiencies for the remarkably simple, tunable F/sub 2//sup +/ solid state laser
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
Phonon drag effects for polyvalent metals: Aluminium
International Nuclear Information System (INIS)
The theory of the phonon-drag contribution to the electron-phonon scattering resistivity is generalized to the polyvalent metals, taking explicit account of the multiple-planewave character of the pseudo-wavefunction and the non-sphericity of the Fermi surface. It is shown that, in marked contrast to the situation for the alkali metals, phonon-drag effects are negligible for the polyvalent metals. (orig.)
Nonlinear phononics using atomically thin membranes
Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander
2014-01-01
Phononic crystals and acoustic meta-materials are used to tailor phonon and sound propagation properties by facilitating 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...
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
Two-dimensional phonon transport in graphene.
Nika, Denis L; Balandin, Alexander A
2012-06-13
Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955
Two-dimensional phonon transport in graphene
International Nuclear Information System (INIS)
Properties of phonons - quanta of the crystal lattice vibrations - in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. (topical review)
Phonon-assisted transient electroluminescence in Si
Energy Technology Data Exchange (ETDEWEB)
Cheng, Tzu-Huan, E-mail: f94943139@ntu.edu.tw [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan (China); Chu-Su, Yu [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan and Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan (China); Liu, Chien-Sheng [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan (China); Lin, Chii-Wann [Institute of Biomedical Engineering and Institute of Electrical Engineering, National Taiwan University, Taipei, Taiwan (China)
2014-06-30
The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.
Phonon-mediated particle detection : an overview
International Nuclear Information System (INIS)
We review the current status of various programs developing phonon-mediated particle detectors for primary applications in particle and astrophysics. We began with a brief summary and description of the general techniques employed by several of these groups. Experimental results on the detection of thermal phonons (e.g. using calorimeters) and athermal / ballistic phonons (e.g. using transition edge sensors or tunnel junctions) will be presented. Finally, we describe the design and operation of novel ''hybrid'' devices, and present results obtained with a cryogenic germanium hybrid detector which senses both phonons and ionization. (orig.)
Phonon-assisted transient electroluminescence in Si
International Nuclear Information System (INIS)
The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.
Polaronic Signatures in Phonon Isotopic Shifts
International Nuclear Information System (INIS)
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure
Polaronic signatures in phonon isotopic shifts
International Nuclear Information System (INIS)
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure
Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire
Directory of Open Access Journals (Sweden)
Galovi? Slobodanka P.
2006-01-01
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.
Phonon counting and intensity interferometry of a nanomechanical resonator.
Cohen, Justin D; Meenehan, Seán M; MacCabe, Gregory S; Gröblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar
2015-04-23
In optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms to secure quantum communication. Pioneering photon counting experiments, such as the intensity interferometry performed by Hanbury Brown and Twiss to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light. As with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. Current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes, as well as to develop technologies for precision sensing and quantum information processing. Here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by Hanbury Brown and Twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser. Owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 ± 0.05. With straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled, including the generation and heralding of single-phonon Fock states and the quantum entanglement of remote mechanical elements. PMID:25903632
Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films
Jin, Zuanming; Xu, Yue; Zhang, Zhengbing; Li, Gaofang; Lin, Xian; Ma, Guohong; Cheng, Zhenxiang; Wang, Xiaolin
2012-02-01
The electronic energy relaxation of polycrystalline BiFeO3 films is studied using ultrafast pump-probe spectroscopy. After photo-excitation with femtosecond laser pulses, the relaxation of hot electrons is identified to decay with two different characteristic times. The fast process is attributed to scattering of electrons with lattice-vibration modes, and the slow one is corresponding to the spin-lattice thermalization. The electron-phonon coupling is characterized by the second moment of the Eliashberg function, ?. Due to the structural strain and symmetry breaking, the electron-phonon interaction strength of tetragonal BiFeO3 films is larger than that of rhombohedral counterparts.
Sound-Particles and Phonons with Spin 1
Directory of Open Access Journals (Sweden)
Samoilov V.
2011-01-01
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.
Directory of Open Access Journals (Sweden)
Firas J. Al-Maliki
2012-09-01
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.
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
Scientific Electronic Library Online (English)
Fabrício Borges, Oliveira; Valéria Martins Dias, Pereira; Ana Paula Nassif Tondato da, Trindade; Antônio Carlos, Shimano; Ronaldo Eugênio Calçada Dias, Gabriel; Ana Paula Oliveira, Borges.
Full Text Available SciELO Brazil | Languages: English, Portuguese Abstract in portuguese OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fos [...] sa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm), para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do 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.
Singh-Sandhu, A; Kumar, G R; Sandhu, Arvinder S.
2002-01-01
The dynamical properties of Cu in a regime relevant to femtosecond micro machining are obtained on picosecond time scales using pump-probe reflectivity study for 100fs, 1015 W cm-2 laser pulses. The electrical resistivity is obtained by solving Helmoltz equations. The dissipation mechanisms and scaling laws are obtained in high and low temperature limits. The 'resistivity saturation' effect in an unexplored regime intermediate to hot plasma and cold solid is studied in detail. The temperature evolution and thermal conductivity is obtained in the temporal range 0 to 30ps after the interaction of laser pulse with solid Cu.
Sklyadneva, I Yu; Heid, R; Bohnen, K-P; Echenique, P M; Chulkov, E V
2012-03-14
We present an ab initio study of the lattice dynamics of the Pb(111) surface. The calculations were carried out within the density-functional theory using a linear response approach in the mixed-basis pseudopotential representation. We observe a rich spectrum of surface localized modes, and make a detailed assignment to measured modes in a recent helium-atom scattering experiment. We find that the inclusion of spin–orbit coupling considerably softens the phonon spectrum of the surface, thereby improving the agreement with experiment significantly. PMID:22354890
Anharmonic decay of non-equilibrium intervalley phonons in silicon
International Nuclear Information System (INIS)
We study phonons produced by transitions between the equivalent X valleys in silicon. We use the Monte Carlo method first to select stochastically the time between phonon collisions, and then to select a final-state pair of phonons from the probability distribution for anharmonic decay. Our results show that intervalley phonons decay into one near-equilibrium transverse acoustic phonon and another intermediate longitudinal phonon either on the acoustic or optical branch. This second phonon has energies between 40 and 50 meV and undergoes another decay before turning into a pair of near-equilibrium transverse acoustic phonons, presenting an additional potential bottleneck.
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 electron–phonon 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 electron–phonon interaction is enhanced by the external phonon coupling. In addition, the external electron–phonon 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 electron–phonon interaction softens the stiffness of the polymer.
Sobol', E. N.; Kitai, M. S.
1998-07-01
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 70°C, 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.
International Nuclear Information System (INIS)
We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L10 FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated.
Measurement of phonon damping by nanostructures
Mohtar, A. Al; Bruyant, A.; Kostcheev, S.; Vaillant, J.; Khoury, A.; Kazan, M.
2014-11-01
The understanding of phonon lifetime and scattering rates is attracting an increasing interest due to the major role of phonon in thermal and electrical conductivity which are key properties for technological applications. The infrared complex dielectric function of a crystal is determined by the harmonic characteristics of the phonon together with the intrinsic and extrinsic phonon scattering rates. In order to investigate the interplay between the phonon intrinsic scattering and the scattering of the phonon by a nanostructured surface, infrared reflectivity measurements from SiC nano-pyramids on SiC substrate have been analysed using a Kramers-Kronig conversion technique to deduce the infrared complex dielectric function. Then, the real and imaginary parts of the dielectric function were fitted simultaneously by using a theoretical model for the dielectric constant that considers frequency-dependent phonon damping at the center of the Brillouin zone. It has been found that surface nanostructuring strongly enhances the overall scattering rate of the phonon at the Brillouin zone center.
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.)
Strong squeezing via phonon mediated spontaneous generation of photon pairs
Qu, Kenan
2014-01-01
We propose a scheme generating robust squeezed light by using double cavity optomechanical system driven by blue detuned laser in one cavity and by red detuned laser in the other. This double cavity system is shown to mimic effectively an interaction that is similar to the one for the downconverter, which is known to be a source of strong squeezing for the light fields. There are however distinctions as the phonons, which lead to such an interaction, can contribute to the quantum noise. We show that the squeezing of the output fields of the order of $10$dB can be achieved even at mirror temperature of the order $10$mK.
Electron-longitudinal-acoustic-phonon scattering in double-quantum-dot based quantum gates
International Nuclear Information System (INIS)
We propose a nanostructure design which can significantly suppress longitudinal-acoustic-phonon-electron scattering in double-quantum-dot based quantum gates for quantum computing. The calculated relaxation rates vs. bias voltage exhibit a double-peak feature with a minimum approaching 105 s-1. In this matter, the energy conservation law prohibits scattering contributions from phonons with large momenta; furthermore, increasing the barrier height between the double quantum dots reduces coupling strength between the dots. Hence, the joint action of the energy conservation law and the decoupling greatly reduces the scattering rates. The degrading effects of temperatures can be reduced simply by increasing the height of the barrier between the dots
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)
Phononic crystals and elastodynamics: Some relevant points
Directory of Open Access Journals (Sweden)
N. Aravantinos-Zafiris
2014-12-01
Full Text Available In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.
Plasphonics: local hybridization of plasmons and phonons.
Marty, Renaud; Mlayah, Adnen; Arbouet, Arnaud; Girard, Christian; Tripathy, Sudhiranjan
2013-02-25
We show that the interaction between localized surface plasmons sustained by a metallic nano-antenna and delocalized phonons lying at the surface of an heteropolar semiconductor can generate a new class of hybrid electromagnetic modes. These plasphonic modes are investigated using an analytical model completed by accurate Green dyadic numerical simulations. When surface plasmon and surface phonon frequencies match, the optical resonances exhibit a large Rabi splitting typical of strongly interacting two-level systems. Based on numerical simulations of the electric near-field maps, we investigate the nature of the plaphonic excitations. In particular, we point out a strong local field enhancement boosted by the phononic surface. This effect is interpreted in terms of light harvesting by the plasmonic antenna from the phononic surface. We thus introduce the concept of active phononic surfaces that may be exploited for far-infared optoelectronic devices and sensors. PMID:23481988
Hydrodynamic phonon transport in suspended graphene.
Lee, Sangyeop; Broido, David; Esfarjani, Keivan; Chen, Gang
2015-01-01
Recent studies of thermal transport in nanomaterials have demonstrated the breakdown of Fourier's law through observations of ballistic transport. Despite its unique features, another instance of the breakdown of Fourier's law, hydrodynamic phonon transport, has drawn less attention because it has been observed only at extremely low temperatures and narrow temperature ranges in bulk materials. Here, we predict on the basis of first-principles calculations that the hydrodynamic phonon transport can occur in suspended graphene at significantly higher temperatures and wider temperature ranges than in bulk materials. The hydrodynamic transport is demonstrated through drift motion of phonons, phonon Poiseuille flow and second sound. The significant hydrodynamic phonon transport in graphene is associated with graphene's two-dimensional features. This work opens a new avenue for understanding and manipulating heat flow in two-dimensional materials. PMID:25693180
LO-phonon generation rate with electron energy collision broadening in polar semiconductors
International Nuclear Information System (INIS)
Rate equations for the LO-phonon distribution function and mean electron energy with the electron energy collision broadening effect included are derived in the frame of Zubarev's theory of non-equilibrium statistical operators. A numerical evaluation of the rate of change of the LO-phonon distribution function is performed for a typical process of laser-excited hot electron relaxation in several polar semiconductors (GaSb, GaAs, InP, CdSe, ZnS). The electron energy collision broadening is found to lead to a new feature in the wave vector dependence of the LO-phonon generation rate. This feature provides an example of an effect which is clearly beyond the Boltzmann equation level of description. (author). 6 figs., 1 tab., 29 refs
Coherent phonon frequency comb generated by few-cycle femtosecond pulses in Si
Directory of Open Access Journals (Sweden)
Petek Hrvoje
2013-03-01
Full Text Available We explore the coherent phonon induced refractive index modulation of a Si(001 surface upon the excitation in near-resonance with the direct band gap of Si. Through the anisotropic e–h pair generation and coherent Raman scattering, ? 10-fs laser pulses exert a sudden electrostrictive force on Si lattice launching coherent LO phonon oscillations at 15.6 THz frequency. The concomitant oscillatory change in the optical constants modulates the reflected probe light at the fundamental LO phonon frequency, generating a broad comb of frequencies at exact integer multiples of the fundamental frequency extending to beyond 100 THz. On the basis of an analytical model, we show that the simultaneous amplitude and phase modulation of the reflected light by the coherent lattice polarization at 15.6 THz generates the frequency comb.
Longitudinal polar optical phonons in InN/GaN single and double het- erostructures
Energy Technology Data Exchange (ETDEWEB)
Ardali, Sukru; Tiras, Engin [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470 (Turkey); Gunes, Mustafa; Balkan, Naci [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Ajagunna, Adebowale Olufunso; Iliopoulos, Eleftherios; Georgakilas, Alexandros [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion-Crete (Greece)
2011-05-15
Longitudinal optical phonon energy in InN epi-layers has been determined independently from the Raman spectroscopy and temperature dependent Hall mobility measurements. Raman spectroscopy technique can be used to obtain directly the LO energy where LO phonon scattering dominates transport at high temperature. Moreover, the Hall mobility is determined by the scattering of electrons with LO phonons so the data for the temperature dependence of Hall mobility have been used to calculate the effective energy of longitudinal optical phonons.The samples investigated were (i) single heterojunction InN with thicknesses of 1.08, 2.07 and 4.7 {mu}m grown onto a 40 nm GaN buffer and (ii) GaN/InN/AlN double heterojunction samples with InN thicknesses of 0.4, 0.6 and 0.8 {mu}m. Hall Effect measurements were carried out as a function of temperature in the range between T = 1.7 and 275 K at fixed magnetic and electric fields. The Raman spectra were obtained at room temperature. In the experiments, the 532 nm line of a nitrogen laser was used as the excitation source and the light was incident onto the samples along of the growth direction (c-axis). The results, obtained from the two independent techniques suggest the following: (1) LO phonon energies obtained from momentum relaxation experiments are generally slightly higher than those obtained from the Raman spectra. (2) LO phonon energy for the single heterojunctions does not depend on the InN thickness. (3) In double heterostructures, with smaller InN thicknesses and hence with increased strain, LO phonon energy increases by 3% (experimental accuracy is < 1%) when the InN layer thickness increases from 400 to 800 nm (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Chalcogenide glass microsphere laser.
Elliott, Gregor R; Murugan, G Senthil; Wilkinson, James S; Zervas, Michalis N; Hewak, Daniel W
2010-12-01
Laser action has been demonstrated in chalcogenide glass microsphere. A sub millimeter neodymium-doped gallium lanthanum sulphide glass sphere was pumped at 808 nm with a laser diode and single and multimode laser action demonstrated at wavelengths between 1075 and 1086 nm. The gallium lanthanum sulphide family of glass offer higher thermal stability compared to other chalcogenide glasses, and this, along with an optimized Q-factor for the microcavity allowed laser action to be achieved. When varying the pump power, changes in the output spectrum suggest nonlinear and/or thermal effects have a strong effect on laser action. PMID:21165022
International Nuclear Information System (INIS)
The optical microscopy method has been employed to analyse the formation of the dislocation structure on the (100) and (111) oriented surface of silicon caused by an intense canning radiation of CO2-laser at a maximum power density of 104 W/cm2. The dislocation structure formation is attributed to the significant thermoelastic stresses occurring as a result of high nonstationarity and nonuniformity of the temperature field in the irradiated zone
Sandhu, Arvinder S.; Dharmadhikari, A. K.; Kumar, G. Ravindra
2002-01-01
The dynamical properties of Cu in a regime relevant to femtosecond micro machining are obtained on picosecond time scales using pump-probe reflectivity study for 100fs, 1015 W cm-2 laser pulses. The electrical resistivity is obtained by solving Helmoltz equations. The dissipation mechanisms and scaling laws are obtained in high and low temperature limits. The 'resistivity saturation' effect in an unexplored regime intermediate to hot plasma and cold solid is studied in detai...
Lantukh, Yu. D.; Ketsle, G. A.; Pashkevich, S. N.; Letuta, S. N.; Razdobreev, D. A.
2006-07-01
This paper discusses the mechanism of amplitude holographic recording in polyvinyl alcohol films with additives of thiazine dyes (thionine, methylene blue) under the action of a helium-neon laser. It is proposed to describe the photochemical transformations of the dye by a sequential reaction scheme with one reversible stage. It is shown that the presence of associates (dimers) of the dyes in the films has a substantial effect on the bleaching kinetics. Plasticization of the polymer makes it possible to control the ratio of the rate constants of the reaction scheme and also results in complete breakdown of the holographic gratings after the recording is completed. The kinetics of spontaneous erasure of the holograms in the test medium are compared with those of the thiazine-dye-deoxyribonucleic-acid (DNA) film system.
International Nuclear Information System (INIS)
Recently, it was reported that a plasma-jet could be efficiently applied for the antisepsis of wounds. In this case, the discharge in an argon gas stream was used to produce a so-called ''cold plasma'' on the skin surface. The thermal action of the plasma on the skin was investigated in the present study by means of laser scanning microscopy (LSM) and by histological analysis. Consequently, the plasma beam was moved with a definite velocity at an optimal distance over the skin surface. The structural changes of the tissue were analyzed. It was found by LSM that a thermal damage could be detected only in the upper cell layers of the stratum corneum (SC) at moving velocities of the plasma beam, usually applied in clinical practice. Deeper parts of the SC were not damaged. The structural changes were so superficial that they could be detected only by LSM but not by analysis of the histological sections
Coherent phonon and surface-enhanced Raman scattering dynamics in solids
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We have demonstrated coherent phonon and surface-enhanced Raman scattering (SERS) dynamics of carbon-related materials: gold (Au) deposited graphite and benzenethiol (BT) self-assembled monolayer (SAM) adsorbed on Au film with roughness. Using ultrafast pump-probe spectroscopy with the enhanced electric field via Au hemispheres or Au film with nanoscale roughness, transient behaviors of high frequency phonons located at surface/interface were sensitively detected. In Au deposited graphite, the electric field near graphite surface around Au nanoparticles, whose typical diameter is ?10 nm, is strongly enhanced. As a result, the disorder-induced mode (D-mode) near the surface was clearly observed. In BT-SAM, the nanoscale roughness of the Au film might contribute to the amplitude enhancement of coherent vibrations up to the detected level. From these results, we believe that coherent SERS spectroscopy will open the door to observe coherent phonon dynamics even at the level of monolayer and single molecules for future. - Highlights: • Coherent phonon spectroscopy with 7.5 fs laser pulse is utilized to measure SERS dynamics. • Au nanostructures were used to enhance coherent vibrations in graphite/self-assembled monolayer. • D-mode coherent phonon in graphite was sensitively detected due to SERS via Au nanostructures. • High frequency vibrations in benzenethiol self-assembled monolayer were detected due to SERS
Optical and phonon spectra of wurtzite ZnO quantum dots and nanocrystals
Fonoberov, Vladimir A.; Alim, Khan A.; Balandin, Alexander A.
2006-03-01
ZnO nanostructures have recently attracted attention due to the proposed optoelectronic and spintronic applications. Envisioned applications require accurate knowledge of exciton states and optical phonons. We report results of the investigation of wurtzite ZnO nanostructures with diameters from 2 nm to 20 nm (quantum dots to nanocrystals). The calculated size dependence of the exciton states and UV photoluminescence spectra of ZnO nanostructures is in agreement with the experimental data [1]. In addition, both interface and confined polar optical phonon modes in ZnO quantum dots and nanocrystals have been calculated and identified in the resonant and non-resonant Raman spectra [2]. It was found that the phonon confinement resulted in phonon frequency shifts of few cm-1 in the non-resonant Raman spectra. We also show that UV laser excitation in resonant-Raman spectroscopy leads to large red shifts of phonon peaks (up to 14 cm-1) due to heating. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center. [1] V.A. Fonoberov and A.A. Balandin, Appl. Phys. Lett. 85, 5971 (2004); [2] V.A. Fonoberov and A.A. Balandin, Phys. Rev. B 70, 233205 (2004); K.A. Alim, V.A. Fonoberov, and A.A. Balandin, Appl. Phys. Lett. 86, 053103 (2004).
Investigation of the Phonon Frequency Shifts in ZnO Quantum Dots
Alim, Khan A.
2005-03-01
Nanostructures made of ZnO have recently attracted attention due to their proposed applications in low-voltage and short-wavelength electro-optical devices. However, the origin of the observed phonon frequency shifts in such nanostructures is not always understood. We carried out both resonant and non-resonant Raman measurements for 20 nm-diameter ZnO quantum dots (QDs) and bulk ZnO reference samples [1]. A comparison with a recently developed theory [2], allowed us to clarify the origin of the phonon frequency shifts in ZnO QDs. It was found that the phonon confinement results in phonon frequency shifts of only few cm-1. At the same time, the UV laser heating of the QD ensemble was found to induce a large red shift of phonon frequencies for up to 14 cm-1. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center. [1] K.A. Alim, V.A. Fonoberov, and A.A. Balandin, Appl. Phys. Lett., in review (2004). [2] V.A. Fonoberov and A.A. Balandin, Phys. Stat. Solidi C 1, 2650 (2004); cond-mat/0405681; cond-mat/0411742.
Nonlinear response function for two-phonon polaritons
International Nuclear Information System (INIS)
A nonlinear response function describing three-polariton processes (two single-phonon polaritons and two-phonon polariton) is derived for a system of interaction phonons and photons. The main features of the nonlinear optical spectra in the two-phonon polariton region are analyzed. (author). 17 refs
Phonons of Metallic Vicinal Surfaces
Kara, A; Kara, Abdelkader; Rahman, Talat S.
2001-01-01
We present an analysis of the vibrational dynamics of metal vicinal surfaces using the embedded atom method to describe the interaction potential and both a real space Green's function method and a slab method to calculate the phonons. We report two main general characteristics : a global shift of the surface vibrational density of states resulting from a softening of the force field. The latter is a direct result of the reduction of coordination for the different type of surface atoms; and an appearance of high frequency modes above the bulk band, resulting from a stiffening of the force field near the step atom. The latter is due to a rearrangement of the atomic positions during the relaxation of the surface atoms yielding a large shortening of the nearest neighbor distances near the step atoms.
International Nuclear Information System (INIS)
The dispersion relations for aluminium have been determined fairly completely at 80°K by measurements with a new three-axis crystal spectrometer at the 30-MW research reactor R2 at Studsvik. Complete dispersion curves have been obtained for the three symmetry directions, together with interpolation points on the zone boundaries and elsewhere. The results are presented as dispersion curves and as contour maps of dispersion surfaces. The series of measurements was the first undertaken with the spectrometer, and to establish a sound experimental routine, considerable attention was devoted to details such as resolution, reproducibility and the avoidance of disturbing effects, A focusing technique was used throughout to optimize resolution. The results consequently were of a rather high degree of accuracy and were utilized to search for Kohn anomalies, but no clear examples were found. Such effects are evidently small in aluminium, but there are indications that a moderate improvement of experimental technique may render them discernible. Phonon widths at 80°K could often be determined from the widths of observed resonances via a calculated resolution width. In another series of measurements at 300°K - not yet completed - widths could always be determined. Examples are given of broadenings and energy shifts in passing from 80 to 300°K. A noteworthy effect was found at q = (0.8,0,0) : the phonon width there increased in an anomalous fashion in passing from 80 to 300°K. Another observation is that points for small q on transverse branches tend to lie significantly above the lines through the origin having slopes corresponding to the velocity of 10-Mc/s sound waves. (author)
Phonon dynamics of uranium chalcogenides (US)
International Nuclear Information System (INIS)
In this paper, we have investigated the phonon dynamics of US solids in NaCl phase using a Rigid Shell model with pair wise interionic interaction potential. The potential consists of the long-range Coulomb and three-body interactions and the short-range van der Waals interaction and the Hafemeister and Flygare type overlap repulsion extended up to the second neighbor ions. The elastic constants obtained from the model have been used to calculate the phonon dispersion relation in the symmetry direction. The phonon dispersion curves of US compound, calculated from the present model, agree with the neutron scattering data. (author)
Phonon Spectrum of SrFe2As2 determined by multizone phonon refinement
Energy Technology Data Exchange (ETDEWEB)
Parshall, D [University of Tennessee, Knoxville (UTK); Heid, R [Kernforschungszentrum Karlsruhe, Germany; Niedziela, Jennifer L [ORNL; Wolf, Th. [Kernforschungszentrum Karlsruhe, Germany; Stone, Matthew B [ORNL; Abernathy, Douglas L [ORNL; Reznik, Dmitry [University of Colorado, Boulder
2014-01-01
The ferropnictidesuperconductors exhibit a sensitive interplay between the lattice and magnetic degrees of freedom, including a number of phonon modes that are much softer than predicted by nonmagnetic calculations using density functional theory (DFT). However, it is not known what effect, if any, the long-range magnetic order has on phonon frequencies above 23 meV, where several phonon branches are very closely spaced in energy and it is challenging to isolate them from each other. We measured these phonons using inelastic time-of-flight neutron scattering in 40 Brillouin zones, and developed a technique to determine their frequencies. We find this method capable of determining phonon energies to 0.1 meV accuracy, and that the DFT calculations using the experimental structure yield qualitatively correct energies and eigenvectors. We do not find any effect of the magnetic transition on these phonons.
International Nuclear Information System (INIS)
An electric current decreases the diameter of monomeric globules and increases the number of large-size globules of human serum albumin. Low-level laser therapy leads to a photochemical process in the protein with a modification of its conformation. The physiotherapeutic curative effect of the electric current and low-level therapy is realized in the immediate change of the conformation takes place in the system 'water-protein' of living organism. The experimental data indicate the dependence of the properties of water and human serum albumin on the dose of electromagnetic fields
Observation of effect of the USPs shortening at their self-action in high-temperature laser plasma
Anikeev, Boris V.; Kas'yanov, Ivan V.; Khaydukov, Evgeniy V.; Khramov, Vladimir N.
2007-06-01
Modifications of temporal parameters of ultrashort laser pulses (USP) with intensity more than 10 12 W/cm2 and duration not less than 700 ps, reflected from boundary "air-plasma" and emitted by the neodymium superregenerator are investigated. We explain shortening of pulses by Doppler effect originating in plasma that results in occurrence in it of properties of an abnormal dispersion. Designed circuits of a superregenerative amplification of a USPs appeared fit for examination of high-speed processes in the plasma excited in air, and also for production of polyatomic carbon compounds (fullerenes).
Laser action along and near the optic axis of a holmium-doped KY(WO?)? crystal.
Cattoor, Romain; Manek-Hönninger, Inka; Rytz, Daniel; Canioni, Lionel; Eichhorn, Marc
2014-11-15
We demonstrate the first (to our knowledge) quasi-three-level conical refraction laser operating at 2 ?m, with 1.6 W of output power at 2074 nm, using a holmium-doped KY(WO4)2 crystal. A maximum slope efficiency of 52% has been achieved, along the optic axis with respect to the absorbed pump power. Furthermore, lasing operation around the optic axis has been performed. In this case, a maximum output power of 3 W has been reached, with a slope efficiency better than 70%, which are the best performances ever reported on this material. PMID:25490480
International Nuclear Information System (INIS)
A method is developed for determining the characteristic relaxation time ? of the diffraction-reflection intensity from a crystal irradiated with low-power laser radiation. Using the Bragg geometry, the relaxation time of the (060) reflection from KDP crystals was obtained ?=0.09(1) s. The temperature field inside the crystal was simulated under the experimental conditions. It was established that the characteristic relaxation time measured is close to the calculated time of the attainment of the temperature-gradient component normal to the irradiated surface
Tuchina, E. S.; Petrov, P. O.; Kozina, K. V.; Ratto, F.; Centi, S.; Pini, R.; Tuchin, V. V.
2014-07-01
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.
Fischer, D W; Beggs, J L; Kenshalo, D L; Shetter, A G
1985-08-01
The possibility of utilizing the CO2 laser for neural anastomoses was investigated in a rat sciatic nerve model. One nerve in each animal was acutely divided and anastomosed using 10-0 nylon epineurial sutures, while the opposite side was joined by "welding" the opposed nerve ends together with CO2 laser pulses. The surgical incisions were reexplored 60 days postoperatively, action potentials were recorded across the anastomoses, and the nerves were removed for light and electron microscopy. The operative patency rate in the suture group was 100%, compared to 87% in the laser group. Among those animals with bilaterally intact nerves, action potentials could be recorded across the anastomotic site in 78% of the sutured preparations and in 85% of nerves spot-welded with the CO2 laser. Morphological studies showed a greater degree of scar tissue formation and constriction in the anastomotic zone of the nerves joined by sutures than was present in laser-treated animals. We believe these preliminary observations suggest that the CO2 laser may have a role to play in peripheral nerve surgery. Further study of this technique is warranted. PMID:3929156
Single electron-phonon interaction in a suspended quantum dot phonon cavity
Höhberger, E M; Brandes, T; Kirschbaum, J; Wegscheider, W; Bichler, M; Kotthaus, J P
2003-01-01
An electron-phonon cavity consisting of a quantum dot embedded in a free-standing GaAs/AlGaAs membrane is characterized in Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.
Yudistira, D; Boes, A; Djafari-Rouhani, B; Pennec, Y; Yeo, L Y; Mitchell, A; Friend, J R
2014-11-21
We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics. PMID:25479504
Monolithic Phononic Crystals with a Surface Acoustic Band Gap from Surface Phonon-Polariton Coupling
Yudistira, D.; Boes, A.; Djafari-Rouhani, B.; Pennec, Y.; Yeo, L. Y.; Mitchell, A.; Friend, J. R.
2014-11-01
We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z -cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics.
International Nuclear Information System (INIS)
Laser-based photoemission with photons of energy 6 eV is used to examine the fine details of the very low-energy electron dispersion and associated dynamics in the nodal region of optimally doped Bi2212. A 'kink' in the dispersion in the immediate vicinity of the Fermi energy is associated with scattering from an optical phonon previously identified in Raman studies. The identification of this phonon as the appropriate mode is confirmed by comparing the scattering rates observed experimentally with the results of calculated scattering rates based on the properties of the phonon mode.
Phononic crystals: Entering an acoustic phase
Barreiro, Julio T.
2015-03-01
Electrons moving in a one-dimensional crystal can acquire a geometrical phase. Sound waves in phononic crystals are now shown to display the same effect -- underlining the similarity between conventional solids and acoustic metamaterials.
Pressure-enabled phonon engineering in metals.
Lanzillo, Nicholas A; Thomas, Jay B; Watson, Bruce; Washington, Morris; Nayak, Saroj K
2014-06-17
We present a combined first-principles and experimental study of the electrical resistivity in aluminum and copper samples under pressures up to 2 GPa. The calculations are based on first-principles density functional perturbation theory, whereas the experimental setup uses a solid media piston-cylinder apparatus at room temperature. We find that upon pressurizing each metal, the phonon spectra are blue-shifted and the net electron-phonon interaction is suppressed relative to the unstrained crystal. This reduction in electron-phonon scattering results in a decrease in the electrical resistivity under pressure, which is more pronounced for aluminum than for copper. We show that density functional perturbation theory can be used to accurately predict the pressure response of the electrical resistivity in these metals. This work demonstrates how the phonon spectra in metals can be engineered through pressure to achieve more attractive electrical properties. PMID:24889627
Resonance tunneling of electrons interacting with phonons
International Nuclear Information System (INIS)
The effect of the electron-phonon interaction on the electrons resonance tunneling through the two-barrier nanostructure is studied within the frames of the consecutive quantum-mechanical model. The wave function is derived from the solution of the Schroedinger equation with the correct boundary conditions in the quasi-classical approximation by the electron-phonon interaction. The current, calculated through the wave function, is averaged by the phonon subsystem by means of the Bloch theorem. The analytical expressions for the static and alternating currents of the resonance-tunnel diode with an account of the electron-phonon interaction, formally coinciding with the probability of the Moessbauer effect, are established
Phonon-mediated electron pairing in graphene
International Nuclear Information System (INIS)
The possibility of superconducting pairing of electrons in doped graphene due to in-plane and out-of-plane phonons is studied. Quadratic coupling of electrons with out-of-plane phonons is considered in details, taking into account both deformation potential and bond-stretch contributions. The order parameter of electron-electron pairing can have different structures due to four-component spinor character of electrons wave function. We consider s-wave pairing, diagonal on conduction and valence bands, but having arbitrary structure with respect to valley degree of freedom. The sign and magnitude of contribution of each phonon mode to effective electron-electron interaction turns out to depend on both the symmetry of phonon mode and the structure of the order parameter. Unconventional orbital-spin symmetry of the order parameter is found.
Design of phonon detectors for neutrinos
International Nuclear Information System (INIS)
Several alternative neutrino detection schemes are described briefly and compared. It is suggested that a ballistic-phonon experiment might be promising. In such an experiment the amplitude received at a bolometer would depend on the distance it is from the neutrino event, and also on the direction because of phonon focusing, so several bolometers suggested to locate the event position from the difference in arrival times. The design of such an experiment is discussed assuming the phonons are detected by conventional superconducting bolometers. Determination of the direction of neutrino flux would be obtained from a study of the distribution of direction of the tracks of recoiling electrons or nuclei. The problem of smearing out the effective source over a distance of approximately a mean free path is addressed, and the need for high-resolution phonon focusing studies is expressed
Pressure-enabled phonon engineering in metals
Lanzillo, Nicholas A.; Thomas, Jay B.; Watson, Bruce; Washington, Morris; Nayak, Saroj K.
2014-01-01
We present a combined first-principles and experimental study of the electrical resistivity in aluminum and copper samples under pressures up to 2 GPa. The calculations are based on first-principles density functional perturbation theory, whereas the experimental setup uses a solid media piston–cylinder apparatus at room temperature. We find that upon pressurizing each metal, the phonon spectra are blue-shifted and the net electron–phonon interaction is suppressed relative to the unstrained crystal. This reduction in electron–phonon scattering results in a decrease in the electrical resistivity under pressure, which is more pronounced for aluminum than for copper. We show that density functional perturbation theory can be used to accurately predict the pressure response of the electrical resistivity in these metals. This work demonstrates how the phonon spectra in metals can be engineered through pressure to achieve more attractive electrical properties. PMID:24889627
Thermal Phonon Resonance in Solid Glass
Minami, Yasuo; Yogi, Takeshi; Sakai, Keiji
2006-05-01
Thermal phonon resonance was observed in a stiff solid material of fused silica, from which a lower intensity of scattered light is expected than from liquids. The improved detection sensitivity of the optical beating Brillouin spectroscopy technique enabled us to observe the spontaneous elastic resonance of the solid sample attributable to thermal density fluctuation with a frequency resolution of 1 kHz. The accuracy in determining phonon velocity was then increased up to 10-5. The high frequency resolution also revealed the fine structure of the resonance peak train brought about by the lateral mode vibration, and the eigen frequencies of the compound mode are in good agreement with those theoretically estimated. Volume and shear elasticities were uniquely determined from the resonance spectra of longitudinal and shear phonons. Phonon absorption at about 100 MHz was also determined from the resonance peak width of the Brillouin component.
Strong Coupling between Nanoscale Metamaterials and Phonons
Energy Technology Data Exchange (ETDEWEB)
Shelton, David J.; Brener, Igal; Ginn, James C.; Sinclair, Michael B.; Peters, David W.; Coffey, Kevin R.; Boreman, Glenn D.
2011-01-01
We use split ring resonators (SRRs) at optical frequencies to study strong coupling between planar metamaterials and phonon vibrations in nanometer-scale dielectric layers. A series of SRR metamaterials were fabricated on a semiconductor wafer with a thin intervening SiO{sub 2} dielectric layer. The dimensions of the SRRs were varied to tune the fundamental metamaterial resonance across the infrared (IR) active phonon band of SiO{sub 2} at 130 meV (31 THz). Strong anticrossing of these resonances was observed, indicative of strong coupling between metamaterial and phonon excitations. This coupling is very general and can occur with any electrically polarizable resonance including phonon vibrations in other thin film materials and semiconductor band-to-band transitions in the near to far IR. These effects may be exploited to reduce loss and to create unique spectral features that are not possible with metamaterials alone.
Phonon-mediated detection of particles
International Nuclear Information System (INIS)
Over the past five years particle physicists, nuclear physicists and astrophysicists have been increasingly interested in using phonons to detect particle interactions. In these detection attempts it is obviously critical to integrate the understanding that the phonon physicists have accumulated on the mechanisms governing the production, propagation and detection of those phonons. Vice versa, some of the issues raised by the particle detection problem may be of significant interest and the high sensitivity methods being developed may become important for phonon physics investigations. These were the motivations for a round table discussion between members of the two communities. This report attempts to summarize the themes of a very interesting discussion. 24 refs., 2 figs., 1 tab
Anharmonic phonons and high-temperature superconductivity
International Nuclear Information System (INIS)
We examine a simple model of anharmonic phonons with application to the superconducting isotope effect. Linear and quadratic electron-phonon coupling are considered for various model potentials. The results of the model calculations are compared with the high-temperature superconductors La2-xSrxCuO4, Y1-xPrxBa2Cu3O7-?, and YBa2Cu3-xMxO7-? with M=Zn, Ni, or Fe
Investigation of the Phonon Spectrum of Nickel
International Nuclear Information System (INIS)
Using a neutron spectrometer and time- of-flight data, the authors have made a study of the inelastic scattering of cold neutrons in nickel. The sample used was an alloy of nickel isotopes and the amplitude of coherent neutron scattering was zero. From the spectrum of inelastically-scattered neutrons, the phonon spectrum of the face-centred cubic lattice of nickel was obtained and a comparison made with the phonon spectrum of the body-centred cubic lattice of vanadium. (author)
LO-phonon overheating in quantum dots
Kral, Karel
2005-01-01
Longitudinal optical phonons have been used to interpret the electronic energy relaxation in quantum dots and at the same time they served as a reservoir, with which the electronic subsystem is in contact. Such a phonon subsystem is expected to be passive, namely, in a long-time limit the whole system should be able to achieve such a stationary state, in which statistical distributions of both subsystems do not change in time. We pay attention to this property of the LO phon...
Electron-phonon interaction in C70
Provasi, D.; Breda, N.; Broglia, R. A.; Colo, G.; Roman, H. E.; Onida, G.
2000-01-01
The matrix elements of the deformation potential of C$_{70}$ are calculated by means of a simple, yet accurate solution of the electron-phonon coupling problem in fullerenes, based on a parametrization of the ground state electronic density of the system in terms of $sp^{2+x}$ hybridized orbitals. The value of the calculated dimensionless total electron-phonon coupling constant is $\\lambda\\approx0.1$, an order of magnitude smaller than in C$_{60}$, consistent with the lack o...
Phonon Squeezing in a Superconducting Molecular Transistor
Zazunov, A.; Feinberg, Denis; Martin, Thierry
2006-01-01
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...
Phonon squeezing in a superconducting molecular transistor.
Zazunov, A; Feinberg, D; Martin, T
2006-11-10
Josephson transport through a single molecule or carbon nanotube is considered in the presence of a local vibrational mode coupled to the electronic charge. The ground-state solution is obtained exactly in the limit of a large superconducting gap and is extended by variational analysis. The Josephson current induces squeezing of the phonon mode, which is controlled by the superconducting phase difference and by the junction asymmetry. Optical probes of nonclassical phonon states are briefly discussed. PMID:17155648
Toward quantitative modeling of silicon phononic thermocrystals
Lacatena, V.; Haras, M.; Robillard, J.-F.; Monfray, S.; Skotnicki, T.; Dubois, E.
2015-03-01
The wealth of technological patterning technologies of deca-nanometer resolution brings opportunities to artificially modulate thermal transport properties. A promising example is given by the recent concepts of "thermocrystals" or "nanophononic crystals" that introduce regular nano-scale inclusions using a pitch scale in between the thermal phonons mean free path and the electron mean free path. In such structures, the lattice thermal conductivity is reduced down to two orders of magnitude with respect to its bulk value. Beyond the promise held by these materials to overcome the well-known "electron crystal-phonon glass" dilemma faced in thermoelectrics, the quantitative prediction of their thermal conductivity poses a challenge. This work paves the way toward understanding and designing silicon nanophononic membranes by means of molecular dynamics simulation. Several systems are studied in order to distinguish the shape contribution from bulk, ultra-thin membranes (8 to 15 nm), 2D phononic crystals, and finally 2D phononic membranes. After having discussed the equilibrium properties of these structures from 300 K to 400 K, the Green-Kubo methodology is used to quantify the thermal conductivity. The results account for several experimental trends and models. It is confirmed that the thin-film geometry as well as the phononic structure act towards a reduction of the thermal conductivity. The further decrease in the phononic engineered membrane clearly demonstrates that both phenomena are cumulative. Finally, limitations of the model and further perspectives are discussed.
Frequency dependence of dispersive phonon images
Scientific Electronic Library Online (English)
K., Jakata; A.G., Every.
2008-10-01
Full Text Available 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.
Upconversion cooling of Er-doped low-phonon fluorescent solids
Garcia-adeva, Angel J.; Balda, Rolindes; Fernandez, Joaquin
2008-01-01
We report on a novel mechanism for laser cooling of fluorescent solids based on infrared-to-visible upconversion often found in rare-earth-doped low-phonon materials. This type of optical cooling presents some advantages with regards to conventional anti-Stokes cooling. Among them, it allows to obtain cooling in a broader range of frequencies around the barycenter of the infrared emitting band.
Two-level tunnelling systems and backward-wave phonon echoes in neutron-irradiated quartz
International Nuclear Information System (INIS)
Backward-wave phonon echoes (BWE) in neutron-irradiated quartz crystals are studied experimentally before and after annealing. It is argued that the annealing behaviour of the echo is consistent with a BWE generation mechanism in two-level tunnelling systems (for low input powers). We derive a theoretical expression, based on the theory of the mixing of two laser fields, which gives a good agreement with our experimental results. (author)
International Nuclear Information System (INIS)
As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0oK) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the intethe 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)
Inversion symmetry breaking induced phonon-phonon anti-crossing in bilayer graphene
Yan, Jun; Villarson, Theresa; Henriksen, Erik A.; Kim, Philip; Pinczuk, Aron
2010-03-01
We use Raman scattering to study the breaking of inversion symmetry in bilayer graphene. The electron and hole doped states of the system reveal phonon band splitting with spectral intensity transfer that is tuned by a polymer electrolyte top gate. The observations suggest that the in-phase and out-of-phase long wavelength optical phonons (G bands) are coupled to each other, and are thus no longer energy eigenstates. The coupling results in an intriguing phonon-phonon anti-crossing phenomenon induced by the broken inversion symmetry. The Raman spectral transfer between the observed two normal modes offers quantitative measurements of the evolution of the phonon wavefunction and suggests that the Raman activity of the out-of-phase mode is negligibly small in the presence of the broken inversion symmetry.
International Nuclear Information System (INIS)
SU(6) quadrupole phonon model (TQM) is equivalent to IBM and SU(6) particle-quadrupole phonon coupling model (PTQM) is equivalent to IBFM; these models are simply embedded in the Bohr-Mottelson quadrupole-phonon model and particle-quadrupole phonon coupling model, respectively. Due to this equivalence, dynamical symmetries (SU(3), SU(5), O(6)) and supersymmetries for TQM/PTQM are the same as for IBM/IBFM. The author discusses the quadrupole-phonon structure for the SU(3) limit, the coherent state, the analogs of Nilsson states and the supersymmetries. A new approximate supersymmetry is proposed which could appear for the situation with even nucleus of SU(3) type and the unique-parity bands in the neighbouring odd nucleus. (Auth.)
Electron-Phonon Coupling and the Soft Phonon Mode in TiSe2
Weber, F.; Rosenkranz, S.; Castellan, J.-P.; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K.-P.; Alatas, A.
2011-12-01
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.
Theoretical study of phonon spectra in ferromagnetic nanoparticles
Energy Technology Data Exchange (ETDEWEB)
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
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.
Cryogenic phonon-mediated particle detectors for dark matter searches and neutrino physics
International Nuclear Information System (INIS)
This work describes the development of cryogenic phonon-mediated particle detectors for dark matter searches and neutrino detection. The detectors described in this work employ transition-edge sensors, which consist of a meander pattern of thin-film superconductor on a silicon substrate. When phonons from a particle interaction in the crystal impinge on the sensor in sufficient density, sections of the line are driven normal and provide a measurable resistance. A large fraction of the thesis describes work to fully characterize the phonon flux from particle interactions. In one set of experiments, ?25% of the phonon energy from 59.54 keV gamma-ray events was found to propagate open-quotes ballisticallyclose quotes (i.e., with little or no scattering) across a 300 ?m thick crystal of silicon. Gamma-rays produce electron recoils in silicon whereas with dark matter and neutrino experiments nuclear recoils are also of interest. Two experiments were done to measure the ballistic component that arises from neutron events, which interact via nuclear recoil. Measurements indicate that the fraction of energy that is ballistic is ?50% greater for nuclear recoils than for electron recoils. Two novel detectors were fabricated and tested in an attempt to improve the sensitivity of the detectors. In the first detector, relatively large Al pads were linked by 2 ?m wide Ti lines in a meander pattern. Phonons impinging on the Al pads create quasiparticles which diffuse in the Alasiparticles 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
Heat transfer by 'diffusive' modes and phonon scattering in beta-phase of solid sulfur hexafluoride
International Nuclear Information System (INIS)
In the present work, the isochoric thermal conductivity of SF6 is calculated using both the expressions for the phonon-phonon and phonon-rotation scattering and taking into account the limitation of phonon mean-free path
Phonons in ternary molybdenum chalcogenide superconductors
International Nuclear Information System (INIS)
Experimental and theoretical investigations of the phonon properties of Chevrel-phase superconductors are reviewed in historical perspective. The crystallographic considerations and lattice heat capacity data which led to the introduction of the early molecular-crystal model of the lattice dynamics are discussed. The technique of phonon spectrum measurements by inelastic neutron scattering studies on polycrystalline samples is described, and the results for these systems are presented in detail. A more recent Born-von Karman force-constant model of the lattice dynamics, that utilizes Lennard-Jones potentials, is described. Physical properties calculated from this model are discussed in the light of experimental results for the heat capacity, neutron-weighted phonon spectra and the Moessbauer effect. The first single-crystal inelastic neutron scattering experiments available are considered briefly. The controversial question of the relationship of the phonon spectra of these materials to the electron-phonon interaction is addressed. Finally, areas of particular interest for future research are identified. (orig.)
Revision of the statistical mechanics of phonons to include phonon line widths
International Nuclear Information System (INIS)
Zubarev in 1960 obtained the smeared Bose-Einstein (B-E) function in order to take into account the fact that the eigenenergy associated with a fixed phonon wave vector q and fixed polarization index j is not precisely defined but instead, is smeared by phonon-phonon and phonon-electron interactions. The ratio GAMMA(qj)/?(qj) is often quite small, i.e., of the order of 0.01 or less, where GAMMA is the phonon linewidth and h-bar ? is the eigenenergy. However, in strongly anharmonic crystals GAMMA/? may be as large as 0.3 at certain points of the Brillouin zone. In such dramatic cases one would suspect that such phonon linewidths would have some observable effect on the thermodynamic properties. The purpose of this work is to derive the expression for the average free energy per mode for a crystal having large phonon linewidths and to test the properties of the thermodynamic functions derivable from the average free energy per mode
A Correlation Function for Phonon Eigenvectors
International Nuclear Information System (INIS)
It was shown by van Hove that the Fourier transform of the neutron scattering intensity is a space-time correlation function of the scattering density. In the special case of a single crystal as the scattering system, the coefficients of a Fourier series can be derived from the one-phonon scattering cross-sections corresponding to a phonon of a particular frequency. Evaluation of the Fourier series gives a space correlation function involving the eigenvectors of the mode of vibration being considered. The function is a special case of the van Hove function, closely related to the Patterson function which is used in X-ray crystallography. In the special case of a phonon of wave vector zero (q = 0) the function has a sufficiently simple interpretation that it may be of practical value. (author)
Phonon multiplexing through 1D chains
Scientific Electronic Library Online (English)
A., Avila; D., Reyes.
2008-12-01
Full Text Available Recently, phonon propagation through atomic structures has become a relevant study issue. The most important applications arise in the thermal field, since phonons can carry thermal and acoustic energy. It is expected that technological advances will make possible the engineering of thermal paths ac [...] cording to convenience. A simple phonon multiplexer was analyzed as a spring-mass model. It consists of mono-atomic chains of atoms with a coupling structure between them. Forces between atoms follow Hooke's law and are restricted to be first nearest neighbor interaction. It was possible to establish simple rules on constitutive parameters such as atom masses and bonding forces that enable one to select a wavelength of transmission. The method used enables the study of structures of much greater complexity than the one presented here.
On the quasiparticle-phonon nuclear model at finite temperature
International Nuclear Information System (INIS)
The system of equations for the parameters describing the quasiparticle and phonon excitations in nucleus is obtained from the unique variational principle for the thermodynamic potential. Quasiparticle-phonon interaction is taken into account perturbatively in the first nonzero approximation
Situation with collective two-phonon states in deformed nuclei
International Nuclear Information System (INIS)
Within the quasiparticle-phonon nuclear model with the operators of phonons depending on the sign of the angular momentum projection, the Pauli principle is taken into account in the two-phonon components of the wave functions. The centroid energies of the collective two-phonon states in even-even deformed nuclei are calculated. It is shown that the inclusion of the Pauli principle leads to their shift by 1-3 MeV towards high energies. The shifts of three-phonon poles due to the Pauli principle are calculated in the three-phonon components of the wave functions. The collective two-phonon states, the centroid energies of which are 3-5 MeV, are expected to be strongly fragmented. The conclusion is confirmed that the collective two-phonon states should not exist in deformed nuclei. The situation in 168Er and in the 228Th isotopes is analysed
Acoustic phonons in Si/Ge supra-crystal
International Nuclear Information System (INIS)
In the presented article we relate on the theoretical investigation of acoustic phonon properties in Si/Ge three-dimensionally ordered quantum dots superlattices (supra-crystals). Our calculations of the acoustic phonon energy spectra and phonon dispersions were performed in the framework of the face-centered cubic cell molecular-dynamic model. We have investigated the dependencies of phonon density of states and phonon group velocity on the phonon energy and have established that the average phonon velocity is close to zero in the wide range of phonon energies > 10 MeV. The obtained results allow us to predict the extremely low value of the lattice thermal conductivity in supra-crystal and correspondingly extremely high value of the thermoelectric figure of merit ZT. (authors)
Collective two-phonon states in deformed nuclei
International Nuclear Information System (INIS)
The Pauli principle in the two-phonon components of the wave function is taken into account within the quasiparticle-phonon nuclear model with phonon operators depending upon the sign of the angular momentum component. The centroid energies of the two-phonon collective states in doubly even deformed nuclei are calculated. It is shown that they are shifted by 1-3 MeV towards greater energies due to the Pauli principle. The shifts of the three-phonon poles caused by the Pauli principle in the three-phonon components of the wave functions are calculated. A strong fragmentation of the two-phonon collective states whose centroid energies equal 3-5 MeV should be expected. Nonexistence of the collective two-phonon states in deformed nuclei is confirmed. The situation in the 168Er nucleus and in Th and U irotopes is analyzed
Evidence for pervasive phonon structure of nuclear excitations
International Nuclear Information System (INIS)
Recent work suggests that phonon and intact multiphonon excitations are pervasive in nuclei whose structures run the gamut of collective types. Some of this evidence for a nearly universal phonon description of low energy nuclear spectral will be summarized
Energy Technology Data Exchange (ETDEWEB)
Xu, D. B., E-mail: dongbin.xu@seagate.com [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Materials Science and Engineering, National University of Singapore, 117576 Singapore (Singapore); Sun, C. J., E-mail: cjsun@aps.anl.gov, E-mail: msecgm@nus.edu.sg; Ho, P.; Chen, J. S.; Chow, G. M., E-mail: cjsun@aps.anl.gov, E-mail: msecgm@nus.edu.sg [Department of Materials Science and Engineering, National University of Singapore, 117576 Singapore (Singapore); Brewe, D. L.; Heald, S. M.; Zhang, X. Y. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Han, S.-W. [Department of Physics Education and Institute of Fusion Science, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)
2014-06-28
We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L1{sub 0} FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated.
Phonon Scattering and Excitons in Carbon Nanotubes.
Perebeinos, Vasili
2005-03-01
Due to their low dimensionality, carbon nanotubes (CNTs) have striking properties, quite different from these of traditional semiconductors, with important implications for technology. The performance of electronic devices relies on carrier mobility, which is extraordinary high in CNTs at low fields. However, at high fields the mobility is dramatically reduced due to inelastic optical phonon scattering. Optical properties of CNTs, essential for electro-optical devices, are dominated by excitons with binding energies and oscillator strengths orders of magnitude larger than those in conventional semiconductors. We calculate the electron-phonon scattering and binding in CNTs, within a tight binding model [1]. We derive the mobility as a function of temperature, electric field, and nanotube chirality using a multi-band Boltzmann treatment. We find the drift velocity saturates at approximately half the graphene Fermi velocity. Polaronic binding give a band-gap renormalization of 70 meV, an order of magnitude larger than previously suggested. We calculate the properties of excitons in CNTs embedded in a dielectric, for a wide range of tube radii and dielectric environments, by solving the Bethe-Salpeter Equation in a tight binding basis. We find that simple scaling relationships give a good description of the binding energy, exciton size, and oscillator strength as a function the tube radius, the dielectric constant of the embedding material, and the chirality [2]. In addition we calculate optical absorption including the exciton-phonon interaction. We find a phonon sideband at 200 meV above the zero phonon line, due to the creation of exciton plus one optical phonon [3]. [1] V. Perebeinos, J. Tersoff, and Ph. Avouris, cond-mat/0411021. [2] V. Perebeinos, J. Tersoff, and Ph. Avouris, Phys. Rev. Lett. 92, 257402 (2004). [3] V. Perebeinos, J. Tersoff, and Ph. Avouris, cond-mat/0411618.
Decoherence measurement of single phonons using spectral interference
Waldermann, F. C.; Sussman, B. J.; Nunn, J.; Lorenz, V. O.; Lee, K. C.; Surmacz, K.; Lee, K. H.; Jaksch, D.; Walmsley, I. A.; Spizziri, P.; Olivero, P.; Prawer, S.
2008-01-01
A technique to measure the decoherence time of optical phonons in a solid is presented. Phonons are excited with a pair of time delayed 80 fs, near infrared pulses via spontaneous, transient Raman scattering. The fringe visibility of the resulting Stokes pulse pair, as a function of time delay, is used to measure the phonon dephasing time. The method avoids the need to use either narrow band or few femtosecond pulses and is useful for low phonon excitations. The dephasing ti...
Neutron-Phonon Interaction in Neutron Star Crusts
Sedrakian, Armen
1998-01-01
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...
Master equation for photon mediated phonon-atom coupled system
Shen, J.; Zhang, X. Y.; Teng, J. H.; Hou, S. C.; Yi, X. X.
2014-04-01
Achieving phonon-atom couplings in cavity optomechanical system could lead to fundamentally new regimes of phonon-matter interaction and the development of sensitive mass and force sensors. Here we derive a master equation to describe the phonon-atom system and numerically simulate the equation. The phonon-atom coupling is mediated by a driven cavity mode. A crossover from the bad cavity limit, which validates the master equation, to the limit of small cavity loss rate is studied.
Optical Phonon Modes and Electron-Phonon Interaction in a Spheroidal Quantum Dot
Ishida, M.; Yamaguchi, M.; Sawaki, N.
Optical phonon modes in a semiconductor quantum dot were analyzed with exactly solvable model structure. A set of universal formulae for the electron and phonon wave functions was derived for spheroids. Using these wavefunctions, the intersubband scattering rates due to emission of phonons were investigated as a function of the size and the shape of the dot. It was shown that the maximum total scattering rate is slightly enhanced by reducing the height of the dot, which is attributed to the increase of the contribution of the interface modes.
Electron-phonon interaction and composition-dependent phonon anomaly in CeHsub(x)
International Nuclear Information System (INIS)
The Raman active phonon in CeHsub(approximately 3) is anomalously soft as compared with that in in CeHsub(approximately 2). It is shown that this can be attributed to enhanced electron-phonon interactions arising from changes in the electronic structure with composition: when going from CeH2 to CeH3 a new s-like valence band is formed, and the valence electrons screen the Raman active mode via virtual transitions into Ce d states. Frequency renormalisation due to the electron-phonon interaction has been calculated from the electronic energy bands. (author)
Electronic structure, phonon spectra and electron-phonon interaction in ScB2
International Nuclear Information System (INIS)
The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron-phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.
Electron-Phonon Coupling and the Soft Phonon Mode in TiSe$_2$
Weber, F.; Rosenkranz, S.; Castellan, J. -p; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K. -p; Alatas, A.
2011-01-01
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...
Electron-Phonon Coupling in Charged Buckminsterfullerene
Breda, N; Colò, G; Román, H E; Alasia, F; Onida, G; Ponomarev, V; Vigezzi, E
1998-01-01
A simple, yet accurate solution of the electron-phonon coupling problem in C_{60} is presented. The basic idea behind it is to be found in the parametrization of the ground state electronic density of the system calculated making use of ab-initio methods, in term of sp$^{2+x}$ hybridized orbitals. This parametrization allows for an economic determination of the deformation potential associated with the fullerene's normal modes. The resulting electron-phonon coupling constants are used to calculate Jahn-Teller effects in C_{60}^-, and multiple satellite peaks in the corresponding photoemission reaction. Theory provides an accurate account of the experimental findings.
Phonon interference effects in molecular junctions
DEFF Research Database (Denmark)
Markussen, Troels
2013-01-01
We study coherent phonon transport through organic, p-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.
Terahertz phonon spectroscopy of doped superconducting cuprates
Ponomarev, Ya. G.; Van, H. H.; Kuzmichev, S. A.; Kulbachinskii, S. V.; Mikheev, M. G.; Sudakova, M. V.; Tchesnokov, S. N.
2013-02-01
Facts are presented evidencing a strong electron-phonon interaction in doped BSCCO superconductors. A pronounced fine structure in dI/ dV characteristics of Josephson junctions has been observed which is caused by interaction of AC Josephson current with Raman-active optical phonon modes. "Quantization" of the "gap" voltage for natural nanosteps on the cryogenically cleaved surfaces of BSCCO proves the existence of the intrinsic Josephson effect. A sharp extra structure in the current-voltage characteristics of nanosteps is attributed to the presence of the extended van Hove singularity.
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)
Spin-Phonon Chains with Bond Coupling
Raas, C; Löw, U; Uhrig, G S; Raas, Carsten
2002-01-01
We investigate the antiadiabatic limit of an antiferromagnetic S=1/2 Heisenberg chain coupled to Einstein phonons via a bond coupling. The flow equation method is used to decouple the spin and the phonon part of the Hamiltonian. In the effective spin model longer range spin-spin interactions are generated. The effective spin chain is frustrated. The resulting temperature dependent couplings are used to determine the magnetic susceptibility and to determine the phase transition from a gapless state to a dimerized gapped phase. The susceptibilities and the phase diagram obtained via the effective couplings are compared with independently calculated quantum Monte Carlo results.
Evidence for second-phonon nuclear wobbling
International Nuclear Information System (INIS)
The nucleus 163Lu has been populated through the reaction 139La(29Si,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2)out/B(E2)in value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation
Phonon-Mediated Anomalous Dynamics of Defects
Najafi, A; Najafi, Ali; Golestanian, Ramin
2002-01-01
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.
Near-forward Raman study of a phonon-polariton reinforcement regime in the Zn(Se,S) alloy
Hajj Hussein, R.; Pagès, O.; Firszt, F.; Marasek, A.; Paszkowicz, W.; Maillard, A.; Broch, L.
2014-08-01
We investigate by near-forward Raman scattering a presumed reinforcement of the (A-C,B-C)-mixed phonon-polariton of a A1-xBxC zincblende alloy when entering its longitudinal optical-like (LO-like) regime near the Brillouin zone centre ?, as predicted within the formalism of the linear dielectric response. A choice system to address such issue is ZnSe0.68S0.32 due to the moderate dispersion of its refractive index in the visible range, a sine qua non condition to bring the phonon-polariton insight near ?. The LO-like reinforcement regime is actually accessed by using the 633.0 nm laser excitation, testified by the strong emergence of the (Zn-Se,Zn-S)-mixed phonon-polariton at ultimately small scattering angles.
Ding, Yujie J
2015-03-01
Raman oscillation, frequency upconversion, and Raman amplification can be achieved in a second-order nonlinear medium at the phonon-polariton resonance. By beating two optical fields, a second-order nonlinear polarization is generated inside the medium. Such a polarization induces a spatially uniform nonpropagating electric field at the beat frequency, which in turn mixes with the input optical field at the lower frequency to generate or amplify the anti-Stokes optical field. Raman oscillation can be efficiently reached for the copropagating configuration. In comparison, efficient frequency upconversion and large amplifications are achievable for the counterpropagating configuration. These Raman processes can be used to effectively remove transverse-optical phonons before decaying to lower-frequency phonons, achieve laser cooling, and significantly enhance coherent anti-Stokes Raman scattering. The counterpropagating configuration offers advantages for amplifying extremely weak signals. PMID:25723418
Advances in semiconductor lasers and applications to optoelectronics
Dutta, Mitra
2000-01-01
This volume includes highlights of the theories underlying the essential phenomena occurring in novel semiconductor lasers as well as the principles of operation of selected heterostructure lasers. To understand scattering processes in heterostructure lasers and related optoelectronic devices, it is essential to consider the role of dimensional confinement of charge carriers as well as acoustical and optical phonons in quantum structures. Indeed, it is important to consider the confinement of both phonons and carriers in the design and modeling of novel semiconductor lasers such as the tunnel
Electron Phonon Superconductivity in LaNiPO
International Nuclear Information System (INIS)
We report first principles calculations of the electronic structure, phonon dispersions and electron phonon coupling of LaNiPO. These calculations show that this material can be explained as a conventional electron phonon superconductor in contrast to the FeAs based high temperature superconductors.
Anisotropic phonon softening in URu2Si2
Butch, Nicholas; Manley, Michael; Jeffries, Jason; Janoschek, Marc; Huang, Kevin; Maple, Brian; Lynn, Jeffrey
2013-03-01
We studied the low-energy phonons of URu2Si2 via inelastic neutron scattering. At the wave-vectors associated with magnetic excitations, the phonons show surprisingly little modification. However, we find important temperature and direction dependence of the phonons in the basal plane. Possible ramifications for the symmetry of the hidden order will be discussed.
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.
Barium strontium titanate ferroelectric tunable photonic and phononic crystals
Jim, Kwok Lung
2009-12-01
This thesis presents the results of theoretical simulations and experimental investigations on developing electro-optically tunable photonic crystals and thermally tunable phononic crystals based on the ferroelectric materials, Barium Strontium Titanate (Ba0.7Sr0.3TiO3, BST). One-dimensional photonic crystal (PC), consists of alternating Ba 0.7Sr0.3TiO3 and MgO layers, was fabricated using pulsed laser deposition. A photonic bandgap has been observed in the transmission measurement which is consistent with simulation using the plane wave expansion (PWE) method and the transfer matrix method. A 2-nm shift towards the longer wavelength is observed when a dc voltage of 240 V (corresponding to an electric field of about 12 MV/m) has been applied across the coplanar electrodes on the film surface. The experimental result suggests that the electric field induced change in the refractive index of Ba0.7Sr0.3TiO 3 is about 0.5%. Photonic bandstructures and photonic bandgap maps of two-dimensional (2D) Ba0.7Sr0.3TiO3-based photonic crystals with different cavity geometries (square or circular air rods) in square lattice were calculated using the PWE method. Bandgap features along different symmetry directions have also been compared. The appropriate geometry of a single-mode rib waveguide based on Ba 0.7Sr0.3TiO3 thin film was determined by applying the effective index method. A photonic crystal cavity embedded Ba0.7 Sr0.3TiO3 rib waveguide which functions as a tunable filter for lambda = 1550 nm was designed with the help of the finite-difference time-domain (FDTD) simulation. A 6-nm shift in the resonant peak for a 0.5% change in the refractive index of Ba0.7Sr0.3TiO 3 was illustrated in the simulation. Photonic crystal cavities were fabricated on a Ba0.7Sr0.3TiO3 rib waveguide by focused ion beam etching with satisfactory results. A drastic variation in the sound velocities was observed across the Curie temperature of Ba0.7Sr0.3TiO3 via the ultrasonic through-transmission technique. Phononic crystal composed of Ba0.7Sr 0.3TiO3 square rods in a matrix of epoxy were fabricated using the dice-and-fill method. The temperature dependence of the phononic bandgaps was characterized by the reflection spectra obtained using the ultrasonic pulse-echo technique. Thermal tuning of the phononic bandgap was observed and the results were in good agreement with the phononic bandstructure calculation by the PWE method.
Electron-phonon and spin-phonon coupling in $NaV_{2}O_{5}
Sherman, E Y; Lemmens, P; Van Loosdrecht, P H M; Güntherodt, G
1999-01-01
We show that the asymmetric crystal environment of the V site in the ladder compound NaV$_{2}$O$_{5}$ leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the charge on the V ions, and favors a transition to a charge-ordered state at low temperatures. In the low temperature phase the charge fluctuations modulate the spin-spin superexchange interaction, resulting in a strong spin-phonon coupling.
Inomogeneous Quantum Groups as Symmetries of Phonons
Bonechi, F; Giachetti, R; Sorace, E; Tarlini, M
1992-01-01
The quantum deformed (1+1) Poincare' algebra is shown to be the kinematical symmetry of the harmonic chain, whose spacing is given by the deformation parameter. Phonons with their symmetries as well as multiphonon processes are derived from the quantum group structure. Inhomogeneous quantum groups are thus proposed as kinematical invariance of discrete systems.
Phononic crystals for liquid sensor applications
International Nuclear Information System (INIS)
Acoustic band gap materials, so-called phononic crystals, are introduced as a new platform for sensing material properties in small cavities. The sensor employs specific transmission windows within the band gap to determine properties of one component that builds the phononic crystal. The dependence of the frequency where transmission takes place is correlated to material properties, specifically to the sound velocity of a liquid. This value is related to several parameters of practical interest like the concentration of one component in a mixture or conversion rate in a microreactor. The capability of the concept will be demonstrated with a one-dimensional arrangement of solid plates and liquid-filled cavities and a two-dimensional periodic arrangement of liquid-filled holes in a solid matrix. The properties of 1D phononic crystals will be analysed in terms of the effective acoustic impedance and the resulting transmission behaviour and experimentally verified. The transmission properties of the 2D phononic crystal will be modelled with the layer multiple-scattering theory. Similar features which can be employed for sensing purposes will be discussed
Phonon Transport in Suspended Single Layer Graphene
Xu, Xiangfan; Wang, Yu; Zhang, Kaiwen; Zhao, Xiangming; Bae, Sukang; Heinrich, Martin; Bui, Cong Tinh; Xie, Rongguo; Thong, John T. L.; Hong, Byung Hee; Loh, Kian Ping; Li, Baowen; Oezyilmaz, Barbaros
2010-01-01
We report the first temperature dependent phonon transport measurements in suspended Cu-CVD single layer graphene (SLG) from 15K to 380K using microfabricated suspended devices. The thermal conductance per unit cross section $\\sigma$/A increases with temperature and exhibits a peak near T~280K ($\\pm$10K) due to the Umklapp process. At low temperatures (T
Synthetic thermoelectric materials comprising phononic crystals
El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang
2013-08-13
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.
Magnetic polarization and two-phonon states
International Nuclear Information System (INIS)
Influence of magnetic core polarization on properties of 2- member of two-phonon quintet of states 21+ x 31- is analyzed. Like for recently identified lowest 1- member of this quintet, an excitation probability of 2- state is strongly affected by polarization of the nucleus
Tuning phonon properties in thermoelectric materials
Srivastava, G. P.
2015-02-01
This review article presents a discussion of theoretical progress made over the past several decades towards our understanding of thermoelectric properties of materials. Particular emphasis is placed upon describing recent progress in ‘tuning’ phonon properties of nanocomposite materials for gaining enhancement of the thermoelectric figure of merit.
Hopkins, Patrick E.; Kassebaum, Jared L.; Norris, Pamela M.
2009-01-01
Electron scattering at interfaces between metals and dielectrics is a major concern in thermal boundary conductance studies. This aspect of energy transfer has been extensively studied and modeled on long time scales when the electrons and phonons are in equilibrium in the metal film. However, there are conflicting results concerning electron-interface scattering and energy transfer in the event of an electron-phonon nonequilibrium, specifically, how this mode of energy transfer affects the electron cooling during electron-phonon nonequilibration. Transient thermoreflectance (TTR) experiments utilizing ultrashort pulsed laser systems can resolve this electron-phonon nonequilibrium, and the thermophysical property relating rate of equilibration to electron-phonon scattering events G can be quantified. In this work, G in Au films of varying thicknesses are measured with the TTR technique. At large fluences (which result in high electron temperatures), the measured G is much larger than predicted from traditional models. This increase in G increases as the film thickness decreases and shows a substrate dependency, with larger values of G measured on more conductive substrates. The data suggest that in a highly nonequilibrium system, there could be some thermal energy lost to the underlying substrate, which can affect G.
Observation of the full exciton and phonon fine structure in CdSe/CdS dot-in-rod heteronanocrystals.
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
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
Phonon Instabilities and Structural Transformations of Group IV Semiconductors
Biswas, Rana
This thesis begins with the study of the stability of a silicon crystal under conditions of high electronic excitation, of the type produced by rapid laser pulses. A calculation of the phonon spectrum of such a crystal is performed with a dielectric model that accounts for covalent bonding and electron excitation, with the simplifying assumption that the carriers retain the laser energy. The calculation yields a softening of the zone boundary transverse acoustic phonons with the {111} zone boundary mode becoming unstable first at excited electron densities in the range of (6-10) x 10('21) cm('-3), which corresponds to 3-5% of the valence electron density. The weakening of the bond charges and the corresponding metallic screening are the main factors causing this instability. These results do not support the plasma annealing hypothesis for laser induced recrystallization. Further, this instability is found to be unimportant for the thermal melting of silicon. Instead, the instability suggests a structual transformation of the diamond crystal where adjacent {111} planes shear relative to each other. The hypothesis that this may be related to the well known pressure induced transformation of silicon from the (alpha)-diamond to the metallic (beta) -tin phase is then investigated. A structural path is constructed between the (alpha) and (beta) phases that uses this shear distortion as the primary ingredient. This path is compared to a higher symmetry path by means of extended-Huckel calculations. Further, extended-Huckel calculations of the electronic structure of (beta)-Si are described, which relate its metallic character to orbital level crossings. In addition to (beta)-tin and diamond, silicon and germanium can exist in complex crystal structures, termed BC8 and ST12, that can be metastably formed under pressure. The properties of silicon and carbon in these distorted tetrahedral structures are studied with self consistent density functional calculations of the total energy, forces and stresses. For silicon, the predicted BC8 structure agrees well with experiment for both the lattice constant and the internal parameter, which was allowed to relax during the calculation. Further, BC8 -silicon is found to have enthalpy slightly higher than the diamond and (beta)-tin phases, so that BC8 can only be a metastable phase in silicon. Additional consideration of structural paths indicate why it can be formed on decreasing pressure from the (beta)-tin phase. For carbon, BC8 is found to be a stable phase above 12 Mbar. This gives a new stability limit for diamond.
Measuring phonon dephasing with ultrafast pulses using Raman spectral interference
Waldermann, Fc; Sussman, Bj; Nunn, J.; Lorenz, Vo; Lee, Kc; Surmacz, K.; Lee, Kh; Jaksch, D.; Walmsley, Ia; Spizziri, P.; Olivero, P.; Prawer, S.
2008-01-01
A technique to measure the decoherence time of optical phonons in a solid is presented. Phonons are excited with a pair of time-delayed 80 fs near infrared pulses via spontaneous transient Raman scattering. The spectral fringe visibility of the resulting Raman pulse pair, as a function of time delay, is used to measure the phonon dephasing time. The method avoids the need to use either narrow band or few femtosecond pulses and is useful for low phonon excitations. The dephasing time of phonon...
Phonon thermal transport and phonon–magnon coupling in polycrystalline BiFeO3 systems
Ramachandran, B.; Wu, K. K.; Kuo, Y. K.; Ramachandra Rao, M. S.
2015-03-01
Temperature-dependent thermal conductivity of polycrystalline BiFeO3, Bi0.9Ba0.05Ca0.05FeO2.95 and Bi0.9Ca0.1FeO2.95 materials was measured using a direct heat pulse technique. Thermal conductivity of the BiFeO3-based materials is analyzed using a phonon model to probe the thermal transport mechanisms in these ferrites. It is found that the calculated thermal conductivity of the BiFeO3-based compounds is in good agreement with experimental data. The suppression of the low-temperature phonon peak in the thermal conductivity of the doped BiFeO3 materials is mainly attributed to the phonon-point-defect scattering. In addition, the contribution of optical phonon–magnon resonance scattering to optical phonon thermal transport reveals the presence of phonon–magnon coupling in these BiFeO3 materials. Finally, magneto-thermal conductivity measurements show the magnon thermal transport in pure and doped BiFeO3 systems.
BEDT-TTF organic superconductors the entangled role of phonons
Girlando, A; Brillante, A; Della Valle, R G; Venuti, E; Girlando, Alberto; Masino, Matteo; Brillante, Aldo; Valle, Raffaele G. Della; Venuti, Elisabetta
2002-01-01
We calculate the lattice phonons and the electron-phonon coupling of the organic superconductor \\kappa-(BEDT-TTF)_2 I_3, reproducing all available experimental data connected to phonon dynamics. Low-frequency intra-molecular vibrations are strongly mixed to lattice phonons. Both acoustic and optical phonons are appreciably coupled to electrons through the modulation of the hopping integrals (e-LP coupling). By comparing the results relevant to superconducting \\kappa- and \\beta-(BEDT-TTF)_2 I_3, we show that electron-phonon coupling is fundamental to the pairing mechanism. Both e-LP and electron-molecular vibration (e-MV) coupling are essential to reproduce the critical temperatures. The e-LP coupling is stronger, but e-MV is instrumental to increase the average phonon frequency.
International Nuclear Information System (INIS)
X-ray diffraction analysis was used to investigate the influence of bulk isothermal and surface laser annealings on crystallization of Fe61Co20Si5B14 metallic glass. It is shown that crystallization proceeds in different ways on isothermal and laser annealings. Low-energy laser treatment makes it possible to produce complex phase composition in a surface layer which may be controlled by irradiation dose rate
Single-photon indistinguishability: influence of phonons
DEFF Research Database (Denmark)
Nielsen, Per Kær; Lodahl, Peter
2012-01-01
Recent years have demonstrated that the interaction with phonons plays an important role in semiconductor based cavity QED systems [2], consisting of a quantum dot (QD) coupled to a single cavity mode [Fig. 1(a)], where the phonon interaction is the main decoherence mechanism. Avoiding decoherence effects is important in linear optical quantum computing [1], where a device emitting fully coherent indistinguishable single photons on demand, is the essential ingredient. In this contribution we present a numerically exact simulation of the effect of phonons on the degree of indistinguishability of photons emitted from a solid-state cavity QED system. Our model rigorously describes non-Markovian effects to all orders in the phonon coupling constant, being based on an exact diagonalization procedure accounting for the time evoluiton of one-time and two-time photon correlation funcitons. We compare to standard approaches for treating the phonon interaction, namely the Markovian Lindblad formalism and the long-time limit of the non-Markovian timeconvolution-less (TCL) approach, and find large quantitative and qualitative differences [3]. Figures 1(b) and (c) show the calculated indistingusihability as a function of the QD-cavity coupling strength for light emitted from the QD and the cavity, respectively, for all the employed methods. Both the Lindblad and TCL theories deviate significantly from our exact results, where, importantly, the exact results predict a pronounced maximum in the degree of indistinguishability, absent in the approximate theories. The maximum arises due to virtual processes in the highly non-Markovian short-time regime, which dominate the decoherence for small QD-cavity coupling, and phonon-mediated real transitions between the upper and lower polariton branches in the long-time regime, dominating the decoherence for large QD-cavity coupling. Our method captures the physics of the regime of small and as well as large QD-cavity coupling, both corresponding to experimentally relevant situations. Importantly, the commonly used Lindblad formalism fails completely in describing the variations of the indistinguishability predicted by the two other models.
Propagation of optically generated acoustic phonons in Si
Shields, J. A.; Msall, M. E.; Carroll, M. S.; Wolfe, J. P.
1993-05-01
This paper deals with the spectral and spatial distributions of nonequilibrium acoustic phonons produced by optical excitation of a high-purity Si crystal at low temperatures (Tremoving the contact of the helium bath from the excitation surface, we have quantified the effects of the bath on the detected heat pulses. As the power density of the optical pulses is increased, qualitative changes occur in the shapes of the heat pulses, and at high density, the quasidiffusive propagation is bypassed by the emergence of a localized source of low-frequency phonons. The threshold density for the formation of the localized source is far below that calculated for a ``hot spot'' based on phonon-phonon interactions. We postulate that the photoexcited carriers, largely in the form of electron-hole droplets, are playing a dominant role in determining the frequency distribution of emitted phonons. Our experiments employ a wide variety of techniques to characterize the propagation of nonequilibrium phonons in silicon: Phonon imaging is used to gauge the size and lifetime of the phonon sources, as well as indicate the frequency distribution of the detected phonons. Comparison is made between direct photoexcitation of silicon and optical excitation of a metal film deposited on the silicon surface. These experiments and Monte Carlo simulations give insight into the diffusion of high-frequency phonons near the interface. The occurrence of a helium bubble at a point of high excitation is shown to have a marked influence on the detected heat pulses.
Structural Properties and Phonon dispertion of NACl
Directory of Open Access Journals (Sweden)
R. Khoda-Bakhsh
2001-06-01
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 Ù. 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.
Thermodynamics of phonon-modulated tunneling centers
International Nuclear Information System (INIS)
In recent years tunneling centers have frequently been used to explain the unusual thermodynamic properties of disordered materials; in these approaches, however, the effect of the tunneling-phonon interaction is neglected. The present study considers the archetype model of phono-assisted tunneling, which is well known from other areas of tunneling physics (quantum diffusion, etc.). It is shown that the full thermodynamic information can be rigorously extracted from a single Green function. An extended factorization procedure beyond Hartree-Fock is introduced, which is checked by sum rules as well as by exact Goldberger-Adams expansions. The phonon-modulated internal energy and specific heat are calculated for different power-law coupling setups
Interaction of Thermal Phonons with Interfaces
Energy Technology Data Exchange (ETDEWEB)
David H. Hurley; Subhash Shinde; Edward Piekos
2013-11-01
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.
Quantum mode phonon forces between chainmolecules
DEFF Research Database (Denmark)
Bohr, Jakob
2001-01-01
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.
Phonon spectroscopy with superconducting tunnel junctions
International Nuclear Information System (INIS)
Superconducting tunnel junctions can be used as generators and detectors of monochromatic phonons of frequency larger than 80 GHz, as was first devised by Eisenmenger and Dayem (1967) and Kinder (1972a, 1973). In this report, we intend to give a general outline of this type of spectroscopy and to present the results obtained so far. The basic physics underlying phonon generation and detection are described in chapter I, a wider approach being given in the references therein. In chapter II, the different types of junctions are considered with respect to their use. Chapter III deals with the evaporation technique for the superconducting junctions. The last part of this report is devoted to the results that we have obtained on ?-irradiated LiF, pure Si and Phosphorous implanted Si. In these chapters, the limitations of the spectrometer are brought out and suggestions for further work are given
Electron-phonon interaction in $C_{70}$
Provasi, D; Broglia, R A; Colò, G; Román, H E; Onida, G
2000-01-01
The matrix elements of the deformation potential of C$_{70}$ are calculated by means of a simple, yet accurate solution of the electron-phonon coupling problem in fullerenes, based on a parametrization of the ground state electronic density of the system in terms of $sp^{2+x}$ hybridized orbitals. The value of the calculated dimensionless total electron-phonon coupling constant is $\\lambda\\approx0.1$, an order of magnitude smaller than in C$_{60}$, consistent with the lack of a superconducting phase transition in C$_{70}$A$_3$ fullerite, and in overall agreement with measurements of the broadening of Raman peaks in C$_{70}$K$_4$. We also calculate the photoemission cross section of C$_{70}^-$, which is found to display less structure than that associated with C$_{60}^-$, in overall agreement with the experimental findings.
Phonon heat transport through periodically stubbed waveguides
International Nuclear Information System (INIS)
We investigate the acoustic phonon band structure, transmission spectrum and thermal conductance in a periodically stubbed waveguide structure by use of the transfer matrix method and the scattering matrix method. We find that the existence of stop-frequencies or dips in the transmission spectrum, which corresponds to the stop bands or gaps in the acoustic band structure. The dependence of the stop band width and the dip width on the stub height is also demonstrated. We also find that the universal quantum thermal conductance can be clearly observed and the thermal conductance increases monotonically with increasing temperature. Our results show that the acoustic phonon band structure, transmission spectrum and thermal conductance can be artificially controlled by adjusting the height of the stub
First tests on phonon threshold spectroscopy
International Nuclear Information System (INIS)
Using the proximity effect of iridium and gold we fabricate sensitive phase transition thermometers. In spite of problems with other material combinations iridium/gold thermometers show an excellent long-term stability. Up to now we reached transition temperatures in the range from 20 to 100 mK on different absorber materials for example silicon, germanium and sapphire. A study of detectors consisting of a dielectric sapphire absorber, an Ir/Au thermometer and an additional superconducting film is presented. In this case some phonons produced by an interaction in the absorber can break up Cooper-Pairs in the superconducting film. Some energy is stored in the quasiparticle system and reemitted into the absorber with a delay. The recombination phonons are again detected with the thermometer. From the pulse shape of the temperature signal the lifetime of the quasiparticles can be extracted. The results for aluminum and tantalum are presented
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.))
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
Electron-Phonon Interaction in Tetrahedral Semiconductors
Cardona, M
2004-01-01
Effects of electron-phonon interactions on the band structure can be experimentally investigated in detail by measuring the temperature dependence of energy gaps or critical points (van Hove singularities) of the optical excitation spectra. These studies have been complemented in recent years by observing the dependence of such spectra on isotopic mass whenever different stable isotopes of a given atom are available at affordable prices. In crystals composed of different atoms, the effect of the vibration of each separate atom can thus be investigated by isotopic substitution. Because of the zero-point vibrations, such effects are present even at zero temperature (T = 0). In this paper we discuss state-of-the-art calculations of the dielectric function spectra and compare them with experimental results, with emphasis on the differences introduced by the electron-phonon interaction. The temperature dependence of various optical parameters will be described by means of one or two (in a few cases three) Einstein...
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
Phonon Squeezing in a Superconducting Molecular Transistor
Zazunov, A; Martin, T; Martin, Thierry
2006-01-01
Josephson transport through a double junction formed by a single molecule or carbon nanotube is considered in the presence of a local vibrational mode which is linearly coupled to the charge on the molecule. An exact solution is obtained in the limit of a large superconducting gap, and it is complemented by a variational analysis in the general case. Coherent charge fluctuations involve polaron dressing and are entangled with non-classical phonon states. The flow of a Josephson current induces squeezing of the phonon mode, controlled by the superconducting phase difference and by the junction asymmetry. Squeezing is maximal in the polaron crossover regime, where a nearly minimum-uncertainty state with about 40 per cent squeezing can be obtained. Optical probes of non-classical states are briefly discussed.
A step closer to visualizing the electron___phonon interplay
Energy Technology Data Exchange (ETDEWEB)
Chen, Y.L.; Lee, W.S.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept. /SLAC, PULSE
2011-01-04
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
Mechanism of phonon localized edge modes
Jiang, Jin-wu; Wang, Jian-sheng
2010-01-01
The phonon localized edge modes are systematically studied, and two conditions are proposed for the existence of the localized edge modes: (I) coupling between different directions ($x$, $y$ or $z$) in the interaction; (II) different boundary conditions in three directions. The generality of these two conditions is illustrated by different lattice structures: one-dimensional (1D) chain, 2D square lattice, 2D graphene, 3D simple cubic lattice, 3D diamond structure, etc; and w...
Phonon-like excitations of instanton liquid
International Nuclear Information System (INIS)
Phonon-like excitations of an anti-instanton-instanton liquid that are due to adiabatic variations in the instanton dimension are considered on the basis of an approximate calculation of the relevant path integral, which is saturated by quasizero modes. The kinetic term and the effective Lagrangian are found for such excitations. The properties of their spectrum, which has a mass gap determined by ?QCD, are discussed
Electron-phonon interaction in nanodevices
Kral, Karel
2008-01-01
The effect of the up-conversion of the electronic energy level occupation was earlier interpreted as an implication of the multiple scattering of the charge carriers on the longitudinal optical phonons of the lattice vibrations in a small system like a quantum dot. In this work we study the influence of this effect on the electronic motion in a nanotransistor represented by a quantum dot connected to two electric wires and a gate electrode. We show that in an asymmetric nano...
Calculation of the phonon spectrum in thorium
International Nuclear Information System (INIS)
Due to the comparatively extended d states in the transition metal thorium, it is argued that the pseudopotential method may be a fairly realistic approach to this element. Calculations of the phonon spectrum with an empirically derived form factor are shown to give quite good agreement with recent experiments. Also the calculated values of the elastic constants, the bulk modulus, the Debye temperature, and the binding energy are found to be most reasonable
Comments on exciton-phonon coupling. II
International Nuclear Information System (INIS)
Two variational calculations of the energy and correlation functions for a simple exciton-phonon coupled system are presented and contrasted to the adiabatic solution and the exact solution. The simpler variational solution leads to two minima and abrupt changes in the properties of the system; an asymmetric variational wavefunction, motivated by the form of perturbation theory for this problem, leads to smooth behavior in agreement with the exact result. (Auth.)
Optical conductivity from local anharmonic phonons
Matsumoto, Hideki; Mori, Tatsuya; Iwamoto, Kei; Goshima, Shohei; Kushibiki, Syunsuke; Toyota, Naoki
2009-01-01
Recently there has been paid much attention to phenomena caused by local anharmonic vibrations of the guest ions encapsulated in polyhedral cages of materials such as pyrochlore oxides, filled skutterdites and clathrates. We theoretically investigate the optical conductivity solely due to these so-called rattling phonons in a one-dimensional anharmonic potential model. The dipole interaction of the guest ions with electric fields induces excitations expressed as transitions ...
Sub-wavelength phononic crystal liquid sensor
Ke, Manzhu; Zubtsov, Mikhail; Lucklum, Ralf
2011-01-01
We introduce an acoustic liquid sensor based on phononic crystals consisting of steel plate with an array of holes filled with liquid. We both theoretically and experimentally demonstrate sensor properties considering the mechanism of the extraordinary acoustic transmission as underlying phenomenon. The frequency of this resonant transmission peak is shown to rely on the speed of sound of the liquid, and the resonant frequency can be used as a measure of speed of sound and rela...
PARAMETRIC AMPLIFICATION OF MICROWAVE PHONONS IN SEMICONDUCTORS
Spector, H.
1981-01-01
Two different nonlinear processes involving the interactions of phonons with electrons in a semiconductor in the presence of a d.c. electric field have been theoretically investigated. The first process involves the mixing of ultrasonic waves to generate new ultrasonic waves at the sum or difference frequencies of the original waves. The mechanisms which couples the waves together involves the interaction of the carriers bunched by one of the waves with the fields induced by the other wave. T...
Soft Phonon Anomalies in Relaxor Ferroelectrics
Shirane, G
2000-01-01
A review is given of the phonon anomalies, which have been termed ``waterfalls,'' that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions.
International Nuclear Information System (INIS)
The transport processes in highly transparent nanocrystalline laser-host ceramics based on C-modification of Y2O3 sesquioxide were investigated by the heat-pulse technique. The propagation kinetics of acoustic phonons was studied in the range of liquid helium temperature (1.7-3.8 K). A structural model for the grain boundary layers is suggested and their thickness is estimated. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
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.
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
Phonon-lifetimes in demixing systems.
Davaasambuu, J; Güthoff, F; Petri, M; Hradil, K; Schober, H; Ollivier, J; Eckold, G
2012-06-27
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
Nonharmonic phonons in ?-iron at high temperatures
Mauger, L.; Lucas, M. S.; Muñoz, J. A.; Tracy, S. J.; Kresch, M.; Xiao, Yuming; Chow, Paul; Fultz, B.
2014-08-01
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.
International Nuclear Information System (INIS)
This in vitro study compares two different types of tooth bleaching agents stimulated with two different irradiation fonts. These fonts accelerate the action of the bleaching agents upon the enamel surface by heating up the materials. We used the xenon plasma arc lamp and a 960 nm fiber-coupled diode laser to irradiate the two materials containing 35% of hydrogen peroxide (Opus White and Opalescence extra). The color of the teeth was measured with a spectrophotometer using the CIELAB color system that gives the numeric values of L*a*b*. (author)
Waveguiding inside the complete band gap of a phononic crystal slab.
Hsiao, Fu-Li; Khelif, Abdelkrim; Moubchir, Hanane; Choujaa, Abdelkrim; Chen, Chii-Chang; Laude, Vincent
2007-11-01
The propagation of acoustic waves in a square-lattice phononic crystal slab consisting of a single layer of spherical steel beads in a solid epoxy matrix is studied experimentally. Waves are excited by an ultrasonic transducer and fully characterized on the slab surface by laser interferometry. A complete band gap is found to extend around 300 kHz, in good agreement with theoretical predictions. The transmission attenuation caused by absorption and band gap effects is obtained as a function of frequency and propagation distance. Well confined acoustic wave propagation inside a line-defect waveguide is further observed experimentally. PMID:18233776
Rabi oscillations in a quantum dot-cavity system coupled to a nonzero temperature phonon bath
International Nuclear Information System (INIS)
We study a quantum dot strongly coupled to a single high-finesse optical microcavity mode. We use a rotating wave approximation (RWA) method, commonly used in ion-laser interactions, together with the Lamb-Dicke approximation to obtain an analytic solution of this problem. The decay of Rabi oscillations because of the electron-phonon coupling is studied at arbitrary temperature and analytical expressions for the collapse and revival times are presented. Analyses without the RWA are presented as means of investigating the energy spectrum
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Li, Baowen
2013-01-01
The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductivity of bulk Si at high temperature,1000 K. Size and mass effects are obvious in manipulating thermal conductivity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show the decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is clearly shown in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal structure.
Substrate influence in electron phonon coupling measurements in thin Au films
Hopkins, Patrick E.; Norris, Pamela M.
2007-05-01
Accurate understanding and measurement of the energy transfer mechanisms during thermal nonequilibrium between electrons and the surrounding material systems is critical for a wide array of applications. With device dimensions decreasing to sizes on the order of the thermal penetration depth, the equilibration of the electrons could be effected by boundary effects in addition to electron-phonon coupling. In this study, the rate of electron equilibration in 20 nm thick Au films is measured with the Transient ThermoReflectance (TTR) technique. At very large incident laser fluences which result in very high electron temperatures, the electron-phonon coupling factors determined from TTR measurements deduced using traditional models are almost an order of magnitude greater than predicted from theory. By taking excess electron energy loss via electron-substrate transport into account with a proposed three temperature model, TTR electron-phonon coupling factor measurements are more in line with theory, indicating that in highly nonequilibrium situations, the high temperature electron system looses substantial energy to the substrate in addition to that transferred to the film lattice through coupling.
Wang, Bin; Appavoo, Kannatassen; Brady, Nathaniel; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit; Hilton, David; Haglund, Richard; Pantelides, Sokrates
2013-03-01
The ultrafast photo-induced phase transition in VO2 is promising for data storage and sensing applications. Our experimental work (the previous talk) shows that in a Au/VO2 hybrid nanostructure, electrons excited in the Au photocathode by an ultrafast laser trigger the insulator-to-metal transition in VO2. Here we report first-principles density-functional calculations showing that the collapse of a 6 THz optical phonon, corresponding to a twisting motion of V atoms, is responsible for the ultrafast phase transition. Above a concentration threshold, we find that injected electrons from Au induce collapse of the VO{2 }phonon, which stimulates the monoclinic-to-rutile structural phase transition. We also show that hole-doping can induce the same effect. The abrupt change of the critical phonon results from the weakening of the V-V bonds induced by the combined flux of injected electrons and holes. Thus, our results explain the experimental finding of plasmonic-electron-driven ultrafast phase transition and represent a step towards manipulating the photo-induced phase transition by surface modification.
Nasieka, Iu.; Boyko, M.; Strelchuk, V.; Danilchenko, B.; Rashkovetskyi, L.; Fochuk, P.
2014-10-01
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.
Energy-selective detection of phonons by superconducting zinc films
International Nuclear Information System (INIS)
Experiments have been performed in which phonons are incident on a zinc film at temperatures much less than the superconducting transition temperature. We find that if the energy of the phonons exceeds a threshold energy epsilon/sub c/, a resistance is induced in the film. The variation of epsilon/sub c/ with applied magnetic field has been studied. This system may be useful as a tunable detector of phonons in the energy range 0 to 20 K
Phonon-assisted tunneling and its dependence on pressure
International Nuclear Information System (INIS)
First the mechanism of phonon-assisted tunneling has been investigated. The indirect tunnel current density has been computed after taking the amplitude of the time dependent perturbation as the energy of the lattice vibration. Later the pressure dependence of the phonon-assisted tunnel current has been computed using Payne's expression for the dependence of phonon frequency on pressure. Very good qualitative agreements are obtained between predicted and observed characteristics. (author)
Transverse Acoustic Phonon Transistor Based on Asymmetric Potential Distribution
Jeong, H.; Jho, Y. D.; Stanton, C. J.
2014-01-01
We experimentally demonstrate a transverse acoustic (TA) phonon transistor. Phonons are coherently initiated by femtosecond photocarrier screening on potential gradients. Although translational symmetry within the isotropic plane normally prohibits optical generation of TA phonons, we show that the combined application of an external bias in the vertical and lateral directions can break the selection rules, generating the forbidden TA mode. The amplitude and on-state time of...
Selective heating of the ferroelectric film soft mode phonons
Prudan, A M; Ktitorov, S A
2007-01-01
Results of the experimental study of the electromagnetic pumping of frequency 0.3 THz upon the soft mode phonons in the (Ba, Sr)TiO3 film are presented. Some features of the phonon state are revealed using the capacitor thermometer and the thermocouple. The soft mode phonon overheating estimated comparing changes of the planar capacitor capacitance was observed to be quite significant
Phonon-mediated non-equilibrium interaction between nanoscale devices
Schinner, G. J.; Tranitz, H. P.; Wegscheider, W.; Kotthaus, J. P.; Ludwig, S.
2009-01-01
Interactions between mesoscopic devices induced by interface acoustic phonons propagating in the plane of a two-dimensional electron system (2DES) are investigated by phonon-spectroscopy. In our experiments ballistic electrons injected from a biased quantum point contact emit phonons and a portion of them are reabsorbed exciting electrons in a nearby degenerate 2DES. We perform energy spectroscopy on these excited electrons employing a tunable electrostatic barrier in an ele...
Donor Spin Qubits in Ge-based Phononic Crystals
Smelyanskiy, V. N.; Hafiychuk, V. V.; Vasko, F. T.; Petukhov, A. G.
2014-01-01
We propose qubits based on shallow donor electron spins in germanium. Spin-orbit interaction for donor spins in germanium is in many orders of magnitude stronger than in silicon. In a uniform bulk material it leads to very short spin lifetimes. However the lifetime increases dramatically when the donor is placed into a quasi-2D phononic crystal and the energy of the Zeeman splitting is tuned to lie within a phonon bandgap. In this situation single phonon processes are suppre...
Phonon excitation and instabilities in biased graphene nanoconstrictions
Gunst, Tue; Lu, Jing Tao; Hedega?rd, Per; Brandbyge, Mads
2013-01-01
We calculate the phonons in a graphene nanoconstriction(GNC) in the presence of a high current density. The Joule-heating, current-induced forces, and coupling to electrode phonons is evaluated using first principles nonequilibrium DFT-NEGF calculations. Close to a resonance in the electronic structure we observe a strongly nonlinear heating with bias and breakdown of the harmonic approximation. This behavior results from negatively damped phonons driven by the current. The ...
Investigation of radiation induced aggregates by phonon techniques
International Nuclear Information System (INIS)
The purpose of this paper is to discuss the determination of the size of extended defects in solids using phonon scattering, a method which has the advantage that it does not create further damage in the crystal during the investigation. We shall first describe the principle of the method as it has been developed using thermal conductivity, then discuss the operation and applicability of the superconducting tunnel junction phonon spectrometer, and finally consider the phonon microscope. (author)
Dephasing in Quantum Dots: Quadratic Coupling to Acoustic Phonons
Muljarov, E. A.; Zimmermann, R.
2003-01-01
A microscopic theory of optical transitions in quantum dots with carrier-phonon interaction is developed. Virtual transitions into higher confined states with acoustic phonon assistance add a quadratic phonon coupling to the standard linear one, thus extending the independent Boson model. Summing infinitely many diagrams in the cumulant, a numerically exact solution for the interband polarization is found. Its full time dependence and the absorption lineshape of the quantum ...
Electron-phonon interaction in cuprate-oxide superconductors
Ohkawa, F J
2003-01-01
We propose a novel electron-phonon interaction arising from the modulation of the superexchange interaction by phonons. It is enhanced by spin and superconducting fluctuations, which are developed mainly because of the superexchange interaction. It must be responsible for the softening of phonons and kinks in the dispersion relation of quasi-particles. However, the superexchange interaction must be mainly responsible for the formation of Cooper pairs.
Phonon--internal-mode hybridization in KCl:CN-
International Nuclear Information System (INIS)
Recent work has shown that the resonant mixing of defect internal modes with lattice phonons can lead to striking modifications of the one-phonon coherent neutron-scattering cross section. Here, line shapes for phonons in KCl:CN- are calculated from a two-level model and shown to agree reasonably well with experiment. Our results demonstrate that neutron scattering can be used to study the coupling of complex defects with the lattice even at low defect concentrations
Periodic Anderson model with electron-phonon correlated conduction band
Zhang, Peng; Reis, Peter; Tam, Ka-ming; Jarrell, Mark; Moreno, Juana; Assaad, Fakher; Mcmahan, Andy
2012-01-01
This paper reports dynamical mean field calculations for the periodic Anderson model in which the conduction band is coupled to phonons. Motivated in part by recent attention to the role of phonons in the $\\gamma$-$\\alpha$ transition in Ce, this model yields a rich and unexpected phase diagram which is of intrinsic interest. Specifically, above a critical value of the electron-phonon interaction, a first order transition with two coexisting phases develops in the temperature...
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)
Electron-Phonon Mass Enhancement in Multi-Layers
Bergmann, Gerd
2006-01-01
A strong electron-phonon interaction in a metal increases the electron density of states in the vicinity of the Fermi energy dramatically. This phenomenon is called electron-phonon mass enhancement. In this paper the question is investigated whether the mass enhancement can be manipulated in multi-layers of two metals with strong and weak electron-phonon interaction. A rich behavior is observed for different thickness ranges of the layers. For thin layers one observes a rath...
Similarity renormalization of the electron--phonon coupling
Mielke, Andreas
1996-01-01
We study the problem of the phonon-induced electron-electron interaction in a solid. Starting with a Hamiltonian that contains an electron-phonon interaction, we perform a similarity renormalization transformation to calculate an effective Hamiltonian. Using this transformation singularities due to degeneracies are avoided explicitely. The effective interactions are calculated to second order in the electron-phonon coupling. It is shown that the effective interaction between...
Electron-Phonon Interaction in Embedded Semiconductor Nanostructures
Grosse, Frank; Zimmermann, Roland
2006-01-01
The modification of acoustic phonons in semiconductor nanostructures embedded in a host crystal is investigated including corrections due to strain within continuum elasticity theory. Effective elastic constants are calculated employing {\\em ab initio} density functional theory. For a spherical InAs quantum dot embedded in GaAs barrier material, the electron-phonon coupling is calculated. Its strength is shown to be suppressed compared to the assumption of bulk phonons.
Electron-Phonon Interaction and Phonon Softening in Systems with Magnetovolume Instabilities
Herper, H.; Entel, P.; Weber, W.
1995-01-01
The interrelation of Invar and martensitic behaviour in transition metal alloys like Fe65Ni35 is discussed on the basis of ab initio calculations for stoichiometric systems like Fe3Ni. We also examined face centered cubic iron as a model system for Antiinvar which like Invar shows a pronounced phonon softening. Neutron scattering experiments on Invar systems have shown that the TA1 phonon mode softens for small wavevectors (vector q) along the [110] direction in the fcc lattice. To day there ...
CO2 phonon mode renormalization using phonon-assisted energy up-conversion
Tanjeem, Nabila; Kawazoe, Tadashi; Yatsui, Takashi
2013-01-01
Molecular dissociation under incident light whose energy is lower than the bond dissociation energy has been achieved through multi step excitation using a coupled state of a photon, electron, and multimode-coherent phonon as known as the dressed photon phonon (DPP). Here, we have investigated the effects of the DPP on CO2, a very stable molecule with high absorption and dissociation energies, by introducing ZnO nanorods to generate the DPP. Then, the changes in CO2 absorption bands were eval...
Phonons and electron-phonon coupling in graphene-h-BN heterostructures
Energy Technology Data Exchange (ETDEWEB)
Slotman, Guus J.; Wijs, Gilles A. de; Fasolino, Annalisa; Katsnelson, Mikhail I. [Institute for Molecules and Materials, Radboud University Nijmegen (Netherlands)
2014-10-15
First principle calculations of the phonons of graphene-h-BN heterostructures are presented and compared to those of the constituents. It is shown that AA and AB' stacking are not only energetically less favoured than AB but also dynamically unstable. Low energy flat phonon branches of h-BN character with out of plane displacement have been identified and their coupling to electrons in graphene has been evaluated. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Large surface charge density oscillations induced by subsurface phonon resonances.
Chis, V; Hellsing, B; Benedek, G; Bernasconi, M; Chulkov, E V; Toennies, J P
2008-11-14
A density functional perturbation theory study of Cu(111) surface dynamics and phonon-induced surface charge density (SCD) oscillations shows that the subsurface phonon resonances such as S3, first predicted by embedded-atom methods, trigger large SCD charge-density oscillations, thus explaining the large helium atom scattering intensity from the anomalous longitudinal resonance found in most metal surfaces. The strong coupling between certain phonons and SCD oscillations is shown to have implications in inelastic electron tunneling spectroscopy and other manifestations of electron-phonon interactions at metal surfaces. PMID:19113358
Two-phonon bound states in imperfect crystals
International Nuclear Information System (INIS)
The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of Gasub(1-c)Alsub(c)P and Gesub(1-c)Sisub(c) are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak, observed in structural phase transitions, is conjectured. (author)
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)
Trans-phonon effects in ultra-fast nanodevices
International Nuclear Information System (INIS)
We report a novel phenomenon in carbon nanotube based ultra-fast mechanical devices, the trans-phonon effect, which resembles the transonic effects in aerodynamics. It is caused by dissipative resonance of nanotube phonons similar to the radial breathing mode, and subsequent drastic surge of the dragging force on the sliding tube, and multiple phonon barriers are encountered as the intertube sliding velocity reaches critical values. It is found that the trans-phonon effects can be tuned by applying geometric constraints or varying chirality combinations of the nanotubes
SU(6) limit of the quasiparticle-phonon nuclear model
International Nuclear Information System (INIS)
Quasiparticle-phonon nuclear model is considered. It is shown that the Hamiltonian of the quasiparticle-phonon nuclear model has the SU(6) limit. Under some conditions this Hamiltonian can be represented as a rotational invariant which is constructed of the generators of the SU(6) algebra. The collective quadrupole random phase approximation phonon operators and their commutators form a closed algebra. The microscopic expressions for the parameters of the quadrupole phonon model are derived. The calculation of maximal numbers of bosons and the test of the conditions giving the SU(6) limit for some Zn isotopes have been performed
Phonon bandgap engineering of strained monolayer MoS?.
Jiang, Jin-Wu
2014-07-21
The phonon band structure of monolayer MoS? 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 MoS?. 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 MoS?. 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 MoS?. The critical strain for buckling is extracted from the band structure analysis of the flexure mode in the monolayer MoS? 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 MoS?, while the biaxial compression as a powerful tool to intrigue buckling in the monolayer MoS?. PMID:24932612
Proposal for an Optomechanical Traveling Wave Phonon-Photon Translator
Safavi-Naeini, Amir H
2010-01-01
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.
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New experimental data are reported supporting the conclusion that the formation of surface compound layers by high-intensity multipulse laser irradiation is determined by a critical value of the oxygen impurities concentration in the ambient nitrogen atmosphere
Phonon dynamics and Urbach energy studies of MgZnO alloys
Huso, Jesse; Che, Hui; Thapa, Dinesh; Canul, Amrah; McCluskey, M. D.; Bergman, Leah
2015-03-01
The MgxZn1-xO alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of MgxZn1-xO thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0-68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2-5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47-66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.
Quantifying electron-phonon coupling in CdTe1?xSex nanocrystals via coherent phonon manipulation
International Nuclear Information System (INIS)
We employ ultrafast transient absorption spectroscopy with temporal pulse shaping to manipulate coherent phonon excitation and quantify the strength of electron-phonon coupling in CdTe1?xSex nanocrystals (NCs). Raman active CdSe and CdTe longitudinal optical phonon (LO) modes are excited and probed in the time domain. By temporally controlling pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe1?xSex NCs, we estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode.
Phase seeding of a terahertz quantum cascade laser
Oustinov, Dimitri; Jukam, Nathan; Rungsawang, Rakchanok; Made?o, Julien; Barbieri, Stefano; Filloux, Pascal; Sirtori, Carlo; Marcadet, Xavier; Tignon, Je?ro?me; Dhillon, Sukhdeep
2010-01-01
The amplification of spontaneous emission is used to initiate laser action. Since the phase of spontaneous emission is random, the phase of the coherent laser emission (the carrier phase) will also be random each time laser action begins. This prevents phase resolved detection of the laser field. Here, we demonstrate how the carrierphase can be fixed in a semiconductor laser: a quantum cascade laser. This is performed by injection seeding a quantum cascade laser with coherent terahertz pulses...
Measurement and control of electron-phonon interactions in graphene
Remi, Sebastian
Despite the weak interaction between electrons and atomic vibrations (phonons) in the one-atom thick crystal of carbon called graphene, the scattering of electrons off phonons limits coherent electron transport in pristine devices over mesoscopic length scales. The future of graphene as a replacement to silicon and other materials in advanced electronic devices will depend on the success of controlling and optimizing electronic transport. In this dissertation, we explore the electron-phonon interaction via Raman scattering, elucidating the effects of filling and emptying charge states on the phonons in both the metallic state and when levels are quantized by an applied perpendicular magnetic field. In zero magnetic field, the phonon energy shifts due to electronic screening by charge carriers. Previously, a logarithmic divergence of the phonon energy was predicted as a function of the charge carrier density. For the first time, we observe signatures of this logarithmic divergence at liquid He temperatures after vacuum annealing on single layers. We also measure the electron-phonon coupling strength, Fermi velocity, and broadening of electronic quantum levels from Raman scattering and correlate these parameters to electronic transport. In a strong perpendicular magnetic field, the energy bands split into discrete Landau levels. Here, we observe kinks and splitting of the optical phonon energy, even when the Landau level transitions are far from resonant with the phonons. We discover that the kinks are attributed to charge filling of Landau levels, as understood from a linearized model based on electron-phonon interactions. Moreover, we show that material parameters determined without magnetic fields also describe phonon behavior in high magnetic fields.
Phonon scattering in graphene over substrate steps
DEFF Research Database (Denmark)
Sevincli, Haldun; Brandbyge, Mads
2014-01-01
We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance 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.
Spectroscopy of nonequilibrium electrons and phonons
Shank, CV
1992-01-01
The physics of nonequilibrium electrons and phonons in semiconductors is an important branch of fundamental physics that has many practical applications, especially in the development of ultrafast and ultrasmall semiconductor devices. This volume is devoted to different trends in the field which are presently at the forefront of research. Special attention is paid to the ultrafast relaxation processes in bulk semiconductors and two-dimensional semiconductor structures, and to their study by different spectroscopic methods, both pulsed and steady-state. The evolution of energy and space distrib
International Nuclear Information System (INIS)
Within the framework of the macroscopic dielectric continuum model, the surface-optical-propagating (SO-PR) mixing phonon modes of a quasi-zero-dimensional (Q0D) wurtzite cylindrical quantum dot (QD) structure are derived and studied. The analytical phonon states of SO-PR mixing modes are given. It is found that there are two types of SO-PR mixing phonon modes, i.e. ?-SO/z-PR mixing modes and the z-SO/?-PR mixing modes existing in Q0D wurtzite QDs. And each SO-PR mixing modes also have symmetrical and antisymmetrical forms. Via the standard procedure of field quantization, the Froehlich Hamiltonians of electron-(SO-PR) mixing phonons interaction are obtained. And the orthogonal relations of polarization eigenvectors for these SO-PR mixing modes are also displayed. Numerical calculations on a wurtzite GaN cylindrical QD are carried out. The results reveal that the dispersive frequencies of all the SO-PR mixing modes are the discrete functions of phonon wave-numbers and azimuthal quantum numbers. The behaviors that the SO-PR mixing phonon modes in wurtzite QDs reduce to the SO modes and PR modes in wurtzite quantum well (QW) and quantum well wire (QWR) systems are analyzed deeply from both of the viewpoints of physics and mathematics. The result shows that the present theories of polar mixing phonon modes in wurtzite cylindrical QDs are consistent with the phonon modes theories in wurtzite QWs and QWR systems. The analytical electron-phonon interaction Hamiltonians obctron-phonon interaction Hamiltonians obtained here are useful for further analyzing phonon influence on optoelectronics properties of wurtzite Q0D QD structures.
Quasiparticle-phonon coupling in inelastic proton scattering
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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)
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
Phonons and charge-transfer excitations in HTS superconductors
Energy Technology Data Exchange (ETDEWEB)
Bishop, A.R.
1989-01-01
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.
Electron-phonon interaction on optical spectra of nanoelectronic devices
Kim, Q.
2002-01-01
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.
Instabilities on graphene's honeycomb lattice with electron-phonon interactions
Classen, Laura; Scherer, Michael M.; Honerkamp, Carsten
2014-07-01
We study the impact of electron-phonon interactions on the many-body instabilities of electrons on the honeycomb lattice and their interplay with repulsive local and nonlocal Coulomb interactions at charge neutrality. To that end, we consider in-plane optical phonon modes with wave vectors close to the ? point as well as to the K ,-K points and calculate the effective phonon-mediated electron-electron interaction by integrating out the phonon modes. Ordering tendencies are studied by means of a momentum-resolved functional renormalization-group approach allowing for an unbiased investigation of the appearing instabilities. In the case of an exclusive and supercritical phonon-mediated interaction, we find a Kekulé and a nematic bond ordering tendency being favored over the s-wave superconducting state. The competition between the different phonon-induced orderings clearly shows a repulsive interaction between phonons at small- and large-wave-vector transfers. We further discuss the influence of phonon-mediated interactions on electronically driven instabilities induced by on-site, nearest-neighbor, and next-nearest-neighbor density-density interactions. We find an extension of the parameter regime of the spin-density-wave order going along with an increase of the critical scales where ordering occurs and a suppression of competing orders.
Phonon thermal transport through tilt grain boundaries in strontium titanate
International Nuclear Information System (INIS)
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
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.)
International Nuclear Information System (INIS)
The formation of carbon structures as a result of decomposition of some organic molecules on the surface of metal fluorides (without molecular decay in a gas) exposed to IR femtosecond laser radiation with a wavelength of 3.3–5.4 ?m is revealed. The determining influence of the laser pulse intensity on the efficiency of the decomposition process has been ascertained. A possible mechanism of the decomposition of molecules on the surface and of the growth of carbon structures has been proposed. (paper)
International Nuclear Information System (INIS)
The specific features of the propagation of soliton-like light beams through a fully ionised two-dimensional cold plasma are considered employing analytical and numerical methods commonly used in nonlinear optics. Exact soliton profiles for the lower and upper soliton branches are found numerically in the presence of optical bistability. It is shown that the interaction of incoherent soliton-like laser beams in such a plasma may result both in the destruction of one of the beams and in production of new ones. The regime of the modulation instability of a plane wave propagating through a cold laser-produced plasma is studied. (nonlinear optical phenomena)
Phonon self-energy effects in high-temperature superconductors
International Nuclear Information System (INIS)
The coupling of phonons to electronic excitations in high-temperature superconductors (HTS) results in a rich variety of self-energy effects. In particular, those phonons that strongly interact with electrons occupying states near the Fermi surface are very sensitive to the opening of the superconducting gap. This is usually reflected in appreciable changes of the phonon renormalization (self-energy) around and below Tc. In addition, when both, the phonons and the pair-breaking excitations show significant Raman activity, the Raman transition amplitudes interfere in a way that also changes the phonon intensity when crossing Tc. We illustrate these effects with recent Raman data for (Cu,C)Ba2Ca3Cu4O10 and NdBa2Cu3O7. (orig.)
Resonance enhancement of electron-phonon interaction in nanostructures
Energy Technology Data Exchange (ETDEWEB)
Maslov, A. Yu.; Proshina, O. V. [Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Polytekhnicheskaya 26, Saint Petersburg 194021 (Russian Federation)
2013-12-04
The theory of electron-phonon interaction in quantum well is developed taking into account the influence of interface optical phonons. A detailed analysis of the dependence of polaron effective mass on the quantum well size and dielectric characteristics of barrier material is performed. It is shown that quasi-two-dimensional polaron may arise in narrow quantum wells. However, the interaction parameters are determined by effective mass of carriers in the quantum well and interface optical phonons frequencies. If the barriers are made of non-polar material, the polaron effective mass depends on the quantum well width. By increasing the quantum well width, a new mechanism of amplification of the electron-phonon interaction is realized. It occurs in the case of coincidence of the optical phonon energy with the energy of one of the electronic transitions. This leads to a nonmonotonic dependence of polaron effective mass on the quantum well width.
Phonon dispersion measured directly from molecular dynamics simulations
Kong, Ling Ti
2011-10-01
A method to measure the phonon dispersion of a crystal based on molecular dynamics simulation is proposed and implemented as an extension to an open source classical molecular dynamics simulation code LAMMPS. In the proposed method, the dynamical matrix is constructed by observing the displacements of atoms during molecular dynamics simulation, making use of the fluctuation-dissipation theory. The dynamical matrix can then be employed to compute the phonon spectra by evaluating its eigenvalues. It is found that the proposed method is capable of yielding the phonon dispersion accurately, while taking into account the anharmonic effect on phonons simultaneously. The implementation is done in the style of fix of LAMMPS, which is designed to run in parallel and to exploit the functions provided by LAMMPS; the measured dynamical matrices could be passed to an auxiliary postprocessing code to evaluate the phonons.
Phonon Squeezed States Quantum Noise Reduction in Solids
Hu, X; Hu, Xuedong; Nori, Franco
1999-01-01
This article discusses quantum fluctuation properties of a crystal lattice, and in particular, phonon squeezed states. Squeezed states of phonons allow a reduction in the quantum fluctuations of the atomic displacements to below the zero-point quantum noise level of coherent phonon states. Here we discuss our studies of both continuous-wave and impulsive second-order Raman scattering mechanisms. The later approach was used to experimentally suppress (by one part in a million only, which might be noise) fluctuations in phonons (and it has not been clearly reproduced by other experimental groups). We calculate the expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, as well as the effects of the phonon squeezed states on macroscopically measurable quantities, such as changes in the dielectric constant. These results are compared with recent experiments. Further information, including preprints and animations, are available in http://www-personal.engin.umich.ed...
Plasma-related phonon-sideband emission in semiconductors
Energy Technology Data Exchange (ETDEWEB)
Chernikov, Alexej; Boettge, Christoph N.; Feldtmann, Thomas; Chatterjee, Sangam; Koch, Martin; Kira, Mackillo; Koch, Stephan W. [Faculty of Physics and Material Sciences Center, Philipps-Universitaet Marburg, Renthof 5, 35032 Marburg (Germany)
2011-04-15
The phonon-assisted recombination in bulk II-VI semi-conductors is analyzed by means of time-resolved photoluminescence spectroscopy. Experimental results on both CdS and CdSe clearly indicate that phonon-sideband emission is not exclusively attributed to the presence of excitons. The contributions of Coulombcorrelated electron-hole plasma to the phonon assisted recombination may be significant, depending on the excitation conditions. This observation is supported by a microscopic many-particle theory of interacting electrons, phonons, and photons. Our theoretical approach generalizes previous investigations by including both correlated and uncorrelated luminescence sources. Our findings contradict and expand the traditional picture of phonon-sideband emission. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Controlling elastic waves with small phononic crystals containing rigid inclusions
Peng, Pai; Qiu, Chunyin; Liu, Zhengyou; Wu, Ying
2014-05-01
We show that a two-dimensional elastic phononic crystal comprising rigid cylinders in a solid matrix possesses a large complete band gap below a cut-off frequency. A mechanical model reveals that the band gap is induced by negative effective mass density, which is affirmed by an effective medium theory based on field averaging. We demonstrate, by two examples, that such elastic phononic crystals can be utilized to design small devices to control low-frequency elastic waves. One example is a waveguide made of a two-layer anisotropic elastic phononic crystal, which can guide and bend elastic waves with wavelengths much larger than the size of the waveguide. The other example is the enhanced elastic transmission of a single-layer elastic phononic crystal loaded with solid inclusions. The effective mass density and reciprocal of the modulus of the single-layer elastic phononic crystal are simultaneously near zero.
Lithium neodymium tetraphosphate laser
International Nuclear Information System (INIS)
Laser action at lambda=1.047 ?m is reported in a lithium neodymium tetraphosphate crystal (LNP; LiNdP4O12) pumped longitudinally with a rhodamine 6G laser (lambda=5965 A) or a chopped Ar ion laser (lambda=5145 A). Comparing the measured threshold and round-trip loss of the resonator of the LNP laser with that of the Nd:YAG laser, the effective emission cross section for the ion in the 4F3/2 manifold of LNP is found to be 1.65 times that of Nd:YAG
Hamiltonian of Acoustic Phonons in Inhomogeneous Solids
Directory of Open Access Journals (Sweden)
Vladimir Labas
2013-03-01
Full Text Available Theoretical solid-state physicists formulate their models usually in the form of a Hamiltonian. In quantum mechanics, the Hamilton operator (Hamiltonian is of fundamental importance in most formulations of quantum theory. Mentioned operator corresponds to the total energy of the system and its spectrum determines the set of possible outcomes when one measures the total energy. Interpretation of results obtained by the applying of models based on the Hamiltonian indicates very specific mechanisms of some observed phenomena that are not fully consistent with the experience. Such approach may occasionally lead to surprises when obtained results are confronted with expectations. The aim of this work is to find Hamilton operator of acoustic phonons in inhomogeneous solids. The transport of energy in the vibrating crystal consisting of ions whose properties differ over long distances is described in the work. We modeled crystal lattice by 1D “inhomogeneous” ionic chain vibrating by acoustic frequencies and found the Hamiltonian of such system in the second quantization. The influence of long-distance inhomogeneities on the acoustic phonons quantum states can be discussed on basis of our results.
Size effects in thermal conduction by phonons
Allen, Philip B.
2014-08-01
Heat transport in nanoscale systems is both hard to measure microscopically, and hard to interpret. Ballistic and diffusive heat flow coexist, adding confusion. This paper looks at a very simple case: a nanoscale crystal repeated periodically. This is a popular model for simulation of bulk heat transport using classical molecular dynamics (MD), and is related to transient thermal grating experiments. Nanoscale effects are seen in perhaps their simplest form. The model is solved by an extension of standard quasiparticle gas theory of bulk solids. Both structure and heat flow are constrained by periodic boundary conditions. Diffusive transport is fully included, while ballistic transport by phonons of a long mean free path is diminished in a specific way. Heat current J (x) and temperature gradient ?T (x') have a nonlocal relationship, via ? (x-x'), over a distance |x-x'| determined by phonon mean free paths. In MD modeling of bulk conductivity, finite computer resources limit system size. Long mean free paths, comparable to the scale of heating and cooling, cause undesired finite-size effects that have to be removed by extrapolation. The present model allows this extrapolation to be quantified. Calculations based on the Peierls-Boltzmann equation, using a generalized Debye model, show that extrapolation involves fractional powers of 1/L. It is also argued that heating and cooling should be distributed sinusoidally [??cos(2?x/L)] to improve convergence of numerics.
Electron--phonon interaction in superconducting vanadium
International Nuclear Information System (INIS)
Electron-phonon interaction in superconducting vanadium is measured through the mechanism of the ultrasonic attenuation coefficient. Measurements were made as a function of temperature and magnetic field in three single crystal vanadium samples with resistivity ratios of 7.8, 245, and 450, to be referred to as samples I, II, and III, respectively. Emphasis has been placed on the mixed state region near H/sub c2/ where the data have been compared with the theoretical predictions of Houghton and Maki (HM). To facilitate comparison of the results, transverse waves were used in all three samples with phonon wave vector, q, parallel to the applied magnetic field, H. The direction of propagation was [110], [110], and [100], for a frequency of 255 MHz, 15 MHz, and 45 MHz, in sample I, II, and III respectively. Longitudinal waves of 135 MHz and q parallel H were also used in sample I. The predicted temperature and field dependence, in all cases, agree with the experimental results. The values obtained for the electron mean free path, used as a fitting parameter for the HM theory to the experimental results, are compared with the values obtained from dc conductivity measurements and from free-electron model predictions for attenuation versus frequency. The zero temperature BCS energy gap is also found for each sample and the resulting good agreement between the BCS prediction, and the experimentally found dependence, of the ultrasonic attenuation on temperature is graphically attenuation on temperature is graphically illustrated
Phonon-tunnelling dissipation in mechanical resonators.
Cole, Garrett D; Wilson-Rae, Ignacio; Werbach, Katharina; Vanner, Michael R; Aspelmeyer, Markus
2011-01-01
Microscale and nanoscale mechanical resonators have recently emerged as ubiquitous devices for use in advanced technological applications, for example, in mobile communications and inertial sensors, and as novel tools for fundamental scientific endeavours. Their performance is in many cases limited by the deleterious effects of mechanical damping. In this study, we report a significant advancement towards understanding and controlling support-induced losses in generic mechanical resonators. We begin by introducing an efficient numerical solver, based on the 'phonon-tunnelling' approach, capable of predicting the design-limited damping of high-quality mechanical resonators. Further, through careful device engineering, we isolate support-induced losses and perform a rigorous experimental test of the strong geometric dependence of this loss mechanism. Our results are in excellent agreement with the theory, demonstrating the predictive power of our approach. In combination with recent progress on complementary dissipation mechanisms, our phonon-tunnelling solver represents a major step towards accurate prediction of the mechanical quality factor. PMID:21407197
Phonon mediated loss in a graphene nanoribbon
Kunal, K.; Aluru, N. R.
2013-08-01
Periodic stretching of a string, under adiabatic condition (no thermal coupling with the environment), will increase its temperature. This represents the case of intrinsic damping where the energy associated with stretching motion is converted into thermal energy. We study this phenomenon in a graphene nanoribbon (GNR), a nano-string. We utilize classical molecular dynamics and study the scaling of dissipation rate (Q factor) with frequency. The dissipation is shown to result from strong non-linear coupling between the stretching vibration and the out-of-plane thermal phonons. A Langevin dynamics framework is developed to describe the out-of-plane phonon dynamics under in-plane stretching. The dissipation mechanism is analyzed using this framework. From the analysis, a bi-relaxation time model is obtained to explain the observed scaling of Q factor with frequency. We also compute the size and temperature dependence of Q factor. The decrease in Q factor with decrease in size (width) is shown to result from the elastic softening of GNR.
Influence of laser heating on the X-ray diffraction intensity of InSb
International Nuclear Information System (INIS)
Hillyard et al. have measured the X-ray diffraction intensity of the (111) peak of InSb after intense laser excitation, which provides insight in the first stages of laser-induced ultrafast melting. They found that the diffraction peak follows a Gaussian decay. This time-dependence has been analyzed using the Debye model for the atomic vibrations, assuming the laser heating to produce a uniform softening of all phonon frequencies. We performed (i) first principle electronic structure calculations, (ii) molecular dynamic simulations to calculate the phonon frequencies at the ?-, X- and L-point and the resulting X-ray intensity. We found, that dramatic phonon softening does not occur at all the investigated k-points but instead the softening of the transverse acoustic phonons at the X-point suffices to explain the measured Gaussian X-ray intensity decay and perfectly reproduces the decay's measured time constant
Banfi, F; Revaz, B; Giannetti, C; Nardi, D; Ferrini, G; Parmigiani, F
2010-01-01
The thermal dynamics induced by ultrashort laser pulses in nanoscale systems, i.e. all-optical time-resolved nanocalorimetry is theoretically investigated from 300 to 1.5 K. We report ab-initio calculations describing the temperature dependence of the electron-phonon interactions for Cu nanodisks supported on Si. The electrons and phonons temperatures are found to decouple on the ns time scale at 10 K, which is two orders of magnitude in excess with respect to that found for standard low-temperature transport experiments. By accounting for the physics behind our results we suggest an alternative route for overhauling the present knowledge of the electron-phonon decoupling mechanism in nanoscale systems by replacing the mK temperature requirements of conventional experiments with experiments in the time-domain.
Evidence of strong electron-phonon interaction in iron doped Bi2Sr2Ca1Cu2O8+D
International Nuclear Information System (INIS)
The authors already shown that infrared laser photo-induced spectra of Bi based ceramic superconductor (n = 2 phase) doped with iron show a highly polarizable environment at about 700 cm-p close to the longitudinal optical mode frequency that we characterize as due to trapped polarons. This modifies the higher frequency side of the Cu-O phonon feature at 630 cm-1 which is currently associated with a stretching mode in the plane. In this paper, the authors report that by increasing the Fe doping up to 25% the authors have succeeded in unveiling an electron-phonon interaction related to that stretching mode. Infrared transmission and reflection spectra show an unusual dip at the longitudinal optical frequency. This feature may with the field that could rise the transverse-longitudinal optical splitting in purely ionic materials. The authors hypothesize that this should lead to a Raman active longitudinal phonon due to the Frolich interaction
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)
International Nuclear Information System (INIS)
the system of equations, enabling to calculate the energy and the structure of excited states, described by the wave function, containing one- and two-phon components was obtained in the framework of quasiparticlephonon model. The requirements of Pauli principle for two-phonon components and phonon correlation in the ground nucleus state are taken into account
Quasi-bound exiton-LO phonon intermediate state in multi-phonon Raman scattering of semiconductors
International Nuclear Information System (INIS)
A new model is proposed to understand multi-phonon Raman spectrum (MRS) of II-VI semiconductors. A quasibound state of exciton-LO phonon complex (EPQBS) in the intermediate state is shown to be responsible for the observed overtone series. The observation of MRS is a natural consequence of our model in which the EPQBS lies in the absorption continuum. (author)
Directory of Open Access Journals (Sweden)
O.Yu. Guseva
2009-09-01
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
Phonon line shapes in the vortex state of the phonon-mediated superconductor YNi2B2C
International Nuclear Information System (INIS)
We present an inelastic neutron-scattering study of phonon line shapes in the vortex state of the type II superconductor YNi2B2C. In a previous study [1] we showed that certain phonons exhibit a clear signature of the superconducting gap 2? on entering the superconducting state. Our interest was to find out whether or not the line shape of such phonons reflects the inhomogeneous nature of the vortex state induced by a magnetic field smaller than the upper critical field Bc2.We found that this is indeed the case because the observed phonon line shapes can be well described by a model considering the phonon as a local probe of the spatial variation of the superconducting gap.
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
Hofmeister, Anne M.; Dong, Jianjun; Branlund, Joy M.
2014-04-01
We show that laser-flash analysis measurements of the temperature (T) dependence of thermal diffusivity (D) for diverse non-metallic (e.g., silicates) single-crystals is consistently represented by D(T) = FT-G + HT above 298 K, with G ranging from 0.3 to 2, depending on structure, and H being ˜10-4 K-1 for 51 single-crystals, 3 polycrystals, and two glasses unaffected by disorder or reconstructive phase transitions. Materials exhibiting this behavior include complex silicates with variable amounts of cation disorder, perovskite structured materials, and graphite. The high-temperature term HT becomes important by ˜1300 K, above which temperature its contribution to D(T) exceeds that of the FT-G term. The combination of the FT-G and HT terms produces the nearly temperature independent high-temperature region of D previously interpreted as the minimal phonon mean free path being limited by the finite interatomic spacing. Based on the simplicity of the fit and large number of materials it represents, this finding has repercussions for high-temperature models of heat transport. One explanation is that the two terms describing D(T) are associated with two distinct microscopic mechanisms; here, we explore the possibility that the thermal diffusivity of an electrical insulator could include both a contribution of lattice phonons (the FT-G term) and a contribution of diffusive bulk phonon-polaritons (BPP) at infrared (IR) frequencies (the HT term). The proposed BPP diffusion exists over length scales smaller than the laboratory sample sizes, and transfers mixed light and vibrational energy at a speed significantly smaller than the speed of light. Our diffusive IR-BPP hypothesis is consistent with other experimental observations such as polarization behavior, dependence of D on the number of IR peaks, and H = 0 for Ge and Si, which lack IR fundamentals. A simple quasi-particle thermal diffusion model is presented to begin understanding the contribution from bulk phonon-polaritons to overall heat conduction.
Makovetskii, D N
2001-01-01
The microwave phonon stimulated emission (SE) has been experimentally and numerically investigated in a nonautonomous microwave acoustic quantum generator, called also microwave phonon laser or phaser (see previous works arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050) Phenomena of branching and long-time refractority (absence of the reaction on the external pulses) for deterministic chaotic and regular processes of SE were observed in experiments with various levels of electromagnetic pumping. At the pumping level growth, the clearly depined increasing of the number of coexisting SE states has been observed both in real physical experiments and in computer simulations. This confirms the analytical estimations of the branching density in the phase space. The nature of the refractority of SE pulses is closely connected with the pointed branching and reflects the crises of strange attractors, i.e. their collisions with unstable periodic components of the higher branches of SE states in t...
Electron-phonon coupling in quantum-well states of the Pb/Si(1?1?1) system
Ligges, M.; Sandhofer, M.; Sklyadneva, I.; Heid, R.; Bohnen, K.-P.; Freutel, S.; Rettig, L.; Zhou, P.; Echenique, P. M.; Chulkov, E. V.; Bovensiepen, U.
2014-09-01
The electron-phonon coupling parameters in the vicinity of the \\overline{\\Gamma} point, \\lambda(\\overline{\\Gamma}) , for electronic quantum well states in epitaxial lead films on a Si(1?1?1) substrate are measured using 5, 7 and 12 ML films and femtosecond laser photoemission spectroscopy. The \\lambda(\\overline{\\Gamma}) values in the range of 0.6-0.9 were obtained by temperature-dependent line width analysis of occupied quantum well states and found to be considerably smaller than the momentum averaged electron-phonon coupling at the Fermi level of bulk lead, (? = 1.1-1.7). The results are compared to density functional theory calculations of the lead films with and without interfacial stress. It is shown that the discrepancy can not be explained by means of confinement effects or simple structural modifications of the Pb films and, thus, is attributed to the influence of the substrate on the Pb electronic and vibrational structures.
Phonons and electron-phonon coupling in YNi2B2C
Energy Technology Data Exchange (ETDEWEB)
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
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.
Phonons and electron-phonon coupling in YNi2B2C
Weber, F.; Pintschovius, L.; Reichardt, W.; Heid, R.; Bohnen, K.-P.; Kreyssig, A.; Reznik, D.; Hradil, K.
2014-03-01
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.
Daurelio, G.; Campanile, E.; D'Alonzo, M.; Memola Capece Minutolo, F.; Spera, M.; Lugarà, M.; Ferrandino, V.
2007-05-01
The material in issue is a case-hardening steel, type 20MnCr5 (UNI 8550), that has been previously undergone to a softening annealing process conferring therefore to the material one equal Hardness Brinnel 200 to 220 HB. This steel is very difficult to weld as by laser technology as by other welding technologies by fusion. It has been experienced a power at first laser of 1500 W (for requirements begins them of understanding of the process and the relative to you parameters to set up then) and of 3000 W, like previewed. They have been used a covering gas and a laser beam focusing mirror. All the welded tests have been at first subordinates to taken care of a visual examination to eye and then to an Image Acquisition System, computerized and connected to both metallographic and stereo microscope. Then cut to you with metallographic apparatus, workings to the abrasive papers and metallographic cloths, in order to end with a chemical etching of type NITAL. The best ones turn out to you have been then always visualize in shape of macro and micro-graphs, acquired with the same Image Acquisition System of type NIKON - LUCIA 4.82 vers. by LIM, to storage and automatically measure the cross-section area (melted zone) and then to calculate the efficiency level, on each joint and bead on plate, expressed in Dau unit, to verify the laser welding efficiency, correlated to the laser working parameters. To a better characterization of the produced joints many micro-hardness tests and relate family hardness trends and profiles have been carried out. At the end from the comparison of the values of ETE % and MR % (Model of Swift- Hook & Gick) and of the values of WE in Dau (Model DA.LU.), lead on some beads of the 20MnCr5, has turned out an ulterior and substantial validity and goodness (as well as easiness of employment and calculation of WE) of this last Model and Unit of Measure. In fact the values of ETE % and WE (in Dau) are appeared substantially similar, respecting both all the substantial correlations between the job parameters, to laser.
Anharmonic Decay of Coherent Optical Phonons in Antimony
Hase, Muneaki; Ushida, Kiminori; Kitajima, Masahiro
2015-02-01
The anharmonic decay of coherent optical phonons in the semimetal Sb has been investigated by a femtosecond pump–probe technique. The coherent A1g mode is observed in the time domain in a wide temperature range of 7–290 K. The decay rate (the inverse of the dephasing time) systematically increases as the lattice temperature increases, which is well explained by anharmonic phonon–phonon coupling, causing the decay of the optical phonon into two acoustic phonon modes. The frequency of the A1g mode decreases with increasing temperature, which is interpreted as the results of both thermal expansion and anharmonic phonon–phonon coupling. The temperature dependence of the amplitude of the coherent A1g mode exhibits a decrease with increasing lattice temperature, which is well reproduced by considering the peak intensity of spontaneous Raman scattering assuming a Lorentzian line shape with the linewidth controlled by the anharmonic decay, and this model is applicable to other metallic systems, such as Zn.
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
Point source in a phononic grating: stop bands give rise to phonon-focusing caustics
Veres, Istvan A.; Profunser, Dieter M.; Maznev, Alex A.; Every, Arthur G.; Matsuda, Osamu; Wright, Oliver B.
2012-12-01
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.
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)
International Nuclear Information System (INIS)
Measurements are reported, for the first time, for detection of nonequilibrium phonons emitted from the inhomogeneous gap states of a nonequilibrium superconductor by means of a phonon transmission technique. The observed phonon signal exhibits a clear spatial structure with a certain periodicity. The connection between the I-V characteristic and the phonon signal is discussed
Study of mid-infrared laser action in chalcogenide rare earth doped glass with Dy3+, Pr3+ and Tb3+
So?jka, L.; Tang, Z.; Zhu, H.; Beres?-pawlik, E.; Furniss, D.; Seddon, Angela B.; Benson, T. M.; Sujecki, S.
2012-01-01
We present a study of chalcogenide glass fiber lasers doped with Dy3+, Pr3+ or Tb3+ that would operate in the mid-infrared wavelength range. A set of chalcogenide glass samples doped with different concentrations of rare earth ions is fabricated. The modeling parameters are directly extracted from FTIR absorption measurements of the fabricated bulk glass samples using Judd-Ofelt, Füchtbauer–Ladenburg theory and McCumber theory. The modeling results show that, for all the ...
International Nuclear Information System (INIS)
The therapy with laser emitting low intensity has been currently used in the most diverse fields of medicine as therapeutic conduct for pain. It is a non invasive, painless, non-thermal and aseptic type therapy, without any collateral effects, having a good cost/benefit relationship. However, for the therapy with low-intensity laser to result in positive effects, a correct diagnosis is fundamental, as well as a protocol of adequate application. n odontology, the majority of patients diagnosed with temporomandibular disorders (TMD), present pain and limitations in the movements of the jaw. In this work, a GaAlAs laser emitting low intensity, was used, ?=785 nm, in patients having a dysfunction of the temporomandibular joint with a complaint of pain. Twenty patients were divided into two groups. The group treated received laser therapy in the temporomandibular articulations and in the muscles affected. The dose applied was 45 J/cm2, while the ten patients in the control group received 0 J/cm2, in a total of nine applications, carried out three times a week, during three weeks. he evaluation of the patients was made through clinical examinations of manual palpation of the masseter, temporal, cervical, posterior neck and sternocleidomastoid muscles, and measurements of opening and laterality of the mouth. The results obtained showed a diminishing of the pain and an increase of the mandibular mobility in the patients treated, when compared to the control group. These results point to this therapy as being an important tool in the treatment of pain in patients with a dysfunction in the TMJ, indicating this therapeutic modality as a co-adjuvant in these treatments. (author)
Phonon Screening in High-Temperature Superconductors
International Nuclear Information System (INIS)
In good conductors optical phonons are usually screened, and therefore not observed. However, sharp features due to infrared-active modes in the copper-oxygen planes are observed in the optical conductivity of Pr1.85 Ce0.15 CuO4 and YBa2Cu 3O6.95 . Oscillator strengths indicate that the screening of these modes is poor or totally absent. These materials are compared with ?-Mo4O11 , in which lattice modes appear suddenly below the charge-density wave transition. It is proposed that poor screening in the cuprates originates from fluctuating charge inhomogeneities in the copper-oxygen planes. (c) 2000 The American Physical Society
The phonon theory of liquid thermodynamics
Bolmatov, D.; Brazhkin, V. V.; Trachenko, K.
2012-05-01
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.
Intermediate Exciton-Phonon Coupling in Tetracene
Mizuno, Kenichi; Matsui, Atsuo; Sloan, G. J.
1984-08-01
Polarized absorption spectra of tetracene (naphthacene) single crystals have been investigated between 300 and 13 K, with particular emphasis on the b-polarized spectrum. The low energy tails of the a- and b-polarized first absorption bands are expressed by the Urbach rule with the steepness coefficients ?a'{=}1.37± 0.12, ?b'{=}1.58± 0.13, with which possibility of self-trapping of excitons is discussed along with the dimensionality of tetracene crystals. The exciton-phonon coupling constants are found to be ga{=}1.09± 0.1 and gb{=}0.95± 0.08, consistent with luminescence experiments which show that excitons in tetracene are self-trapped very shallowly. The line halfwidth, the oscillator strength of the first and the second absorption bands, refractive indices, and surface exciton structure are briefly discussed.
Coupling phonons and spins in diamond
Bennett, Steven; Kolkowitz, Shimon; Unterreithmeier, Quirin; Rabl, Peter; Bleszynski-Jayich, Ania; Harris, Jack; Lukin, Mikhail
2012-06-01
We present theoretical considerations for coupling quantized mechanical motion to the electronic spin of a nitrogen-vacancy (NV) defect center in diamond. In a recent experiment, a single NV spin was used to detect both driven and thermal motion of a magnetic force microscope cantilever at room temperature, reading out the spin state optically. This demonstration raises interesting theoretical questions, such as the feasibility of reaching the strong coupling regime and of measuring the quantum zero-point motion of the cantilever using the NV spin as a detector. We discuss these possibilities for the magnetically coupled system, as well as alternative spin-phonon coupling mechanisms in diamond with prospects for improved magnetometry and mechanical cavity QED.
Phonon hydrodynamics in two-dimensional materials
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.
Phonon hydrodynamics in two-dimensional materials.
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-01-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane. PMID:25744932
Phonon modes in a disordered lattice
International Nuclear Information System (INIS)
A simple cubic lattice, in which a small fraction of sites are replaced at random by atoms of a different kind and the resulting vibrational excitations are studied. Both the mass and force constant disorders are considered. The equation of motion of the Green function is developed following Matsubara and Yonezawa neglecting shear modes; the resulting expression for dispersion relation is summed up following Keneyashi and Jones to the lowest order in concentration. The results are obtained analytically and are found to be exact upto the linear term in concentration. Expressions have been obtained for the renormalised energies and the damping of the long wavelength phonon modes. In the special case of simple disorder, the results are compared with those of Langer. (K.B.)
Double Dirac cones in phononic crystals
Li, Yan
2014-07-07
A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.
Cavity-type hypersonic phononic crystals
International Nuclear Information System (INIS)
We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter. (paper)
Double Dirac cones in phononic crystals
Li, Yan; Wu, Ying; Mei, Jun
2014-07-01
A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.
The Phononic Casimir Effect: An Analog Model
Ford, L H
2008-01-01
We discuss the quantization of sound waves in a fluid with a linear dispersion relation and calculate the quantum density fluctuations of the fluid in several cases. These include a fluid in its ground state. In this case, we discuss the scattering cross section of light by the density fluctuations, and find that in many situations it is small compared to the thermal fluctuations, but not negligibly small and might be observable at room temperature. We also consider a fluid in a squeezed state of phonons and fluids containing boundaries. We suggest that the latter may be a useful analog model for better understanding boundary effects in quantum field theory. In all cases involving boundaries which we consider, the mean squared density fluctuations are reduced by the presence of the boundary. This implies a reduction in the light scattering cross section, which is potentially an observable effect.
Phonon Overlaps in Molecular Quantum Dot Systems
Chang, Connie; Sethna, James
2004-03-01
We model the amplitudes and frequencies of the vibrational sidebands for the new molecular quantum dot systems. We calculate the Franck-Condon phonon overlaps in the 3N-dimensional configuration sapce. We solve the general case where the vibrational frequencies and eigenmodes change during the transition. We perform PM3 and DFT calculations for the case of the dumb bell-shaped C140 molecule. We find that the strongest amplitudes are associated with the 11 meV stretch mode, in agreement with experiment. The experimental amplitudes vary from molecule to molecule; indicating that the molecular overlaps are environment dependent. We explore overlaps in the presence of external electric fields from image charges and counter ions.
Energy Technology Data Exchange (ETDEWEB)
Rezende, Sandra Bastos
2001-07-01
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/cm{sup 2} , and for groups G3 and G4 it was 53 mW/cm{sup 2}. The total doses were D = 3 J/cm{sup 2} for groups G2 and G4, and D = 1,3 J/cm{sup 2} 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/cm{sup 2} and the dose of 1,3 J/cm{sup 2} 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)
Energy Technology Data Exchange (ETDEWEB)
Rocha, Dalva Maria
2001-07-01
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)
International Nuclear Information System (INIS)
In a high powered laser system it is proposed that combustion gases be bled off from a gas turbine engine and their composition adjusted by burning extra fuel in the bleed gases or adding extra substances. Suitable aerodynamic expansion produces a population inversion resulting in laser action in the CO2 species. Alternatively, bleed gases may be taken from the high pressure compressor of the gas turbine engine and an appropriate fuel burned therein. If required, other adjustments may also be made to the composition and the resulting gaseous mixture subjected to aerodynamic expansion to induce laser action as before. (auth)
Electron-phonon interaction in proximity of a Mott transition
International Nuclear Information System (INIS)
The effects of electron-phonon interaction on the electronic properties of a strongly correlated metal on the verge of a Mott metal-insulator transition are studied by means of dynamical mean-field theory. We show that electron-phonon interactions induce a phase separation instability close to the density driven Mott transition, and give rise to significant renormalization of electronic properties like charge susceptibility. Nonetheless, the strong correlation reduces the effectiveness of the electron-phonon coupling in driving a polaronic crossover
Interface Phonons and Polaron Effect in Quantum Wires
Directory of Open Access Journals (Sweden)
Maslov A
2010-01-01
Full Text Available Abstract The theory of large radius polaron in the quantum wire is developed. The interaction of charge particles with interface optical phonons as well as with optical phonons localized in the quantum wire is taken into account. The interface phonon contribution is shown to be dominant for narrow quantum wires. The wave functions and polaron binding energy are found. It is determined that polaron binding energy depends on the electron mass inside the wire and on the polarization properties of the barrier material.
Nonperturbative analysis of coupled quantum dots in a phonon bath
Keil, M; Keil, Markus; Schoeller, Herbert
2002-01-01
Transport through coupled quantum dots in a phonon bath is studied using the recently developed real-time renormalization-group method. Thereby, the problem can be treated beyond perturbation theory regarding the complete interaction. A reliable solution for the stationary tunnel current is obtained for the case of moderately strong couplings of the dots to the leads and to the phonon bath. Any other parameter is arbitrary, and the complete electron-phonon interaction is taken into account. Experimental results are quantitatively reproduced by taking into account a finite extension of the wavefunctions within the dots. Its dependence on the energy difference between the dots is derived.
Transverse acoustic phonons in germanium near the melting point
Hennion, B.; Schott, M.
1984-01-01
The transverse acoustic phonon dispersion in germanium has been studied along [111] and [100] up to 935 °C, only 2 degrees below the melting point Tm. No evidence of softening is found, neither near the Brillouin Zone boundary, nor uniformly throughout the BZ. The phonon energies decrease slowly and linearly with increasing T from 100 K to Tm . This suggests that the free electron density at Tm is less than 1021 cm-3. The phonon linewidths are very narrow up to Tm : ? 0.035 ± 0.015 THz, c...
Phonon Cavity Models for Quantum Dot Based Qubits
Vorrath, T; Krämer, B; Brandes, T
2002-01-01
Phonon cavities are believed to be the next step towards a control of dephasing in semiconductor quantum dot `qubits'. In this paper, we discuss two models for phonon cavities - a surface acoustic wave (SAW) inter-digitated transducer on an infinite half-space, and an elastic thin slab. The inelastic current through double quantum dots in non-perfect SAW cavities exhibits a gap at small energies and is completely suppressed in a perfect, infinite system. In the free-standing slab model, van Hove singularities evolve in the phonon spectral density. We find that these singularities cause additional side peaks in the inelastic current.
Electron spin-phonon relaxation in quantum dots
Scientific Electronic Library Online (English)
A. M., Alcalde; G. E., Marques.
2004-06-01
Full Text Available We calculate the spin relaxation rates in parabolic quantum dots due to the phonon modulation of the spin-orbit interaction in presence of an external magnetic field. Both, deformation potential (DP) and piezoelectric (PE) electron-phonon couplings are included in the Pavlov-Firsov spin-phonon Hamil [...] tonian. We demonstrate that the spin relaxation rates are particularly sensitive with the Landé g-factor, and that for InAs dots the DP can be necessarily considered in the spin relaxation analysis. Low-temperature (T ~ 0) relaxation rates are found to be small and to depend strongly on size, g-factor, and on magnetic field.
Analog model for quantum gravity effects: phonons in random fluids.
Krein, G; Menezes, G; Svaiter, N F
2010-09-24
We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. We show that, in this model, after performing the random averages over the noise function a free conventional scalar quantum field theory describing free phonons becomes a self-interacting model. PMID:21230759
Terahertz phonon scattering in yttrium-aluminium garnet crystals
International Nuclear Information System (INIS)
Results are presented of experiments on observation of superlinear luminescence of R2-lines of Cr3++ ions in Y3Al5O12 crystals at 2K. Analysis of experimental data has enabled to conclude that the luminescence excitation is not associated with a local heating of the exposed bulk but depends on a multiple reabsorption (trapping) of phonons, resonant to transition between components of the 2E chromium ion state. Probabilities of different mechanisms of phonon scattering are estimated, criteria for a possibility establishing of a local thermal equilibrium in the garnet at different regimes on excess phonon excitation are determined
The anharmonic phonon decay rate in group-III nitrides
International Nuclear Information System (INIS)
Measured lifetimes of hot phonons in group-III nitrides have been explained theoretically by considering three-phonon anharmonic interaction processes. The basic ingredients of the theory include full phonon dispersion relations obtained from the application of an adiabatic bond charge model and crystal anharmonic potential within the isotropic elastic continuum model. The role of various decay routes, such as Klemens, Ridley, Vallee-Bogani and Barman-Srivastava channels, in determining the lifetimes of the Raman active zone-centre longitudinal optical (LO) modes in BN (zincblende structure) and A1(LO) modes in AlN, GaN and InN (wurtzite structure) has been quantified.
Confined and interface phonons in combined cylindrical nanoheterosystem
Directory of Open Access Journals (Sweden)
O.M.Makhanets
2006-01-01
Full Text Available The spectra of all types of phonons existing in a complicated combined nanoheterosystem consisting of three cylindrical quantum dots embedded into the cylindrical quantum wire placed into vacuum are studied within the dielectric continuum model. It is shown that there are confined optical (LO and interface phonons of two types: top surface optical (TSO and side surface optical (SSO modes of vibration in such a nanosystem. The dependences of phonon energies on the quasiwave numbers and geometrical parameters of quantum dots are investigated and analysed.
Vibrationally assisted transitions and phonon spectra in crystalline solids
International Nuclear Information System (INIS)
The vibrationally assisted electronic (vibronic) transitions of localized centers in crystalline solids provide relevant information regarding the phonon spectra of the host materials. We present the vibronic spectra of some compounds with particular attention to the case of the transition metal ions V2+ and Cr3+ embedded in simple ionic crystals such as MgO or more complex systems such as YAG. The vibronic spectra are interpreted in light of the radiative selection rules and are compared with phonon data obtained with other techniques such as neutron scattering, infrared and Raman spectroscopies. Conclusions regarding the effectiveness of vibronic spectra in uncovering the phonon spectral distributions are presented.
The effects of electron-phonon interactions on bandgaps
Energy Technology Data Exchange (ETDEWEB)
Hague, J P, E-mail: J.P.Hague@open.ac.uk [Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)
2011-03-01
I compute the spectral functions of a 1D Holstein polaron moving in a modulated potential, to examine the effects of electron-phonon interactions on band gaps. The imaginary time Green function is computed using diagrammatic quantum Monte Carlo, which exactly sums the diagrammatic series. From the imaginary time Green function, spectral functions are computed. The electron-phonon interaction flattens the electronic dispersion and leads to an increase in the gap at momentum k = {pi}/2. At strong coupling, polaron sidebands form in the gap. These results demonstrate the strong effect that electron-phonon interactions can have on band gaps.
Analog model for quantum gravity effects: phonons in random fluids
Krein, G; Svaiter, N F
2010-01-01
We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. We show that in this model, after performing the random averages over the noise function a free conventional scalar quantum field theory describing free phonons becomes a self-interacting model.
Proposal for an optomechanical traveling wave phonon-photon translator
Safavi-Naeini, Amir H.; Painter, Oskar
2011-01-01
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.
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.
Heat Transfer by Phonons in Landauer-Datta-Lundstrom Approach
Directory of Open Access Journals (Sweden)
Kruglyak Yu.A.
2014-08-01
Full Text Available The Landauer-Datta-Lundstrom generalized transport model is applied to heat transfer by phonons. In both cases of electrons and phonons the Landauer approach generalized and extended by Datta and Lundstom gives correct quantitative description of transport processes for resistors of any dimension and size in ballistic, quasi-ballistic, and diffusive linear response regimes when there are differences in both voltage and temperature across the device. It is shown that the lattice thermal conductivity can be written in a form that is very similar to the electrical conductivity. Important differences between electrons and phonons are discussed.
Influence of anharmonic phonon decay on self-heating in Si nanowire transistors
Energy Technology Data Exchange (ETDEWEB)
Rhyner, Reto, E-mail: rhyner@iis.ee.ethz.ch; Luisier, Mathieu, E-mail: mluisier@iis.ee.ethz.ch [Integrated Systems Laboratory, ETH Zürich, Gloriastr. 35, 8092 Zürich (Switzerland)
2014-08-11
Anharmonic phonon-phonon scattering is incorporated into an electro-thermal quantum transport approach based on the nonequilibrium Green's function formalism. Electron-phonon and phonon-phonon interactions are taken into account through scattering self-energies solved in the self-consistent Born approximation. While studying self-heating effects in ultra-scaled Si nanowire transistors, it is found that the phonon decay process softens the artificial accumulation of high energy phonons caused by electron relaxations close to the drain region. This leads to an increase of the device current in the ON-state and a reduction of the effective lattice temperature.
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
Theoretical study of the phonon spectra of multiferroic BiFeO{sub 3} nanoparticles
Energy Technology Data Exchange (ETDEWEB)
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
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.
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.
Thermal transport across metal-insulator interface via electron-phonon interaction
Zhang, Lifa; Lu?, Jing-tao; Wang, Jian-sheng; Li, Baowen
2013-01-01
The thermal transport across metal-insulator interface can be characterized by electron-phonon interaction through which an electron lead is coupled to a phonon lead if phonon-phonon coupling at the interface is very weak. We investigate the thermal conductance and rectification flowing between the electron part and the phonon part using nonequilibrium Green's function method. It is found that the thermal conductance has a nonmonotonic behavior as a function of average tempe...
Quantum spin liquid in antiferromagnetic chain S=1/2 with Acoustic Phonons
Aplesnin, S. S.
2002-01-01
A spin and phonon excitations spectrum are studied using quantum Monte Carlo method in antiferromagnetic chain with spins $S=1/2$ coupled nonadiabaticity with acoustic phonons . It is found the critical coupling exists to open gap in the triplet excitation spectrum for any phonon velocity. The phase boundaries of delocalized phonons and propagated the bound states of magnon and a phonon are calculated. It is shown that the spherical symmetry of the spin-spin correlation func...
International Nuclear Information System (INIS)
In the full wave function of the electron-phonon system represented by means of a functional integral describing the evolution of the system from an arbitrary initial state, all the integrations over phonon coordinates are performed and the shifts of oscillation centres of the phonon modes are found. Non-stationary density matrix depending on both electron and phonon coordinates is obtained for any mixed ensemble of electron-phonon systems
Phonon dispersion and electron-phonon coupling in MgB2 and AlB2.
Bohnen, K P; Heid, R; Renker, B
2001-06-18
We present a first principles investigation of the lattice dynamics and electron-phonon coupling of the superconductor MgB2 and the isostructural AlB2 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. Complete phonon dispersion curves and Eliashberg functions alpha2F are calculated for both systems. The main differences are related to high frequency in-plane boron vibrations, which are strongly softened in MgB2 and exhibit an exceptionally strong electron-phonon coupling. We also report on Raman measurements, which support the theoretical findings. Implications for the superconducting transition temperature are briefly discussed. PMID:11415354
Smirnova, Nadya A.; Pietralla, Norbert; Mizusaki, Takahiro; Isacker, Piet
2000-01-01
The interrelation between the octupole phonon and the low-lying proton-neutron mixed-symmetry quadrupole phonon in near-spherical nuclei is investigated. The one-phonon states decay by collective E3 and E2 transitions to the ground state and by relatively strong E1 and M1 transitions to the isoscalar 2+ state. We apply the proton-neutron version of the Interacting Boson Model including quadrupole and octupole bosons (sdf-IBM-2). Two F-spin symmetric dynamical symmetry limits...
Scientific Electronic Library Online (English)
Aristides, Palhares; Silvana Artioli, Schellini; Claudia Helena, Pellizzon; Carlos Roberto, Padovani; Patrícia, Dorsa.
2009-02-01
Full Text Available SciELO Brazil | Language: English Abstract in portuguese OBJETIVO: Avaliar o efeito do laser de baixa intensidade sobre a contração da pseudocápsula que ocorre ao redor de implantes de silicone. MÉTODOS: 60 ratos machos divididos em dois grupos receberam implante de silicone. Grupo I: implante no subcutâneo da região dorsal, sem tratamento após a cirurgia [...] ; Grupo II: animais receberam sete sessões de irradiação com laser de baixa intensidade após o implante. Trinta, 60 e 180 dias após a cirurgia, foi feita a tonometria dos implantes, Em seguida, os animais foram sacrificados, removendo-se o material de estudo que foi preparado para exame histológico, avaliando-se morfometricamente a espessura da pseudocápsula e a reação inflamatória. A análise estatistica pela técnica da Análise de Variância e Teste de Tukey (P Abstract in english PURPOSE: To evaluate the effect of low intensity laser on the pseudocapsula contraction that occurs around silicone implants. METHODS: 60 male rats divided in two experimental groups received a silicone implant in the subcutaneous of the dorsal region. Group I: animals received implants in the subcu [...] taneous dorsal region and did not receive any treatment; Group II: animals received seven irradiation sessions with low intensity laser after they had received subcutaneous implants. Thirty, 60 and 180 days after the surgery, tonometric evaluation of the implants was conducted. After that, the animals were sacrificed, study material was removed and prepared for histological examination. The thickness of the pseudocapsule and the inflammatory reaction were morphometrically quantified. Data obtained were statistically analyzed using the Variance method, and Tukey's Test(P
Transmission of longitudinal phonons through a mass-spring nanoring
Rabani, Hassan; Mardaani, Mohammad
2015-03-01
In this paper, we study the coherent phonon transport through a cyclic mass-spring structure which is embedded between two longitudinal phononic leads within the harmonic approximation. We assume only the in-plane vibrations for the atoms of the structure and also the nearest neighbor interaction between them. By starting from the system potential energy and then using the Green's function method, we construct a formalism to compute the phononic transmission coefficient and density of states/modes of the system. The numerical calculations are performed for a hexagonal mass-spring ring in the presence and absence of a massive impurity. The results reveal that, the variation of value of the masses or spring constants in the ring leads to appearance of the Fano resonance in the transmission spectrum. This phenomenon occurs at a special phonon frequency independent of the impurity position in the structure.
Theory of surface phonons at metal surfaces: recent advances.
Benedek, G; Bernasconi, M; Chis, V; Chulkov, E; Echenique, P M; Hellsing, B; Peter Toennies, J
2010-03-01
Recent studies of the surface dynamics of Al(001) and Cu(111) based on density functional perturbation theory have substantiated the existence of subsurface optical phonon resonances of all three polarizations, thus confirming early predictions of the embedded-atom method. The hybridization of the shear-vertical optical resonance with the longitudinal acoustic phonon branch accounts for the ubiquitous anomalous acoustic resonance as an intrinsic feature of metal surfaces. The DFPT calculation of the phonon-induced surface charge density oscillations shows that helium atom scattering spectroscopy (HAS) can indeed probe subsurface resonances. This opens new perspectives to HAS for the measurement of subsurface phonon dispersion curves in thin films, as proved by recent HAS studies on Pb and Fe ultrathin films on copper. After discussing these recent advances, this paper briefly reviews other important trends of surface dynamics expressed in recent years. PMID:21389396
Phonon-mode couplings studied by pump-probe photoemission
Sentef, Michael; Kemper, Alexander; Moritz, Brian; Freericks, James; Shen, Zhi-Xun; Devereaux, Thomas
2013-03-01
Motivated by recent pump-probe photoemission experiments on cuprate superconductors, we show how the coupling of electrons to phonon modes at the same time leads to a prominent kink in the equilibrium band dispersion and to a distinct behavior of relaxation time scales in nonequilibrium experiments. Here, using the nonequilibrium solution of a model photoexcited electron-phonon system we show that the return of the electrons to equilibrium is governed by the equilibrium self-energy so that the phonon frequency sets a window for``slow'' versus ``fast'' relaxation. The overall structure of the relaxation spectroscopy in the time domain allows for a reliable and quantitative extraction of the electron-phonon coupling strength.
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
Calculation of Phonon Dispersion and Thermal Conductivity in Carbon Nanotubes
Varshney, Mayank
2005-03-01
Many potential applications of carbon nanotubes in nanoelectronic circuits rely on effective removing of excess heat from the device active area. Heat in carbon nanotubes is mostly carried by acoustic phonons. In this work we have calculated phonon dispersion in carbon nanotubes using atomistic approach. The phonon dispersion was then used to calculate phonon density of states, heat capacitance and thermal conductivity. The thermal conductivity has been determined using the modified Callaway -- Klemens approach, which accounts for the low-dimensional size effects [1]. The results of our calculations are compared with the experimental Raman spectroscopic study of carbon nanotubes and reported values of the thermal conductivity. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center. [1] A.A. Balandin, Thermal Conductivity of Semiconductor Nanostructures, in Encyclopedia of Nanoscience and Nanotechnology (ASP, Los Angeles, 2004) p. 425.
Interatomic potential for accurate phonons and defects in UO2
International Nuclear Information System (INIS)
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
Dynamical symplectic symmetry in the quasiparticle-phonon nuclear model
International Nuclear Information System (INIS)
It is shown that in some constraints the quasiparticle-phonon nuclear model (QPM) has the dynamical symplectic symmetric limit. The conditions for the phonon amplitudes, under which the generators of the Sp(2d, R) algebra and of its central inhomogeneous extension - the WSp(2d, R) algebra can be constructed from the phonon and biphonon QPM operators, are obtained. The contribution of the Sp(2d, R) symmetry in the general WSp(2d, R) symmetry of the QPM is discussed. The exact Dyson boson realizations for the phonon and biphonon operators in the spaces of Perelomov partially coherent states and Barut-Girardello partially coherent states are derived. Based on these realizations in the symplectic symmetry limit of the QPM Hamiltonian the microscopic versions for the Hamiltonians of Sp(6, R) and WSp(6, R) models are suggested
Phonon localization in cubic GaN/AlN superlattices
Rodrigues, A. D.; de Godoy, M. P. F.; Mietze, C.; As, D. J.
2014-05-01
To enhance the device’s 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.
Phonon-assisted decoherence in coupled quantum dots
Thilagam, A
2007-01-01
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.
The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy
Energy Technology Data Exchange (ETDEWEB)
D.W. Lynch
2004-09-30
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.
Electron-phonon coupling as an order-one problem
Powell, B J; Baruah, T; Pederson, Mark R.; Baruah, Tunna
2005-01-01
The coupling between electrons and phonons plays important roles in physics, chemistry and biology. However, the accurate calculation of the electron-phonon coupling constants is computationally expensive as it involves solving the Schrodinger equation for O(N) nuclear configurations, where N is the number of nuclei. Herein we show that by considering the forces on the nuclei caused by the addition or subtraction of an arbitrarily small electronic charge one may calculate the electron-phonon coupling constants from O(1) solutions of the Schrodinger equation. We show that Janak's theorem means that this procedure is exact within the density functional formalism. We demonstrate that the O(1) approach produces numerically accurate results by calculating the electron-phonon coupling constants for a series of molecules ranging in size from H_2 to C_60. We use our approach to introduce a computationally fast approximation for the adiabatic ionisation potentials and electron affinities which is shown to be accurate ...
Phonons in a Nanoparticle Mechanically Coupled to a Substrate
Patton, K R; Patton, Kelly R.; Geller, Michael R.
2002-01-01
The discrete nature of the vibrational modes of an isolated nanometer-scale solid dramatically modifies its low-energy electron and phonon dynamics from that of a bulk crystal. However, nanocrystals are usually coupled--even if only weakly--to an environment consisting of other nanocrystals, a support matrix, or a solid substrate, and this environmental interaction will modify the vibrational properties at low frequencies. In this paper we investigate the modification of the vibrational modes of an insulating spherical nanoparticle caused by a weak {\\it mechanical} coupling to a semi-infinite substrate. The phonons of the bulk substrate act as a bath of harmonic oscillators, and the coupling to this reservoir shifts and broadens the nanoparticle's modes. The vibrational density of states in the nanoparticle is obtained by solving the Dyson equation for the phonon propagator, and we show that environmental interaction is especially important at low frequencies. As a probe of the modified phonon spectrum, we co...
Moire-induced replica of graphene phonons on Ir(111)
International Nuclear Information System (INIS)
The phonon dispersion of singly oriented graphene on Ir(111) has been determined by angle-resolved inelastic electron scattering. Replica of graphene phonon bands are induced by the moire superstructure. Calculations for a linear chain of C atoms attached to an infinitely heavy substrate reveal that imposing a superstructure by periodically varying the C-C interaction and the C-substrate coupling induces replicated phonons at wave vectors reflecting the supercell periodicity. Deviations between the phonon dispersion of graphene on Ir(111) and of pristine graphene are analyzed and rationalized in terms of the weak graphene-Ir(111) interaction. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonon excitation and instabilities in biased graphene nanoconstrictions
DEFF Research Database (Denmark)
Gunst, Tue; Lu, Jing Tao
2013-01-01
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.
Moire-induced replica of graphene phonons on Ir(111)
Energy Technology Data Exchange (ETDEWEB)
Endlich, Michael; Kroeger, Joerg [Institut fuer Physik, Technische Universitaet Ilmenau (Germany); Miranda, Henrique P.C.; Molina-Sanchez, Alejandro [Physics and Materials Science Research Unit, University of Luxembourg (Luxembourg); Wirtz, Ludger [Physics and Materials Science Research Unit, University of Luxembourg (Luxembourg); Institute for Electronics, Microelectronics, and Nanotechnology (IEMN), CNRS UMR 8520, Dept. ISEN, Villeneuve d' Ascq (France)
2014-10-15
The phonon dispersion of singly oriented graphene on Ir(111) has been determined by angle-resolved inelastic electron scattering. Replica of graphene phonon bands are induced by the moire superstructure. Calculations for a linear chain of C atoms attached to an infinitely heavy substrate reveal that imposing a superstructure by periodically varying the C-C interaction and the C-substrate coupling induces replicated phonons at wave vectors reflecting the supercell periodicity. Deviations between the phonon dispersion of graphene on Ir(111) and of pristine graphene are analyzed and rationalized in terms of the weak graphene-Ir(111) interaction. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonon Dynamics and Inelastic Neutron Scattering of Sodium Niobate
Mishra, S K; Mittal, R; Zbiri, M; Rols, S; Schober, H; Chaplot, S L
2013-01-01
Sodium niobate (NaNbO3) exhibits most complex sequence of structural phase transitions in perovskite family and therefore provides as excellent model system for understanding the mechanism of structural phase transitions. We report temperature dependence of inelastic neutron scattering measurements of phonon densities of states in sodium niobate. The measurements are carried out in various crystallographic phases of this material at various temperatures from 300 K to 1048 K. The phonon spectra exhibit peaks centered around 19, 37, 51, 70 and 105 meV. Interestingly, the peak around 70 meV shifts significantly towards lower energy with increasing temperature, while the other peaks do not exhibit an appreciable change. The phonon spectra at 783 K show prominent change and become more diffusive as compared to those at 303 K. In order to better analyze these features, we have performed first principles lattice dynamics calculations based on the density functional theory. The computed phonon density of states is fo...
Energy Technology Data Exchange (ETDEWEB)
Kityk, I.V. [Institute of Physics, J. Dlugosz University Czestochowa, Al. Armii Krajowej 13/15, Czestochowa (Poland)]. E-mail: i.kityk@ajd.czest.pl; Guignard, M. [UMR CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, 35000 Rennes (France); Nazabal, V. [UMR CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, 35000 Rennes (France); Zhang, X.H. [UMR CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, 35000 Rennes (France); Troles, J. [UMR CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, 35000 Rennes (France); Smektala, F. [UMR CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, 35000 Rennes (France); Sahraoui, B. [Laboratoire POMA, Universite d' Angers Bld. Lavouisier 2, Angers, UMR CNRS 6136 (France); Boudebs, G. [Laboratoire POMA, Universite d' Angers Bld. Lavouisier 2, Angers, UMR CNRS 6136 (France)
2007-04-01
The non-linear optical response of sulphide glass-containing {beta}-GeS{sub 2} microcrystallites, has been studied at a fundamental wavelength of {lambda}=5.5 {mu}m under additional irradiation by IR-pulses of {lambda}=3.7 {mu}m. A substantial increase of the non-linear susceptibility with IR-power and size of the microcrystallites has been found. Molecular dynamics calculations linked to quantum chemical calculations show that this effect could be explained by substantial contributions of the microcrystallite interfaces and due to the phonon sub-system. The role of anharmonic electron-phonon effects is experimentally confirmed by the observation of an optimal delay of 8 ps between the pump laser pulses at 3.7 {mu}m and the probing laser pulses at 5.5 {mu}m, which generate the observed second harmonic signal.
Holstein polaron: the effect of multiple phonon modes
Covaci, Lucian; Berciu, Mona
2007-01-01
We generalize the Momentum Average approximations MA$^{(0)}$ and MA$^{(1)}$ to study the effects of coupling to multiple optical phonons on the properties of a Holstein polaron. As for a single phonon mode, these approximations are numerically very efficient. They become exact for very weak or very strong couplings, and are highly accurate in the intermediate regimes, {\\em e.g.} the spectral weights obey exactly the first six, respectively eight, sum rules. Our results show ...
Interaction between optical phonons and Josephson vortices in layered superconductors
International Nuclear Information System (INIS)
On the basis of the expression for the permittivity of a layered high-temperature superconductor one investigated into the effect of optical phonons on the stability of the inphase pattern of motion of the Josephson vortices in a layered superconductor. One analyzed the dispersion features of the linear waves. It is shown that the inphase pattern of the motion of the Josephson vortices may spontaneously occur near the frequencies of the optical phonons
Forward Electron-Phonon Scattering in Normal and Superconducting States
Dolgov, O V; Kulic, M L; Oudovenko, V S
1998-01-01
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.
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Yang, Nuo; Li, Baowen
2013-01-01
The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductiv...
Optomechanical Quantum Information Processing with Photons and Phonons
Stannigel, K.; Komar, P.; Habraken, S. J. M.; Bennett, S. D.; Lukin, M. D.; Zoller, P.; Rabl, P.
2012-07-01
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.
Electron-phonon coupling and Peierls transition in metallic nanotubes
Sedeki, A; Bourbonnais, C
1999-01-01
We reexamine the putative Peierls transition in a (5,5) metallic nanotube. We show that the conduction electrons at the Fermi level do not couple to the longitudinal acoustic phonon but rather to a folded-in graphene zone edge phonon having the proper Kekule modulation symmetry. The calculation for the mean-field transition temperature gives 15 K, a value comparable to previous estimates. We discuss the significance of this transition temperature.
Optical phonon scattering of cavity polaritons in an electroluminescent device
Delteil, A.; Vasanelli, A.; Jouy, P.; Barate, D.; Moreno, J. C.; Teissier, R.; Baranov, A. N.; Sirtori, C.
2012-01-01
A signature of the scattering between microcavity polaritons and longitudinal optical phonons has been observed in the electroluminescence spectrum of an intersubband device operating in the light-matter strong coupling regime. By electrical pumping we resonantly populate the upper polariton branch at different energies as a function of the applied bias. The electroluminescent signal arising from these states is seconded by a phonon replica from the lower branch.
Phonon-assisted decoherence in coupled quantum dots
Thilagam, A.; Lohe, M. A.
2007-01-01
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 ...
Gap formation and soft phonon mode in the Holstein model
Meyer, D; Bulla, R
2002-01-01
We investigate electron-phonon coupling in many-electron systems using dynamical mean-field theory in combination with the numerical renormalization group. This non-perturbative method reveals significant precursor effects to the gap formation at intermediate coupling strengths. The emergence of a soft phonon mode and very strong lattice fluctuations can be understood in terms of Kondo-like physics due to the development of a double-well structure in the effective potential for the ions.
Optomechanical quantum information processing with photons and phonons
Stannigel, K; Habraken, S J M; Bennett, S D; Lukin, M D; Zoller, P; Rabl, P
2012-01-01
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.
Nonlinear Optomechanics: Two-phonon cooling and squeezing
Nunnenkamp, Andreas; Børkje, Kjetil; Harris, Jack; Girvin, Steven
2010-03-01
Motivated by recent optomechanics experiments using the membrane-in-the-middle geometry [Thompson et al., Nature 452, 06715 (2008)] we explore the physics of optomechanical systems where the mechanical oscillator is coupled quadratically rather than linearly to one mode of the optical cavity field. We derive an expression for the minimal phonon number achievable by two-phonon cooling, explain how to achieve mechanical squeezing by driving the cavity on both sidebands and calculate the squeezing spectrum of the output cavity field.
Effect of phonons on the ac conductance of molecular junctions.
Ueda, Akiko; Entin-Wohlman, Ora; Aharony, Amnon
2011-01-01
We theoretically examine the effect of a single phonon mode on the structure of the frequency dependence of the ac conductance of molecular junctions, in the linear response regime. The conductance is enhanced (suppressed) by the electron-phonon interaction when the chemical potential is below (above) the energy of the electronic state on the molecule.PACS numbers: 71.38.-k, 73.21.La, 73.23.-b. PMID:21711740
The inverted pendulum, interface phonons and optic Tamm states
Combe, Nicolas
2011-01-01
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 ...
X-ray studies of phonon softening in tise2.
Holt, M; Zschack, P; Hong, H; Chou, M Y; Chiang, T C
2001-04-23
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