Phonon Modes and the Maintenance Condition of a Crystalline Beam
Wei, Jie; Li, Xiao-Ping; Okamoto, Hiromi; Sessler, Andrew M; Yuri, Yosuke
2005-01-01
Previously it has been shown that the maintenance condition for a crystalline beam requires that there not be a resonance between the crystal phonon frequencies and the frequency associated with a beam moving through a lattice of N periods. This resonance can be avoided provided the phonon frequencies are all below half of the lattice frequency. Here we make a detailed study of the phonon modes of a crystalline beam. Analytic results obtained in a smooth approximation using the ground-state crystalline beam structure is compared with numerical evaluation employing Fourier transform of Molecular Dynamic (MD) modes. The MD also determines when a crystalline beam is stable. The maintenance condition, when combined with either the simple analytic theory or the numerical evaluation of phonon modes, is shown to be in excellent agreement with the MD calculations of crystal stability.
First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures
Energy Technology Data Exchange (ETDEWEB)
Sandip Mazumder; Ju Li
2010-06-30
The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion
Use of thulium-sensitized rare earth-doped low phonon energy crystalline hosts for IR sources.
Ganem, Joseph; Bowman, Steven R
2013-11-01
Crystalline hosts with low phonon energies enable novel energy transfer processes when doped with rare earth ions. Two applications of energy transfer for rare earth ions in thulium-sensitized low phonon energy crystals that result in infrared luminescence are discussed. One application is an endothermic, phonon-assisted cross-relaxation process in thulium-doped yttrium chloride that converts lattice phonons to infrared emission, which raises the possibility of a fundamentally new method for achieving solid-state optical cooling. The other application is an optically pumped mid-IR phosphor using thulium-praseodymium-doped potassium lead chloride that converts 805-nm diode light to broadband emission from 4,000 to 5,500 nm. These two applications in chloride crystals are discussed in terms of critical radii calculated from Forster-Dexter energy transfer theory. It is found that the critical radii for electric dipole-dipole interactions in low phonon energy chloride crystals are comparable to those in conventional oxide and fluoride crystals. It is the reduction in multi-phonon relaxation rates in chloride crystals that enable these additional energy transfer processes and infrared luminescence.
Diffusion of phonons through (along and across) the ultrathin crystalline films
Šetrajčić, J. P.; Jaćimovski, S. K.; Vučenović, S. M.
2017-11-01
Instead of usual approach, applying displacement-displacement Green's functions, the momentum-momentum Green's functions will be used to calculate the diffusion tensor. With this type of Green's function we have calculated and analyzed dispersion law in film-structures. A small number of phonon energy levels along the direction of boundary surfaces joint of the film are discrete-ones and in this case standing waves could occur. This is consequence of quantum size effects. These Green's functions enter into Kubo's formula defining diffusion properties of the system and possible heat transfer direction through observed structures. Calculation of the diffusion tensor for phonons in film-structure requires solving of the system of difference equations. Boundary conditions are included into mentioned system through the Hamiltonian of the film-structure. It has been shown that the diagonal elements of the diffusion tensor express discrete behavior of the dispersion law of elementary excitations. More important result is-that they are temperature independent and that their values are much higher comparing with bulk structures. This result favors better heat conduction of the film, but in direction which is perpendicular to boundary film surface. In the same time this significantly favors appearance 2D superconducting surfaces inside the ultra-thin crystal structure, which are parallel to the boundary surface.
Phonon Transport at Crystalline Si/Ge Interfaces: The Role of Interfacial Modes of Vibration.
Gordiz, Kiarash; Henry, Asegun
2016-03-16
We studied the modal contributions to heat conduction at crystalline Si and crystalline Ge interfaces and found that more than 15% of the interface conductance arises from less than 0.1% of the modes in the structure. Using the recently developed interface conductance modal analysis (ICMA) method along with a new complimentary methodology, we mapped the correlations between modes, which revealed that a small group of interfacial modes, which exist between 12-13 THz, exhibit extremely strong correlation with other modes in the system. It is found that these interfacial modes (e.g., modes with large eigen vectors for interfacial atoms) are enabled by the degree of anharmonicity near the interface, which is higher than in the bulk, and therefore allows this small group of modes to couple to all others. The analysis sheds light on the nature of localized vibrations at interfaces and can be enlightening for other investigations of localization.
Freedman, Justin P.
Electronic and optical devices continue to decrease in size year after year. Today, devices feature length scales that are commensurate to energy carrier mean free paths. As a result, the physical principles that govern their operation and energy transport processes continue to dramatically change. This work aims to understand the nanoscale thermal transport processes in crystalline materials and across metal-dielectric interfaces. Solid-state devices, such as light emitting diodes (LED) and high power electronics, are replacing older technologies, such as incandescent and fluorescent lighting. Nitride-based semiconductors are the primary material candidates to replace these older technologies, in part because of their high thermal conductivity. In Chapter 2, the phonon mean free path dependent contributions to thermal conductivity in LED-based materials are presented. Using high frequency surface temperature modulation that generates nondiffusive phonon transport the phonon mean free path spectra of GaAs, GaN, AlN, and 4H-SiC at temperatures near 80 K, 150 K, 300 K, and 400 K are shown. This work demonstrates that phonons with mean free paths greater than 230 +/- 120 nm, 1000 +/- 200 nm, 2500 +/- 800 nm, and 4200 +/- 850 nm contribute ˜50% of the bulk thermal conductivity of GaAs, GaN, AlN, and 4H-SiC near room temperature. By nondimensionalizing the data based on Umklapp scattering rates of phonons, a universal phonon mean free path spectrum in small unit cell crystalline semiconductors at high temperature is identified. In Chapter 3, a theoretical framework based on the electron-phonon coupled Boltzmann transport equations (BTEs) is presented for the interpretation of nondiffusive thermal conductivity measurements in gold made via frequency domain thermoreflectance (FDTR). The thermal conductivity of a bulk gold crystal was measured over a temperature range of 23 K to 304 K as a function of FDTR's laser spot size. Through comparison of an analytical solution to
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...
Morrison, Adrian F.; Herbert, John M.
2017-06-01
Recently, we introduced an ab initio version of the Frenkel-Davydov exciton model for computing excited-state properties of molecular crystals and aggregates. Within this model, supersystem excited states are approximated as linear combinations of excitations localized on molecular sites, and the electronic Hamiltonian is constructed and diagonalized in a direct-product basis of non-orthogonal configuration state functions computed for isolated fragments. Here, we derive and implement analytic derivative couplings for this model, including nuclear derivatives of the natural transition orbital and symmetric orthogonalization transformations that are part of the approximation. Nuclear derivatives of the exciton Hamiltonian's matrix elements, required in order to compute the nonadiabatic couplings, are equivalent to the "Holstein" and "Peierls" exciton/phonon couplings that are widely discussed in the context of model Hamiltonians for energy and charge transport in organic photovoltaics. As an example, we compute the couplings that modulate triplet exciton transport in crystalline tetracene, which is relevant in the context of carrier diffusion following singlet exciton fission.
Morrison, Adrian F; Herbert, John M
2017-06-14
Recently, we introduced an ab initio version of the Frenkel-Davydov exciton model for computing excited-state properties of molecular crystals and aggregates. Within this model, supersystem excited states are approximated as linear combinations of excitations localized on molecular sites, and the electronic Hamiltonian is constructed and diagonalized in a direct-product basis of non-orthogonal configuration state functions computed for isolated fragments. Here, we derive and implement analytic derivative couplings for this model, including nuclear derivatives of the natural transition orbital and symmetric orthogonalization transformations that are part of the approximation. Nuclear derivatives of the exciton Hamiltonian's matrix elements, required in order to compute the nonadiabatic couplings, are equivalent to the "Holstein" and "Peierls" exciton/phonon couplings that are widely discussed in the context of model Hamiltonians for energy and charge transport in organic photovoltaics. As an example, we compute the couplings that modulate triplet exciton transport in crystalline tetracene, which is relevant in the context of carrier diffusion following singlet exciton fission.
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
Phononic High Harmonic Generation
Ganesan, Adarsh; Do, Cuong; Seshia, Ashwin A.
2016-01-01
This paper reports the first experimental evidence for phononic low-order to high-order harmonic conversion leading to high harmonic generation. Similar to parametric resonance, phononic high harmonic generation is also mediated by a threshold dependent instability of a driven phonon mode. Once the threshold for instability is met, a cascade of harmonic generation processes is triggered. Firstly, the up-conversion of first harmonic phonons into second harmonic phonons is established. Subseque...
Manipulation of Phonons with Phononic Crystals
Energy Technology Data Exchange (ETDEWEB)
Leseman, Zayd Chad [Univ. of New Mexico, Albuquerque, NM (United States)
2015-07-09
There were three research goals associated with this project. First, was to experimentally demonstrate phonon spectrum control at THz frequencies using Phononic Crystals (PnCs), i.e. demonstrate coherent phonon scattering with PnCs. Second, was to experimentally demonstrate analog PnC circuitry components at GHz frequencies. The final research goal was to gain a fundamental understanding of phonon interaction using computational methods. As a result of this work, 7 journal papers have been published, 1 patent awarded, 14 conference presentations given, 4 conference publications, and 2 poster presentations given.
Kondo-like phonon scattering in thermoelectric clathrates
Ikeda, M.; Euchner, H.; Yan, X.; Tomes, P.; Prokofiev, A; Prochaska, L.; Lientschnig, G.; Svagera, R.; Hartmann, S.; Gati, E.; Lang, M.; Paschen, S.
2017-01-01
Crystalline solids are generally known as excellent heat conductors, amorphous materials or glasses as thermal insulators. It has thus come as a surprise that certain crystal structures defy this paradigm. A prominent example are type-I clathrates and other materials with guest-host structures. They sustain low-energy Einstein-like modes in their phonon spectra, but are also prone to various types of disorder and phonon-electron scattering and thus the mechanism responsible for their ultralow...
Phonon thermal transport through tilt grain boundaries in strontium titanate
Energy Technology Data Exchange (ETDEWEB)
Zheng, Zexi; Chen, Xiang; Yang, Shengfeng; Xiong, Liming; Chen, Youping [Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States); Deng, Bowen; Chernatynskiy, Aleksandr [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2014-08-21
In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO{sub 3}. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO{sub 3} contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.
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.
Phonon-induced polariton superlattices
DEFF Research Database (Denmark)
de Lima, Jr., M. M.; Poel, Mike van der; Santos, P. V.
2006-01-01
We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement...... of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion....
Multiple topological phases in phononic crystals
Chen, Zeguo
2017-11-20
We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.
Perrin, Bernard
2007-06-01
The conference PHONONS 2007 was held 15-20 July 2007 in the Conservatoire National des Arts et Métiers (CNAM) Paris, France. CNAM is a college of higher technology for training students in the application of science to industry, founded by Henri Grégoire in 1794. This was the 12th International Conference on Phonon Scattering in Condensed Matter. This international conference series, held every 3 years, started in France at Sainte-Maxime in 1972. It was then followed by meetings at Nottingham (1975), Providence (1979), Stuttgart (1983), Urbana-Champaign (1986), Heidelberg (1989), Ithaca (1992), Sapporo (1995), Lancaster (1998), Dartmouth (2001) and St Petersburg (2004). PHONONS 2007 was attended by 346 delegates from 37 different countries as follows: France 120, Japan 45, Germany 25, USA 25, Russia 21, Italy 13, Poland 9, UK 9, Canada 7, The Netherlands 7, Finland 6, Spain 6, Taiwan 6, Greece 4, India 4, Israel 4, Ukraine 4, Serbia 3, South Africa 3, Argentina 2, Belgium 2, China 2, Iran 2, Korea 2, Romania 2, Switzerland 2, and one each from Belarus, Bosnia-Herzegovina, Brazil, Bulgaria, Egypt, Estonia, Mexico, Moldova, Morocco, Saudi Arabia, Turkey. There were 5 plenary lectures, 14 invited talks and 84 oral contributions; 225 posters were presented during three poster sessions. The first plenary lecture was given by H J Maris who presented fascinating movies featuring the motion of a single electron in liquid helium. Robert Blick gave us a review on the new possibilities afforded by nanotechnology to design nano-electomechanical systems (NEMS) and the way to use them to study elementary and fundamental processes. The growing interest for phonon transport studies in nanostructured materials was demonstrated by Arun Majumdar. Andrey Akimov described how ultrafast acoustic solitons can monitor the optical properties of quantum wells. Finally, Maurice Chapellier told us how phonons can help tracking dark matter. These 328 presentations gave rise to 185 articles
Directory of Open Access Journals (Sweden)
Georgios Gkantzounis
2017-11-01
Full Text Available We employ a recently introduced class of artificial structurally-disordered phononic structures that exhibit large and robust elastic frequency band gaps for efficient phonon guiding. Phononic crystals are periodic structures that prohibit the propagation of elastic waves through destructive interference and exhibit large band gaps and ballistic propagation of elastic waves in the permitted frequency ranges. In contrast, random-structured materials do not exhibit band gaps and favour localization or diffusive propagation. Here, we use structures with correlated disorder constructed from the so-called stealthy hyperuniform disordered point patterns, which can smoothly vary from completely random to periodic (full order by adjusting a single parameter. Such amorphous-like structures exhibit large band gaps (comparable to the periodic ones, both ballistic-like and diffusive propagation of elastic waves, and a large number of localized modes near the band edges. The presence of large elastic band gaps allows the creation of waveguides in hyperuniform materials, and we analyse various waveguide architectures displaying nearly 100% transmission in the GHz regime. Such phononic-circuit architectures are expected to have a direct impact on integrated micro-electro-mechanical filters and modulators for wireless communications and acousto-optical sensing applications.
Phonon properties of americium phosphide
Arya, B. S.; Aynyas, Mahendra; Sanyal, S. P.
2016-05-01
Phonon properties of AmP have been studied by using breathing shell models (BSM) which includes breathing motion of electrons of the Am atoms due to f-d hybridization. The phonon dispersion curves, specific heat calculated from present model. The calculated phonon dispersion curves of AmP are presented follow the same trend as observed in uranium phosphide. We discuss the significance of this approach in predicting the phonon dispersion curves of these compounds and examine the role of electron-phonon interaction.
Phononic crystals fundamentals and applications
Adibi, Ali
2016-01-01
This book provides an in-depth analysis as well as an overview of phononic crystals. This book discusses numerous techniques for the analysis of phononic crystals and covers, among other material, sonic and ultrasonic structures, hypersonic planar structures and their characterization, and novel applications of phononic crystals. This is an ideal book for those working with micro and nanotechnology, MEMS (microelectromechanical systems), and acoustic devices. This book also: Presents an introduction to the fundamentals and properties of phononic crystals Covers simulation techniques for the analysis of phononic crystals Discusses sonic and ultrasonic, hypersonic and planar, and three-dimensional phononic crystal structures Illustrates how phononic crystal structures are being deployed in communication systems and sensing systems.
Using high pressure to study thermal transport and phonon scattering mechanisms
Hohensee, Gregory Thomas
The aerospace industry studies nanocomposites for heat dissipation and moderation of thermal expansion, and the semiconductor industry faces a Joule heating barrier in devices with high power density. My primary experimental tools are the diamond anvil cell (DAC) coupled with time-domain thermoreflectance (TDTR). TDTR is a precise optical method well-suited to measuring thermal conductivities and conductances at the nanoscale and across interfaces. The DAC-TDTR method yields thermal property data as a function of pressure, rather than temperature. This relatively unexplored independent variable can separate the components of thermal conductance and serve as an independent test for phonon-defect scattering models. I studied the effect of non-equilibrium thermal transport at the aluminum-coated surface of an exotic cuprate material Ca9La5Cu 24O41, which boasts a tenfold enhanced thermal conductivity along one crystalline axis where two-leg copper-oxygen spin-ladder structures carry heat in the form of thermalized magnetic excitations. Highly anisotropic materials are of interest for controlled thermal management applications, and the spin-ladder magnetic heat carriers ("magnons") are not well understood. I found that below room temperature, the apparent thermal conductivity of Ca9La5Cu24O41 depends on the frequency of the applied surface heating in TDTR. This occurs because the thermal penetration depth in the TDTR experiment is comparable to the length-scale for the equilibration of the magnons that are the dominant channel for heat conduction and the phonons that dominate the heat capacity. I applied a two-temperature model to analyze the TDTR data and extracted an effective volumetric magnon-phonon coupling parameter g for Ca9La5Cu24O 41 at temperatures from 75 K to 300 K; g varies by approximately two orders of magnitude over this range of temperature and has the value g = 1015 W m-3 K-1 near the peak of the thermal conductivity at T ≈ 180 K. To examine
Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics
Directory of Open Access Journals (Sweden)
Bruce L. Davis
2011-12-01
Full Text Available The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell and the phononic crystal lattice (defined by a supercell contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant, dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.
Phonon-eigenspectrum-based formulation of the atomistic Green's function method
Sadasivam, Sridhar; Waghmare, Umesh V.; Fisher, Timothy S.
2017-11-01
While the atomistic Green's function (AGF) method has the potential to compute spectrally resolved phonon transport across interfaces, most prior formulations of the AGF method provide only the total phonon transmission function that includes contributions from all phonon branches or channels. In this work, we present a formulation of the conventional AGF technique in terms of phonon eigenspectra that provides a natural decomposition of the total transmission function into contributions from various phonon modes. The method involves the use of Dyson and Lippmann-Schwinger equations to determine surface Green's functions from the phonon eigenspectrum of the bulk, and establishes a direct connection between the transmission function and the bulk phonon spectra of the materials forming the interface. We elucidate our formulation of the AGF technique through its application to a microscopic picture of phonon mode conversion at Si-Ge interfaces with atomic intermixing. Intermixing of atoms near the interface is shown to increase the phase space available for phonon mode conversion and to enhance thermal interface conductance at moderate levels of atomic mixing. The eigenspectrum-based AGF method should be useful in determination of microscopic mechanisms of phonon scattering and identification of the specific modes that dominate thermal transport across an interface.
Kudryashov, S I
2002-01-01
It is experimentally shown for the first time that by the effect of the feed-up laser pulse of 100 fs duration on the silicon target the consecutive structural transitions of the substance into the new crystalline and liquid metallic phase occur both during the laser pulse feed-up and after 0.1-10 sup 3 ps, depending on the material excitation conditions. The thresholds of the observed structural transitions are determined and the phonon nodes, responsible for therefore, are identified. The structural transitions dynamics in the silicon by the 01.-10 sup 3 ps times is described within the frames of the model of the phonon modes instability, originating due to the plasma electron-hole effect and also due to the intra- and intermode phonon-phonon anharmonic interactions
Tunable Topological Phononic Crystals
Chen, Ze-Guo
2016-05-27
Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.
Velocity dependence of sliding friction on a crystalline surface
Directory of Open Access Journals (Sweden)
Christian Apostoli
2017-10-01
Full Text Available We introduce and study a minimal 1D model for the simulation of dynamic friction and dissipation at the atomic scale. This model consists of a point mass (slider that moves over and interacts weakly with a linear chain of particles interconnected by springs, representing a crystalline substrate. This interaction converts a part of the kinetic energy of the slider into phonon waves in the substrate. As a result, the slider experiences a friction force. As a function of the slider speed, we observe dissipation peaks at specific values of the slider speed, whose nature we understand by means of a Fourier analysis of the excited phonon modes. By relating the phonon phase velocities with the slider velocity, we obtain an equation whose solutions predict which phonons are being excited by the slider moving at a given speed.
Reprogrammable Phononic Metasurfaces.
Bilal, Osama R; Foehr, André; Daraio, Chiara
2017-10-01
Phononic metamaterials rely on the presence of resonances in a structured medium to control the propagation of elastic waves. Their response depends on the geometry of their fundamental building blocks. A major challenge in metamaterials design is the realization of basic building blocks that can be tuned dynamically. Here, a metamaterial plate is realized that can be dynamically tuned by harnessing geometric and magnetic nonlinearities in the individual unit cells. The proposed tuning mechanism allows a stiffness variability of the individual unit cells and can control the amplitude of transmitted excitation through the plate over three orders of magnitude. The concepts can be extended to metamaterials at different scales, and they can be applied in a broad range of engineering applications, from seismic shielding at low frequency to ultrasonic cloaking at higher frequency ranges. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Electrons and Phonons in High Temperature Superconductors
Directory of Open Access Journals (Sweden)
Anu Singh
2013-01-01
Full Text Available The defect-induced anharmonic phonon-electron problem in high-temperature superconductors has been investigated with the help of double time thermodynamic electron and phonon Green’s function theory using a comprehensive Hamiltonian which includes the contribution due to unperturbed electrons and phonons, anharmonic phonons, impurities, and interactions of electrons and phonons. This formulation enables one to resolve the problem of electronic heat transport and equilibrium phenomenon in high-temperature superconductors in an amicable way. The problem of electronic heat capacity and electron-phonon problem has been taken up with special reference to the anharmonicity, defect concentration electron-phonon coupling, and temperature dependence.
On the Phononic Bandgap of Carbon Nanotubes
Directory of Open Access Journals (Sweden)
Kohei Yamamoto
2013-01-01
phononic bandgaps and its dependence on the diameters of CNTs. We find that, though the rule where CNTs have phononic bandgaps is the same as in the electronic structure case, the diameter dependence is different. The phononic bandgaps of the zigzag-CNTs reveal “three” kinds of diameter dependence due to the anisotropy of graphene phonon band around the K point in k-space. We also show the crossover from one- to two-dimensional characteristics in phononic bandgaps.
Phonon symmetries in hexagonal boron nitride probed by incoherent light emission
Vuong, T. Q. P.; Cassabois, G.; Valvin, P.; Jacques, V.; Van Der Lee, A.; Zobelli, A.; Watanabe, K.; Taniguchi, T.; Gil, B.
2017-03-01
Layered compounds are stacks of weakly bound two-dimensional atomic crystals, with a prototypal hexagonal structure in graphene, transition metal dichalcogenides and boron nitride. This crystalline anisotropy results in vibrational modes with specific symmetries depending on the in-plane or out-of-plane atomic displacements. We show that polarization-resolved photoluminescence measurements in hexagonal boron nitride reflect the phonon symmetries in this layered semiconductor. Experiments performed with a detection on the sample edge, perpendicular to the c-axis, reveal the strong polarization-dependence of the emission lines corresponding to the recombination assisted by the three acoustic phonon modes. We elucidate the dipole orientation of the fundamental indirect exciton. We demonstrate evidence of the so-far missing phonon replica due to the optical out-of-plane phonon mode.
Hybrid phonons in nanostructures
Ridley, Brian K
2017-01-01
Crystalline semiconductor nanostructures have special properties associated with electrons and lattice vibrations and their interaction, and this is the topic of the book. The result of spatial confinement of electrons is indicated in the nomenclature of nonostructures: quantum wells, quantum wires, and quantum dots. Confinement also has a profound effect on lattice vibrations and an account of this is the prime focus. The documentation of the confinement of acoustic modes goes back to Lord Rayleigh’s work in the late nineteenth century, but no such documentation exists for optical modes. Indeed, it is only comparatively recently that any theory of the elastic properties of optical modes exists, and the account given in the book is comprehensive. A model of the lattice dynamics of the diamond lattice is given that reveals the quantitative distinction between acoustic and optical modes and the difference of connection rules that must apply at an interface. The presence of interfaces in nanostructures forces ...
Optimizing phonon space in the phonon-coupling model
Tselyaev, V.; Lyutorovich, N.; Speth, J.; Reinhard, P.-G.
2017-08-01
We present a new scheme to select the most relevant phonons in the phonon-coupling model, named here the time-blocking approximation (TBA). The new criterion, based on the phonon-nucleon coupling strengths rather than on B (E L ) values, is more selective and thus produces much smaller phonon spaces in the TBA. This is beneficial in two respects: first, it curbs the computational cost, and second, it reduces the danger of double counting in the expansion basis of the TBA. We use here the TBA in a form where the coupling strength is regularized to keep the given Hartree-Fock ground state stable. The scheme is implemented in a random-phase approximation and TBA code based on the Skyrme energy functional. We first explore carefully the cutoff dependence with the new criterion and can work out a natural (optimal) cutoff parameter. Then we use the freshly developed and tested scheme for a survey of giant resonances and low-lying collective states in six doubly magic nuclei looking also at the dependence of the results when varying the Skyrme parametrization.
Evidence for spin-phonon coupling
Indian Academy of Sciences (India)
We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the superexchange integral be- tween the Mn3+ spins. The effective charge of oxygen (ZO) calculated using the measured. LO–TO splitting increases below TN. Keywords. Spin-phonon coupling; longitudinal and transverse ...
Electron-phonon interaction spectra in beryllium
Energy Technology Data Exchange (ETDEWEB)
Najdyuk, Yu.G.; Shklyarevskij, O.I. (AN Ukrainskoj SSR, Kharkov. Fiziko-Tekhnicheskij Inst. Nizkikh Temperatur)
1982-09-01
Micro-contact (MC) method was used to investigate spectra of electron-phonon interaction (EPI) in berillium. MC spectra and the known dependences of phonon state density in this metal have been compared in detail. It is shown that the MC spectra can be used for refining the berillium phonon spectrum. The EPI integral parameter has been determined in the free electron model.
Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films
Energy Technology Data Exchange (ETDEWEB)
Chase, T. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Trigo, M.; Reid, A. H.; Dürr, H. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Li, R.; Vecchione, T.; Shen, X.; Weathersby, S.; Coffee, R.; Hartmann, N.; Wang, X. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Reis, D. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States)
2016-01-25
We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement.
DynaPhoPy: A code for extracting phonon quasiparticles from molecular dynamics simulations
Carreras, Abel; Togo, Atsushi; Tanaka, Isao
2017-12-01
We have developed a computational code, DYNAPHOPY, that allows us to extract the microscopic anharmonic phonon properties from molecular dynamics (MD) simulations using the normal-mode-decomposition technique as presented by Sun et al. (2014). Using this code we calculated the quasiparticle phonon frequencies and linewidths of crystalline silicon at different temperatures using both of first-principles and the Tersoff empirical potential approaches. In this work we show the dependence of these properties on the temperature using both approaches and compare them with reported experimental data obtained by Raman spectroscopy (Balkanski et al., 1983; Tsu and Hernandez, 1982).
Phonon generation and phonon energy current fluctuation in quantum dot molecules.
Wu, B H; Cao, J C
2009-06-17
We study the phonon dynamics in a biased molecular junction with the interplay of electron-phonon coupling and Coulomb interaction. These interactions are taken into account within the self-consistent Born approximation and mean-field methods. It is found that the Coulomb interaction can enhance the nonequilibrium phonon generation. A general formula for the zero-frequency power spectral density of the phonon energy current fluctuation is presented in terms of the nonequilibrium phonon Green's functions.
DEFF Research Database (Denmark)
Mah, Pei T.; Fraser, Sara J.; Reish, Matthew E.
2015-01-01
Low-frequency Raman spectroscopy, which directly probes phonon lattice modes of crystal structures, has much unexplored potential for sensitive qualitative and quantitative analysis of crystallinity in drugs and excipients. In this study, the level of crystallinity in tablets containing amorphous...
Nanoscale control of phonon excitations in graphene
Kim, Hyo Won; Ko, Wonhee; Ku, Jiyeon; Ryu, Seunghwa; Hwang, Sung Woo
Phonons, which are collective excitations in a lattice of atoms or molecules, play a major role in determining various physical properties of condensed matter, such as thermal and electrical conductivities. In particular, phonons in graphene interact strongly with electrons; however, unlike in usual metals, these interactions between phonons and massless Dirac fermions appear to mirror the rather complicated physics of those between light and relativistic electrons. Therefore, a fundamental understanding of the underlying physics through systematic studies of phonon interactions and excitations in graphene is crucial for realizing graphene-based devices. In this study, we demonstrate that the local phonon properties of graphene can be controlled at the nanoscale by tuning the interaction strength between graphene and an underlying Pt substrate. Using scanning probe methods, we determine that the reduced interaction due to embedded Ar atoms facilitates electron-phonon excitations, further influencing phonon-assisted inelastic electron tunneling.
Crystalline and Crystalline International Disposal Activities
Energy Technology Data Exchange (ETDEWEB)
Viswanathan, Hari S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, Shaoping [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, Paul William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Makedonska, Nataliia [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, Jeffrey De' Haven [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Karra, Satish [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dittrich, Timothy M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-12-21
This report presents the results of work conducted between September 2014 and July 2015 at Los Alamos National Laboratory in the crystalline disposal and crystalline international disposal work packages of the Used Fuel Disposition Campaign (UFDC) for DOE-NE’s Fuel Cycle Research and Development program.
Phonons from neutron powder diffraction
Energy Technology Data Exchange (ETDEWEB)
Dimitrov, D.A.; Louca, D.; Roeder, H. (Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States))
1999-09-01
The spherically averaged structure function S([vert bar][bold q][vert bar]) obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of S([vert bar][bold q][vert bar]) 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 ([vert bar][bold q][vert bar][ne]0) phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure [dynamics from powder diffraction] has been [ital successfully] implemented as demonstrated here for two systems, a simple metal fcc Ni and an ionic crystal CaF[sub 2]. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from neutron powder diffraction. [copyright] [ital 1999] [ital The American Physical Society
Coherent Phonon Rabi Oscillations with a High-Frequency Carbon Nanotube Phonon Cavity.
Zhu, Dong; Wang, Xin-He; Kong, Wei-Cheng; Deng, Guang-Wei; Wang, Jiang-Tao; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Jiang, Kai-Li; Dai, Xing-Can; Guo, Guang-Can; Nori, Franco; Guo, Guo-Ping
2017-02-08
Phonon-cavity electromechanics allows the manipulation of mechanical oscillations similar to photon-cavity systems. Many advances on this subject have been achieved in various materials. In addition, the coherent phonon transfer (phonon Rabi oscillations) between the phonon cavity mode and another oscillation mode has attracted many interest in nanoscience. Here, we demonstrate coherent phonon transfer in a carbon nanotube phonon-cavity system with two mechanical modes exhibiting strong dynamical coupling. The gate-tunable phonon oscillation modes are manipulated and detected by extending the red-detuned pump idea of photonic cavity electromechanics. The first- and second-order coherent phonon transfers are observed with Rabi frequencies 591 and 125 kHz, respectively. The frequency quality factor product fQ m ∼ 2 × 10 12 Hz achieved here is larger than k B T base /h, which may enable the future realization of Rabi oscillations in the quantum regime.
Circular Phonon Dichroism in Weyl Semimetals
Liu, Donghao; Shi, Junren
2017-08-01
We derive the phonon dynamics of magnetic metals in the presence of strong spin-orbit coupling. We show that both a dissipationless viscosity and a dissipative viscosity arise in the dynamics. While the dissipationless viscosity splits the dispersion of left-handed and right-handed circularly polarized phonons, the dissipative viscosity damps them differently, inducing circular phonon dichroism. The effect offers a new degree of manipulation of phonons, i.e., the control of the phonon polarization. We investigate the effect in Weyl semimetals. We find that there exists strong circular phonon dichroism in Weyl semimetals breaking both the time-reversal and the inversion symmetry, making them potential materials for realizing the acoustic circular polarizer.
Wide-Stopband Aperiodic Phononic Filters
Rostem, Karwan; Chuss, David; Denis, K. L.; Wollack, E. J.
2016-01-01
We demonstrate that a phonon stopband can be synthesized from an aperiodic structure comprising a discrete set of phononic filter stages. Each element of the set has a dispersion relation that defines a complete bandgap when calculated under a Bloch boundary condition. Hence, the effective stopband width in an aperiodic phononic filter (PnF) may readily exceed that of a phononic crystal with a single lattice constant or a coherence scale. With simulations of multi-moded phononic waveguides, we discuss the effects of finite geometry and mode-converting junctions on the phonon transmission in PnFs. The principles described may be utilized to form a wide stopband in acoustic and surface wave media. Relative to the quantum of thermal conductance for a uniform mesoscopic beam, a PnF with a stopband covering 1.6-10.4 GHz is estimated to reduce the thermal conductance by an order of magnitude at 75 mK.
Phonon-induced diamagnetic force and its effect on the lattice thermal conductivity.
Jin, Hyungyu; Restrepo, Oscar D; Antolin, Nikolas; Boona, Stephen R; Windl, Wolfgang; Myers, Roberto C; Heremans, Joseph P
2015-06-01
Phonons are displacements of atoms around their rest positions in a crystalline solid. They carry sound and heat, but are not classically associated with magnetism. Here, we show that phonons are, in fact, sensitive to magnetic fields, even in diamagnetic materials. We do so by demonstrating experimentally that acoustic phonons in a diamagnetic semiconductor (InSb) scatter more strongly from one another when a magnetic field is applied. We attribute this observation to the magnetic-field sensitivity of the anharmonicity of the interatomic bonds that govern the probability of phonon-phonon interactions. The displacements of atoms locally affect the orbital motion of valence band electrons, which, in the presence of an external magnetic field, spatially modulates the orbital diamagnetism around the displaced atoms. The spatial gradient in magnetic moment results in an anharmonic magnetic force exerted on the displaced atom. The process is modelled by ab initio calculations that, without the use of a single adjustable parameter, reproduce the observed 12% decrease in the lattice thermal conductivity under a 7 T magnetic field at a temperature of 5.2 K.
2016-07-11
converted into a solid inorganic matrix afterwards. Metal-chalcogenide complexes (MCCs) have been demonstrated to be soluble precursors for a broad range...AFRL-AFOSR-VA-TR-2016-0246 Elucidating the Wavelength Dependence of Phonon Scattering in Nanoparticle- Matrix Composites using PhononSpectroscopy...SUBTITLE Elucidating the Wavelength Dependence of Phonon Scattering in Nanoparticle- Matrix Composites using PhononSpectroscopy 5a. CONTRACT NUMBER
Realization of phonon laser with femtosecond technology
Sun, Chi-Kuang; Huang, Yue-Kai; Chern, Gia-Wei
2002-06-01
One of the most desirable properties of phonon system is sound amplification by stimulated emission of phonon radiation, coined as SASER or called phonon laser or acoustic laser, which is the acoustic counterpart of LASER. Phonon stimulated emission, or sound amplification, has been previously observed fro several occasions in extremely low temperatures, however a lasing behavior of the phonon oscillators has never been established. It is also desirable to build a phonon laser operating at room temperature. Here we present an optically pumped nano-sized phonon laser with an output acoustic wavelength of 9.3 nm, operating at room temperature. The nano phonon laser is composed by InGaN/GaN multiple-quantum-wells (MQWs). By using femtosecond ultraviolet pulses as pumping sources, coherent acoustic phonon amplification with large acoustic gain was observed. When the induced acoustic gain is higher than the acoustic loss due to its traveling nature, a clear laser-like threshold behavior was observed, which resembles a pulsed optical laser. This demonstration will open a new way toward nano-ultrasonics.
Splash, pop, sizzle: Information processing with phononic computing
Directory of Open Access Journals (Sweden)
Sophia R. Sklan
2015-05-01
Full Text Available Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic.
Enhanced electron-phonon coupling for a semiconductor charge qubit in a surface phonon cavity
Chen, J. C. H.; Sato, Y.; Kosaka, R.; Hashisaka, M.; Muraki, K.; Fujisawa, T.
2015-10-01
Electron-phonon coupling is a major decoherence mechanism, which often causes scattering and energy dissipation in semiconductor electronic systems. However, this electron-phonon coupling may be used in a positive way for reaching the strong or ultra-strong coupling regime in an acoustic version of the cavity quantum electrodynamic system. Here we propose and demonstrate a phonon cavity for surface acoustic waves, which is made of periodic metal fingers that constitute Bragg reflectors on a GaAs/AlGaAs heterostructure. Phonon band gap and cavity phonon modes are identified by frequency, time and spatially resolved measurements of the piezoelectric potential. Tunneling spectroscopy on a double quantum dot indicates the enhancement of phonon assisted transitions in a charge qubit. This encourages studying of acoustic cavity quantum electrodynamics with surface phonons.
Crystalline and Crystalline International Disposal Activities
Energy Technology Data Exchange (ETDEWEB)
Viswanathan, Hari S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, Shaoping [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dittrich, Timothy M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, Jeffrey De' Haven [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Karra, Satish [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Makedonska, Nataliia [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, Paul William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-06
This report presents the results of work conducted between September 2015 and July 2016 at Los Alamos National Laboratory in the crystalline disposal and crystalline international disposal work packages of the Used Fuel Disposition Campaign (UFDC) for DOE-NE’s Fuel Cycle Research and Development program. Los Alamos focused on two main activities during this period: Discrete fracture network (DFN) modeling to describe flow and radionuclide transport in complex fracture networks that are typical of crystalline rock environments, and a comprehensive interpretation of three different colloid-facilitated radionuclide transport experiments conducted in a fractured granodiorite at the Grimsel Test Site in Switzerland between 2002 and 2013. Chapter 1 presents the results of the DFN work and is divided into three main sections: (1) we show results of our recent study on the correlation between fracture size and fracture transmissivity (2) we present an analysis and visualization prototype using the concept of a flow topology graph for characterization of discrete fracture networks, and (3) we describe the Crystalline International work in support of the Swedish Task Force. Chapter 2 presents interpretation of the colloidfacilitated radionuclide transport experiments in the crystalline rock at the Grimsel Test Site.
Resonant tunneling in a pulsed phonon field
DEFF Research Database (Denmark)
Kral, P.; Jauho, Antti-Pekka
1999-01-01
, The nonequilibrium spectral function for the resonance displays the formation and decay of the phonon sidebands on ultrashort time scales. The time-dependent tunneling current through the individual phonon satellites reflects this quasiparticle formation by oscillations, whose time scale is set by the frequency...
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.
,
1992-01-01
Crystalline silica is the scientific name for a group of minerals composed of silicon and oxygen. The term crystalline refers to the fact that the oxygen and silicon atoms are arranged in a threedimensional repeating pattern. This group of minerals has shaped human history since the beginning of civilization. From the sand used for making glass to the piezoelectric quartz crystals used in advanced communication systems, crystalline silica has been a part of our technological development. Crystalline silica's pervasiveness in our technology is matched only by its abundance in nature. It's found in samples from every geologic era and from every location around the globe. Scientists have known for decades that prolonged and excessive exposure to crystalline silica dust in mining environments can cause silicosis, a noncancerous lung disease. During the 1980's, studies were conducted that suggested that crystalline silica also was a carcinogen. As a result of these findings, crystalline silica has been regulated under the Occupational Safety and Health Administration's (OSHA) Hazard Communication Standard (HCS). Under HCS, OSHAregulated businesses that use materials containing 0.1% or more crystalline silica must follow Federal guidelines concerning hazard communication and worker training. Although the HCS does not require that samples be analyzed for crystalline silica, mineral suppliers or OSHAregulated
Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys
Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas
2017-11-01
We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe, and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving {κ }{InSe}fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, in InSe, GaSe and GaS thermal transport is governed by in-plane vibrations. Alloying of InSe, GaSe, and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ˜2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.
Light-enhanced electron-phonon coupling from nonlinear electron-phonon coupling
Sentef, M. A.
2017-05-01
We investigate an exact nonequilibrium solution of a two-site electron-phonon model, where an infrared-active phonon that is nonlinearly coupled to the electrons is driven by a laser field. The time-resolved electronic spectrum shows coherence-incoherence spectral weight transfer, a clear signature of light-enhanced electron-phonon coupling. The present study is motivated by recent evidence for enhanced electron-phonon coupling in pump-probe terahertz and angle-resolved photoemission spectroscopy in bilayer graphene when driven near resonance with an infrared-active phonon mode [E. Pomarico et al., Phys. Rev. B 95, 024304 (2017), 10.1103/PhysRevB.95.024304], and by a theoretical study suggesting that transient electronic attraction arises from nonlinear electron-phonon coupling [D. M. Kennes et al., Nat. Phys. 13, 479 (2017), 10.1038/nphys4024]. We show that a linear scaling of light-enhanced electron-phonon coupling with the pump field intensity emerges, in accordance with a time-nonlocal self-energy based on a mean-field decoupling using quasiclassical phonon coherent states. Finally, we demonstrate that this leads to enhanced double occupancies in accordance with an effective electron-electron attraction. Our results suggest that materials with strong phonon nonlinearities provide an ideal playground to achieve light-enhanced electron-phonon coupling and possibly light-induced superconductivity.
Feng, Tianli; Ruan, Xiulin
2018-01-01
We have developed a formalism of the exact solution to linearized phonon Boltzmann transport equation (BTE) for thermal conductivity calculation including three- and four-phonon scattering. We find strikingly high four-phonon scattering rates in single-layer graphene (SLG) based on the optimized Tersoff potential. The reflection symmetry in graphene, which forbids the three-ZA (out-of-plane acoustic) scattering, allows the four-ZA processes ZA +ZA ⇌ZA +ZA and ZA ⇌ZA +ZA + ZA. As a result, the large phonon population of the low-energy ZA branch originated from the quadratic phonon dispersion leads to high four-phonon scattering rates, even much higher than the three-phonon scattering rates at room temperature. These four-phonon processes are dominated by the normal processes, which lead to a failure of the single mode relaxation time approximation. Therefore, we have solved the exact phonon BTE using an iterative scheme and then calculated the length- and temperature-dependent thermal conductivities. We find that the predicted thermal conductivity of SLG is lower than the previously predicted value from the three-phonon scattering only. The relative contribution of the ZA branch is reduced from 70% to 30% when four-phonon scattering is included. Furthermore, we have demonstrated that the four-phonon scattering in multilayer graphene and graphite is not strong due to the ZA splitting by interlayer van der Waals interaction. We also demonstrate that the five-phonon process in SLG is not strong due to the restriction of reflection symmetry.
Crystalline boron nitride aerogels
Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta
2017-04-04
This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.
Rotational Modes in Phononic Crystals
Wu, Ying; Peng, Pai; Mei, Jun
2014-03-01
We propose a lumped model for the rotational modes in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model not only can reproduce the dispersion relations in a certain range with one fitted parameter, but also gives simple analytical expressions for the frequencies of the eigenmodes at the high symmetry points in the Brillouin zone. These expressions provide physical understandings of the rotational modes as well as certain translational and hybrid mode, and predict the presence of accidental degeneracy of the rotational and dipolar modes, which leads to a Dirac-like cone in the Brillouin zone center. Supported by KAUST Baseline Research Fund, National Natural Science Foundation of China (Grants No. 10804086 and No. 11274120), and the Fundamental Research Funds for the Central Universities (Grant No. 2012ZZ0077).
Electron-phonon coupling from finite differences.
Monserrat, Bartomeu
2018-01-12
The interaction between electrons and phonons underlies multiple phenomena in physics, chemistry, and materials science. Examples include superconductivity, electronic transport, and the temperature dependence of optical spectra. A first-principles description of electron-phonon coupling enables the study of the above phenomena with accuracy and material specificity, which can be used to understand experiments and to predict novel effects and functionality. In this topical review, we describe the first-principles calculation of electron-phonon coupling from finite differences. The finite differences approach provides several advantages compared to alternative methods, in particular (i) any underlying electronic structure method can be used, and (ii) terms beyond the lowest order in the electron-phonon interaction can be readily incorporated. But these advantages are associated with a large computational cost that has until recently prevented the widespread adoption of this method. We describe some recent advances, including nondiagonal supercells and thermal lines, that resolve these difficulties, and make the calculation of electron-phonon coupling from finite differences a powerful tool. We review multiple applications of the calculation of electron-phonon coupling from finite differences, including the temperature dependence of optical spectra, superconductivity, charge transport, and the role of defects in semiconductors. These examples illustrate the advantages of finite differences, with cases where semilocal density functional theory is not appropriate for the calculation of electron-phonon coupling and many-body methods such as the $GW$ approximation are required, as well as examples in which higher-order terms in the electron-phonon interaction are essential for an accurate description of the relevant phenomena. We expect that the finite difference approach will play a central role in future studies of the electron-phonon interaction. . © 2018 IOP
Electron–phonon coupling from finite differences
Monserrat, Bartomeu
2018-02-01
The interaction between electrons and phonons underlies multiple phenomena in physics, chemistry, and materials science. Examples include superconductivity, electronic transport, and the temperature dependence of optical spectra. A first-principles description of electron–phonon coupling enables the study of the above phenomena with accuracy and material specificity, which can be used to understand experiments and to predict novel effects and functionality. In this topical review, we describe the first-principles calculation of electron–phonon coupling from finite differences. The finite differences approach provides several advantages compared to alternative methods, in particular (i) any underlying electronic structure method can be used, and (ii) terms beyond the lowest order in the electron–phonon interaction can be readily incorporated. But these advantages are associated with a large computational cost that has until recently prevented the widespread adoption of this method. We describe some recent advances, including nondiagonal supercells and thermal lines, that resolve these difficulties, and make the calculation of electron–phonon coupling from finite differences a powerful tool. We review multiple applications of the calculation of electron–phonon coupling from finite differences, including the temperature dependence of optical spectra, superconductivity, charge transport, and the role of defects in semiconductors. These examples illustrate the advantages of finite differences, with cases where semilocal density functional theory is not appropriate for the calculation of electron–phonon coupling and many-body methods such as the GW approximation are required, as well as examples in which higher-order terms in the electron–phonon interaction are essential for an accurate description of the relevant phenomena. We expect that the finite difference approach will play a central role in future studies of the electron–phonon interaction.
Indian Academy of Sciences (India)
Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental ...
Exploring the effect of hole localization on the charge-phonon dynamics of hole doped delafossite.
Mazumder, Nilesh; Mandal, Prasanta; Roy, Rajarshi; Ghorai, Uttam Kumar; Saha, Subhajit; Chattopadhyay, Kalyan Kumar
2017-09-20
For weak or moderate doping, electrical measurement is not suitable for detecting changes in the charge localization inside a semiconductor. Here, to investigate the nature of charge-phonon coupling in the presence of gradually delocalized holes within a weak doping regime (~1016 cm-3), we examine the temperature dependent Raman spectra (303-817 K) of prototype hole doped delafossite [Formula: see text] (x = 0/0.03, y = 0/0.01). For both [Formula: see text] and [Formula: see text] phonons, negative lineshape asymmetry and relative thermal hardening are distinctly observed upon [Formula: see text] and [Formula: see text] doping. Using Allen formalism, charge density of states at the Fermi level per spin and molecule, and charge delocalization associated to [Formula: see text] plane, are estimated to increase appreciably upon codoping compared to the [Formula: see text]-axis. We delineate the interdependence between charge-phonon coupling constant ([Formula: see text]) and anharmonic phonon lifetime ([Formula: see text]), and deduce that excitation of delocalized holes weakly coupled with phonons of larger [Formula: see text] is the governing feature of observed Fano asymmetry ([Formula: see text]) reversal.
Influence of phonons on semiconductor quantum emission
Energy Technology Data Exchange (ETDEWEB)
Feldtmann, Thomas
2009-07-06
A microscopic theory of interacting charge carriers, lattice vibrations, and light modes in semiconductor systems is presented. The theory is applied to study quantum dots and phonon-assisted luminescence in bulk semiconductors and heterostructures. (orig.)
Length-scale dependent phonon interactions
Srivastava, Gyaneshwar
2014-01-01
This book presents a comprehensive description of phonons and their interactions in systems with different dimensions and length scales. Internationally-recognized leaders describe theories and measurements of phonon interactions in relation to the design of materials with exotic properties such as metamaterials, nano-mechanical systems, next-generation electronic, photonic, and acoustic devices, energy harvesting, optical information storage, and applications of phonon lasers in a variety of fields. The emergence of techniques for control of semiconductor properties and geometry has enabled engineers to design structures in which functionality is derived from controlling electron behavior. As manufacturing techniques have greatly expanded the list of available materials and the range of attainable length scales, similar opportunities now exist for designing devices whose functionality is derived from controlling phonon behavior. However, progress in this area is hampered by gaps in our knowledge of phono...
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.
Phonon engineering in proximity enhanced superconductor heterostructures.
Tang, Yong-Chao; Kwon, Sangil; Mohebbi, Hamid R; Cory, David G; Miao, Guo-Xing
2017-06-27
In this research, we tailor the phonon density of states (DOS) in thin superconducting films to suppress quasiparticle losses. We examine a model system of a proximity-enhanced three-layered Al/Nb/Al heterostructure and show that the local quantized phonon spectrum of the ultrathin Al cladding layers in the heterostructure has a pronounced effect on the superconducting resonator's quality factors. Instead of a monotonic increase of quality factors with decreasing temperatures, we observe the quality factor reaches a maximum at 1.2 K in 5/50/5 nm Al/Nb/Al microstrip resonators, because of a quantized phonon ladder. The phonon DOS may be engineered to enhance the performance of quantum devices.
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...
Phonon broadening in high entropy alloys
Körmann, Fritz; Ikeda, Yuji; Grabowski, Blazej; Sluiter, Marcel H. F.
2017-09-01
Refractory high entropy alloys feature outstanding properties making them a promising materials class for next-generation high-temperature applications. At high temperatures, materials properties are strongly affected by lattice vibrations (phonons). Phonons critically influence thermal stability, thermodynamic and elastic properties, as well as thermal conductivity. In contrast to perfect crystals and ordered alloys, the inherently present mass and force constant fluctuations in multi-component random alloys (high entropy alloys) can induce significant phonon scattering and broadening. Despite their importance, phonon scattering and broadening have so far only scarcely been investigated for high entropy alloys. We tackle this challenge from a theoretical perspective and employ ab initio calculations to systematically study the impact of force constant and mass fluctuations on the phonon spectral functions of 12 body-centered cubic random alloys, from binaries up to 5-component high entropy alloys, addressing the key question of how chemical complexity impacts phonons. We find that it is crucial to include both mass and force constant fluctuations. If one or the other is neglected, qualitatively wrong results can be obtained such as artificial phonon band gaps. We analyze how the results obtained for the phonons translate into thermodynamically integrated quantities, specifically the vibrational entropy. Changes in the vibrational entropy with increasing the number of elements can be as large as changes in the configurational entropy and are thus important for phase stability considerations. The set of studied alloys includes MoTa, MoTaNb, MoTaNbW, MoTaNbWV, VW, VWNb, VWTa, VWNbTa, VTaNbTi, VWNbTaTi, HfZrNb, HfMoTaTiZr.
Coherent control of optical phonons in bismuth
Cheng, Yu-Hsiang; Gao, Frank Y.; Teitelbaum, Samuel W.; Nelson, Keith A.
2017-10-01
We have conducted degenerate pump-pump-probe experiments on semimetal bismuth with femtosecond time resolution, varying both pump-probe and interpump time delays. The observed phonon dynamics, including the amplitude, damping, frequency, and phase, can be modeled by the interference of two chirped damped oscillators. No lattice anharmonicity along the trigonal axis is observed. We also find evidence of phonon-mediated relaxation of the energy density at the sample surface.
Phonon Cooling by an Optomechanical Heat Pump.
Dong, Ying; Bariani, F; Meystre, P
2015-11-27
We propose and analyze theoretically a cavity optomechanical analog of a heat pump that uses a polariton fluid to cool mechanical modes coupled to a single precooled phonon mode via external modulation of the substrate of the mechanical resonator. This approach permits us to cool phonon modes of arbitrary frequencies not limited by the cavity-optical field detuning deep into the quantum regime from room temperature.
Triamterene crystalline nephropathy.
Nasr, Samih H; Milliner, Dawn S; Wooldridge, Thomas D; Sethi, Sanjeev
2014-01-01
Medications can cause a tubulointerstitial insult leading to acute kidney injury through multiple mechanisms. Acute tubular injury, a dose-dependent process, occurs due to direct toxicity on tubular cells. Acute interstitial nephritis characterized by interstitial inflammation and tubulitis develops from drugs that incite an allergic reaction. Other less common mechanisms include osmotic nephrosis and crystalline nephropathy. The latter complication is rare but has been associated with several drugs, such as sulfadiazine, indinavir, methotrexate, and ciprofloxacin. Triamterene crystalline nephropathy has been reported only rarely, and its histologic characteristics are not well characterized. We report 2 cases of triamterene crystalline nephropathy, one of which initially was misdiagnosed as 2,8-dihydroxyadenine crystalline nephropathy. Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.
... carcinogen. Additionally, breathing crystalline silica dust can cause silicosis , which in severe cases can be disabling, or ... take in oxygen. There is no cure for silicosis. Since silicosis affects lung function, it makes one ...
Waveguiding in supported phononic crystal plates
Vasseur, J.; Hladky-Hennion, A.-C.; Deymier, P.; Djafari-Rouhani, B.; Duval, F.; Dubus, B.; Pennec, Y.
2007-12-01
We investigate, with the help of the finite element method, the existence of absolute band gaps in the band structure of a free-standing phononic crystal plate and of a phononic crystal slab deposited on a substrate. The two-dimensional phononic crystal is constituted by a square array of holes drilled in an active piezoelectric (PZT5A or AlN) matrix. For both matrix materials, an absolute band gap occurs in the band structure of the free-standing plate provided the thickness of the plate is on the order of magnitude of the lattice parameter. When the plate is deposited on a Si substrate, the absolute band gap still remains when the matrix of the phononic crystal is made of PZT5A. The AlN phononic crystal plate losses its gap when supported by the Si substrate. In the case of the PZT5A matrix, we also study the possibility of localized modes associated with a linear defect created by removing one row of air holes in the deposited phononic crystal plate.
Aspects of frozen-phonon calculations theory and application to high temperature superconductors
Kouba, R
1999-01-01
kept but the structural parameters (lattice constants, internal coordinates) are optimized prior to the frozen phonon calculation. This yields a theoretical framework in which an overall excellent agreement between theoretically and experimentally determined frequency values is obtainable. This thesis is concerned with two aspects of the frozen phonon technique - an ab-initio method to study the lattice dynamics of a crystal. In the first part of the work a complete formulation of the iterative linear-response (ILR) scheme for crystalline solids within the framework of the linearized augmented plane-wave (LAPW) method is presented. Analytical expressions are provided which are well suited for a direct implementation into existing all-electron LAPW band structure programs. The charge response of valence as well as core electrons is fully taken into account. Of particular importance is the development of efficient algorithms which reduce the complexity of specific aspects related to the calculation of the first...
Multi-phonon dynamics of the ultra-fast photoinduced transition of (EDO-TTF)2SbF6
Lorenc, Maciej; Moisan, Nicolas; Servol, Marina; Cailleau, Hervé; Koshihara, Shin-ya; Maesato, Mitsuhiko; Shao, Xiangfeng; Nakano, Yoshiaki; Yamochi, Hideki; Saito, Gunzi; Collet, Eric
2009-02-01
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.
Phonon optimized interatomic potential for aluminum
Muraleedharan, Murali Gopal; Rohskopf, Andrew; Yang, Vigor; Henry, Asegun
2017-12-01
We address the problem of generating a phonon optimized interatomic potential (POP) for aluminum. The POP methodology, which has already been shown to work for semiconductors such as silicon and germanium, uses an evolutionary strategy based on a genetic algorithm (GA) to optimize the free parameters in an empirical interatomic potential (EIP). For aluminum, we used the Vashishta functional form. The training data set was generated ab initio, consisting of forces, energy vs. volume, stresses, and harmonic and cubic force constants obtained from density functional theory (DFT) calculations. Existing potentials for aluminum, such as the embedded atom method (EAM) and charge-optimized many-body (COMB3) potential, show larger errors when the EIP forces are compared with those predicted by DFT, and thus they are not particularly well suited for reproducing phonon properties. Using a comprehensive Vashishta functional form, which involves short and long-ranged interactions, as well as three-body terms, we were able to better capture interactions that reproduce phonon properties accurately. Furthermore, the Vashishta potential is flexible enough to be extended to Al2O3 and the interface between Al-Al2O3, which is technologically important for combustion of solid Al nano powders. The POP developed here is tested for accuracy by comparing phonon thermal conductivity accumulation plots, density of states, and dispersion relations with DFT results. It is shown to perform well in molecular dynamics (MD) simulations as well, where the phonon thermal conductivity is calculated via the Green-Kubo relation. The results are within 10% of the values obtained by solving the Boltzmann transport equation (BTE), employing Fermi's Golden Rule to predict the phonon-phonon relaxation times.
Phonon optimized interatomic potential for aluminum
Directory of Open Access Journals (Sweden)
Murali Gopal Muraleedharan
2017-12-01
Full Text Available We address the problem of generating a phonon optimized interatomic potential (POP for aluminum. The POP methodology, which has already been shown to work for semiconductors such as silicon and germanium, uses an evolutionary strategy based on a genetic algorithm (GA to optimize the free parameters in an empirical interatomic potential (EIP. For aluminum, we used the Vashishta functional form. The training data set was generated ab initio, consisting of forces, energy vs. volume, stresses, and harmonic and cubic force constants obtained from density functional theory (DFT calculations. Existing potentials for aluminum, such as the embedded atom method (EAM and charge-optimized many-body (COMB3 potential, show larger errors when the EIP forces are compared with those predicted by DFT, and thus they are not particularly well suited for reproducing phonon properties. Using a comprehensive Vashishta functional form, which involves short and long-ranged interactions, as well as three-body terms, we were able to better capture interactions that reproduce phonon properties accurately. Furthermore, the Vashishta potential is flexible enough to be extended to Al2O3 and the interface between Al-Al2O3, which is technologically important for combustion of solid Al nano powders. The POP developed here is tested for accuracy by comparing phonon thermal conductivity accumulation plots, density of states, and dispersion relations with DFT results. It is shown to perform well in molecular dynamics (MD simulations as well, where the phonon thermal conductivity is calculated via the Green-Kubo relation. The results are within 10% of the values obtained by solving the Boltzmann transport equation (BTE, employing Fermi’s Golden Rule to predict the phonon-phonon relaxation times.
The human crystallin gene families
Directory of Open Access Journals (Sweden)
Wistow Graeme
2012-12-01
Full Text Available Abstract Crystallins are the abundant, long-lived proteins of the eye lens. The major human crystallins belong to two different superfamilies: the small heat-shock proteins (α-crystallins and the βγ-crystallins. During evolution, other proteins have sometimes been recruited as crystallins to modify the properties of the lens. In the developing human lens, the enzyme betaine-homocysteine methyltransferase serves such a role. Evolutionary modification has also resulted in loss of expression of some human crystallin genes or of specific splice forms. Crystallin organization is essential for lens transparency and mutations; even minor changes to surface residues can cause cataract and loss of vision.
Thermodynamics of Crystalline States
Fujimoto, Minoru
2010-01-01
Thermodynamics is a well-established discipline of physics for properties of matter in thermal equilibrium surroundings. Applying to crystals, however, the laws encounter undefined properties of crystal lattices, which therefore need to be determined for a clear and well-defined description of crystalline states. Thermodynamics of Crystalline States explores the roles played by order variables and dynamic lattices in crystals in a wholly new way. This book is divided into three parts. The book begins by clarifying basic concepts for stable crystals. Next, binary phase transitions are discussed to study collective motion of order variables, as described mostly as classical phenomena. In the third part, the multi-electron system is discussed theoretically, as a quantum-mechanical example, for the superconducting state in metallic crystals. Throughout the book, the role played by the lattice is emphasized and examined in-depth. Thermodynamics of Crystalline States is an introductory treatise and textbook on meso...
The interface optical phonon and electron-phonon interaction in GaN/AlN spherical heterostructures
Huang, W. D.; Ren, Y. J.; Wei, S. Y.; Wang, J. H.
2008-07-01
Based on the dielectric-continuum model, the expression of polarization eigenvector, the dispersion relations, and the electron-phonon interaction Fröhlich-like Hamiltonian for interface optical (IO) phonons in multilayer GaN/AlN spherical heterostructures are obtained. As an application of the theory, the dispersion relations and electron-phonon coupling function strengths of the IO phonons are calculated for four-layer GaN/AlN/GaN/AlN spherical heterostructures. The results show that the lower frequency phonons have a much greater contribution to the coupling function Γ _lIO (r) than higher frequency phonons.
Liquid crystalline dihydroazulene photoswitches
DEFF Research Database (Denmark)
Petersen, Anne Ugleholdt; Jevric, Martyn; Mandle, Richard J.
2015-01-01
A large selection of photochromic dihydroazulene (DHA) molecules incorporating various substituents at position 2 of the DHA core was prepared and investigated for their ability to form liquid crystalline phases. Incorporation of an octyloxy-substituted biphenyl substituent resulted in nematic...... to the DHA where the alignment is maintained. The systematic structural variation has revealed that a biaryl spacer between the DHA and the alkyl chain is needed for liquid crystallinity and that the one aromatic ring in the spacer cannot be substituted by a triazole. This work presents an important step...
Energy Technology Data Exchange (ETDEWEB)
Kuleyev, I. G., E-mail: kuleev@imp.uran.ru; Kuleyev, I. I.; Bakharev, S. M.; Ustinov, V. V. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2016-09-15
We study the effect of anisotropy in elastic properties on the electron–phonon drag and thermoelectric phenomena in gapless semiconductors with degenerate charge-carrier statistics. It is shown that phonon focusing leads to a number of new effects in the drag thermopower at low temperatures, when diffusive phonon scattering from the boundaries is the predominant relaxation mechanism. We analyze the effect of phonon focusing on the dependences of the thermoelectromotive force (thermopower) in HgSe:Fe crystals on geometric parameters and the heat-flow directions relative to the crystal axes in the Knudsen regime of the phonon gas flow. The crystallographic directions that ensure the maximum and minimum values of the thermopower are determined and the role of quasi-longitudinal and quasi-transverse phonons in the drag thermopower in HgSe:Fe crystals at low temperatures is analyzed. It is shown that the main contribution to the drag thermopower comes from slow quasi-transverse phonons in the directions of focusing in long samples.
Phonon tunneling through a double barrier system
Energy Technology Data Exchange (ETDEWEB)
Villegas, Diosdado [Departamento de Física, Universidad Central “Marta Abreu” de Las Villas, CP 54830, Santa Clara, Villa Clara (Cuba); Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico); León-Pérez, Fernando de [Centro Universitario de la Defensa de Zaragoza, Ctra. de Huesca s/n, E-50090 Zaragoza (Spain); Pérez-Álvarez, R. [Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca (Mexico); Arriaga, J., E-mail: arriaga@ifuap.buap.mx [Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico)
2015-04-15
The tunneling of optical and acoustic phonons at normal incidence on a double-barrier is studied in this paper. Transmission coefficients and resonance conditions are derived theoretically under the assumption that the long-wavelength approximation is valid. It is shown that the behavior of the transmission coefficients for the symmetric double barrier has a Lorentzian form close to resonant frequencies and that Breit–Wigner's formula have a general validity in one-dimensional phonon tunneling. Authors also study the so-called generalized Hartman effect in the tunneling of long-wavelength phonons and show that this effect is a numerical artifact resulting from taking the opaque limit before exploring the variation with a finite barrier width. This study could be useful for the design of acoustic devices.
Phonon Sidebands in Monolayer Transition Metal Dichalcogenides
Christiansen, Dominik; Selig, Malte; Berghäuser, Gunnar; Schmidt, Robert; Niehues, Iris; Schneider, Robert; Arora, Ashish; de Vasconcellos, Steffen Michaelis; Bratschitsch, Rudolf; Malic, Ermin; Knorr, Andreas
2017-11-01
Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.
Toward quantitative modeling of silicon phononic thermocrystals
Energy Technology Data Exchange (ETDEWEB)
Lacatena, V. [STMicroelectronics, 850, rue Jean Monnet, F-38926 Crolles (France); IEMN UMR CNRS 8520, Institut d' Electronique, de Microélectronique et de Nanotechnologie, Avenue Poincaré, F-59652 Villeneuve d' Ascq (France); Haras, M.; Robillard, J.-F., E-mail: jean-francois.robillard@isen.iemn.univ-lille1.fr; Dubois, E. [IEMN UMR CNRS 8520, Institut d' Electronique, de Microélectronique et de Nanotechnologie, Avenue Poincaré, F-59652 Villeneuve d' Ascq (France); Monfray, S.; Skotnicki, T. [STMicroelectronics, 850, rue Jean Monnet, F-38926 Crolles (France)
2015-03-16
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.
POLYAMIDE WITH REDUCED CRYSTALLINITY
HARINGS, JULES; DESHMUKH, YOGESH SHESHRAO; VINKEN, ESTHER; RASTOGI, SANJAY
2009-01-01
The invention relates to a novel process for making compositions comprising a polyamid, water and a salt, having reduced crystallinity, wherein the process comprising the steps of: a. mixing the polyamide, water and a salt b. heating the mixture to a temperature above 100°C in a range between 120°C
Norrby, S.; Koopmans, S.; Terwee, T.
2006-01-01
Replacement of the crystalline lens with a synthetic soft material (ACL) has been shown to produce 3 to 5 D of accommodation following pharmacologic stimulation in primates for up to 1 year postoperatively. The eyes were relatively clear, suggesting that an injectable synthetic lens is a feasible
Phonon interference effects in molecular junctions.
Markussen, Troels
2013-12-28
We study coherent phonon transport through organic, π-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.
Cross-Kerr Nonlinearity for Phonon Counting
Ding, Shiqian; Maslennikov, Gleb; Hablützel, Roland; Matsukevich, Dzmitry
2017-11-01
State measurement of a quantum harmonic oscillator is essential in quantum optics and quantum information processing. In a system of trapped ions, we experimentally demonstrate the projective measurement of the state of the ions' motional mode via an effective cross-Kerr coupling to another motional mode. This coupling is induced by the intrinsic nonlinearity of the Coulomb interaction between the ions. We spectroscopically resolve the frequency shift of the motional sideband of the first mode due to the presence of single phonons in the second mode and use it to reconstruct the phonon number distribution of the second mode.
Electron and Phonon Transport in Molecular Junctions
DEFF Research Database (Denmark)
Li, Qian
Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions....... The system we are interested in here are π-stacked molecules connected with two semi-infinite leads. π-stacked aromatic rings, connected via π-π electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport...
Phonon dispersions in graphene sheet and single-walled carbon ...
Indian Academy of Sciences (India)
(i.e. ZO mode) and consists of TO and LO modes. The phonons in a nanotube can be derived from zone folding method using phonons of a single layer of the hexagonal sheet. The present work aims to explore the agree- ment between theory and experiment. A better knowledge of the phonon dispersion of graphene is.
Optical pumping of hot phonons in GaAs
Energy Technology Data Exchange (ETDEWEB)
Collins, C.L.; Yu, P.Y.
1982-06-30
Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated.
Phonon frequency shift and effect of correlation on the electron ...
Indian Academy of Sciences (India)
... of phonon to thef-electrons), anisotropic Fermi surface, Kondo volume collapse etc and the manifestation of the deformation potential. (the coupling of phonons to the conduction electrons), have persuaded many to emphasize the role of the electron–phonon interaction [2,5] to explain some of the low temperature. 305 ...
Yang, Jia-Yue; Cheng, Long; Hu, Ming
2017-12-01
Intermetallic clathrates, one class of guest-host systems with perfectly crystalline structures, hold great potential to be the "phonon glass - electron crystal" thermoelectric materials. Previous studies focus on revealing the atomistic origins of blocked phononic transport, yet little attention is drawn to the enhanced electronic transport. In this work, we investigate the binary type-I M8Si46 (M = Sr, Ba, Tl, and Pb) clathrates and unravel how rattlers concurrently block phononic transport and enhance electronic transport from first-principles. By comparing the empty and filled clathrates, the lattice thermal conductivity is greatly reduced by a factor of 21 due to the decrease in phonon relaxation time for propagative phonons over 0-6 THz by 1.5 orders of magnitude. On the other hand, rattlers bridge charge gaps among cages by donating electrons and thus drastically increase electrical conductivity. The concurrent realization of blocked phononic transport and enhanced electronic transport boosts the figure-of-merit (ZT) of empty clathrate by 4 orders of magnitude. Furthermore, by manipulating metallic rattlers and n-type doping, the power factor is markedly improved and ZT can reach 0.55 at 800 K. These results provide a quantitative description of the guest-host interaction and coupling dynamics from first-principles. The proposed strategy of manipulating ratting atoms and in-situ doping offers important guidance to engineer clathrates with high thermoelectric performance.
Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys
Energy Technology Data Exchange (ETDEWEB)
Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas
2017-10-17
We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving κInSe< κGaSe< κGaS. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, thermal transport is governed by in-plane vibrations in InSe, GaSe and GaS, similar to buckled monolayer materials such as silicene. Alloying of InSe, GaSe and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ~2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.
Thermal design studies in superconducting rf cavities: Phonon peak and Kapitza conductance
Directory of Open Access Journals (Sweden)
A. Aizaz
2010-09-01
Full Text Available Thermal design studies of superconducting radio frequency (SRF cavities involve two thermal parameters, namely the temperature dependent thermal conductivity of Nb at low temperatures and the heat transfer coefficient at the Nb-He II interface, commonly known as the Kapitza conductance. During the fabrication process of the SRF cavities, Nb sheet is plastically deformed through a deep drawing process to obtain the desired shape. The effect of plastic deformation on low temperature thermal conductivity as well as Kapitza conductance has been studied experimentally. Strain induced during the plastic deformation process reduces the thermal conductivity in its phonon transmission regime (disappearance of phonon peak by 80%, which may explain the performance limitations of the defect-free SRF cavities during their high field operations. Low temperature annealing of the deformed Nb sample could not recover the phonon peak. However, moderate temperature annealing during the titanification process recovered the phonon peak in the thermal conductivity curve. Kapitza conductance measurements for the Nb-He II interface for various surface topologies have also been carried out before and after the annealing. These measurements reveal consistently increased Kapitza conductance after the annealing process was carried out in the two temperature regimes.
Geometrical optics limit of phonon transport in a channel of disclinations
Fumeron, Sébastien; Berche, Bertrand; Moraes, Fernando; Santos, Fernando A. N.; Pereira, Erms
2017-05-01
The presence of topological defects in a material can modify its electrical, acoustic or thermal properties. However, when a group of defects is present, the calculations can become quite cumbersome due to the differential equations that can emerge from the modeling. In this work, we express phonons as geodesics of a 2 + 1 spacetime in the presence of a channel of dislocation dipoles in a crystalline environment described analytically in the continuum limit with differential geometry methods. We show that such a simple model of 1D array of topological defects is able to guide phonon waves. The presence of defects indeed distorts the effective metric of the material, leading to an anisotropic landscape of refraction index which curves the path followed by phonons, with focusing/defocusing properties depending on the angle of the incident wave. As a consequence, using Boltzmann transfer equation, we show that the defects may induce an enhancement or a depletion of the elastic energy transport. We comment on the possibility of designing artificial materials through the presence of topological defects.
Thermal effects on the Raman phonon of few-layer phosphorene
Directory of Open Access Journals (Sweden)
Zhi-Peng Ling
2015-12-01
Full Text Available Two-dimensional phosphorene is a promising channel material for next generation transistor applications due to its superior carrier transport property. Here, we report the influence of thermal effects on the Raman phonon of few-layer phosphorene formed on hafnium-dioxide (HfO2 high-k dielectric. When annealed at elevated temperatures (up to 200 °C, the phosphorene film was found to exhibit a blue shift in both the out-of-plane (A1g and in-plane (B2g and A2g phonon modes as a result of compressive strain effect. This is attributed to the out-diffusion of hafnium (Hf atoms from the underlying HfO2 dielectric, which compresses the phosphorene in both the zigzag and armchair directions. With a further increase in thermal energy beyond 250 °C, strain relaxation within phosphorene eventually took place. When this happens, the phosphorene was unable to retain its intrinsic crystallinity prior to annealing, as evident from the broadening of full-width at half maximum of the Raman phonon. These results provide an important insight into the impact of thermal effects on the structural integrity of phosphorene when integrated with high-k gate dielectric.
Phonon density of states in nanocrystalline Fe
Indian Academy of Sciences (India)
Kara and Rahman [10] did the cluster calculations using the interaction potential based on the embedded ... It is found that in the interior of the clusters large capillary pressure is built up and the surface tension derived .... results due to flatness of phonon dispersion relations in the transverse branch in the [111] direction at ζ ...
Structure factors and phonon dispersion in liquid
Indian Academy of Sciences (India)
Technology and Engineering, M.S. University of Baroda, Vadodara 390 001, India. 2Electronics Department, Narmada College of Science and Commerce, Bharuch 392 011,. India. E-mail: apratapmsu@yahoo.com. Abstract. The phonon spectra for liquid Li and Na have been computed through the phenomenological model ...
Phonon dispersion curves of CsCN
Indian Academy of Sciences (India)
Abstract. The motivation for the present work was gained from the recent publication on phonon dispersion curves (PDCs) of CsCN from the neutron scattering technique. We have applied the extended three-body force shell model (ETSM) by incorporating the effect of coupling between the translation modes and the ...
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...
Phonon limited electronic transport in Pb
DEFF Research Database (Denmark)
Rittweger, Florian; Hinsche, Nicki Frank; Mertig, Ingrid
2017-01-01
We present a fully ab initio based scheme to compute electronic transport properties, i.e. the electrical conductivity σ and thermopower S, in the presence of electron-phonon interaction. We explicitly investigate the k-dependent structure of the Éliashberg spectral function, the coupling strengt...
Phonon dispersion relation of liquid metals
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 72; Issue 6 ... The phonon dispersion curves of some liquid metals, viz. ... Department of Physics, Veer Narmad South Gujarat University, Surat 395 007, India; Department of Physics, Gujarat University, Ahmedabad 380 009, India; Department of Physics, Sardar Patel ...
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...
Thermodynamics of Crystalline States
Fujimoto, Minoru
2013-01-01
Thermodynamics is a well-established discipline of physics for properties of matter in thermal equilibrium with the surroundings. Applying to crystals, however, the laws encounter undefined properties of crystal lattice, which therefore need to be determined for a clear and well-defined description of crystalline states. Thermodynamics of Crystalline States explores the roles played by order variables and dynamic lattices in crystals in a wholly new way. The book begins by clarifying basic concepts for stable crystals. Next, binary phase transitions are discussed to study collective motion of order variables, as described mostly as classical phenomena. New to this edition is the examination of magnetic crystals, where magnetic symmetry is essential for magnetic phase transitions. The multi-electron system is also discussed theoretically, as a quantum-mechanical example, for superconductivity in metallic crystals. Throughout the book, the role played by the lattice is emphasized and studied in-depth. Thermod...
1990-02-28
Kunststoffe (German Plastics) 78(5):411-419. Calundann, G., M. Jaffe, R. S. Jones, and H. Yoon. 1988. Fibre Reinforcements for Composite Materials, A... Kunststoffe - German Plastics 77(10):1032-1035. 47 Williams, D. J. 1987. P. 405 in Nonlinear Optical Properties of Organic Molecules and Crystals, Vol. 1...crystalline acrylate. Makromol. Chem.-Macromol. Chem. Phys. 189(l):185-194. Browstow, W. 1988. Kunststoffe (German Plastics) 78:411. Clark, N. A. and
Uveitic crystalline maculopathy.
Or, Chris; Kirker, Andrew W; Forooghian, Farzin
2015-01-01
The purpose of this case report is to present a novel cause of crystalline maculopathy. A 52-year-old Japanese female presented with a 4-month history of decreased vision in the left eye. Best corrected visual acuity in the left eye was 20/40. Dilated fundus examination of the right eye was unremarkable, but that of the left eye demonstrated foveal yellow-green intraretinal crystals and mild vitritis. Optical coherence tomography of the left eye revealed small intraretinal fluid cysts and intraretinal crystals. Ultra-widefield fluorescein angiography was normal in the right eye, but that of the left eye demonstrated features of intermediate uveitis. There was no history or findings to suggest any cause for the crystals other than the uveitis. We propose that this may represent a novel category of crystalline retinopathy, termed uveitic crystalline maculopathy. We hypothesize that breakdown of the blood-retinal barrier as seen in uveitis may contribute to the deposition of crystals in the macula, although the precise composition of the crystals is unknown.
West African crystalline maculopathy.
Browning, David J
2004-05-01
To report new observations in West African crystalline maculopathy. Retrospective, observational case series. Three patients drawn from a private retina practice. Review of clinical charts and photographic studies. Distribution of intraretinal crystals and changes after laser photocoagulation, and history of ingesting foods typical in a West African diet but atypical for an American diet. All patients were older than 50 years, had diabetic retinopathy, ate green vegetables not found in American diets, and showed no deleterious effects of the crystals. Kola nut ingestion in 2 patients was remote and sparse, and was unknown in a third patient. The first 2 affected patients originating outside the Ibo tribe of Nigeria are reported. The pattern of retinal crystals can be changed, and the quantity of crystals reduced, by laser photocoagulation of associated diabetic retinopathy. West African crystalline retinopathy is distinguishable from other causes of crystalline retinopathy. It may reflect a component of the West African diet, seems to have diabetic retinopathy as a promoting factor via breakdown of the blood-retina barrier, and can be modified by laser photocoagulation of diabetic retinopathy. Increased awareness of the condition will allow physicians seeing West African immigrants to make the diagnosis and treat the patients appropriately.
Review of microwave electro-phononics in semiconductor nanostructures
Akimov, Andrey V.; Poyser, Caroline L.; Kent, Anthony J.
2017-05-01
Electro-phononics aims at developing devices which transform high frequency acoustic waves into electrical or microwave signals and back. This would eliminate the need for expensive and nonportable mode-locked lasers in phononic experiments increasing their ease and portability. The present review describes the main achievements in electro-phononics during the last decade. The first three sections of the review concern well developed ultrasonic and picosecond acoustic methods. While the next three sections give a review of recent experiments with various semiconductor nanodevices which allow the detection and generation of coherent acoustic phonons. Depending on the design of the electro-phononic device, it becomes possible to measure the actual or rectified temporal evolutions of the high-frequency acoustic field. A variation on these techniques is to exploit heterodyne mixing of coherent phonons with microwaves, it is then possible to perform sub-THz phonon spectroscopy experiments by lowering the frequency of the detected signal and using GHz detection electrical techniques. A further interesting approach is the phononic chip where various electro-phononic devices are integrated into a single complex nanostructure. Electro-phononic principles of the generation of THz phonons are developed utilizing the unique properties of doped semiconductor superlattices.
Wei, YuJie; Peng, ShenYou
2017-11-01
The dependence of dislocation mobility on stress is the fundamental ingredient for the deformation in crystalline materials. Strength and ductility, the two most important properties characterizing mechanical behavior of crystalline metals, are in general governed by dislocation motion. Recording the position of a moving dislocation in a short time window is still challenging, and direct observations which enable us to deduce the speed-stress relationship of dislocations are still missing. Using large-scale molecular dynamics simulations, we obtain the motion of an obstacle-free twinning partial dislocation in face centred cubic crystals with spatial resolution at the angstrom scale and picosecond temporal information. The dislocation exhibits two limiting speeds: the first is subsonic and occurs when the resolved shear stress is on the order of hundreds of megapascal. While the stress is raised to gigapascal level, an abrupt jump of dislocation velocity occurs, from subsonic to supersonic regime. The two speed limits are governed respectively by the local transverse and longitudinal phonons associated with the stressed dislocation, as the two types of phonons facilitate dislocation gliding at different stress levels.
Surfactant assisted control on optical, fluorescence and phonon lifetime in α-Bi2O3 microrods
Hariharan, S.; Udayabhaskar, R.; T. R., Ravindran; Karthikeyan, B.
2016-06-01
We report preparation of pure and surfactant added α-Bi2O3 microrods through simple chemical method at moderate temperature. Cetyltrimethyl ammonium bromide (CTAB) is used as a surfactant. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, UV-Vis absorption and photoluminescence (PL) measurements were carried out to understand the effect of surfactant (CTAB) on structural, phonon and optical properties of the prepared material. It is observed that the crystallite size, optical band gap and the structural defects (oxygen vacancies) decreases due to the effect of surfactant. Raman spectral studies exhibit various phonon modes of Bi2O3 and also decrease in the FWHM of the phonon modes is observed after the addition of CTAB.
Yu, Jen-Kan; Mitrovic, Slobodan; Heath, James R.
2016-08-16
A nanomesh phononic structure includes: a sheet including a first material, the sheet having a plurality of phononic-sized features spaced apart at a phononic pitch, the phononic pitch being smaller than or equal to twice a maximum phonon mean free path of the first material and the phononic size being smaller than or equal to the maximum phonon mean free path of the first material.
Phononic crystal slabs: fundamentals and applications
Khelif, Abdelkrim
2012-01-01
International audience; We present in this paper theoretical and experimental studies of guided acoustic wave propagating in phononic crystal slabs. By the insertion of scatters or the deposition of pillars on slabs, we are able to built up these artificial crystals. With appropriate choice of the geometrical parameters, we show that these structures can display complete band gaps in silicone membrane based on a Bragg or a local resonance mechanism. Additionally, the introduction of defects i...
Universal exchange-driven phonon splitting
Deisenhofer, Joachim; Kant, Christian; Schmidt, Michael; Wang, Zhe; Mayr, Franz; Tsurkan, Vladimir; Loidl, Alois
2012-02-01
We report on a linear dependence of the phonon splitting on the non-dominant exchange coupling Jnd in the antiferromagnetic monoxides MnO, Fe0.92O, CoO and NiO, and in the highly frustrated antiferromagnetic spinels CdCr2O4, MgCr2O4 and ZnCr2O4. For the monoxides our results directly confirm the theoretical prediction of a predominantly exchange induced splitting of the zone-centre optical phonon [1,2]. We find the linear relation δφ= βJndS^2 with slope β = 3.7. This relation also holds for a very different class of systems, namely the highly frustrated chromium spinels. Our finding suggests a universal dependence of the exchange-induced phonon splitting at the antiferromagnetic transition on the non-dominant exchange coupling [3].[4pt] [1] S. Massidda et al., Phys. Rev. Lett. 82, 430 (1999).[0pt] [2] W. Luo et al., Solid State Commun. 142, 504 (2007).[0pt] [3] Ch. Kant et al., arxiv:1109.4809.
Nonlocal dynamics of dissipative phononic fluids
Nemati, Navid; Lee, Yoonkyung E.; Lafarge, Denis; Duclos, Aroune; Fang, Nicholas
2017-06-01
We describe the nonlocal effective properties of a two-dimensional dissipative phononic crystal made by periodic arrays of rigid and motionless cylinders embedded in a viscothermal fluid such as air. The description is based on a nonlocal theory of sound propagation in stationary random fluid/rigid media that was proposed by Lafarge and Nemati [Wave Motion 50, 1016 (2013), 10.1016/j.wavemoti.2013.04.007]. This scheme arises from a deep analogy with electromagnetism and a set of physics-based postulates including, particularly, the action-response procedures, whereby the effective density and bulk modulus are determined. Here, we revisit this approach, and clarify further its founding physical principles through presenting it in a unified formulation together with the two-scale asymptotic homogenization theory that is interpreted as the local limit. Strong evidence is provided to show that the validity of the principles and postulates within the nonlocal theory extends to high-frequency bands, well beyond the long-wavelength regime. In particular, we demonstrate that up to the third Brillouin zone including the Bragg scattering, the complex and dispersive phase velocity of the least-attenuated wave in the phononic crystal which is generated by our nonlocal scheme agrees exactly with that reproduced by a direct approach based on the Bloch theorem and multiple scattering method. In high frequencies, the effective wave and its associated parameters are analyzed by treating the phononic crystal as a random medium.
Phononic Josephson oscillation and self-trapping with two-phonon exchange interaction
Xu, Xun-Wei; Chen, Ai-Xi; Liu, Yu-xi
2017-08-01
We propose a bosonic Josephson junction (BJJ) in two nonlinear mechanical resonators coupled through two-phonon exchange interaction induced by quadratic optomechanical couplings. The nonlinear dynamical equations and effective Hamiltonian are derived to describe behaviors of the BJJ. We show that the BJJ can work in two different dynamical regimes: Josephson oscillation and macroscopic self-trapping. The system can transfer from one regime to the other one when the self-interaction and asymmetric parameters exceed their critical values. We show that the transition from Josephson oscillation to macroscopic self-trapping can be induced by the phonon damping of the asymmetric BJJ. Our results open up a way to demonstrate BJJ with two-phonon exchange interaction and might be applied to other systems.
Phonon hydrodynamics for nanoscale heat transport at ordinary temperatures
Guo, Yangyu; Wang, Moran
2018-01-01
The classical Fourier's law fails in extremely small and ultrafast heat conduction even at ordinary temperatures due to strong thermodynamic nonequilibrium effects. In this work, a macroscopic phonon hydrodynamic equation beyond Fourier's law with a relaxation term and nonlocal terms is derived through a perturbation expansion to the phonon Boltzmann equation around a four-moment nonequilibrium solution. The temperature jump and heat flux tangential retardant boundary conditions are developed based on the Maxwell model of the phonon-boundary interaction. Extensive steady-state and transient nanoscale heat transport cases are modeled by the phonon hydrodynamic model, which produces quantitative predictions in good agreement with available phonon Boltzmann equation solutions and experimental results. The phonon hydrodynamic model provides a simple and elegant mathematical description of non-Fourier heat conduction with a clear and intuitive physical picture. The present work will promote deeper understanding and macroscopic modeling of heat transport in extreme states.
Heterodyne x-ray diffuse scattering from coherent phonons.
Kozina, M; Trigo, M; Chollet, M; Clark, J N; Glownia, J M; Gossard, A C; Henighan, T; Jiang, M P; Lu, H; Majumdar, A; Zhu, D; Reis, D A
2017-09-01
Here, we report Fourier-transform inelastic x-ray scattering measurements of photoexcited GaAs with embedded ErAs nanoparticles. We observe temporal oscillations in the x-ray scattering intensity, which we attribute to inelastic scattering from coherent acoustic phonons. Unlike in thermal equilibrium, where inelastic x-ray scattering is proportional to the phonon occupation, we show that the scattering is proportional to the phonon amplitude for coherent states. The wavevectors of the observed phonons extend beyond the excitation wavevector. The nanoparticles break the discrete translational symmetry of the lattice, enabling the generation of large wavevector coherent phonons. Elastic scattering of x-ray photons from the nanoparticles provides a reference for heterodyne mixing, yielding signals proportional to the phonon amplitude.
NATO Advanced Study Institute on Nonequilibrium Phonon Dynamics
1985-01-01
Phonons are always present in the solid state even at an absolute temperature of 0 K where zero point vibrations still abound. Moreover, phonons interact with all other excitations of the solid state and, thereby, influence most of its properties. Historically experimental information on phonon transport came from measurements of thermal conductivity. Over the past two decades much more, and much more detailed, information on phonon transport and on many of the inherent phonon interaction processes have come to light from experiments which use nonequilibrium phonons to study their dynamics. The resultant research field has most recently blossomed with the development of ever more sophisticated experimental and theoretical methods which can be applied to it. In fact, the field is moving so rapidly that new members of the research community have difficulties in keeping up to date. This NATO Advanced Study Institute (ASI) was organized with the objective of overcoming the information barrier between those expert...
Lifetimes of Confined Acoustic Phonons in Ultrathin Silicon Membranes
Cuffe, John; Chávez, Emigdio; Chapuis, Olivier; Alzina, Francesc; C. M. Sotomayor Torres
2013-01-01
We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic s...
Phonon excitation and instabilities in biased graphene nanoconstrictions
DEFF Research Database (Denmark)
Gunst, Tue; Lu, Jing Tao; Hedegård, Per
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...... 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....
57Fe NIS studies of phonon DOS in superconducting FeSe{sub 0.5}Te{sub 0.5} single crystals
Energy Technology Data Exchange (ETDEWEB)
Wortmann, Gerhard [Department of Physics, University of Paderborn, Paderborn (Germany); Ksenofontov, Vadim; Gasi, Teuta; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University, Mainz (Germany); Chumakov, Aleksandr [European Synchrotron Radiation Facility, Grenoble (France); Tsurkan, Vladimir; Deisenhofer, Joachim; Loidl, Alois [Institute of Physics, University of Augsburg, Augsburg (Germany)
2011-07-01
FeSe and isostructural FeSe{sub 0.5}Te{sub 0.5} could provide valuable information for the understanding of the principal mechanisms of superconductivity (SC) in the novel Fe-based superconductors. Using {sup 57}Fe nuclear inelastic scattering (NIS) we have measured the phonon-DOS in single-crystalline samples of FeSe{sub 0.5}Te{sub 0.5} parallel and perpendicular to the c-axis. A study of the phonon-DOS as function of temperature revealed a very similar temperature dependence as observed in FeSe, also no changes of the phonon-DOS above and below T{sub c} = 14.5 K. Together with results of conventional {sup 57}Fe-Moessbauer studies, we can exclude any phonon softening connected with the observed SC. Based on these results and previous studies of FeSe, we discuss the role of phonons in the mechanisms for SC in the Fe-based systems.
Energy Technology Data Exchange (ETDEWEB)
Campi, Davide; Bernasconi, Marco, E-mail: marco.bernasconi@mater.unimib.it [Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 55, I-20125, Milano (Italy); Donadio, Davide [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Sosso, Gabriele C. [Computational Science, Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, via Giuseppe Buffi 13, CH-6900 Lugano (Switzerland); Behler, Jörg [Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44780 Bochum (Germany)
2015-01-07
Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.
Campi, Davide; Donadio, Davide; Sosso, Gabriele C.; Behler, Jörg; Bernasconi, Marco
2015-01-01
Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.
Assili, Mohamed; Haddad, Sonia
2014-01-01
We derive the frequency shifts and the broadening of $\\Gamma$ point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic...
Long, Yao; Chen, Jun
2018-01-01
We develop a method to calculate the local vibrational mode and phonon refraction probability of a 1,3,5-triamino-2,4,6-trinitrobenzene/graphite interface, and use them to evaluate the interfacial free energy, heat capacity and thermal conductivity. We find that the heat exchange across the interface is sensitive with five incident phonon states. The frequencies, vibrational modes, refraction angles and refraction probabilities of the sensitive states are calculated. The relationship between vibrational modes and thermodynamic properties at the interface is obtained.
Liquid crystalline order in polymers
Blumstein, Alexandre
1978-01-01
Liquid Crystalline Order in Polymers examines the topic of liquid crystalline order in systems containing rigid synthetic macromolecular chains. Each chapter of the book provides a review of one important area of the field. Chapter 1 discusses scattering in polymer systems with liquid crystalline order. It also introduces the field of liquid crystals. Chapter 2 treats the origin of liquid crystalline order in macromolecules by describing the in-depth study of conformation of such macromolecules in their unassociated state. The chapters that follow describe successively the liquid crystalli
Coupling between electronic transport and longitudinal phonons in suspended nanotubes
Energy Technology Data Exchange (ETDEWEB)
Sapmaz, S; Jarillo-Herrero, P; Blanter, Ya M; Zant, H S J van der [Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft (Netherlands)
2005-11-15
Current-voltage characteristics of suspended single-wall carbon nanotube (NT) quantum dots show a series of steps equally spaced in voltage. The energy scale of this harmonic, low-energy excitation spectrum is consistent with that of the longitudinal low-k phonon mode in the NT. Agreement is found with a Franck-Condon-based model in which the phonon-assisted tunnelling process is modelled as a coupling of electronic levels to underdamped quantum harmonic oscillators. Comparison with this model indicates a rather strong electron-phonon coupling factor of order unity. We investigate different electron-phonon coupling mechanisms and give estimates of the coupling factor.
Soft phonon mode dynamics in Aurivillius-type structures
Maurya, Deepam; Charkhesht, Ali; Nayak, Sanjeev K.; Sun, Fu-Chang; George, Deepu; Pramanick, Abhijit; Kang, Min-Gyu; Song, Hyun-Cheol; Alexander, Marshall M.; Lou, Djamila; Khodaparast, Giti A.; Alpay, S. P.; Vinh, N. Q.; Priya, Shashank
2017-10-01
We report the dynamics of soft phonon modes and their role toward various structural transformations in Aurivillius materials by employing terahertz frequency-domain spectroscopy, atomic pair distribution function analysis, and first-principles calculations. We have chosen B i4T i3O12 as a model system and identified soft phonon modes associated with the paraelectric tetragonal to the ferroelectric monoclinic transition. Three soft phonon modes have been discovered that exhibit a strong temperature dependence. We have determined that the anharmonicity in Bi-O bonds plays a significant role in phonon softening, and that Bi cations play an important role in the emergence of ferroelectricity.
Frictional drag between quantum wells mediated by phonon exchange
DEFF Research Database (Denmark)
Bønsager, M.C.; Flensberg, Karsten; Hu, Ben Yu-Kuang
1998-01-01
lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation......We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either...
Focusing of ultrasonic waves by negative refraction in phononic crystals
Directory of Open Access Journals (Sweden)
J. H. Page
2016-12-01
Full Text Available Negative refraction and focusing phenomena in phononic crystals is reviewed, starting with their initial discovery over 10 years ago in flat three-dimensional (3D phononic crystals. This work soon led to direct observations of negative refraction in 2D phononic crystals, and an extensive series of experiments, simulations and theoretical predictions to explore and optimize focusing by flat phononic crystal lenses. More recently, the emphasis has been on demonstrating how super-resolution focusing that beats the diffraction limit can be achieved. Ultrasonic experiments, in combination with theory and simulations, have played an important role in developing a detailed understanding of these phenomena.
Terahertz Spectroscopy of Crystalline and Non-Crystalline Solids
DEFF Research Database (Denmark)
Parrott, Edward P. J.; Fischer, Bernd M.; Gladden, Lynn F.
2013-01-01
Terahertz spectroscopy of crystalline and non-crystalline solids is probably one of the most active research fields within the terahertz community. Many potential applications, amongst which spectral recognition is probably one of the most prominent, have significantly stimulated the development...
Coherent phonon optics in a chip with an electrically controlled active device.
Poyser, Caroline L; Akimov, Andrey V; Campion, Richard P; Kent, Anthony J
2015-02-05
Phonon optics concerns operations with high-frequency acoustic waves in solid media in a similar way to how traditional optics operates with the light beams (i.e. photons). Phonon optics experiments with coherent terahertz and sub-terahertz phonons promise a revolution in various technical applications related to high-frequency acoustics, imaging, and heat transport. Previously, phonon optics used passive methods for manipulations with propagating phonon beams that did not enable their external control. Here we fabricate a phononic chip, which includes a generator of coherent monochromatic phonons with frequency 378 GHz, a sensitive coherent phonon detector, and an active layer: a doped semiconductor superlattice, with electrical contacts, inserted into the phonon propagation path. In the experiments, we demonstrate the modulation of the coherent phonon flux by an external electrical bias applied to the active layer. Phonon optics using external control broadens the spectrum of prospective applications of phononics on the nanometer scale.
DEFF Research Database (Denmark)
Tsaturyan, Yeghishe; Barg, Andreas; Simonsen, Anders
2014-01-01
so that it assumes the form of a cm-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane’s high-Q modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield......, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane’s silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane’s frame...
Xu, Lubo; Wang, Lei
2017-04-01
We extend a previously proposed resonance phonon approach that is based on the linear response theory. By studying the complex response function in depth, we work out the phonon relaxation time besides the oscillating frequency of the phonons in a few one-dimensional nonlinear lattices. The results in the large wave-number-k regime agree with the expectations of the effective phonon theory. However, in the small-k limit they follow different scaling laws. The phonon mean free path can also be calculated indirectly. It coincides well with that derived from the anharmonic phonon approach. A power-law divergent heat conduction, i.e., the heat conductivity κ depends on lattice length N by κ ˜Nβ with β >0 , then is supported for the momentum-conserving lattices. Furthermore, this approach can be applied to diatomic lattices. So obtained relaxation time quantitatively agrees with that from the effective phonon theory. As for the mean free path, the resonance phonon approach can detect both the acoustic and the optical branches, whereas the anharmonic phonon approach can only detect a combined branch, i.e., the acoustic branch for small k and the optical branch for large k .
Optical studies of crystalline organic superconductors under extreme conditions
McDonald, R D
2001-01-01
the aim being to make an optical measurement of the pressure dependence of the charge carrier effective mass. Chapter 4 concentrates on the vibrational modes of kappa-(BEDT-TTF) sub 2 Cu(SCN) sub 2. This chapter reports the first Raman scattering experiments on an organic superconductor at high pressure. Comparison of the infrared reflectance and Raman scattering measurements are used to elucidate the role of electron-phonon coupling in this material's superconductivity. Chapter 5 reports the first non-resonant measurements of the GHz conductivity of an organic molecular superconductor. These experiments probe the unconventional metallic properties of an organic superconductor during the onset of superconductivity. This thesis reports experiments which involve the interaction of light and matter to probe the properties of crystalline organic superconductors. The organic superconductors of the BEDT-TTF family are prototypical correlated electron systems; their low-temperature ground states are dominated by man...
Phonon hydrodynamics and its applications in nanoscale heat transport
Guo, Yangyu; Wang, Moran
2015-09-01
Phonon hydrodynamics is an effective macroscopic method to study heat transport in dielectric solid and semiconductor. It has a clear and intuitive physical picture, transforming the abstract and ambiguous heat transport process into a concrete and evident process of phonon gas flow. Furthermore, with the aid of the abundant models and methods developed in classical hydrodynamics, phonon hydrodynamics becomes much easier to implement in comparison to the current popular approaches based on the first-principle method and kinetic theories involving complicated computations. Therefore, it is a promising tool for studying micro- and nanoscale heat transport in rapidly developing micro and nano science and technology. However, there still lacks a comprehensive account of the theoretical foundations, development and implementation of this approach. This work represents such an attempt in providing a full landscape, from physical fundamental and kinetic theory of phonons to phonon hydrodynamics in view of descriptions of phonon systems at microscopic, mesoscopic and macroscopic levels. Thus a systematical kinetic framework, summing up so far scattered theoretical models and methods in phonon hydrodynamics as individual cases, is established through a frame of a Chapman-Enskog solution to phonon Boltzmann equation. Then the basic tenets and procedures in implementing phonon hydrodynamics in nanoscale heat transport are presented through a review of its recent wide applications in modeling thermal transport properties of nanostructures. Finally, we discuss some pending questions and perspectives highlighted by a novel concept of generalized phonon hydrodynamics and possible applications in micro/nano phononics, which will shed more light on more profound understanding and credible applications of this new approach in micro- and nanoscale heat transport science.
Crystalline Bioceramic Materials
Directory of Open Access Journals (Sweden)
de Aza, P. N.
2005-06-01
Full Text Available A strong interest in the use of ceramics for biomedical engineering applications developed in the late 1960´s. Used initially as alternatives to metallic materials in order to increase the biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics; bioactive or surface reactive bioceramics and bioresorbable ceramics. This review will only refer to bioceramics “sensus stricto”, it is to say, those ceramic materials constituted for nonmetallic inorganic compounds, crystallines and consolidated by thermal treatments of powders to high temperatures. Leaving bioglasses, glass-ceramics and biocements apart, since, although all of them are obtained by thermal treatments to high temperatures, the first are amorphous, the second are obtained by desvitrification of a glass and in them vitreous phase normally prevails on the crystalline phases and the third are consolidated by means of a hydraulic or chemical reaction to room temperature. A review of the composition, physiochemical properties and biological behaviour of the principal types of crystalline bioceramics is given, based on the literature data and on the own experience of the authors.
A finales de los años sesenta se despertó un gran interés por el uso de los materiales cerámicos para aplicaciones biomédicas. Inicialmente utilizados como una alternativa a los materiales metálicos, con el propósito de incrementar la biocompatibilidad de los implantes, las biocerámicas se han convertido en una clase diversa de biomateriales, incluyendo actualmente tres tipos: cerámicas cuasi inertes; cerámicas bioactivas o reactivas superficialmente y cerámicas reabsorbibles o biodegradables. En la presente revisión se hace referencia a las biocerámicas en sentido estricto, es decir, a aquellos materiales constitutitos por compuestos inorgánicos no metálicos, cristalinos y consolidados
Falter, Claus
2005-01-01
We investigate the complete phonon dispersion, the phonon induced electronic charge response and the corresponding self-consistent change of the crystal potential an electron feels as a direct measure of the electron-phonon interaction in the high-temperature superconductors within a microscopic model in the framework of linear response theory. Moreover, dielectric and infrared properties are calculated. The experimentally observed strong renormalization of the in-plane oxygen bond-stretching modes which appears upon doping in the high-temperature superconductors is discussed. It is shown that the characteristic softening, indicating a strong nonlocal electron-phonon interaction, is most likely a generic effect of the CuO plane and is driven by a nonlocal coupling of the displaced ions to the localized charge-fluctuations at the Cu and the Oxy ions. At hand of the oxygen bond-stretching modes it is illustrated how lattice-, charge- and spin-degrees of freedom may act synergetically for anisotropic pairing in the high-temperature superconductors. The different behaviour of these modes during the insulator-metal transition via the underdoped phase is calculated and from a comparison of these generic modes in the different phases conclusions about the electronic state are drawn. For the non-cuprate potassium doped high-temperature superconductor Ba-Bi-O also a very strong and anisotropic renormalization of the oxygen bond-stretching modes is predicted. In another investigation c-axis polarized infrared- and Raman-active modes of the HTSC's are calculated in terms of charge fluctuations and anisotropic dipole-fluctuations. Mode assignments discussed controversially in the literature are proposed. Finally, interlayer phonons propagating along the c-axis and their accompanying charge response are investigated. Depending on the strength of the interlayer coupling calculations are performed ranging from the static, adiabatic response regime to the non-adiabatic regime
Semi-Dirac points in phononic crystals
Zhang, Xiujuan
2014-01-01
A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. It was originally discovered in electron systems, in which the associated quasi-particles are massless along one direction, like those in graphene, but effective-mass-like along the other. It was reported that a semi-Dirac point is associated with the topological phase transition between a semi-metallic phase and a band insulator. Very recently, the classical analogy of a semi-Dirac cone has been reported in an electromagnetic system. Here, we demonstrate that, by accidental degeneracy, two-dimensional phononic crystals consisting of square arrays of elliptical cylinders embedded in water are also able to produce the particular dispersion relation of a semi-Dirac cone in the center of the Brillouin zone. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. If the scatterers are made of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso-frequency surface of the phononic crystal, in which an open hyperbola is changed into a closed ellipse. This topological transition results in drastic change in wave manipulation. On the other hand, the theory also reveals that the phononic crystal is a double-zero-index material along the x-direction and photonic-band-edge material along the perpendicular direction (y-direction). If the scatterers are made of steel, in which the acoustic wave velocity is higher than that in water, the effective medium description fails, even though the semi-Dirac dispersion relation looks similar to that in the previous case. Therefore different wave transport behavior is expected. The semi-Dirac points in phononic crystals described in
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
Phononic crystals bring sound to a focus
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Dehesa, Jose
2004-09-01
Three years ago researchers at the University of California at San Diego created a storm in the world of optics when they announced that they had made a material that exhibited negative refraction. Light rays entering such a 'negative index' material are not bent towards the normal -- as happens in all known materials in nature -- but beyond the normal. Now physicists in China and Canada have demonstrated the equivalent phenomenon with sound waves in a material known as a 'phononic crystal'. (U.K.)
Phonon dispersions in graphene sheet and single-walled carbon ...
Indian Academy of Sciences (India)
High-frequency regime is above 1200 cm−1 (i.e. ZO mode) and consists of TO and LO modes. The phonons in a nanotube can be derived from zone folding method using phonons of a single layer of the hexagonal sheet. The present work aims to explore the agreement between theory and experiment. A better knowledge ...
Strong Carrier-Phonon Coupling in Lead Halide Perovskite Nanocrystals
Iaru, Claudiu M; Geuchies, Jaco J; Koenraad, Paul M; Vanmaekelbergh, Daniël; Silov, Andrei Yu
2017-01-01
We highlight the importance of carrier-phonon coupling in inorganic lead halide perovskite nanocrystals. The low-temperature photoluminescence (PL) spectrum of CsPbBr3 has been investigated under a nonresonant and a nonstandard, quasi-resonant excitation scheme, and phonon replicas of the main PL
Modelling exciton–phonon interactions in optically driven quantum dots
DEFF Research Database (Denmark)
Nazir, Ahsan; McCutcheon, Dara
2016-01-01
We provide a self-contained review of master equation approaches to modelling phonon effects in optically driven self-assembled quantum dots. Coupling of the (quasi) two-level excitonic system to phonons leads to dissipation and dephasing, the rates of which depend on the excitation conditions...
One- and two-phonon capture processes in quantum dots
DEFF Research Database (Denmark)
Magnúsdóttir, Ingibjörg; Uskov, Alexander; Bischoff, Svend
2002-01-01
Multiphonon capture processes are investigated theoretically and found to contribute efficiently to the carrier injection into quantum dots. It is shown that two-phonon capture contributes where single-phonon capture is energetically inhibited and can lead to electron capture times of a few...
Phonon and thermal properties of achiral single wall carbon ...
Indian Academy of Sciences (India)
A detailed theoretical study of the phonon and thermal properties of achiral single wall carbon nanotubes has been carried out using force constant model considering up to third nearest-neighbor interactions. We have calculated the phonon dispersions, density of states, radial breathing modes (RBM) and the specific heats ...
Spectral Analysis of Surface Controlled Phonon Transport in Nanophononic Metamaterials
Neogi, Sanghamitra; Donadio, Davide
Phonon engineering in nanostructured semiconductors has shown promises to further advance the performance of energy applications beyond the state-of-the-art limit. In nanostructured materials, phonon transport is greatly affected by the surface nanoscale character. The concept of nanophononic metamaterial (NPM) was introduced recently to affect nanoscale thermal transport with the inclusion of local surface resonators. We carried out a systematic investigation of phonon transport in locally resonant silicon-based NPMs. We used classical equilibrium molecular dynamics and a Boltzmann transport equation approach with the relaxation time approximation to investigate the nature of phononic thermal transport in nanopatterned silicon membranes with thicknesses of the order of 10 nm and below. We find the presence of local surface resonators has a significant effect on the phonon dispersion and has a direct consequence of suppression of group velocities of phonons in the NPMs. We completed the investigation by relating nanoscale resonant character (geometry and material composition) with phonon scattering, and consequently, phonon transport in the locally resonant silicon membrane NPMs This project is funded by the program FP7-ENERGY-2012-1-2STAGE under Contract Number 309150.
Relaxation between electrons and surface phonons of a ...
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 63; Issue 5. Relaxation between ... The energy relaxation between the hot degenerate electrons of a homogeneously photoexcited metal film and the surface phonons (phonon wave vectors in two dimensions) is considered under Debye approximation. The state of ...
Waveguiding in two-dimensional piezoelectric phononic crystal plates
Vasseur, J. O.; Hladky-Hennion, A.-C.; Djafari-Rouhani, B.; Duval, F.; Dubus, B.; Pennec, Y.; Deymier, P. A.
2007-06-01
We investigate the possibility of designing phononic crystal-based devices for telecommunication applications using materials commonly employed in microfabrication. We focus our attention on a phononic crystal made of a square array of cylindrical holes drilled in an active piezoelectric PZT5A matrix. Two different structures are considered, namely, a freestanding phononic crystal plate and a plate deposited on a silicon substrate. The geometrical characteristics of the phononic crystal plates (lattice parameter and thickness) were chosen to ensure the existence of an absolute band gap around 1.5GHz; a common frequency in radio frequency telecommunications. Computations of the dispersion curves of these active structures were conducted with the help of the finite element method. We demonstrate the existence of absolute band gaps in the band structure of the phononic crystal plates and, then, the possibility of guided modes inside a linear defect created by removing one row of air holes in the phononic crystal. In the case of the supported phononic crystal plates, we show the existence of an absolute forbidden band in the plate modes when the thickness of the substrate significantly exceeds the plate thickness. We discuss the conditions to realize waveguiding through a linear defect inside the supported plate. The present work provides evidences that phononic crystal properties can be integrated with existing silicon based microdevice technology.
Thermal rectification based on phonon hydrodynamics and thermomass theory
Directory of Open Access Journals (Sweden)
Dong Yuan
2016-06-01
Full Text Available The thermal diode is the fundamental device for phononics. There are various mechanisms for thermal rectification, e.g. different temperature dependent thermal conductivity of two ends, asymmetric interfacial resistance, and nonlocal behavior of phonon transport in asymmetric structures. The phonon hydrodynamics and thermomass theory treat the heat conduction in a fluidic viewpoint. The phonon gas flowing through the media is characterized by the balance equation of momentum, like the Navier-Stokes equation for fluid mechanics. Generalized heat conduction law thereby contains the spatial acceleration (convection term and the viscous (Laplacian term. The viscous term predicts the size dependent thermal conductivity. Rectification appears due to the MFP supersession of phonons. The convection term also predicts rectification because of the inertia effect, like a gas passing through a nozzle or diffuser.
Electron-phonon interaction in strongly correlated systems
Moskalenko, V. A.
1997-06-01
By a canonical transformation, the Hubbard model, supplemented with the Holstein interaction of localized electrons and nondispersive optical phonons, is transformed into a model where the hoppings of polarons from one lattice site into another are possible and are accompanied by the hoppings of an unbounded number of phonons. This, together with the fact that strong one-site interactions of electrons are inherent in the Hubbard model, leads to the necessity of introducing a new diagram technique based on irreducible one-site multi-particle Green’s functions or Kubo cumulants. The presence of phonons leads to renormalization of single-particle and multi-particle Green’s functions. The Dyson equation for the renormalized electron Green’s function is obtained. However, we did not manage to obtain the Dyson equation for the phonon functions due to the multiplicity of phonons taking part in the hopping. The validity of the theorem of connected diagrams is proved.
Controlling elastic waves with small phononic crystals containing rigid inclusions
Peng, Pai
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. © CopyrightEPLA, 2014.
Suppression of Phonon Transport in Molecular Christmas Trees.
Famili, Marjan; Grace, Iain; Sadeghi, Hatef; Lambert, Colin J
2017-05-19
Minimising the phonon thermal conductance of self-assembled molecular films, whilst preserving their electrical properties, is highly desirable, both for thermal management at the nanoscale and for the design of high-efficiency thermoelectric materials. Here we highlight a new strategy for minimising the phonon thermal conductance of Christmas-tree-like molecules composed of a long trunk, along which phonons can propagate, attached to pendant molecular branches. We demonstrate that phonon transport along the trunk is suppressed by Fano resonances associated with internal vibrational modes of the branches and that thermal conductance is suppressed most-effectively in molecules with pendant branches of different lengths. As examples, we use density functional theory to demonstrate the reduction in phonon transport in tree-like molecules formed from alkane or acene trunks with various pendant branches. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Attenuation limits in longitudinal phononic crystals
Luschi, L.; Iannaccone, G.; Pieri, F.
2017-12-01
The acoustic attenuation inside the bandgaps is, together with the bandgap width, a fundamental design parameter for phononic-crystal-based systems. We discuss approximate expressions for the maximum attenuation inside the bandgaps of one-dimensional longitudinal phononic crystals and its dependence on the acoustic contrast and the fractional bandwidth. We provide different approximations at small and large fractional bandwidths, computed from the trace of the transmission matrix of the crystal elementary cell. We show that, for relatively small gaps, the attenuation is roughly proportional to the fractional bandwidth, in analogy with the flexural case. For larger gaps, a large attenuation can be obtained only for high (and possibly impractical) acoustic contrasts. Approximate expressions are validated through comparison with FEM results. We also derive asymptotic upper limits for the bandgap borders and show that high contrasts do not necessarily lead to wide bandgaps, a fact connected to geometrical phase inversion for the acoustic wave in the crystal. We finally compare the attenuation of flexural and longitudinal waves at a fixed fractional bandwidth and derive regions of optimum attenuation for the two propagation modes.
Phonon-Driven Oscillatory Plasmonic Excitonic Nanomaterials
Energy Technology Data Exchange (ETDEWEB)
Kirschner, Matthew S. [Department; Ding, Wendu [Department; Li, Yuxiu [Center; College; Chapman, Craig T. [Department; Lei, Aiwen [College; Lin, Xiao-Min [Center; Chen, Lin X. [Department; Chemical; Schatz, George C. [Department; Schaller, Richard D. [Department; Center
2017-12-08
We demonstrate that coherent acoustic phonons derived from plasmonic nanoparticles can modulate electronic interactions with proximal excitonic molecular species. A series of gold bipyramids with systematically varied aspect ratios and corresponding localized surface plasmon resonance energies, functionalized with a J-aggregated thiacarbocyanine dye molecule, produce two hybridized states that exhibit clear anti-crossing behavior with a Rabi splitting energy of 120 meV. In metal nanoparticles, photoexcitation generates coherent acoustic phonons that cause oscillations in the plasmon resonance energy. In the coupled system, these photo-generated oscillations alter the metal nanoparticle’s energetic contribution to the hybridized system and, as a result, change the coupling between the plasmon and exciton. We demonstrate that such modulations in the hybridization is consistent across a wide range of bipyramid ensembles. We also use Finite-Difference Time Domain calculations to develop a simple model describing this behavior. Such oscillatory plasmonic-excitonic nanomaterials (OPENs) offer a route to manipulate and dynamically-tune the interactions of plasmonic/excitonic systems and unlock a range of potential applications.
Temperature dependence of phonons in photosynthesis proteins
Xu, Mengyang; Myles, Dean; Blankenship, Robert; Markelz, Andrea
Protein long range vibrations are essential to biological function. For many proteins, these vibrations steer functional conformational changes. For photoharvesting proteins, the structural vibrations play an additional critical role in energy transfer to the reaction center by both phonon assisted energy transfer and energy dissipation. The characterization of these vibrations to understand how they are optimized to balance photoharvesting and photoprotection is challenging. To date this characterization has mainly relied on fluorescence line narrowing measurements at cryogenic temperatures. However, protein dynamics has a strong temperature dependence, with an apparent turn on in anharmonicity between 180-220 K. If this transition affects intramolecular vibrations, the low temperature measurements will not represent the phonon spectrum at biological temperatures. Here we use the new technique of anisotropic terahertz microscopy (ATM) to measure the intramolecular vibrations of FMO complex. ATM is uniquely capable of isolating protein vibrations from isotropic background. We find resonances both red and blue shift with temperature above the dynamical transition. The results indicate that the characterization of vibrations must be performed at biologically relevant temperatures to properly understand the energy overlap with the excitation energy transfer. This work was supported by NSF:DBI 1556359, BioXFEL seed Grant funding from NSF:DBI 1231306, DOE: DE-SC0016317, and the Bruce Holm University at Buffalo Research Foundation Grant.
Nonlinear modal enrichment in phononic crystals
Gonella, Stefano; Ganesh, R.
Recent years have seen the advent of strategies to design metamaterials and phononic crystals with adaptive characteristics. Adaptivity is the ability of a system to autonomously modify its behavior in response to detected changes in the operating conditions. In this work we discuss the opportunities for the design of adaptive phononic crystals enabled by the exploitation of the nonlinearity embedded in the system. A well-known manifestation of nonlinearity is the generation of higher harmonics which, in complex dispersive systems, enables a rearrangement of the spectral response whereby part of the energy of an excited wave is deployed to a higher-frequency region of the band diagram, with the possibility to hop onto a different branch. The result is a mixture of modes with different (and possibly complementary) characteristics and an augmentation of the dynamic functionalities of the medium. In this work, we illustrate the versatility of this paradigm through a portfolio of lattice configurations. In these examples, mode hopping manifests either through the activation of new directional patterns in the wavefield, or through an enrichment of the wave modal content, for example by activating longitudinal components in wavefields originally dominated by shear mechanisms. National Science Foundation (CAREER Award CMMI-1452488).
Phonon bottleneck identification in disordered nanoporous materials
Romano, Giuseppe; Grossman, Jeffrey C.
2017-09-01
Nanoporous materials are a promising platform for thermoelectrics in that they offer high thermal conductivity tunability while preserving good electrical properties, a crucial requirement for high-efficiency thermal energy conversion. Understanding the impact of the pore arrangement on thermal transport is pivotal to engineering realistic materials, where pore disorder is unavoidable. Although there has been considerable progress in modeling thermal size effects in nanostructures, it has remained a challenge to screen such materials over a large phase space due to the slow simulation time required for accurate results. We use density functional theory in connection with the Boltzmann transport equation to perform calculations of thermal conductivity in disordered porous materials. By leveraging graph theory and regressive analysis, we identify the set of pores representing the phonon bottleneck and obtain a descriptor for thermal transport, based on the sum of the pore-pore distances between such pores. This approach provide a simple tool to estimate phonon suppression in realistic porous materials for thermoelectric applications and enhance our understanding of heat transport in disordered materials.
Energy Technology Data Exchange (ETDEWEB)
Lima, Helcio Ramos de [Associacao Brasileira de Fisicos em Medicina, Sao Paulo, SP (Brazil)
1996-12-31
A theoretical study for the quadratic mean displacement of quanta of vibration waves of crystalline lattices of the cubic crystals is presented. The study is applied to the inactivated NaI detector with estimates according to the behaviour of the Einstein`s equation applied to the Helium. Under the aspect of photon-phonon interaction, described by Blakemore, the chaotic behaviour of the phonons open discussion about the possibility of noises in measurements of energies near 100 KeV 10 refs., 1 fig.
Crystalline inclusions in granulocytic sarcoma.
Strauchen, James A; Gordon, Ronald E
2002-01-01
Two cases of granulocytic sarcoma were found to contain numerous crystalline inclusions identified on hematoxylin-eosin-stained sections as clusters of pointed needlelike crystals present in foci of necrosis or within macrophages. The crystals were negative for chloroacetate esterase and myeloperoxidase. Electron microscopy demonstrated homogeneously dense, bipyramidal structures, indistinguishable from Charcot-Leyden crystals. Granulocytic sarcomas may contain crystalline inclusions similar to Charcot-Leyden crystals; these structures should be distinguished from crystalline immunoglobulin inclusions occurring in cases of plasma cell myeloma and lymphoplasmacytic lymphoma, which may have a similar appearance.
Energy Technology Data Exchange (ETDEWEB)
Tuetuencue, H M [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Duman, S [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Bagci, S [Sakarya ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, 54140, Adapazari (Turkey); Srivastava, G P [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
2007-12-15
We report results of first-principles calculations for structural properties, electronic structure, phonon spectrum and electron-phonon interaction for the antiperovskite compound AlCNi{sub 3}. The structural properties are calculated using a plane-wave-pseudopotential method and the density functional theory within the generalised gradient approximation. The electronic structure and density of states for AlCNi{sub 3} are presented and compared with previous theoretical calculations. Our structural and electronic results are used, within the implementation of a linear response technique, for calculations of phonon states. We have observed that all phonon modes are stable along the [100] direction while unstable phonon modes are found in the [110] and [111] symmetry directions. At the Brillouin zone edge point X, the electron-phonon coupling parameters for phonon modes in AlCNi{sub 3} are calculated to be smaller than their corresponding values for MgCNi{sub 3}. This result indicates that the electron-phonon interaction is not very strong in AlCNi{sub 3}.
Thermal resistances of crystalline and amorphous few-layer oxide thin films
Chen, Liang; Kumari, Niru; Hou, Yu
2017-11-01
Thermal insulation at nanoscale is of crucial importance for non-volatile memory devices such as phase change memory and memristors. We perform non-equilibrium molecular dynamics simulations to study the effects of interface materials and structures on thermal transport across the few-layer dielectric nanostructures. The thermal resistance across few-layer nanostructures and thermal boundary resistance at interfaces consisting of SiO2/HfO2, SiO2/ZrO2 or SiO2/Al2O3 are obtained for both the crystalline and amorphous structures. Based on the comparison temperature profiles and phonon density of states, we show that the thermal boundary resistances are much larger in crystalline few-layer oxides than the amorphous ones due to the mismatch of phonon density of state between distinct oxide layers. Compared with the bulk SiO2, the increase of thermal resistance across crystalline few-layer oxides results from the thermal boundary resistance while the increase of thermal resistance across amorphous few-layer oxides is attributed to the lower thermal conductivity of the amorphous thin films.
DEFF Research Database (Denmark)
Majgaard, Klaus
2016-01-01
Purpose: The ability to act in a purposeful and effective way amid institutional tensions and paradoxes is, right now, a highly prized quality in public leadership. The purpose of this chapter is to qualify moderately brave acts as a learning format that combines the analytical and performative...... skills implied in this kind of agency. Design/methodology/approach: The chapter explores the engagement with paradoxes as a narrative praxis. From existing literature, it sums up an understanding of agency as a social process of mediating paradoxes in order to make action possible. Drawing on Northrop...
Liquid-crystalline lanthanide complexes
Binnemans, Koen
2000-01-01
The paper describes the recent developments in the field of liquid-crystalline lanthanide complexes. The role of trivalent lanthanide ions as the central metal ion in metallomesogens is considered. An outlook for the future is given.
Crystalline silica-induced inflammation
2010-01-01
M. Tech. The persistent presence of neutrophils is associated with a wide range of inflammatory diseases. Resolution of inflammation in these diseases is also associated with the ingestion of apoptotic neutrophils by macrophages. Inflammation and apoptosis of inflammatory cells are common known features observed in the lung following exposure to crystalline silica. What is not known is how well these apoptotic cells are cleared by macrophages in the presence of crystalline silica? To inves...
Influence of phonon-phonon coupling on superconducting state in honeycomb-type crystal lattice
Drzazga, E. A.; Szczȩśniak, R.; Domagalska, I. A.
2018-01-01
We have taken into account the superconducting state inducing in the crystal lattice of the honeycomb-type. In the framework of the Eliashberg theory, we have determined the thermodynamic properties of the system. The phonon spectral function, which is the input parameter in the Eliashberg equations, has been calculated by using the thermodynamic Green functions. We have considered the model of the coupled Einstein oscillators with frequency ω0 = 100 meV. We have shown that the increasing inter-phonon coupling constant (f) causes the rapid growth of the critical temperature ([TC]max = 36.2 K) just below the maximum value of f equal to 0.25ω0. Simultaneously, the order parameter and the thermodynamic critical field take the values increasingly distant from the predictions of the BCS theory, which results from the strong-coupling and the retardation effects.
Assili, M.; Haddad, S.
2014-09-01
We derive the frequency shifts and the broadening of Γ-point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic spectrum, induced by the strain, results in a polarization dependence of the LO and TO modes. This dependence is in agreement with the experimental results showing a periodic modulation of the Raman intensity of the split G peak. Moreover, the anomalous behavior of the frequency shift reported in undeformed graphene is found to be robust under strain.
Energy Technology Data Exchange (ETDEWEB)
Hernández, S.; López-Vidrier, J.; López-Conesa, L.; Peiró, F.; Garrido, B. [MIND-IN2UB, Departament d' Electrònica, Universitat de Barcelona, Martí i Franquès 1, E-08028, Barcelona (Spain); Hiller, D.; Gutsch, S.; Zacharias, M. [IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 103, D-79110, Freiburg (Germany); Ibáñez, J. [Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Lluís Solé i Sabarís s/n, E-08028, Barcelona (Spain); Estradé, S. [MIND-IN2UB, Departament d' Electrònica, Universitat de Barcelona, Martí i Franquès 1, E-08028, Barcelona (Spain); CCiT, Scientific and Technical Center, Universitat de Barcelona, Lluís Solé i Sabarís 1, E-08028 Barcelona (Spain)
2014-05-28
We use Raman scattering to investigate the size distribution, built-in strains and the crystalline degree of Si-nanoclusters (Si-nc) in high-quality Si-rich oxynitride/SiO{sub 2} multilayered samples obtained by plasma enhanced chemical vapor deposition and subsequent annealing at 1150 °C. An initial structural characterization of the samples was performed by means of energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction (XRD) to obtain information about the cluster size and the presence of significant amounts of crystalline phase. The contributions to the Raman spectra from crystalline and amorphous Si were analyzed by using a phonon confinement model that includes the Si-nc size distribution, the influence of the matrix compressive stress on the clusters, and the presence of amorphous Si domains. Our lineshape analysis confirms the existence of silicon precipitates in crystalline state, in good agreement with XRD results, and provides also information about the presence of a large compressive stress over the Si-nc induced by the SiO{sub 2} matrix. By using the Raman spectra from low temperature annealed samples (i.e., before the crystallization of the Si-nc), the relative scattering cross-section between crystalline and amorphous Si was evaluated as a function of the crystalline Si size. Taking into account this parameter and the integrated intensities for each phase as extracted from the Raman spectra, we were able to evaluate the degree of crystallization of the precipitated Si-nc. Our data suggest that all samples exhibit high crystalline fractions, with values up to 89% for the biggest Si-nc. The Raman study, supported by the EFTEM characterization, indicates that this system undergoes a practically abrupt phase separation, in which the precipitated Si-nanoclusters are formed by a crystalline inner part surrounded by a thin amorphous shell of approximately 1–2 atomic layers.
Phonon structures of GaN-based random semiconductor alloys
Zhou, Mei; Chen, Xiaobin; Li, Gang; Zheng, Fawei; Zhang, Ping
2017-12-01
Accurate modeling of thermal properties is strikingly important for developing next-generation electronics with high performance. Many thermal properties are closely related to phonon dispersions, such as sound velocity. However, random substituted semiconductor alloys AxB1-x usually lack translational symmetry, and simulation with periodic boundary conditions often requires large supercells, which makes phonon dispersion highly folded and hardly comparable with experimental results. Here, we adopt a large supercell with randomly distributed A and B atoms to investigate substitution effect on the phonon dispersions of semiconductor alloys systematically by using phonon unfolding method [F. Zheng, P. Zhang, Comput. Mater. Sci. 125, 218 (2016)]. The results reveal the extent to which phonon band characteristics in (In,Ga)N and Ga(N,P) are preserved or lost at different compositions and q points. Generally, most characteristics of phonon dispersions can be preserved with indium substitution of gallium in GaN, while substitution of nitrogen with phosphorus strongly perturbs the phonon dispersion of GaN, showing a rapid disintegration of the Bloch characteristics of optical modes and introducing localized impurity modes. In addition, the sound velocities of both (In,Ga)N and Ga(N,P) display a nearly linear behavior as a function of substitution compositions. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-80481-0.
Relative merits of phononics vs. plasmonics: the energy balance approach
Khurgin, Jacob B.
2018-01-01
The common feature of various plasmonic schemes is their ability to confine optical fields of surface plasmon polaritons (SPPs) into subwavelength volumes and thus achieve a large enhancement of linear and nonlinear optical properties. This ability, however, is severely limited by the large ohmic loss inherent to even the best of metals. However, in the mid- and far-infrared ranges of the spectrum, there exists a viable alternative to metals - polar dielectrics and semiconductors, in which dielectric permittivity (the real part) turns negative in the Reststrahlen region. This feature engenders the so-called surface phonon polaritons, capable of confining the field in a way akin to their plasmonic analogs, the SPPs. Since the damping rate of polar phonons is substantially less than that of free electrons, it is not unreasonable to expect that phononic devices may outperform their plasmonic counterparts. Yet a more rigorous analysis of the comparative merits of phononics and plasmonics reveals a more nuanced answer, namely, that while phononic schemes do exhibit narrower resonances and can achieve a very high degree of energy concentration, most of the energy is contained in the form of lattice vibrations so that enhancement of the electric field and, hence, the Purcell factor is rather small compared to what can be achieved with metal nanoantennas. Still, the sheer narrowness of phononic resonances is expected to make phononics viable in applications where frequency selectivity is important.
Phonon spectral function of the Holstein polaron
Energy Technology Data Exchange (ETDEWEB)
Loos, J [Institute of Physics, Academy of Sciences of the Czech Republic, Prague (Czech Republic); Hohenadler, M [Institute for Theoretical and Computational Physics, TU Graz (Austria); Alvermann, A [Institute of Physics, Ernst-Moritz-Arndt University Greifswald (Germany); Fehske, H [Institute of Physics, Ernst-Moritz-Arndt University Greifswald (Germany)
2006-08-09
The phonon spectral function of the one-dimensional Holstein model is obtained within weak-coupling and strong-coupling approximations based on analytical self-energy calculations. The characteristic excitations found in the limit of small charge-carrier density are related to the known (electronic) spectral properties of Holstein polarons such as the polaron band dispersion. Particular emphasis is laid on the different physics occurring in the adiabatic and anti-adiabatic regimes, respectively. Comparison is made with a cluster approach exploiting exact numerical results on small systems to yield an approximation for the thermodynamic limit. This method, similar to cluster perturbation theory, confirms the analytical findings, and also yields accurate results in the intermediate-coupling regime.
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.
Femtosecond study of self-trapped vibrational excitons in crystalline acetanilide.
Edler, J; Hamm, P; Scott, A C
2002-02-11
Femtosecond IR spectroscopy of delocalized NH excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded peptide units exists and does stabilize the excitation. Two phonons with frequencies of 48 and 76 cm (-1) are identified as the major degrees of freedom that mediate self-trapping. After selective excitation of the free exciton, self-trapping occurs within a few 100 fs. Excitation of the self-trapped states disappears from the spectral window of this investigation on a 1 ps time scale, followed by a slow ground state recovery of the hot ground state within 18 ps.
Non-equilibrium phonon generation and detection in microstructure devices
Hertzberg, J. B.
2011-01-01
We demonstrate a method to excite locally a controllable, non-thermal distribution of acoustic phonon modes ranging from 0 to ∼200 GHz in a silicon microstructure, by decay of excited quasiparticle states in an attached superconducting tunnel junction (STJ). The phonons transiting the structure ballistically are detected by a second STJ, allowing comparison of direct with indirect transport pathways. This method may be applied to study how different phonon modes contribute to the thermal conductivity of nanostructures. © 2011 American Institute of Physics.
Phononic frequency comb via three-mode parametric resonance
Ganesan, Adarsh; Do, Cuong; Seshia, Ashwin
2018-01-01
This paper is motivated by the recent demonstration of a phononic frequency comb. While previous experiments have shown the existence of a three-wave mixing pathway in a system of two-coupled phonon modes, this work demonstrates a similar pathway in a system of three-coupled phonon modes. This paper also presents a number of interesting experimental facts concomitant to the three-mode parametric resonance based frequency comb observed in a specific micromechanical device. The experimental validation of frequency combs via three-mode parametric resonance along with the previous demonstration of two-mode frequency combs points to the ultimate possibility of multimode frequency combs.
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.
Acoustic wave characterization of silicon phononic crystal plate
Feng, Duan; Jiang, Wanli; Xu, Dehui; Xiong, Bin; Wang, Yuelin
2015-08-01
In this paper, characterization of megahertz Lamb waves in a silicon phononic crystal based asymmetry filter by laser Doppler vibrometer is demonstrated. The acoustic power from a piezoelectric substrate was transmitted into the silicon superstrate by fluid coupling method, and measured results show that the displacement amplitude of the acoustic wave in the superstrate was approximately one fifth of that in the piezoelectric substrate. Effect of the phononic bandgap on the propagation of Lamb wave in the silicon superstrate is also measured, and the result shows that the phononic crystal structure could reflect part of the acoustic waves back.
Flexural-Phonon Scattering Induced by Electrostatic Gating in Graphene
DEFF Research Database (Denmark)
Gunst, Tue; Kaasbjerg, Kristen; Brandbyge, Mads
2017-01-01
Graphene has an extremely high carrier mobility partly due to its planar mirror symmetry inhibiting scattering by the highly occupied acoustic flexural phonons. Electrostatic gating of a graphene device can break the planar mirror symmetry, yielding a coupling mechanism to the flexural phonons......-limiting factor, and show how the carrier density and temperature scaling of the mobility depends on the electrostatic environment. Our findings may explain the high deformation potential for in-plane acoustic phonons extracted from experiments and, furthermore, suggest a direct relation between device symmetry...
Phonon Transport through Point Contacts between Graphitic Nanomaterials
Yang, Juekuan; Shen, Meng; Yang, Yang; Evans, William J.; Wei, Zhiyong; Chen, Weiyu; Zinn, Alfred A.; Chen, Yunfei; Prasher, Ravi; Xu, Terry T.; Keblinski, Pawel; Li, Deyu
2014-05-01
Measurements of thermal transport through contacts between individual multiwall carbon nanotubes show that, contrary to common expectation, the normalized contact thermal conductance per unit area depends linearly on the tube diameter. The result is corroborated with and extended to multilayer graphene nanoribbons through molecular dynamics simulations. Semiquantitative analyses show that these intriguing observations are consistent with an explanation based on an unexpectedly large phonon mean free path in the c-axis direction of graphite, phonon reflection at free surfaces, and phonon focusing in highly anisotropic graphitic materials.
Spin-seebeck effect: a phonon driven spin distribution.
Jaworski, C M; Yang, J; Mack, S; Awschalom, D D; Myers, R C; Heremans, J P
2011-05-06
Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.
Phonon Self-Energy Corrections to Nonzero Wave-Vector Phonon Modes in Single-Layer Graphene
Araujo, P. T.; Mafra, D. L.; Sato, K.; Saito, R.; Kong, J.; Dresselhaus, M. S.
2012-07-01
Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q=0) wave vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene originating from a double-resonant Raman process with q≠0. The observed phonon renormalization effects are different from what is observed for the zone-center q=0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with nonzero wave vectors (q≠0) in single-layer graphene in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q=0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G⋆ Raman feature at 2450cm-1 to include the iTO+LA combination modes with q≠0 and also the 2iTO overtone modes with q=0, showing both to be associated with wave vectors near the high symmetry point K in the Brillouin zone.
Phonon self-energy corrections to non-zero wavevector phonon modes in single-layer graphene
Araujo, Paulo; Mafra, Daniela; Sato, Kentaro; Saito, Richiiro; Kong, Jing; Dresselhaus, Mildred
2012-02-01
Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q = 0) wave-vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene (1LG) in the frequency range from 2350 to 2750 cm-1, which shows the G* and the G'-band features originating from a double-resonant Raman process with q 0. The observed phonon renormalization effects are different from what is observed for the zone-center q = 0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with non-zero wave-vectors (q 0) in 1LG in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q = 0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G* Raman feature at 2450 cm-1 to include the iTO+LA combination modes with q 0 and the 2iTO overtone modes with q = 0, showing both to be associated with wave-vectors near the high symmetry point K in the Brillouin zone.
Phonon self-energy corrections to nonzero wave-vector phonon modes in single-layer graphene.
Araujo, P T; Mafra, D L; Sato, K; Saito, R; Kong, J; Dresselhaus, M S
2012-07-27
Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q=0) wave vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene originating from a double-resonant Raman process with q≠0. The observed phonon renormalization effects are different from what is observed for the zone-center q=0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with nonzero wave vectors (q≠0) in single-layer graphene in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q=0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G(⋆) Raman feature at 2450 cm(-1) to include the iTO+LA combination modes with q≠0 and also the 2iTO overtone modes with q=0, showing both to be associated with wave vectors near the high symmetry point K in the Brillouin zone.
Tallman, Robert E.
Raman scattering is utilized to explore the effects of applied pressure and strain on anharmonic phonon interactions and nucleation of structural transitions in several bulk and nanoparticle semiconductor systems. The systems investigated are bulk ZnS and ZnSe in several isotopic compositions, InP/CdS core/shell nanoparticles exhibiting confined and surface optical Raman modes, and amorphous selenium films undergoing photo-induced crystallization. The anharmonic decay of long-wavelength optical modes into two-phonon acoustic combinations modes is studied in 64Zn32S, 64Zn34S, natZnatS bulk crystals by measuring the TO(Gamma) Raman line-shape as a function of applied hydrostatic pressure. The experiments are carried out at room temperature and 16K for pressures up to 150 kbars using diamond-anvil cells. The most striking effects occur in 68Zn32S where the TO(Gamma) peak narrows by a factor of 10 and increases in intensity at pressures for which the TO(Gamma) frequency has been tuned into a gap in the two-phonon density of states (DOS). In all the isotopic compositions, the observed phonon decay processes can be adequately explained by a second order perturbation treatment of the anharmonic coupling between TO(Gamma) and TA + LA combinations at various critical points, combined with an adiabatic bond-charge model for the phonon DOS and the known mode Gruneisen parameters. Bulk ZnSe crystals exhibit very different behavior. Here we find that anharmonic decay alone can not explain the excessive (˜ 60 cm-1 ) broadening in the TO(Gamma) Raman peak observed as the pressure approaches to within 50kbar of the ZB -> B1 phase transition (at P ˜ 137 kbar). Rather the broadening appears to arise from antecedent nucleation of structural changes within nanoscopic domains, with the mechanism for line-shape changes being mode mixing via localization and disorder instead of anharmonicity. To sort out these contributions, pressure experiments on natural ZnSe and on isotopically pure
Theory of acoustic-phonon transmission in finite-size superlattice systems
Mizuno, Seiji; Tamura, Shin-ichiro
1992-01-01
We develop a theory for acoustic-phonon transmission through a periodic superlattice with a finite number of periods. In particular, analytical expressions for the product of transfer matrices and phonon transmission rate are derived for the phonon propagation normal to the layer interfaces. The results are applied to the resonance phenomena of phonons in the triple-superlattice structure, i.e., the stack ABA of the periodic superlattices A and B. The phonon transmission rate and the resonanc...
Phonon transport in single-layer Boron nanoribbons
Zhang, Zhongwei; Peng, Qing; Chen, Yuanping
2016-01-01
Inspired by the successful synthesis of several allotropes, boron sheets have been one of the hottest spot areas of focus in various fields. Here, we study phonon transport in three types of boron nanoribbons with zigzag and armchair edges by using a non-equilibrium Green's function combined with first principles methods. Diverse transport properties are found in the nanoribbons. At the room temperature, their highest thermal conductance can be comparable with that of graphene, while the lowest thermal conductance is less than half of graphene's. The three boron sheets exhibit different anisotropic transport characteristics. Two of these sheets have stronger phonon transport abilities along the zigzag edges than the armchair edges, while in the case of the third, the results are reversed. With the analysis of phonon dispersion, bonding charge density, and simplified models of atomic chains, the mechanisms of the diverse phonon properties are discussed. Because all boron allotropes consists of hexagonal and tr...
Non-equilibrium ballistic phonon transport in microstructures
Hertzberg, Jared; Otelaja, Obafemi; Robinson, Richard
2011-03-01
We demonstrate a method to locally excite and detect phonon modes in silicon microstructures. Decay of quasiparticles injected into an adjacent superconducting film excites phonons in a non-thermal spectral distribution. Phonons of frequency of order 100 GHz are detected by the excitations they cause in a second superconducting film, after ballistically traversing microstructures of 10 to 50 micron dimension. Measurements are made at temperatures of 0.3 to 1.2 K. Such a device advances the goal of building a nanoscale phonon spectrometer to study acoustic confinement and surface scattering effects. This work is supported by KAUST (KUS-C1-018-02), NSF (DMR 0520404), and DOE (DE-SC0001086).
Ab initio study of electron-phonon coupling in rubrene
Ordejón, P.; Boskovic, D.; Panhans, M.; Ortmann, F.
2017-07-01
The use of ab initio methods for accurate simulations of electronic, phononic, and electron-phonon properties of molecular materials such as organic crystals is a challenge that is often tackled stepwise based on molecular properties calculated in gas phase and perturbatively treated parameters relevant for solid phases. In contrast, in this work we report a full first-principles description of such properties for the prototypical rubrene crystals. More specifically, we determine a Holstein-Peierls-type Hamiltonian for rubrene, including local and nonlocal electron-phonon couplings. Thereby, a recipe for circumventing the issue of numerical inaccuracies with low-frequency phonons is presented. In addition, we study the phenyl group motion with a molecular dynamics approach.
Gate tunable infrared phonon anomalies in bilayer graphene.
Kuzmenko, A B; Benfatto, L; Cappelluti, E; Crassee, I; van der Marel, D; Blake, P; Novoselov, K S; Geim, A K
2009-09-11
We observe a giant increase of the infrared intensity and a softening of the in-plane antisymmetric phonon mode E(u) ( approximately 0.2 eV) in bilayer graphene as a function of the gate-induced doping. The phonon peak has a pronounced Fano-like asymmetry. We suggest that the intensity growth and the softening originate from the coupling of the phonon mode to the narrow electronic transition between parallel bands of the same character, while the asymmetry is due to the interaction with the continuum of transitions between the lowest hole and electron bands. The growth of the peak can be interpreted as a "charged-phonon" effect observed previously in organic chain conductors and doped fullerenes, which can be tuned in graphene with the gate voltage.
Seebeck Coefficient of SOI Layer Induced by Phonon Transport
Directory of Open Access Journals (Sweden)
Faiz Salleh
2015-04-01
Full Text Available The Seebeck coefficient of a patterned Si wire on P-doped SOI (Si-on-insulator layer with a carrier concentration of 1018 cm-3 was measured near room temperature. The Seebeck coefficient is found to be smaller than that in the SOI layer and to be closer to the calculated Seebeck coefficient including the electronic contribution. The decrease in the Seebeck coefficient of Si wire is likely to occur due to the elimination of the contribution of phonon drag part. From the theoretical calculation of scattering rates by considering the scattering processes in phonon system, it is considered that an increase in phonon-boundary scattering and simultaneously a decrease at the cross section of SOI layer are likely responsible for eliminating the phonon drag effect.
Phonon-assisted relaxation in a frustrated antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Mutka, H. [Institute Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex 9 (France)]. E-mail: mutka@ill.fr; Payen, C. [Institut des Materiaux Jean Rouxel, UMR 6502, Universite de Nantes, B.P. 32229, F-44322 Nantes Cedex 3 (France); Bono, D. [Laboratoire de Physique des Solides, UMR8502, Universite Paris Sud, 91405 Orsay (France); Ehlers, G. [Institute Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex 9 (France); Fouquet, P. [Institute Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex 9 (France); Johnson, M.R. [Institute Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex 9 (France); Mendels, P. [Laboratoire de Physique des Solides, UMR8502, Universite Paris Sud, 91405 Orsay (France); Mevellec, J.Y. [Institut des Materiaux Jean Rouxel, UMR 6502, Universite de Nantes, B.P. 32229, F-44322 Nantes Cedex 3 (France); Stewart, J.R. [Institute Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex 9 (France)
2007-03-15
A thermally activated magnetic relaxation is observed using neutron spin-echo in the pyrochlore slab (kagome bilayer) compound SrCr{sub 9x}Ga{sub 12-9x}O{sub 19}(x=0.95) in a restricted temperature range, 4K
On-chip photonic-phononic emitter-receiver apparatus
Cox, Jonathan Albert; Jarecki, Jr., Robert L.; Rakich, Peter Thomas; Wang, Zheng; Shin, Heedeuk; Siddiqui, Aleem; Starbuck, Andrew Lea
2017-07-04
A radio-frequency photonic devices employs photon-phonon coupling for information transfer. The device includes a membrane in which a two-dimensionally periodic phononic crystal (PnC) structure is patterned. The device also includes at least a first optical waveguide embedded in the membrane. At least a first line-defect region interrupts the PnC structure. The first optical waveguide is embedded within the line-defect region.
Properties of interface phonon spectra in complicated cylindrical nanosystem
Directory of Open Access Journals (Sweden)
O.M.Voitsekhivska
2007-01-01
Full Text Available The spectra of two types of interface phonons (top and side optical are studied within the framework of dielectric continuum model for combined nanoheterosystems consisting of semiconductor cylindrical quantum dots inside the cylindrical quantum wire placed into dielectric or semiconductor medium. The dependencies of both types of interface phonon energies on the quasiwave numbers and geometric parameters of nanosystem are calculated and analysed.
Optical phonons in colloidal CdSe nanorods
Energy Technology Data Exchange (ETDEWEB)
Lange, Holger; Mohr, Marcel; Thomsen, Christian [Institut fuer Festkoerperphysik, Technische Universitaet Berlin (Germany); Artemyev, Mikhail [Institute for Physico-Chemical Problems, Belorussian State University, Minsk (Belarus); Woggon, Ulrike; Niermann, Tore [Institut fuer Optik und Atomare Physik, Technische Universitaet Berlin (Germany)
2010-10-15
In this work the vibrational properties of colloidal CdSe nanorods (NRs) and CdSe-ZnS core-shell NRs are investigated via Raman spectroscopy. The longitudinal optical (LO) phonons in NRs are confined to the NR volume. The confinement of the phonon wave function leads to a relaxation of the q = 0 rule and the phonon frequency is found to depend on the NR diameter. The coupling strength between LO phonons and excitons also depends on the NR diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. However, the coupling strength is found to rise for decreasing diameters. This is due to the increasing contributions of higher frequency phonons for smaller nanoparticle sizes. A radial breathing mode with a diameter dependent frequency is deduced from ab initio calculations and its existence in NRs is verified experimentally. The diameter-dependence of the modes' frequency can be used to estimate the NR diameter from a Raman measurement. In core-shell structures, the lattice mismatch between core and shell leads to a compressive strain of the core lattice. The exciton wave function changes with the modified boundary. This is reflected in an altered exciton-phonon coupling strength. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Experimental studies of electron-phonon interactions in gallium nitride
Stanton, N M
2001-01-01
This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructure grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons emitted when hot electrons relax their excess energy complements the measurements of relaxation rates. Absorption of acoustic phonons by the epilayers, using both fixed and extended metal film phonon sources, allowed investigation into the effectiveness of the 2k sub F cutoff in the low mobility layers. The experimental findings are compared with the predictions of theory. AIGaN/GaN heterostructures were characterised and measurements of the energy relaxation rate in the temperature range 4K-40K obtained. Excellent agreement wi...
Phononic crystals with one-dimensional defect as sensor materials
Aly, Arafa H.; Mehaney, Ahmed
2017-09-01
Recently, sensor technology has attracted great attention in many fields due to its importance in many engineering applications. In the present work, we introduce a study using the innovative properties of phononic crystals in enhancing a new type of sensors based on the intensity of transmitted frequencies inside the phononic band gaps. Based on the transfer matrix method and Bloch theory, the expressions of the reflection coefficient and dispersion relation are presented. Firstly, the influences of filling fraction ratio and the angle of incidence on the band gap width are discussed. Secondly, the localization of waves inside band gaps is discussed by enhancing the properties of the defected phononic crystal. Compared to the periodic structure, localization modes involved within the band structure of phononic crystals with one and two defect layers are presented and compared. Trapped localized modes can be detected easily and provide more information about defected structures. Such method could increase the knowledge of manufacturing defects by measuring the intensity of propagated waves in the resonant cavities and waveguides. Moreover, several factors enhance the role of the defect layer on the transmission properties of defected phononic crystals are presented. The acoustic band gap can be used to detect or sense the type of liquids filling the defect layer. The liquids make specific resonant modes through the phononic band gaps that related to the properties of each liquid. The frequency where the maximum resonant modes occur is correlated to material properties and allows to determine several parameters such as the type of an unknown material.
High-Temperature Raman Spectroscopy of Nano-Crystalline Carbon in Silicon Oxycarbide
Directory of Open Access Journals (Sweden)
Felix Rosenburg
2018-01-01
Full Text Available The microstructure of segregated carbon in silicon oxycarbide (SiOC, hot-pressed at T = 1600 °C and p = 50 MPa, has been investigated by VIS Raman spectroscopy (λ = 514 nm within the temperature range 25–1000 °C in air. The occurrence of the G, D’ and D bands at 1590, 1620 and 1350 cm−1, together with a lateral crystal size La < 10 nm and an average distance between lattice defects LD ≈ 8 nm, provides evidence that carbon exists as nano-crystalline phase in SiOC containing 11 and 17 vol % carbon. Both samples show a linear red shift of the G band up to the highest temperature applied, which is in agreement with the description of the anharmonic contribution to the lattice potential by the modified Tersoff potential. The temperature coefficient χG = −0.024 ± 0.001 cm−1/°C is close to that of disordered carbon, e.g., carbon nanowalls or commercial activated graphite. The line width of the G band is independent of temperature with FWHM-values of 35 cm−1 (C-11 and 45 cm−1 (C-17, suggesting that scattering with defects and impurities outweighs the phonon-phonon and phonon-electron interactions. Analysis of the Raman line intensities indicates vacancies as dominating defects.
Polarization dependent behavior of CdS around the first and second LO-phonon modes
Energy Technology Data Exchange (ETDEWEB)
Frausto-Reyes, C., E-mail: cfraus@cio.mx [Centro de Investigaciones en Optica AC, Unidad Aguascalientes, Prolong., Constitucion 607, Fracc. Reserva Loma Bonita, CP 20200, Apartado Postal 507, Ags. (Mexico); Molina-Contreras, J.R., E-mail: rmolina@correo.ita.mx [Departamento de Ingenieria Electrica y Electronica, Instituto Tecnologico de Aguascalientes, Av. Lopez Mateos 1081 Oriente, Fracc. Bonna Gens, CP 20256, Aguascalientes, Ags. (Mexico); Lopez-Alvarez, Y.F. [Departamento de Ingenieria Electrica y Electronica, Instituto Tecnologico de Aguascalientes, Av. Lopez Mateos 1081 Oriente, Fracc. Bonna Gens, CP 20256, Aguascalientes, Ags. (Mexico); Medel-Ruiz, C.I.; Perez Ladron de Guevara, H. [Universidad de Guadalajara, Centro Universitario de los Lagos, Av. Enrique Diaz de Leon s/n, Fracc. Paseos de la Montana, CP 47460, Lagos de Moreno, Jal. (Mexico); Ortiz-Morales, M. [Centro de Investigaciones en Optica AC, Unidad Aguascalientes, Prolong., Constitucion 607, Fracc. Reserva Loma Bonita, CP 20200, Apartado Postal 507, Ags. (Mexico)
2010-10-25
The present work report studies on resonant Raman experimental line shape for CdS around the first and second LO-phonon modes. The application of our method to the study of LO-phonon modes of CdS suggests that the scattered intensity is dominated by the surface and dependent on polarization. Results showed that the Raman spectra for CdS, roughly fall into three groups: a broad line-wing with apparent maxima around 194 cm{sup -1} in the range of 140 and 240 cm{sup -1} which can be ascribed to overtone scattering from acoustic phonons; a band near the 1LO phonon mode which can be attributed to a combination of one-phonon scattering and peak acoustic phonon and finally, a band near the 2LO phonon mode which can be attributed to a combination of two-phonon scattering and peak acoustic phonon.
Crystalline organomercuric acetates via organoboranes
Energy Technology Data Exchange (ETDEWEB)
Kunda, S.A.; Varma, R.S.; Kabalka, G.W.
1984-01-01
It is shown that the organomercuric acetates (OMA) can be synthesized rapidly using organomercury derivatives as intermediates. The OMAs can be readily prepared as crystalline solids. The reactions proceed with sufficient rapidity to make the synthesis useful for isotopic labelling of physiologically active compounds.
Generic Crystalline Disposal Reference Case
Energy Technology Data Exchange (ETDEWEB)
Painter, Scott Leroy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, Shaoping [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Harp, Dylan Robert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Perry, Frank Vinton [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Wang, Yifeng [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-02-20
A generic reference case for disposal of spent nuclear fuel and high-level radioactive waste in crystalline rock is outlined. The generic cases are intended to support development of disposal system modeling capability by establishing relevant baseline conditions and parameters. Establishment of a generic reference case requires that the emplacement concept, waste inventory, waste form, waste package, backfill/buffer properties, EBS failure scenarios, host rock properties, and biosphere be specified. The focus in this report is on those elements that are unique to crystalline disposal, especially the geosphere representation. Three emplacement concepts are suggested for further analyses: a waste packages containing 4 PWR assemblies emplaced in boreholes in the floors of tunnels (KBS-3 concept), a 12-assembly waste package emplaced in tunnels, and a 32-assembly dual purpose canister emplaced in tunnels. In addition, three failure scenarios were suggested for future use: a nominal scenario involving corrosion of the waste package in the tunnel emplacement concepts, a manufacturing defect scenario applicable to the KBS-3 concept, and a disruptive glaciation scenario applicable to both emplacement concepts. The computational approaches required to analyze EBS failure and transport processes in a crystalline rock repository are similar to those of argillite/shale, with the most significant difference being that the EBS in a crystalline rock repository will likely experience highly heterogeneous flow rates, which should be represented in the model. The computational approaches required to analyze radionuclide transport in the natural system are very different because of the highly channelized nature of fracture flow. Computational workflows tailored to crystalline rock based on discrete transport pathways extracted from discrete fracture network models are recommended.
Phonon-enhanced relaxation and excitation in the Holstein-Hubbard model
Werner, Philipp; Eckstein, Martin
2013-10-01
We study quenches of the interaction and electron-phonon coupling parameter in the Hubbard-Holstein model, using nonequilibrium dynamical mean field theory. The calculations are based on a generalized Lang-Firsov scheme for time-dependent interactions or externally driven phonons, and an approximate strong-coupling impurity solver. The interaction quench calculations reveal the phonon-assisted decay of excess doublons, while the quenches of the electron-phonon coupling lead to persistent oscillations of the phonons and to a phonon-enhanced doublon production.
Kang, Chang-Jong; Ahn, Kyo-Hoon; Lee, Kwan-Woo; Min, Byung Il
2013-05-01
SrPt3P has recently been reported to exhibit superconductivity with Tc = 8.4 K. To explore its superconducting mechanism, we have performed electron and phonon band calculations based on the density functional theory, and found that the superconductivity in SrPt3P is described well by the strong coupling phonon-mediated mechanism. We have demonstrated that superconducting charge carriers come from pdπ-hybridized bands between Pt and P ions, which couple to low energy (˜5 meV) phonon modes confined on the ab in-plane. These in-plane phonon modes, which do not break antipolar nature of SrPt3P, enhance both the electron--phonon coupling constant λ and the critical temperature Tc. There is no hint of a specific phonon softening feature in the phonon dispersion, and the effect of the spin--orbit coupling on the superconductivity is found to be negligible.
Raman spectra and electron-phonon coupling in disordered graphene with gate-tunable doping
Energy Technology Data Exchange (ETDEWEB)
Childres, Isaac, E-mail: ichildre@purdue.edu [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); Jauregui, Luis A. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Chen, Yong P. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)
2014-12-21
We report a Raman spectroscopy study of graphene field-effect transistors with a controlled amount of defects introduced in graphene by exposure to electron-beam irradiation. Raman spectra are taken at T = 8 K over a range of back gate voltages (V{sub g}) for various irradiation dosages (R{sub e}). We study effects in the Raman spectra due to V{sub g}-induced doping and artificially created disorder at various R{sub e}. With moderate disorder (irradiation), the Raman G peak with respect to the graphene carrier density (n{sub FE}) exhibits a minimum in peak frequency and a maximum in peak width near the charge-neutral point (CNP). These trends are similar to those seen in previous works on pristine graphene and have been attributed to a reduction of electron-phonon coupling strength (D) and removal of the Kohn anomaly as the Fermi level moves away from the CNP. We also observe a maximum in I{sub 2D}/I{sub G} and weak maximum in I{sub D}/I{sub G} near the CNP. All the observed dependences of Raman parameters on n{sub FE} weaken at stronger disorder (higher R{sub e}), implying that disorder causes a reduction of D as well. Our findings are valuable for understanding Raman spectra and electron-phonon physics in doped and disordered graphene.
Soft phononic crystals with deformation-independent band gaps
2017-01-01
Soft phononic crystals have the advantages over their stiff counterparts of being flexible and reconfigurable. Normally, the band gaps of soft phononic crystals will be modified after deformation due to both geometric and constitutive nonlinearity. Indeed these are important properties that can be exploited to tune the dynamic properties of the material. However, in some instances, it may be that one wishes to deform the medium while retaining the band gap structure. A special class of soft phononic crystals is described here with band gaps that are independent or almost-independent of the imposed mechanical deformation, which enables the design of phononic crystals with robust performance. This remarkable behaviour originates from transformation elasticity theory, which leaves the wave equation and the eigenfrequencies invariant after deformation. The necessary condition to achieve such a property is that the Lagrangian elasticity tensor of the hyperelastic material should be constant, i.e. independent of deformation. It is demonstrated that incompressible neo-Hookean materials exhibit such a unique property. Semilinear materials also possess this property under special loading conditions. Phononic crystals composed of these two materials are studied theoretically and the predictions of invariance, or the manner in which the response deviates from invariance, are confirmed via numerical simulation. PMID:28484331
Phonon spectra, electronic, and thermodynamic properties of WS2nanotubes.
Evarestov, Robert A; Bandura, Andrei V; Porsev, Vitaly V; Kovalenko, Alexey V
2017-11-15
Hybrid density functional theory calculations are performed for the first time on the phonon dispersion and thermodynamic properties of WS 2 -based single-wall nanotubes. Symmetry analysis is presented for phonon modes in nanotubes using the standard (crystallographic) factorization for line groups. Symmetry and the number of infra-red and Raman active modes in achiral WS 2 nanotubes are given for armchair and zigzag chiralities. It is demonstrated that a number of infrared and Raman active modes is independent on the nanotube diameter. The zone-folding approach is applied to find out an impact of curvature on electron and phonon band structure of nanotubes rolled up from the monolayer. Phonon frequencies obtained both for layers and nanotubes are used to compute the thermal contributions to their thermodynamic functions. The temperature dependences of energy, entropy, and heat capacity of nanotubes are estimated with respect to those of the monolayer. The role of phonons in the stability estimation of nanotubes is discussed based on Helmholtz free energy calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Phonon properties of copper oxide phases from first principles
Giar, Marcel; Heinemann, Markus; Heiliger, Christian
2017-08-01
We present density functional theory (DFT) calculations on phonon dispersions, phonon density of states, and thermodynamic quantities for the three copper oxide phases Cu2O ,Cu4O3 , and CuO. For monoclinic CuO we consider the correct antiferromagnetic ground state. Sound velocities for the acoustic phonon branches and Debye temperatures are calculated and are found to be in good agreement with experiment. We further show how the method for the treatment of dipole-dipole interactions in dynamical matrices of Gonze and Lee [Phys. Rev. B 55, 10355 (1997), 10.1103/PhysRevB.55.10355] may be incorporated in the real-space (direct) method for interatomic force constants (FCs). The role of the long-ranged dipole-dipole interactions in the phonon dispersion is discussed. Based on this method, we outline a perturbationlike scheme to compute first-order derivatives of the phonon mode frequencies with respect to the wave vector which can be used to compute velocities of sound.
Toward single electron resolution phonon mediated ionization detectors
Energy Technology Data Exchange (ETDEWEB)
Mirabolfathi, Nader, E-mail: mirabolfathi@physics.tamu.edu [Department of Physics and Astronomy, Texas A& M University (United States); Harris, H. Rusty; Mahapatra, Rupak; Sundqvist, Kyle; Jastram, Andrew [Department of Physics and Astronomy, Texas A& M University (United States); Serfass, Bruno; Faiez, Dana; Sadoulet, Bernard [Department of Physics, University of California at Berkeley (United States)
2017-05-21
Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14 eV{sub ee}. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5 GeV/c{sup 2} but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7 eV{sub ee} for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of ∼2.8 eV{sub ee}. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.
Soft phononic crystals with deformation-independent band gaps
Zhang, Pu; Parnell, William J.
2017-04-01
Soft phononic crystals have the advantages over their stiff counterparts of being flexible and reconfigurable. Normally, the band gaps of soft phononic crystals will be modified after deformation due to both geometric and constitutive nonlinearity. Indeed these are important properties that can be exploited to tune the dynamic properties of the material. However, in some instances, it may be that one wishes to deform the medium while retaining the band gap structure. A special class of soft phononic crystals is described here with band gaps that are independent or almost-independent of the imposed mechanical deformation, which enables the design of phononic crystals with robust performance. This remarkable behaviour originates from transformation elasticity theory, which leaves the wave equation and the eigenfrequencies invariant after deformation. The necessary condition to achieve such a property is that the Lagrangian elasticity tensor of the hyperelastic material should be constant, i.e. independent of deformation. It is demonstrated that incompressible neo-Hookean materials exhibit such a unique property. Semilinear materials also possess this property under special loading conditions. Phononic crystals composed of these two materials are studied theoretically and the predictions of invariance, or the manner in which the response deviates from invariance, are confirmed via numerical simulation.
Functional crossover in the dispersion relations of magnons and phonons
Hoser, A.; Köbler, U.
2016-09-01
Experimental data are presented showing that the dispersion relations of magnons and acoustic phonons can consist of two sections with different functions of wave vector. In the low wave vector range a power function of wave vector often holds over a finite q-range while dispersions for larger wave vector values better approach the atomistic model predictions. In the magnon spectra ∼⃒qx power functions with exponents x=1.25, 1.5 and 2 are identified. The dispersion of the acoustic phonons can be a linear function of wave vector over a surprisingly large range of energy. Since the slope of the linear section agrees with the known sound velocities it can be concluded that the dispersion of the acoustic phonons has got attracted by the linear dispersion of the mass less Debye bosons (sound waves). Due to the different (translational) symmetries of bosons and atomistic excitations (magnons, phonons) the associated dispersions can attract each other. In the same way the different ∼⃒qx power functions in the magnon dispersions indicate that magnon dispersions are attracted by the dispersion of the bosons of the magnetic continuum (Goldstone bosons). This allows evaluation of the otherwise difficult to obtain dispersions of the Goldstone bosons from the known magnon dispersions. Interestingly, the dispersions of Goldstone bosons (Debye bosons) attract magnon dispersions (phonon dispersions) and not vice versa.
Reduction of thermal conductivity in phononic nanomesh structures
Yu, Jen-Kan
2010-07-25
Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications1,2 and in the cooling of integrated circuits3. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity. © 2010 Macmillan Publishers Limited. All rights reserved.
Phonon Transport in Semiconductor interface: An atomistic approach
Chalopin, Yann
2010-03-01
Thermal dissipation and thermal insulation are among crucial issues encountered in high speed electronics devices and thermoelectrics systems. Both applications rely on controlling the transport properties of the heat carriers at semiconductor interfaces. From microscopic perspective, it is of fundamental interest to understand how the transport of phonons is impacted by an interface formed by two semiconductor layers. In a typical junction, the mechanism of reflection/transmission of vibrational energy causes strong modifications in the conductance regime. Thus, it is important to address the thermal transport at a contact junction in the framework of phonon wave propagation. Our approach is based on the fluctuation/dissipation theorem in order to calculate the thermal conductance of an interface. Using molecular dynamics simulations, we address the problems associated to using Si/Ge Si/SiGe junctions. We propose a methodology that enables the recovery of the transmission of the phonon modes by correlating the atomic motions of the phonon modes. Furthermore, we conclude that the phonon transmission function can be reconstructed such that it is integrated in the spectral expression of the conductance.
Lithium niobate phononic crystal for surface acoustic waves
Benchabane, S.; Khelif, A.; Rauch, J. Y.; Robert, L.; Laude, V.
2006-02-01
The recent theoretical and experimental demonstrations of stop bands for surface acoustic waves have greatly enlarged the potential application field for phononic crystals. The possibility of a direct excitation of these surface waves on a piezoelectric material, and their already extensive use in ultrasonics make them an interesting basis for phononic crystal based, acoustic signal processing devices. In this paper, we report on the demonstration of the existence of an absolute band gap for surface waves in a piezoelectric phononic crystal. The Surface Acoustic Wave propagation in a square lattice, two-dimensional lithium niobate phononic crystal is both theoretically and experimentally studied. A plane wave expansion method is used to predict the band gap position and width. The crystal was then fabricated by reactive ion etching of a bulk lithium niobate substrate. Standard interdigital transducers were used to characterize the phononic structure by direct electrical generation and detection of surface waves. A full band gap around 200 MHz was experimentally demonstrated, and close agreement is found with theoretical predictions.
Energy Technology Data Exchange (ETDEWEB)
Flach, B.
2000-01-01
This thesis has two topics: One is the investigation of an adsorbate induced phonon anomaly on W(110) and Mo{sub 1-x}Re{sub x}(110) (x = 5, 15, 25%) with inelastic helium atom scattering (HAS). The other one is the study of the growth, morphology and dynamics of ultra-thin lithium films deposited on W(110). In 1992 a giant phonon anomaly was found by J. Luedecke on the hydrogen saturated W(110) and Mo(110) surfaces. The anomaly consists of a deep and sharp indentation in the phonon dispersion curves in which the phonon energy nearly drops to zero ({omega}{sub 1}). In addition, a small and broad dip in the surface Rayleigh mode is observed ({omega}{sub 2}). The anomaly appears in the anti {gamma}-H- as well as in the anti {gamma}-S-direction of the surface Brillouin zone (SBZ). Since its first discovery, numerous other experimental and theoretical studies have followed. In the present work the effects is reinvestigated and experimental parameters, such as the crystal temperature and the incident energy, were changed in order to study their influence on the anomalous phonon behavior. In the case of H/Mo(110) the substrate was changed as well by alloying with small amounts of rhenium. In the present experiments a strong crystal temperature dependence of the {omega}{sub 2}-branch was found which leads to lower energies at the 'dip' for smaller temperatures, while the {omega}{sub 1}-anomaly remains unchanged. Such behavior agrees well with the picture that the {omega}{sub 2}-branch is due to a Kohn anomaly. (orig.)
Programmable high crystallinity carbon patterns
Wang, Xuewen; Wang, Hong; Gu, Yang; Fu, Wei; Zheng, Lu; Liu, Guowei; He, Yongmin; Long, Yi; Zhao, Wu; Zhang, Jie; Zhang, Ting; Liu, Zheng
2017-06-01
Carbon nanomaterials such as carbon nanotube and graphene are promising candidates for next-generation flexible electronics. However, the practical application of carbon electronics requires controlled fabrication of those materials with micro-patterned structures on flexible substrate at wafer-scale and low cost. Inspiring from the conventional photolithography process and pyrolysis of photoresist, herein, we demonstrate the synthesis of high-quality micro-patterned high crystallinity carbon. The method employed pre-patterned pyrolyzed photoresist as carbon precursors, in order to minimize the mobility of carbon during the high temperature growth, which results into high quality carbon patterns with a lateral resolution up to ~2 µm. The flexible carbon electronics are demonstrated by transferring the as-patterned high crystallinity carbon patterns to the flexible substrate, and showing asymmetric tensile-compressive response with high output resolution. These results will pave the way to the next-generation carbon-based flexible electronics and mechanical sensors.
Biocompatibility of crystalline opal nanoparticles
Directory of Open Access Journals (Sweden)
Hernández-Ortiz Marlen
2012-10-01
Full Text Available Abstract Background Silica nanoparticles are being developed as a host of biomedical and biotechnological applications. For this reason, there are more studies about biocompatibility of silica with amorphous and crystalline structure. Except hydrated silica (opal, despite is presents directly and indirectly in humans. Two sizes of crystalline opal nanoparticles were investigated in this work under criteria of toxicology. Methods In particular, cytotoxic and genotoxic effects caused by opal nanoparticles (80 and 120 nm were evaluated in cultured mouse cells via a set of bioassays, methylthiazolyldiphenyl-tetrazolium-bromide (MTT and 5-bromo-2′-deoxyuridine (BrdU. Results 3T3-NIH cells were incubated for 24 and 72 h in contact with nanocrystalline opal particles, not presented significant statistically difference in the results of cytotoxicity. Genotoxicity tests of crystalline opal nanoparticles were performed by the BrdU assay on the same cultured cells for 24 h incubation. The reduction of BrdU-incorporated cells indicates that nanocrystalline opal exposure did not caused unrepairable damage DNA. Conclusions There is no relationship between that particles size and MTT reduction, as well as BrdU incorporation, such that the opal particles did not induce cytotoxic effect and genotoxicity in cultured mouse cells.
Temperature Dependent Variations of Phonon Interactions in Nanocrystalline Cerium Oxide
Directory of Open Access Journals (Sweden)
Sugandha Dogra Pandey
2015-01-01
Full Text Available The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was investigated in the temperature range of 80–440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.
Electromagnetic excitation of phonons at C(001) surfaces
Energy Technology Data Exchange (ETDEWEB)
Perez-Sanchez, F L [Escuela de Ciencias, Universidad Autonoma ' Benito Juarez' de Oaxaca, Avenida Universidad S/N, Ex-Hacienda de Cinco Senores, Ciudad Universitaria, Oaxaca de Juarez, Oaxaca, 68120 (Mexico); Perez-Rodriguez, F, E-mail: fperez@sirio.ifuap.buap.m [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Post. J-48, Puebla 72570 (Mexico)
2009-09-02
The photon-phonon coupling at C(001)-(2 x 1) surfaces and its manifestation in far-infrared reflectance anisotropy spectra (FIR-RAS) are theoretically investigated. We solve the coupled system of equations for the electromagnetic field and lattice vibrations, described within the adiabatic bond charge model (ABCM), with the method of expansion into bulk phonon and photon modes. The calculated FIR-RAS exhibit resonances associated with zone-center surface phonons in good agreement with available HREELS experiments and predictions of vibrational modes for diamond (001)-(2 x 1) surfaces from ABCM and ab initio calculations. Interestingly, the reflectance anisotropy spectra for a C(001)-(2 x 1) surface turn out to be qualitatively different from the spectra for a Si(001)-(2 x 1) surface, reported previously.
Classification of topological phonons in linear mechanical metamaterials.
Süsstrunk, Roman; Huber, Sebastian D
2016-08-16
Topological phononic crystals, alike their electronic counterparts, are characterized by a bulk-edge correspondence where the interior of a material dictates the existence of stable surface or boundary modes. In the mechanical setup, such surface modes can be used for various applications such as wave guiding, vibration isolation, or the design of static properties such as stable floppy modes where parts of a system move freely. Here, we provide a classification scheme of topological phonons based on local symmetries. We import and adapt the classification of noninteracting electron systems and embed it into the mechanical setup. Moreover, we provide an extensive set of examples that illustrate our scheme and can be used to generate models in unexplored symmetry classes. Our work unifies the vast recent literature on topological phonons and paves the way to future applications of topological surface modes in mechanical metamaterials.
Research Update: Phonon engineering of nanocrystalline silicon thermoelectrics
Directory of Open Access Journals (Sweden)
Junichiro Shiomi
2016-10-01
Full Text Available Nanocrystalline silicon thermoelectrics can be a solution to improve the cost-effectiveness of thermoelectric technology from both material and integration viewpoints. While their figure-of-merit is still developing, recent advances in theoretical/numerical calculations, property measurements, and structural synthesis/fabrication have opened up possibilities to develop the materials based on fundamental physics of phonon transport. Here, this is demonstrated by reviewing a series of works on nanocrystalline silicon materials using calculations of multiscale phonon transport, measurements of interfacial heat conduction, and synthesis from nanoparticles. Integration of these approaches allows us to engineer phonon transport to improve the thermoelectric performance by introducing local silicon-oxide structures.
Calculational aspects of electron-phonon coupling at surfaces
Energy Technology Data Exchange (ETDEWEB)
Nojima, Akihiro; Yamashita, Koichi [Department of Chemical System Engineering, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan); Hellsing, Bo [Department of Physics, Goeteborg University, Fysikgraend 3, S-412 96 Goeteborg (Sweden)], E-mail: nojima@tcl.t.u-tokyo.ac.jp
2008-06-04
We study the validity of two frequently used approximations in calculations of electron-phonon coupling at surfaces. The rigid-ion approximation is a standard approximation used for the bulk metals. On the basis of density functional theory calculations, we find that for Be this approximation is as valid for surface atoms as for bulk atoms. In addition, the slab method for calculations of a phonon induced surface state lifetime is examined. The convergence of the electron-phonon matrix element with respect to the thickness of the slab is studied for several systems. When the number of slab layers is increased, the net effect of decreasing overlap and increasing number of final states depends strongly on the decay length of the surface state wavefunction and the band structure.
Anharmonic phonons and magnons in BiFeO3
Energy Technology Data Exchange (ETDEWEB)
Delaire, Olivier A [ORNL; Ma, Jie [ORNL; Stone, Matthew B [ORNL; Huq, Ashfia [ORNL; Gout, Delphine J [ORNL; Brown, Craig [National Institute of Standards and Technology (NIST); Wang, Kefeng [Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing; Ren, Zhifeng [Boston College, Chestnut Hill
2012-01-01
The phonon density of states (DOS) and magnetic excitation spectrum of polycrystalline BiFeO3 were measured for temperatures 200 < T < 750K , using inelastic neutron scattering (INS). Our results indicate that the magnetic spectrum of BiFeO3 closely resembles that of similar Fe perovskites, such as LaFeO3, despite the cycloid modulation in BiFeO3. We do not find any evidence for a spin gap. A strong T-dependence of the phonon DOS was found, with a marked broadening of the whole spectrum, providing evidence of strong anharmonicity. This anharmonicity is corroborated by large amplitude motions of Bi and O ions observed with neutron diffraction. These results highlight the importance of spin-phonon coupling in this material.
Superballistic characteristics in transient phonon ballistic-diffusive transport
Tang, Dao-Sheng; Cao, Bing-Yang
2017-09-01
While diffusive, superdiffusive, and ballistic phonon transports have been widely investigated, the superballistic phenomenon, where the time index of the energy mean square displacement with respect to time is greater than 2, has been neither predicted nor observed. In this work, we report on the superballistic characteristics obtained from simulations of transient phonon ballistic-diffusive transport both during and after the input of a heat pulse into a nanoscale film. The superballistic behaviors are well described by a previously proposed model for electron wave packet spreading employing a point source and further explained by the superposition effect of heat pulses. The relative superposition time, a dimensionless parameter, is defined to describe the degree of the heat pulse superposition. The analysis of superballistic characteristics in this work is expected to guide experiments for detecting the phonon superballistic transport. Also, it provides a potential phenomenological description for the superballistic phenomena in more complex systems.
Temperature-dependent dispersion model of float zone crystalline silicon
Franta, Daniel; Dubroka, Adam; Wang, Chennan; Giglia, Angelo; Vohánka, Jirí; Franta, Pavel; Ohlídal, Ivan
2017-11-01
In this paper, we present the temperature dependent dispersion model of float zone crystalline silicon. The theoretical background for valence electronic excitations is introduced in the theoretical part of this paper. This model is based on application of sum rules and parametrization of transition strength functions corresponding to the individual elementary phonon and electronic excitations. The parameters of the model are determined by fitting ellipsometric and spectrophotometric experimental data in the spectral range from far infrared (70 cm-1) to extreme ultraviolet (40 eV). The ellipsometric data were measured in the temperature range 5-700 K. The excitations of the valence electrons to the conduction band are divided into the indirect and direct electronic transitions. The indirect transitions are modeled by truncated Lorentzian terms, whereas the direct transitions are modeled using Gaussian broadened piecewise smooth functions representing 3D and 2D van Hove singularities modified by excitonic effects. Since the experimental data up to high energies (40 eV) are available, we are able to determine the value of the effective number of valence electrons. The Tauc-Lorentz dispersion model is used for modeling high energy electron excitations. Two slightly different values of the effective number of valence electrons are obtained for the Jellison-Modine (4.51) and Campi-Coriasso (4.37) parametrization. Our goal is to obtain the model of dielectric response of crystalline silicon which depends only on photon energy, temperature and small number of material parameters, e.g. the concentration of substituted carbon and interstitial oxygen. The model presented in this paper is accurate enough to replace tabulated values of c-Si optical constants used in the optical characterization of thin films diposited on silicon substrates. The spectral dependencies of the optical constants obtained in our work are compared to results obtained by other authors.
Phonon-Mediated Electron-Phonon Interaction in Hubbard-Holstein Model
Nath, S.; Ghosh, N. K.
2016-01-01
We explore the influence of inter-site electron-phonon (EP) interaction λ on some ground state and finite temperature properties of Hubbard-Holstein model using exact diagonalization technique. Both the adiabatic and non-adiabatic limits have been considered. Results show that the EP correlation function χ increases gradually for the adiabatic case with λ while a sharp transition is observed at λ = λ c(U/t) for the non-adiabatic case. On-site (S0) and inter-site (S1) bipolarons are formed which tend to bind at λ ≥ λ _c(U/t). Schematic phase diagram has been shown. Entropy calculations show that the system goes to a more ordered state when λ ≥ λ _c(U/t) due to the formation of EP pairs. Broad peaks are observed in the specific heat curves which move to higher temperature region with λ suggesting an effective increase in exchange energy.
How Moderate is Kwame Gyekye's Moderate Communitarianism ...
African Journals Online (AJOL)
This article undertakes a critical examination of Kwame Gyekye's main arguments for moderate communitarianism. Contrary to the general belief among African scholars, it contends that Gyekye's moderate communitarianism, as he presents it in Tradition and Modernity (1997), is not as moderate as he believes it to be.
Yudistira, Didit; Pennec, Yan; Djafari Rouhani, Bahram; Dupont, Samuel; Laude, Vincent
2012-02-01
We demonstrate the existence of non-radiative complete surface acoustic wave (SAW) bandgaps for two-dimensional piezoelectric phononic crystals of holes. Holes of finite depth in a semi-infinite LiNbO3 substrate are specifically considered. SAW bandgaps are determined from the band structure calculated with a three-dimensional finite element method taking into account material anisotropy and piezoelectricity. The effect of hole geometry on the bandgaps has been investigated. It is further found that the complete band gap does not close for moderately conical holes.
Energy Technology Data Exchange (ETDEWEB)
Meevasana, Warawat
2010-05-26
Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO{sub 3} (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La{sub 2}CuO{sub 4} by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO{sub 3}. Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a {lambda}{prime} {approx} 0.3 and an overall bandwidth renormalization suggesting an overall {lambda}{prime} {approx} 0.7 coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.
Sandeep; Dahiya, Sunita; Singh, Navneet
2017-11-01
An analytical treatment based on the hydrodynamic model of plasmas is developed to study parametric amplification and oscillation of optical phonon modes in weakly polar narrow direct-gap magnetized semiconductor plasmas. Second-order optical susceptibility arising due to nonlinear polarization and the basic operational characteristics of the parametric device, viz. threshold nature, power gain mechanisms and conversion efficiency, are obtained. The effects of doping, magnetic field and excitation intensity, on the above operational characteristics have been studied in detail. Numerical estimates are made for an n-InSb crystal at 5 K duly irradiated by a pulsed 10.6 μm CO2 laser. The analysis suggests the possibility of observing super-fluorescent parametric emission and oscillation in moderately doped n-InSb crystal under off-resonant nanosecond pulsed not-too-high power laser irradiation, the crystal being immersed in a large magnetic field.
Band structures and localization properties of aperiodic layered phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)
2012-03-15
The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.
Hot electrons in low-dimensional phonon systems
Qu, S. -X.; Cleland, A. N.; Geller, M. R.
2005-01-01
A simple bulk model of electron-phonon coupling in metals has been surprisingly successful in explaining experiments on metal films that actually involve surface- or other low-dimensional phonons. However, by an exact application of this standard model to a semi-infinite substrate with a free surface, making use of the actual vibrational modes of the substrate, we show that such agreement is fortuitous, and that the model actually predicts a low-temperature crossover from the familiar T^5 tem...
Effect of Holstein phonons on the electronic properties of graphene
Energy Technology Data Exchange (ETDEWEB)
Stauber, T [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain); Peres, N M R [Center of Physics and Department of Physics, University of Minho, P-4710-057, Braga (Portugal)
2008-02-06
We obtain the self-energy of the electronic propagator due to the presence of Holstein polarons within the first Born approximation. This leads to a renormalization of the Fermi velocity of 1%. We further compute the optical conductivity of the system at the Dirac point and at finite doping within the Kubo formula. We argue that the effects due to Holstein phonons are negligible and that the Boltzmann approach, which does not include inter-band transitions and can thus not treat optical phonons due to their high energy of {Dirac_h}{omega}{sub 0} {approx} 0.1-0.2 eV, remains valid.
Unraveling the acoustic electron-phonon interaction in graphene
DEFF Research Database (Denmark)
Kaasbjerg, Kristen; Thygesen, Kristian S.; Jacobsen, Karsten W.
2012-01-01
Using a first-principles approach we calculate the electron-phonon couplings in graphene for the transverse and longitudinal acoustic phonons. Analytic forms of the coupling matrix elements valid in the long-wavelength limit are found to give an almost quantitative description of the first...... that the intrinsic effective acoustic deformation potential of graphene is Ξeff=6.8 eV and that the temperature dependence of the mobility μ~T-α in the Bloch-Gru¨neisen regime increases beyond an α=4 dependence even in the absence of screening when the true coupling matrix elements are considered. The α>4...
Evolution of full phononic band gaps in periodic cellular structures
Wormser, Maximilian; Warmuth, Franziska; Körner, Carolin
2017-10-01
Cellular materials not only show interesting static properties, but can also be used to manipulate dynamic mechanical waves. In this contribution, the existence of phononic band gaps in periodic cellular structures is experimentally shown via sonic transmission experiment. Cellular structures with varying numbers of cells are excited by piezoceramic actuators and the transmitted waves are measured by piezoceramic sensors. The minimum number of cells necessary to form a clear band gap is determined. A rotation of the cells does not have an influence on the formation of the gap, indicating a complete phononic band gap. The experimental results are in good agreement with the numerically obtained dispersion relation.
Cavity-mediated coupling of phonons and magnons
Gao, Yong-Pan; Cao, Cong; Wang, Tie-Jun; Zhang, Yong; Wang, Chuan
2017-08-01
Optomagnonics and optomechanics have various applications, ranging from tunable light sources to optical manipulation for quantum information science. We propose a hybrid system based on the interaction between a phonon and a magnon that can be tuned by an electromagnetic field based on the radiation pressure and magneto-optical effects. The self-energies of the magnon and phonon induced by the electromagnetic field and the influence of the thermal noise are studied. Moreover, the topological features of the hybrid system are illustrated considering the dynamical encircling with the exceptional points, and the chiral characteristics under these encirclements are found.
Phonon thermal transport in metallic glasses below 100 K
Energy Technology Data Exchange (ETDEWEB)
Matey, James Regis [Univ. of Illinois, Urbana-Champaign, IL (United States)
1978-01-01
Measurements of the phonon thermal conductivity of a variety of metallic glasses were made. In each case, the temperature dependence and magnitude of the phonon thermal conductivity of the glassy metal was very similar to that characteristic of nonmetallic glasses. Variation of sound velocity measurements were made on a glassy palladium silicon alloy and a qualitative similarity was found between its behavior and the behavior of nonmetallic glasses. These findings and results from other laboratories have led to the conclusion that the localized excitations responsible for the anomalous behavior of nonmetallic glasses are also present in the metallic glasses.
Two-phonon capture processes into quantum dots: The role of intermediate states
DEFF Research Database (Denmark)
Magnúsdóttir, Ingibjörg; Uskov, A. V.; Bischoff, Svend
2003-01-01
We present a study of carrier capture into quantum dots via emission of longitudinal optical phonons. Two-phonon capture times are found to be of the order of some picoseconds at carrier densities 10^1^7cm^-^3 in situations where single-phonon capture processes are energetically prohibited....... The influence of different intermediate carrier states on the two-phonon capture rate is investigated and found to exhibit effects of interference between the different contributions....
Comparative study of thermal conductivity in crystalline and amorphous nanocomposite
Juangsa, Firman Bagja; Muroya, Yoshiki; Ryu, Meguya; Morikawa, Junko; Nozaki, Tomohiro
2017-06-01
Silicon nanocrystals (SiNCs)/polystyrene (PS) nanocomposite has been observed to have a significant decrease in thermal conductivity in terms of the SiNC fraction with unspecified factors remained unclear. In this paper, amorphous silicon nanoparticles (a-SiNPs) with a mean diameter of 6 nm and PS nanocomposites were synthesized, and their thermal conductivity, including the density and specific heat, was compared with our previous work which investigated well-crystalized SiNPs (6 nm) and PS nanocomposite. The difference between amorphous and crystalline structure is insignificant, but phonon scattering at SiNPs and PS boundary is the key influencing factor of thermal conductivity reduction. The effective thermal conductivity models for nanocomposite revealed that the thermal boundary resistance, explained by Kapitza principle, is estimated to be 4 × 10-7 m2K/W, showing the significant effect of nanostructured heterogenic surface resistance on overall heat transfer behavior. Preservation of unique properties nanoscale materials and low-cost fabrication by silicon inks process at room temperature give the promising potential of SiNPs based heat transfer management.
Optical-phonon-induced frictional drag in coupled two-dimensional electron gases
DEFF Research Database (Denmark)
Hu, Ben Yu-Kuang
1998-01-01
at low T and large separations), it might be expected that the optical phonons will contribute a large effect at high temperatures. The two key differences between optical-and acoustic-phonon-mediated drag are (i) the optical-phonon-mediated interlayer interaction is short-ranged due to the negligible...
Theoretical study of the transverse acoustic phonons of GaSb at ...
Indian Academy of Sciences (India)
Abstract. We have investigated the phonon dispersion curves and one-phonon density of states up to the pressure of 8 GPa using a theoretical model, namely the rigid ion model. The transverse acoustic phonons as a function of pressure have been compared with the recently measured inelastic neutron scattering data ...
Phonons in high- Tc CaBi 2Sr 2Cu 2O 8
Gupta, H. C.
1989-02-01
The phonons have been investigated in CaBi 2Sr 2Cu 2O 8 using radial and tangential force constants. From the point of view of superconductivity, it is found that the phonons associated with the Bi-O layers will play an analogous role to the phonons due to Cu-O perovskite-like layers.
Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
Isaeva, E.I.; Lichtenstein, A.I.; Vekilov, Y.K.; Smirnova, E.A.; Abrikosov, I.A.; Simak, S.I.; Ahuja, R.; Johansson, B.
2004-01-01
The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available
Electron-phonon coupling using many-body GW theory
Monserrat, Bartomeu; Vanderbilt, David
Electron-phonon coupling drives a plethora of phenomena, such as superconductivity in metals, or the temperature dependence of optical properties in semiconductors. There is increasing evidence that semi-local density functional theory (DFT) is not adequate for the description of electron-phonon coupling, and instead effects such as electronic correlation need to be included. Unfortunately, methods beyond semi-local DFT are computationally demanding, limiting the study of these phenomena. In this talk we will introduce the idea of ``thermal lines'', which can be used to explore the vibrational phase space of solids and molecules at small computational cost. In particular, we will describe how thermal lines can be exploited to calculate the temperature dependence of band structures beyond semi-local DFT, by using many-body GW theory, or by including the effects of spin-orbit coupling. We will present first-principles results showing the effects of electron correlation on the strength of electron-phonon coupling, and the effects of electron-phonon coupling on topological states of matter. Supported by Robinson College, Cambridge, and the Cambridge Philosophical Society.
Tunable topological phases in photonic and phononic crystals
Chen, Zeguo
2018-02-18
Topological photonics/phononics, inspired by the discovery of topological insulators, is a prosperous field of research, in which remarkable one-way propagation edge states are robust against impurities or defect without backscattering. This dissertation discusses the implementation of multiple topological phases in specific designed photonic and phononic crystals. First, it reports a tunable quantum Hall phase in acoustic ring-waveguide system. A new three-band model focused on the topological transitions at the Γ point is studied, which gives the functionality that nontrivial topology can be tuned by changing the strengths of the couplings and/or the broken time-reversal symmetry. The resulted tunable topological edge states are also numerically verified. Second, based on our previous studied acoustic ring-waveguide system, we introduce anisotropy by tuning the couplings along different directions. We find that the bandgap topology is related to the frequency and directions. We report our proposal on a frequency filter designed from such an anisotropic topological phononic crystal. Third, motivated by the recent progress on quantum spin Hall phases, we propose a design of time-reversal symmetry broken quantum spin Hall insulators in photonics, in which a new quantum anomalous Hall phase emerges. It supports a chiral edge state with certain spin orientations, which is robust against the magnetic impurities. We also report the realization of the quantum anomalous Hall phase in phononics.
Effects of electron–phonon interaction and impurity on optical ...
Indian Academy of Sciences (India)
2017-02-10
Feb 10, 2017 ... Abstract. We have investigated the influence of electron–phonon (e–p) interaction and hydrogenic donor impu- rity simultaneously on energy difference, binding energy, the linear, nonlinear and total refractive index changes and absorption coefficients of a hexagonal-shaped quantum wire. For this goal ...
Theory of parametrically amplified electron-phonon superconductivity
Energy Technology Data Exchange (ETDEWEB)
Babadi, Mehrtash; Knap, Michael; Martin, Ivar; Refael, Gil; Demler, Eugene
2017-07-01
Ultrafast optical manipulation of ordered phases in strongly correlated materials is a topic of significant theoretical, experimental, and technological interest. Inspired by a recent experiment on light-induced superconductivity in fullerenes [M. Mitrano et al., Nature (London) 530, 461 (2016)], we develop a comprehensive theory of light-induced superconductivity in driven electron-phonon systemswith lattice nonlinearities. In analogy with the operation of parametric amplifiers, we show how the interplay between the external drive and lattice nonlinearities lead to significantly enhanced effective electron-phonon couplings. We provide a detailed and unbiased study of the nonequilibrium dynamics of the driven system using the real-time Green's function technique. To this end, we develop a Floquet generalization of the Migdal-Eliashberg theory and derive a numerically tractable set of quantum Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We study the role of parametric phonon generation and electronic heating in destroying the transient superconducting state. Finally, we predict the transient formation of electronic Floquet bands in time-and angle-resolved photoemission spectroscopy experiments as a consequence of the proposed mechanism.
Excitation and decay of two-phonon giant dipole resonances
Energy Technology Data Exchange (ETDEWEB)
Boretzky, K. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik]|[Mainz Univ. (Germany). Inst. fuer Kernchemie; Aumann, T.; Emling, H.; Holzmann, R.; Ilievski, S.; Leifels, Y. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Cub, J. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)]|[Technische Univ. Darmstadt (Germany). Inst. fuer Kernphysik; Elze, T.W.; Gruenschloss, A.; Leistenschneider, A.; Stroth, J. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Kulessa, R.; Lubkiewicz, E.; Wajda, E.; Walus, W. [Uniwersytet Jagiellonski, Cracow (Poland). Inst. Fizyki; Kratz, J.V. [Mainz Univ. (Germany). Inst. fuer Kernchemie
1998-09-01
In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states. (orig.)
Excitation and Decay of Two-Phonon Giant Dipole Resonances
Energy Technology Data Exchange (ETDEWEB)
Boretzky, K.; Aumann, T.; Cub, J.; Elze, Th.W.; Emling, H.; Gruenschloss, A.; Holzmann, R.; Ilievski, S.; Kulessa, R.; Kratz, J.V.; Leifels, Y.; Leistenschneider, A.; Lubkiewicz, E.; Stroth, J.; Wajda, E.; Walus, W
1999-03-29
In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states.
Decoherence in semiconductor cavity QED systems due to phonon couplings
DEFF Research Database (Denmark)
Nielsen, Per Kær; Mørk, Jesper
2014-01-01
We investigate the effect of electron-phonon interactions on the coherence properties of single photons emitted from a semiconductor cavity QED (quantum electrodynamics) system, i.e., a quantum dot embedded in an optical cavity. The degree of indistinguishability, governing the quantum mechanical...... diagonalization approach. We find that for large cavity decay rates the perturbation theory may break down....
Theory of parametrically amplified electron-phonon superconductivity
Babadi, Mehrtash; Knap, Michael; Martin, Ivar; Refael, Gil; Demler, Eugene
2017-07-01
Ultrafast optical manipulation of ordered phases in strongly correlated materials is a topic of significant theoretical, experimental, and technological interest. Inspired by a recent experiment on light-induced superconductivity in fullerenes [M. Mitrano et al., Nature (London) 530, 461 (2016), 10.1038/nature16522], we develop a comprehensive theory of light-induced superconductivity in driven electron-phonon systems with lattice nonlinearities. In analogy with the operation of parametric amplifiers, we show how the interplay between the external drive and lattice nonlinearities lead to significantly enhanced effective electron-phonon couplings. We provide a detailed and unbiased study of the nonequilibrium dynamics of the driven system using the real-time Green's function technique. To this end, we develop a Floquet generalization of the Migdal-Eliashberg theory and derive a numerically tractable set of quantum Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We study the role of parametric phonon generation and electronic heating in destroying the transient superconducting state. Finally, we predict the transient formation of electronic Floquet bands in time- and angle-resolved photoemission spectroscopy experiments as a consequence of the proposed mechanism.
Constitutive equation for polymer networks with phonon fluctuations
DEFF Research Database (Denmark)
Hansen, Rasmus; Skov, Anne Ladegaard; Hassager, Ole
2008-01-01
Recent research by Xing [Phys. Rev. Lett. 98, 075502 (2007)] has provided an expression for the Helmholtz free energy related to phonon fluctuations in polymer networks. We extend this result by constructing the corresponding nonlinear constitutive equation, usable for entirely general, volume...
Phonon conduction in GaN-diamond composite substrates
Cho, Jungwan; Francis, Daniel; Altman, David H.; Asheghi, Mehdi; Goodson, Kenneth E.
2017-02-01
The integration of strongly contrasting materials can enable performance benefits for semiconductor devices. One example is composite substrates of gallium nitride (GaN) and diamond, which promise dramatically improved conduction cooling of high-power GaN transistors. Here, we examine phonon conduction in GaN-diamond composite substrates fabricated using a GaN epilayer transfer process through transmission electron microscopy, measurements using time-domain thermoreflectance, and semiclassical transport theory for phonons interacting with interfaces and defects. Thermoreflectance amplitude and ratio signals are analyzed at multiple modulation frequencies to simultaneously extract the thermal conductivity of GaN layers and the thermal boundary resistance across GaN-diamond interfaces at room temperature. Uncertainties in the measurement of these two properties are estimated considering those of parameters, including the thickness of a topmost metal transducer layer, given as an input to a multilayer thermal model, as well as those associated with simultaneously fitting the two properties. The volume resistance of an intermediate, disordered SiN layer between the GaN and diamond, as well as a presence of near-interfacial defects in the GaN and diamond, dominates the measured GaN-diamond thermal boundary resistances as low as 17 m2 K GW-1. The GaN thermal conductivity data are consistent with the semiclassical phonon thermal conductivity integral model that accounts for the size effect as well as phonon scattering on point defects at concentrations near 3 × 1018 cm-3.
Calculation Of Phonon Dispersion Frequencies For Bcc Tantalum ...
African Journals Online (AJOL)
The phonon dispersion frequencies are calculated from first principles for bcc Tantalum using a resonance pseudopotential model. It was also possible, using this scheme, to account for the anomalous feature of the Ta dispersion curve observed experimentally in the (ε,o,o,) direction where the frequencies of the transverse ...
Phonon-enhanced crystal growth and lattice healing
Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna
2013-05-28
A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.
The Effect of Phonon Relaxation Process on Absorption Spectra ...
African Journals Online (AJOL)
In this work we study the effect of phonon relaxation process on the absorption spectra using the Green's function technique. The Green's function technique which is widely used in many particle problems is used to solve the Kubo formula which describes the optical absorption process. Finally the configurational diagram is ...
Phonon-drag thermopower in 3D Dirac semimetals.
Kubakaddi, S S
2015-11-18
A theory of low-temperature phonon-drag thermopower S(g) in three-dimensional (3D) Dirac semimetals has been developed considering screened electron-phonon deformation potential coupling. Numerical investigations of S(g), in the boundary scattering regime for phonons, are made in 3D Dirac semimetal Cd3As2, as a function of temperature T and electron concentration n e. S(g) is found to increase rapidly for about T Dirac 3D electrons. Comparison with diffusion thermopower S(d) shows that S (g) dominates (and is much greater than) S(d) for about T > 0.2 K. Herring's law S(g) μ p ~ T (-1), relating phonon limited mobility μ p and S(g) in the BG regime, is shown to be valid in 3D Dirac semimetals. The results obtained here are compared with those in 3D semiconductors, low-dimensional semiconductor heterojunctions and graphene. We conclude that n e-dependent measurements, rather than T-dependent ones, provide a clearer signature of the 3D Dirac semimetal phase.
Phonon and thermal properties of achiral single wall carbon ...
Indian Academy of Sciences (India)
This exceptionally high value of thermal conductivity reflects the one-dimensional conduction behavior of nanotubes with least phonon scattering. Recent ..... In this way one can interpret the double peak structure of the high-energy sub-band of carbon nanotubes. In the case of achiral tubes it was found that the magnitude ...
A Comprehensive Approach to Phonon Control for Enhanced Device Performance
2006-07-12
Fundamental Optical and Quantum Effects in Condensed Matter, ed. by E. Molinari, V. Pellegrini a and A. Pinczuk. 90. "Simulations of the phonon Bragg...clude the J.H. Ahlers Achievement Award and the John Simon Guggenheim Fellow Award. Rachel Goldman was the recipient of the 2002 Peter Mark Memorial
A new hybrid phononic crystal in low frequencies
Energy Technology Data Exchange (ETDEWEB)
Zhang, Z., E-mail: zhangz@dlut.edu.cn; Han, X.K.
2016-11-25
A novel hybrid phononic crystal is designed to obtain wider band gaps in low frequency range. The hybrid phononic crystal consists of rubber slab with periodic holes and plumbum stubs. In comparison with the phononic crystal without periodic holes, the new designed phononic crystal can obtain wider band gaps and better vibration damping characteristics. The wider band gap can be attributed to the interaction of local resonance and Bragg scattering. The controlling of the BG is explained by the strain energy of the hybrid PC and the introduced effective mass. The effects of the geometrical parameters and the shapes of the stubs and holes on the controlling of waves are further studied. - Highlights: • A novel hybrid PC structure is proposed in current work. The new designed hybrid PC shows wider BG in low frequency range and better vibration damping characteristics. • Strain energy and effective mass are introduced for the investigations on the mechanism of the controlling of BGs in PC structure. • The effects of the geometrical parameters and the shapes of the stubs and holes on the controlling of waves are further studied for optimal design.
Electron-phonon coupling in the rare-earth metals
DEFF Research Database (Denmark)
Skriver, Hans Lomholt; Mertig, I.
1990-01-01
We have estimated the strength of the mass enhancement of the conduction electrons due to electron-phonon interaction in the rare metals Sc, Y, and La–Lu. The underlying self-consistent energy bands were obtained by means of the scalar relativistic linear-muffin-tin-orbital method, and the electron...
Electron-phonon coupling of the actinide metals
DEFF Research Database (Denmark)
Skriver, H. L.; Mertig, I.
1985-01-01
-phonon parameter λ is found to attain its maximum value in Ac, and they predict a transition temperature of 9K for this metal. In the light actinides Th through Pu, λ is found to be of order 0.4 and within a factor of 2 of experiments which is also the accuracy found in studies of the transition metals...
Passive control of fully developed turbulent flow by subsurface phonons
Hussein, Mahmoud; Biringen, Sedat; Hsieh, Alan; Bacquet, Clemence; Bastawrous, Mary
2017-11-01
Flow control is a central problem in fluid dynamics where the goal is to alter a flow's natural state to achieve improved performance, such as delay of laminar-to-turbulent transition or reduction of drag in a fully developed turbulent flow. Meeting this goal promises to significantly reduce the dependence on fossil fuels for global transport, impacting air and sea vehicles as well as long-range pipelines. In earlier work, we have shown that phonon motion underneath a surface interacting with a flow may be tuned to cause the flow to stabilize, or destabilize, as desired. This concept was demonstrated by simulating a fully developed plane Poiseuille (channel) flow whereby a small portion of an otherwise rigid wall is replaced with a one-dimensional phononic crystal. A Tollmien-Schlichting wave was introduced to the flow as an evolving disturbance. Upon tuning the frequency-dependent phase and amplitude relations of the surface of the phononic crystal that interfaces with the flow, an artificially introduced instability was shown to stabilize, or destabilize, as needed. In this work, we demonstrate the applicability of the phononic subsurface paradigm to the suppression of turbulence production events in fully developed turbulent flow.
Coupling between the Magnetic Excitations and the Phonons in Praseodymium
DEFF Research Database (Denmark)
Jensen, J.
1976-01-01
The dispersion relation of the magnetic excitations of the hexagonal ions in DHCP Pr and the selection rules for the linear coupling to the phonons are determined by general symmetry considerations. The magnetic excitations propagating in the symmetry directions are considered in the cases of an ...
Enhanced Electron-Phonon Coupling at Metal Surfaces
Energy Technology Data Exchange (ETDEWEB)
Plummer, Ward E.
2010-08-04
The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.
Relaxation between electrons and surface phonons of a ...
Indian Academy of Sciences (India)
to the calculation of energy transfer rate from degenerate hot electrons to surface phonons. We consider the case of a homogeneously photoexcited (no spatial dif- fusion) nanoscale metal film, in which the electron mean free path is more than the film thickness (as in case of metals, in which even at high temperatures, the.
Pseudospins and Topological Effects of Phonons in a Kekulé Lattice
Liu, Yizhou; Lian, Chao-Sheng; Li, Yang; Xu, Yong; Duan, Wenhui
2017-12-01
The search for exotic topological effects of phonons has attracted enormous interest for both fundamental science and practical applications. By studying phonons in a Kekulé lattice, we find a new type of pseudospin characterized by quantized Berry phases and pseudoangular momenta, which introduces various novel topological effects, including topologically protected pseudospin-polarized interface states and a phonon pseudospin Hall effect. We further demonstrate a pseudospin-contrasting optical selection rule and a pseudospin Zeeman effect, giving a complete generation-manipulation-detection paradigm of the phonon pseudospin. The pseudospin and topology-related physics revealed for phonons is general and applicable for electrons, photons, and other particles.
Control of quantum dot laser emission by coherent phonon wave packets
Wigger, D.; Czerniuk, T.; Reiter, D. E.; Bayer, M.; Kuhn, T.
2017-10-01
Travelling coherent phonons can be actively used to manipulate the optical properties of semiconductor nanostructures on the picosecond time scale. Phonon wave packets that interact with a quantum dot (QD) ensemble can significantly vary the output intensity of a laser, which uses the QDs as active medium. Based on a recently developed theoretical model to describe this coupled phonon-QD-photon system, we here study how the laser response on phonon wave packets depends on several parameters, for example phonon pulse properties and laser pump rate.
Stevens, C. E.; Dey, P.; Paul, J.; Wang, Z.; Zhang, H.; Romero, A. H.; Shan, J.; Hilton, D. J.; Karaiskaj, D.
2017-10-01
We investigate the excitonic dephasing of transition metal dichalcogenides, namely MoS2, MoSe2 and WSe2 atomic monolayer thick and bulk crystals, in order to understand the factors that determine the optical coherence in these materials. Coherent nonlinear optical spectroscopy, temperature dependent absorption combined with theoretical calculations of the phonon spectra, reveal the important role electron-phonon interactions plat in dephasing process. The temperature dependence of the electronic band gap and the excitonic linewidth combined with 'ab initio' calculations of the phonon energies and the phonon density of state reveal strong interaction with the E‧ and E″ phonon modes.
Electronic properties with and without electron-phonon coupling
Allen, Philip
To decent approximation, electronic properties P of solids have a temperature dependence of the type ΔP(T) = Σ (dP/dωi) [ni(T) +1/2], where ωi is the frequency of the ith vibrational normal mode, and ni is the Bose-Einstein equilibrium occupation of the mode. The coupling constant (dP/dωi) comes from electron-phonon interactions. At T =0, the ``1/2'' gives the zero-point electron-phonon renormalization of the property P, and at T>ΘD, the total shift ΔP becomes linear in T, extrapolating toward ΔP =0 at T =0. This form of T-dependence arises from the adiabatic or Born-Oppenheimer approximation, where electrons essentially ``don't notice'' the time-dependence of thermal lattice fluctuations. In other words, the leading order theory for P is ΔP(T) = Σ (d2P/duiduj), responding to the thermal average mean square lattice displacement, as if it were static. There are two situations where non-adiabatic effects alter things. (1) In metals at low T, the thermal smearing kBT of the sharp Fermi edge gets small (ωi insulators with polar phonons, Froehlich polaron effects enter, and k-integrals diverge unless phonon energies are kept. Most non-adiabatic effects become unimportant by room temperature, but the low T consequences can be very interesting (e.g. superconductivity.) This talk will discuss the confusing history and predict some future developments in this field. invited session: ''Predictive Modeling of Electron-Phonon Coupling in Condensed-Matter Physics'' My talk will be coordinated with that of Xavier Gonze. It would be best to schedule them back-to-back.
Surface induced phonon decay rates in thin film nano-structures
Energy Technology Data Exchange (ETDEWEB)
Photiadis, D M [Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375-5320, (United States)
2007-12-15
Nano-scale structure significantly impacts phonon transport and related phonon relaxation rates, with order of magnitude effects on the thermal conductivity of dielectric thin films and quantum wires, and even larger effects on the lifetimes of ultrasonic phonons of micro- (nano-) oscillators. In both cases, efforts to explain the data have been hampered by our lack of knowledge of the effects of confined dimensionality on phonon-phonon scattering rates. Using a phonon Boltzmann equation with appropriate boundary conditions on the free surfaces to take surface roughness into account, we have obtained an expression yielding phonon lifetimes in 2-D dielectric nanostructures(thin films) resulting from phonon-phonon scattering in conjunction with phonon-surface scattering. We present these theoretical results and, in the limit in which surface induced losses dominate, obtain explicit predictions for the phonon lifetimes. The predicted temperature dependence of the ultrason{exclamation_point} ic loss does not explain the observed saturation of the loss at low temperatures({tau}(T) {yields} const), but does give results of the order of magnitude of measured ultrasonic lifetimes.
Surface induced phonon decay rates in thin film nano-structures
Photiadis, D. M.
2007-12-01
Nano-scale structure significantly impacts phonon transport and related phonon relaxation rates, with order of magnitude effects on the thermal conductivity of dielectric thin films and quantum wires, and even larger effects on the lifetimes of ultrasonic phonons of micro- (nano-) oscillators. In both cases, efforts to explain the data have been hampered by our lack of knowledge of the effects of confined dimensionality on phonon-phonon scattering rates. Using a phonon Boltzmann equation with appropriate boundary conditions on the free surfaces to take surface roughness into account, we have obtained an expression yielding phonon lifetimes in 2-D dielectric nanostructures(thin films) resulting from phonon-phonon scattering in conjunction with phonon-surface scattering. We present these theoretical results and, in the limit in which surface induced losses dominate, obtain explicit predictions for the phonon lifetimes. The predicted temperature dependence of the ultrason! ic loss does not explain the observed saturation of the loss at low temperatures(τ(T) → const), but does give results of the order of magnitude of measured ultrasonic lifetimes.
Damage characterization for particles filled semi-crystalline polymer
Lauro, Franck; Balieu, Romain; Bennani, Bruno; Haugou, Gregory; Bourel, Benjamin; Chaari, Fahmi; Matsumoto, Tsukatada; Mottola, Ernesto
2015-09-01
Damage evolution and characterization in semi-crystalline polymer filled with particles under various loadings is still a challenge. A specific damage characterization method using Digital Image Correlation is proposed for a wide range of strain rates considering tensile tests with hydraulic jacks as well as Hopkinson's bars. This damage measurement is obtained by using and adapting the SEE method [1] which was developed to characterize the behaviour laws at constant strain rates of polymeric materials in dynamic. To validate the characterization process, various damage measurement techniques are used under quasi-static conditions before to apply the procedure in dynamic. So, the well-known damage characterization by loss of stiffness technique under quasi-static loading is applied to a polypropylene. In addition, an in-situ tensile test, carried out in a microtomograph, is used to observe the cavitation phenomenon in real time. A good correlation is obtained between all these techniques and consequently the proposed technique is supposed suitable for measuring the ductile damage observed in semi-crystalline polymers under dynamic loading. By applying it to the semi-crystalline polymer at moderate and high speed loadings, the damage evolution is measured and it is observed that the damage evolution is not strain rate dependent but the failure strain on the contrary is strain rate dependent.
Bending cyclic load test for crystalline silicon photovoltaic modules
Suzuki, Soh; Doi, Takuya; Masuda, Atsushi; Tanahashi, Tadanori
2018-02-01
The failures induced by thermomechanical fatigue within crystalline silicon photovoltaic modules are a common issue that can occur in any climate. In order to understand these failures, we confirmed the effects of compressive or tensile stresses (which were cyclically loaded on photovoltaic cells and cell interconnect ribbons) at subzero, moderate, and high temperatures. We found that cell cracks were induced predominantly at low temperatures, irrespective of the compression or tension applied to the cells, although the orientation of cell cracks was dependent on the stress applied. The fracture of cell interconnect ribbons was caused by cyclical compressive stress at moderate and high temperatures, and this failure was promoted by the elevation of temperature. On the basis of these results, the causes of these failures are comprehensively discussed in relation to the viscoelasticity of the encapsulant.
Photo-excited charge carrier suppress sub-terahertz phonon mode in silicon at room temperature
Liao, Bolin; Maznev, Alexei; Nelson, Keith; Chen, Gang
There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon-phonon interactions, it has been a challenge to directly measure electron-phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building upon conventional pump-probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single phonon mode due to the electron-phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron-phonon interaction on phonon transport in doped semiconductors. This work is supported by S3TEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-FG02-09ER46577.
Zhu, Yi; Chen, Frank; Park, Joonkyu; Sasikumar, Kiran; Hu, Bin; Damodaran, Anoop R.; Jung, Il Woong; Highland, Matthew J.; Cai, Zhonghou; Tung, I.-Cheng; Walko, Donald A.; Freeland, John W.; Martin, Lane W.; Sankaranarayanan, Subramanian K. R. S.; Evans, Paul G.; Lindenberg, Aaron M.; Wen, Haidan
2017-11-01
Nanoscale phonon transport is a key process that governs thermal conduction in a wide range of materials and devices. Creating controlled phonon populations by resonant excitation at terahertz (THz) frequencies can drastically change the characteristics of nanoscale thermal transport and allow a direct real-space characterization of phonon mean-free paths. Using metamaterial-enhanced terahertz excitation, we tailored a phononic excitation by selectively populating low-frequency phonons within a nanoscale volume in a ferroelectric BaTi O3 thin film. Real-space time-resolved x-ray diffraction microscopy following THz excitation reveals ballistic phonon transport over a distance of hundreds of nm, two orders of magnitude longer than the averaged phonon mean-free path in BaTi O3 . On longer length scales, diffusive phonon transport dominates the recovery of the transient strain response, largely due to heat conduction into the substrate. The measured real-space phonon transport can be directly compared with the phonon mean-free path as predicted by molecular dynamics modeling. This time-resolved real-space visualization of THz-matter interactions opens up opportunities to engineer and image nanoscale transient structural states with new functionalities.
Structural and phonon transmission study of Ge-Au-Ge eutectically bonded interfaces
Energy Technology Data Exchange (ETDEWEB)
Knowlton, W.B. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering]|[Lawrence Berkeley Lab., CA (United States). Materials Sciences Div.
1995-07-01
This thesis presents a structural analysis and phonon transparency investigation of the Ge-Au-Ge eutectic bond interface. Interface development was intended to maximize the interfacial ballistic phonon transparency to enhance the detection of the dark matter candidate WIMPs. The process which was developed provides an interface which produces minimal stress, low amounts of impurities, and insures Ge lattice continuity through the interface. For initial Au thicknesses of greater than 1,000 {angstrom} Au per substrate side, eutectic epitaxial growth resulted in a Au dendritic structure with 95% cross sectional and 90% planar Au interfacial area coverages. In sections in which Ge bridged the interface, lattice continuity across the interface was apparent. Epitaxial solidification of the eutectic interface with initial Au thicknesses < 500 A per substrate side produced Au agglomerations thereby reducing the Au planar interfacial area coverage to as little as 30%. The mechanism for Au coalescence was attributed to lateral diffusion of Ge and Au in the liquid phase during solidification. Phonon transmission studies were performed on eutectic interfaces with initial Au thicknesses of 1,000 {angstrom}, 500 {angstrom}, and 300 {angstrom} per substrate side. Phonon imaging of eutectically bonded samples with initial Au thicknesses of 300 {angstrom}/side revealed reproducible interfacial percent phonon transmissions from 60% to 70%. Line scan phonon imaging verified the results. Phonon propagation TOF spectra distinctly showed the predominant phonon propagation mode was ballistic. This was substantiated by phonon focusing effects apparent in the phonon imaging data. The degree of interface transparency to phonons and resulting phonon propagation modes correlate with the structure of the interface following eutectic solidification. Structural studies of samples with initial Au thickness of 1,000 {angstrom}/side appear to correspond with the phonon transmission study.
Signature of electron-phonon interaction in high temperature superconductors
Directory of Open Access Journals (Sweden)
Vinod Ashokan
2011-09-01
Full Text Available The theory of thermal conductivity of high temperature superconductors (HTS based on electron and phonon line width (life times formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high Tc superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.
Phonon wave interference in graphene and boron nitride superlattice
Energy Technology Data Exchange (ETDEWEB)
Chen, Xue-Kun; Zhou, Wu-Xing; Tang, Li-Ming; Chen, Ke-Qiu, E-mail: keqiuchen@hnu.edu.cn [Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082 (China); Xie, Zhong-Xiang [Department of Mathematics and Physics, Hunan Institute of Technology, Hengyang 421002 (China)
2016-07-11
The thermal transport properties of the graphene and boron nitride superlattice (CBNSL) are investigated via nonequilibrium molecular dynamics simulations. The simulation results show that a minimum lattice thermal conductivity can be achieved by changing the period length of the superlattice. Additionally, it is found that the period length at the minimum shifts to lower values at higher temperatures, and that the depth of the minimum increases with decreasing temperature. In particular, at 200 K, the thermal conductivities of CBNSLs with certain specific period lengths are nearly equal to the corresponding values at 300 K. A detailed analysis of the phonon spectra shows that this anomalous thermal conductivity behavior is a result of strong phonon wave interference. These observations indicate a promising strategy for manipulation of thermal transport in superlattices.
Rich hybridized-polarization surface phonon polaritons in hyperbolic metamaterials
Directory of Open Access Journals (Sweden)
Q. Zhang
2017-10-01
Full Text Available We investigated hybridized-polarization surface phonon polaritons (HSPhPs of transversely truncated a metamaterial (MM that consists of alternating ionic-crystal and ordinary-dielectric layers. We predicted five HSPhPs in the reststrahlen frequency window of ionic-crystal layers, which belong to five different types, respectively. One is of Dyakonov-like type and another is traditional-like. The other three HSPhPs are of new type. We used a numerical-simulating method of attenuated total reflection (ATR measurements to examine them. The obtained ATR spectra also demonstrate that they are observable and exhibit their polarization features. These results expand the potential-application space of phononics and photonics in the infrared to the terahertz range.
Stochastic Approach to Phonon-Assisted Optical Absorption.
Zacharias, Marios; Patrick, Christopher E; Giustino, Feliciano
2015-10-23
We develop a first-principles theory of phonon-assisted optical absorption in semiconductors and insulators which incorporates the temperature dependence of the electronic structure. We show that the Hall-Bardeen-Blatt theory of indirect optical absorption and the Allen-Heine theory of temperature-dependent band structures can be derived from the present formalism by retaining only one-phonon processes. We demonstrate this method by calculating the optical absorption coefficient of silicon using an importance sampling Monte Carlo scheme, and we obtain temperature-dependent line shapes and band gaps in good agreement with experiment. The present approach opens the way to predictive calculations of the optical properties of solids at finite temperature.
Electron and phonon properties and gas storage in carbon honeycomb
Gao, Yan; Zhong, Chengyong; Zhang, Zhongwei; Xie, Yuee; Zhang, Shengbai
2016-01-01
A new kind of three-dimensional carbon allotropes, termed carbon honeycomb (CHC), has recently been synthesized [PRL 116, 055501 (2016)]. Based on the experimental results, a family of graphene networks are constructed, and their electronic and phonon properties are calculated by using first principles methods. All networks are porous metal with two types of electron transport channels along the honeycomb axis and they are isolated from each other: one type of channels is originated from the orbital interactions of the carbon zigzag chains and is topologically protected, while the other type of channels is from the straight lines of the carbon atoms that link the zigzag chains and is topologically trivial. The velocity of the electrons can reach ~106 m/s. Phonon transport in these allotropes is strongly anisotropic, and the thermal conductivities can be very low when compared with graphite by at least a factor of 15. Our calculations further indicate that these porous carbon networks possess high storage capa...
Lumped model for rotational modes in phononic crystals
Peng, Pai
2012-10-16
We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in determining the band structure, and reproduces the dispersion relations in a certain range. The model increases the possibilities of manipulating wave propagation in phononic crystals. In particular, expressions derived from the model for eigenfrequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.
The Use of Phononic Crystals to Design Piezoelectric Power Transducers
Directory of Open Access Journals (Sweden)
Silvia Ronda
2017-03-01
Full Text Available It was recently proposed that the lateral resonances around the working resonance band of ultrasonic piezoelectric sandwich transducers can be stopped by a periodic array of circular holes drilled along the main propagation direction (a phononic crystal. In this work, the performance of different transducer designs made with this procedure is tested using laser vibrometry, electric impedance tests and finite element models (FEM. It is shown that in terms of mechanical vibration amplitude and acoustic efficiency, the best design for physiotherapy applications is when both, the piezoceramic and an aluminum capsule are phononic structures. The procedure described here can be applied to the design of power ultrasonic devices, physiotherapy transducers and other external medical power ultrasound applications where piston-like vibration in a narrow band is required.
Band structures in Sierpinski triangle fractal porous phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Wang, Kai; Liu, Ying, E-mail: yliu5@bjtu.edu.cn; Liang, Tianshu
2016-10-01
In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.
Rich hybridized-polarization surface phonon polaritons in hyperbolic metamaterials
Zhang, Q.; Zhou, S.; Fu, S. F.; Wang, X. Z.
2017-10-01
We investigated hybridized-polarization surface phonon polaritons (HSPhPs) of transversely truncated a metamaterial (MM) that consists of alternating ionic-crystal and ordinary-dielectric layers. We predicted five HSPhPs in the reststrahlen frequency window of ionic-crystal layers, which belong to five different types, respectively. One is of Dyakonov-like type and another is traditional-like. The other three HSPhPs are of new type. We used a numerical-simulating method of attenuated total reflection (ATR) measurements to examine them. The obtained ATR spectra also demonstrate that they are observable and exhibit their polarization features. These results expand the potential-application space of phononics and photonics in the infrared to the terahertz range.
Significant Reduction of Graphene Thermal Conductivity by Phononic Crystal Structure
Yang, Lina; CHEN, JIE; Yang, Nuo; Li, Baowen
2014-01-01
We studied the thermal conductivity of graphene phononic crystal (GPnC), also named as graphene nanomesh, by molecular dynamics simulations. The dependences of thermal conductivity of GPnCs on both length and temperature are investigated. It is found that the thermal conductivity of GPnCs is significantly lower than that of graphene and can be efficiently tuned by changing the porosity and period length. For example, the ratio of thermal conductivity of GPnC to thermal conductivity of graphen...
Two-phonon giant dipole resonance in {sup 208}Pb
Energy Technology Data Exchange (ETDEWEB)
Boretzky, K. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Stroth, J. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Wajda, E. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)]|[Krakow Univ. (Poland). Inst. of Physics; Aumann, T. [Mainz Univ. (Germany). Inst. fuer Kernchemie; Blaich, T. [Mainz Univ. (Germany). Inst. fuer Kernchemie; Cub, J. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Elze, T.W. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Emling, H. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Henning, W. [Argonne National Lab., IL (United States); Holzmann, R. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Klingler, H. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Kulessa, R. [Krakow Univ. (Poland). Inst. of Physics; Kratz, J.V. [Mainz Univ. (Germany). Inst. fuer Kernchemie; Lambrecht, D. [Mainz Univ. (Germany). Inst. fuer Kernchemie; Leifels, Y. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Lubkiewicz, E. [Krakow Univ. (Poland). Inst. of Physics; Stelzer, K. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Walus, W. [Krakow Univ. (Poland). Inst. of Physics; Zinser, M. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Zude, E. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); LAND Collaboration
1996-06-01
Excitation of the two-phonon isovector giant dipole resonance was observed in {sup 208}Pb projectiles incident on different target nuclei (C, Sn, Ho, Pb, U) at high energy (640 A.MeV). Evidence is found for a two-step electromagnetic excitation mechanism. An enhancement of 1.33(16) for the excitation cross section is observed relative to the harmonic approximation. Neutron- and {gamma}-decay probabilities are derived as well. (orig.)
Effect of pressure on the phonon properties of europium ...
Indian Academy of Sciences (India)
Unknown
phonon density of states and compared them with the first order Raman scattering results. The calculation of ... raman et al 1974). The structural phase transition pre- ssures for EuO, EuS, EuSe and EuTe are 30–40 GPa,. 22 GPa, 15 GPa and 10 GPa, respectively. ... †Paper presented at the 5th IUMRS ICA98, October 1998,.
Phonon Emission from a Two-Dimensional Electron Gas.
Ouali, Fatma Fouzia
Available from UMI in association with The British Library. Requires signed TDF. The work presented in this thesis is a study of the electron-phonon interaction in Si mosfets in both zero and magnetic fields. In the first part, a new experimental technique was proposed which allows, for the first time, the separation of the momentum scattering rate due to phonons from the scattering rate due to extrinsic processes. The technique was applied to a Si mosfet sample, in which weak localization effects are small, for temperatures up to 23K. It was found that, in this temperature range, the contribution of phonon scattering rate to momentum was negligible using the corrected values of T_{rm e} obtained by Akimov et al (1991), in contrast with the initial analysis obtained using the published data of Akimov et al (1991). In the second part, the location of the phonon emission was studied in a magnetic field of 6T over a wide range of powers (0.1 to 333 muW/mm ^2), and in particular in the quantum Hall regime (QHR). It was observed, for the first time, that in the QHR: (i) the energy dissipation occurs at the two diagonally opposite corners of the device, which correspond to the entry and exit points of the electrons and (ii) the dissipation in each of these corners is equal, i.e. the power dissipated in each is 50 +/- 1.3% of the total. These measurements are the first to demonstrate these effects and, although others have been made since, the precision of the symmetry of the dissipation remains the highest that has been reported.
Energy Guiding and Harvesting through Phonon-Engineered Graphene
2016-01-28
Graphene The views, opinions and/or findings contained in this report are those of the author(s) and should not contrued as an official Department of the...ABSTRACT Final Report: Energy Guiding and Harvesting through Phonon-Engineered Graphene Report Title The work performed under this proposal was primarily...Justin Wu, Xinran Wang, Kristof Tahy, Debdeep Jena, Hongjie Dai, Eric Pop. Thermally Limited Current Carrying Ability of Graphene Nanoribbons
Indian Academy of Sciences (India)
a = b = 3.51 Å and c = 10.53 Å. The single-crystal sample of YN2B2C weighing. 2.26 g was mounted in a standard orange cryostat at LLB and in a closed-cycle .... perturbation approach was used for calculating properties of the lattice dynamics and electron-phonon coupling. Details can be found in R Heid and K-P Bohnen, ...
Phonon spectrum, mechanical and thermophysical properties of thorium carbide
Energy Technology Data Exchange (ETDEWEB)
Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Cientı´ficas y Técnicas (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Cientı´ficas y Técnicas (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina)
2013-06-15
In this work, we study, by means of density functional perturbation theory and the pseudopotential method, mechanical and thermophysical properties of thorium carbide. These properties are derived from the lattice dynamics in the quasi-harmonic approximation. The phonon spectrum of ThC presented in this article, to the best authors’ knowledge, have not been studied, neither experimentally, nor theoretically. We compare mechanical properties, volume thermal expansion and molar specific capacities with previous results and find a very good agreement.
Analysis of Bending Waves in Phononic Crystal Beams with Defects
Directory of Open Access Journals (Sweden)
Yongqiang Guo
2018-01-01
Full Text Available Existing investigations on imperfect phononic crystal beams mainly concern periodic multi-span beams carrying either one or two channel waves with random or deterministic disorder in span-length. This paper studies the two channel bending waves in phononic crystal beams consisting of many phases of materials with defects introduced as one structural segment having different cross-sectional dimensions or material parameters. The method of reverberation-ray matrix (MRRM based on the Timoshenko beam theory, which can conduct high-frequency analysis, is extended for the theoretical analysis of dispersion and transmission of bending waves. The supercell technique and the Floquet–Bloch theorem are adopted for modeling the dispersion characteristics, and the whole finite structural model is used to calculate the transmission spectra. Experimental measurements and numerical calculations are provided to validate the displacement transmission obtained by the proposed MRRM, with the effect of damping on transmission spectra being concerned. The high-frequency calculation applicability of the proposed MRRM is also confirmed by comparing the present results with the corresponding ones either using the transfer matrix method (TMM or MRRM based on Euler—Bernoulli beam theory. The influences of defect size, defect form, and unit-cell number on the transmission spectra and the band structures are discussed. The drawn conclusions may be useful for designing or evaluating the defected phononic crystal beams in bending wave control. In addition, our conclusions are especially potential for identifying the defect location through bending wave signals.
3-D phononic crystals with ultra-wide band gaps
Lu, Yan; Yang, Yang; Guest, James K.; Srivastava, Ankit
2017-01-01
In this paper gradient based topology optimization (TO) is used to discover 3-D phononic structures that exhibit ultra-wide normalized all-angle all-mode band gaps. The challenging computational task of repeated 3-D phononic band-structure evaluations is accomplished by a combination of a fast mixed variational eigenvalue solver and distributed Graphic Processing Unit (GPU) parallel computations. The TO algorithm utilizes the material distribution-based approach and a gradient-based optimizer. The design sensitivity for the mixed variational eigenvalue problem is derived using the adjoint method and is implemented through highly efficient vectorization techniques. We present optimized results for two-material simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC) crystal structures and show that in each of these cases different initial designs converge to single inclusion network topologies within their corresponding primitive cells. The optimized results show that large phononic stop bands for bulk wave propagation can be achieved at lower than close packed spherical configurations leading to lighter unit cells. For tungsten carbide - epoxy crystals we identify all angle all mode normalized stop bands exceeding 100%, which is larger than what is possible with only spherical inclusions. PMID:28233812
Three-dimensional phonon population anisotropy in silicon nanomembranes
Energy Technology Data Exchange (ETDEWEB)
McElhinny, Kyle M.; Gopalakrishnan, Gokul; Holt, Martin V.; Czaplewski, David A.; Evans, Paul G.
2017-07-01
Nanoscale single crystals possess modified phonon dispersions due to the truncation of the crystal. The introduction of surfaces alters the population of phonons relative to the bulk and introduces anisotropy arising from the breaking of translational symmetry. Such modifications exist throughout the Brillouin zone, even in structures with dimensions of several nanometers, posing a challenge to the characterization of vibrational properties and leading to uncertainty in predicting the thermal, optical, and electronic properties of nanomaterials. Synchrotron x-ray thermal diffuse scattering studies find that freestanding Si nanomembranes with thicknesses as large as 21 nm exhibit a higher scattering intensity per unit thickness than bulk silicon. In addition, the anisotropy arising from the finite thickness of these membranes produces particularly intense scattering along reciprocal-space directions normal to the membrane surface compared to corresponding in-plane directions. These results reveal the dimensions at which calculations of materials properties and device characteristics based on bulk phonon dispersions require consideration of the nanoscale size of the crystal.
Phonon-Limited-Linewidth of Brillouin Lasers at Cryogenic Temperatures
Suh, Myoung-Gyun; Yang, Qi-Fan; Vahala, Kerry J.
2017-10-01
Laser linewidth is of central importance in spectroscopy, frequency metrology, and all applications of lasers requiring high coherence. It is also of fundamental importance, because the Schawlow-Townes laser linewidth limit is of quantum origin. Recently, a theory of stimulated Brillouin laser (SBL) linewidth has been reported. While the SBL linewidth formula exhibits power and optical Q factor dependences that are identical to the Schawlow-Townes formula, a source of noise not present in conventional lasers, phonon occupancy of the Brillouin mechanical mode is predicted to be the dominant SBL linewidth contribution. Moreover, the quantum limit of the SBL linewidth is predicted to be twice the Schawlow-Townes limit on account of phonon participation. To help confirm this theory the SBL fundamental linewidth is measured at cryogenic temperatures in a silica microresonator. Its temperature dependence and the SBL linewidth theory are combined to predict the number of thermomechanical quanta at three temperatures. The result agrees with the Bose-Einstein phonon occupancy of the microwave-rate Brillouin mode in support of the SBL linewidth theory prediction.
Breakdown of Optical Phonons' Splitting in Two-Dimensional Materials.
Sohier, Thibault; Gibertini, Marco; Calandra, Matteo; Mauri, Francesco; Marzari, Nicola
2017-06-14
We investigate the long-wavelength dispersion of longitudinal and transverse optical phonon modes in polar two-dimensional materials, multilayers, and their heterostructures. Using analytical models and density-functional perturbation theory in a two-dimensional framework, we show that at variance with the three-dimensional case these modes are degenerate at the zone center but the macroscopic electric field associated with the longitudinal-optical modes gives rise to a finite slope at the zone center in their corresponding phonon dispersions. This slope increases linearly with the number of layers and it is determined solely by the Born effective charges of the material and the dielectric properties of the surrounding media. Screening from the environment can greatly reduce the slope splitting between the longitudinal and transverse optical modes and can be seen in the experimentally relevant case of boron nitride-graphene heterostructures. As the phonon momentum increases, the intrinsic screening properties of the two-dimensional material dictate the transition to a momentum-independent splitting similar to that of three-dimensional materials. These considerations are essential to understand electrical transport and optical coupling in two-dimensional systems.
Phonon-assisted absorption of excitons in Cu2O
Schöne, Florian; Stolz, Heinrich; Naka, Nobuko
2017-09-01
The basic theoretical foundation for the modeling of phonon-assisted absorption spectra in direct band-gap semiconductors, introduced by Elliott 60 years ago [R. J. Elliott, Phys. Rev. 108, 1384 (1957), 10.1103/PhysRev.108.1384] using second order perturbation theory, results in a square root shaped dependency close to the absorption edge. A careful analysis of the experiments [N. Naka et al., Jpn. J. Appl. Phys. 44, 5096 (2005), 10.1143/JJAP.44.5096] reveals that for the yellow S excitons in Cu2O the lineshape does not follow that square root dependence. The reexamination of the theory shows that the basic assumptions of constant matrix elements and constant energy denominators is invalid for semiconductors with dominant exciton effects like Cu2O , where the phonon-assisted absorption proceeds via intermediate exciton states. The overlap between these and the final exciton states strongly determines the dependence of the absorption on the photon energy. To describe the experimental observed line shape of the indirect absorption of the yellow S exciton states we find it necessary to assume a momentum dependent deformation potential for the optical phonons.
Unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials
DEFF Research Database (Denmark)
Willatzen, Morten; Wang, Zhong Lin
2015-01-01
A unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials is presented whereby the lattice displacement vector and the internal ionic displacement vector are found simultaneously. It is shown that phonon couplings exist in pairs only; either between the electric...... potential and the lattice displacement coordinate perpendicular to the phonon wave vector or between the two other lattice displacement components. The former leads to coupled acousto-optical phonons by virtue of the piezoelectric effect. We then establish three new conjectures that entirely stem from...... piezoelectricity in a cubic structured material slab. First, it is shown that isolated optical phonon modes generally cannot exist in piezoelectric cubic slabs. Second, we prove that confined acousto-optical phonon modes only exist for a discrete set of in-plane wave numbers in piezoelectric cubic slabs. Third...
Zhang, Yu; Yam, ChiYung; Chen, GuanHua
2015-04-28
A time-dependent inelastic electron transport theory for strong electron-phonon interaction is established via the equations of motion method combined with the small polaron transformation. In this work, the dissipation via electron-phonon coupling is taken into account in the strong coupling regime, which validates the small polaron transformation. The corresponding equations of motion are developed, which are used to study the quantum interference effect and phonon-induced decoherence dynamics in molecular junctions. Numerical studies show clearly quantum interference effect of the transport electrons through two quasi-degenerate states with different couplings to the leads. We also found that the quantum interference can be suppressed by the electron-phonon interaction where the phase coherence is destroyed by phonon scattering. This indicates the importance of electron-phonon interaction in systems with prominent quantum interference effect.
Raman selection rule of surface optical phonon in ZnS nanobelts
Ho, Chih-Hsiang
2016-02-18
We report Raman scattering results of high-quality wurtzite ZnS nanobelts (NBs) grown by chemical vapor deposition. In Raman spectrum, the ensembles of ZnS NBs exhibit first order phonon modes at 274 cm-1 and 350 cm-1, corresponding to A1/E1 transverse optical and A1/E1 longitudinal optical phonons, in addition with strong surface optical (SO) phonon mode at 329 cm-1. The existence of SO band is confirmed by its shift with different surrounding dielectric media. Polarization dependent Raman spectrum was performed on a single ZnS NB and for the first time SO phonon band has been detected on a single nanobelt. Different selection rules of SO phonon modeshown from their corresponding E1/A1 phonon modeswere attributed to the anisotropic translational symmetry breaking on the NB surface.
Zhang, Zu-Quan; Lü, Jing-Tao
2017-09-01
Using the nonequilibrium Green's function method, we consider heat transport in an insulating ferromagnetic spin chain model with spin-phonon interaction under an external magnetic field. Employing the Holstein-Primakoff transformation to the spin system, we treat the resulted magnon-phonon interaction within the self-consistent Born approximation. We find the magnon-phonon coupling can change qualitatively the magnon thermal conductance in the high-temperature regime. At a spectral mismatched ferromagnetic-normal insulator interface, we also find thermal rectification and negative differential thermal conductance due to the magnon-phonon interaction. We show that these effects can be effectively tuned by the external applied magnetic field, a convenient advantage absent in anharmonic phonon and electron-phonon systems studied before.
Electron LO-phonon interaction in wurtzite GaN quantum wells under a magnetic field
Cao, J. C.; Lü, J. T.; Guo, Qixin
2008-08-01
We calculate the electron-LO-phonon relaxation rates in wurtzite GaN quantum wells in the presence of a magnetic field parallel to the growth direction. Using the dielectric continuum model (DCM), we are able to include contributions from both the interface and the quasi-confined phonon modes. The relaxation rate expression takes the phonon dispersion into account, and is applicable to all phonon modes. We find that the relaxation rates show strong oscillations as a function of the applied magnetic field. In relatively wide (8 nm) quantum wells, the inclusion of interface phonon mode decreases this oscillation amplitude. But in thin wells (5 nm), the interface phonon mode is of the same importance as the quasi-confined mode, and it strongly modifies the oscillation behavior.
Quasiparticle properties of a coupled quantum-wire electron-phonon system
DEFF Research Database (Denmark)
Hwang, E. H.; Hu, Ben Yu-Kuang; Sarma, S. Das
1996-01-01
We study leading-order many-body effects of longitudinal-optical phonons on electronic properties of one-dimensional quantum-wire systems. We calculate the quasiparticle properties of a weakly polar one-dimensional electron gas in the presence of both electron-phonon and electron-electron...... interactions, The leading-order dynamical screening approximation (GW approximation) is used to obtain the electron self-energy, the quasiparticle spectral function, and the quasiparticle damping rate in our calculation by treating electrons and phonons on an equal footing. Our theory includes effects (within...... the random-phase approximation) of Fermi statistics, Landau damping, plasmon-phonon mode coupling, phonon renormalization, dynamical screening, and impurity scattering. In general, electron-electron and electron-phonon many-body renormalization effects are found to be nonmultiplicative and nonadditive in our...
A 1D Optomechanical crystal with a complete phononic band gap
Gomis-Bresco, J; Oudich, M; El-Jallal, S; Griol, A; Puerto, D; Chavez, E; Pennec, Y; Djafari-Rouhani, B; Alzina, F; Martínez, A; Torres, C M Sotomayor
2014-01-01
Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and coupling of optical waves and mechanical vibrations at the nanoscale. Amongst the different physical implementations,optomechanical (OM) crystals built on semiconductor slabs are particularly interesting since they enable the integration and manipulation of multiple OM elements in a single chip and provide GHz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and GHz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap at the frequencies of interest, which in principle should allow longer dephasing time, since acoustic leakage is minimized. In this work we demonstrate the excitation of acoustic modes in a 1D OM crystal properly designed to display a full phononic bandgap for acoustic modes at about 4 GHz. The confined phonons have an OM coupling rangin...
Hori, Takuma; Shiomi, Junichiro
2013-03-01
Nanostructuring are efficient process to lower the lattice thermal conductivity and thus enhance thermoelectric performance of semiconducting materials. Here, detailed knowledge of phonon transport properties in the nanostructures is needed for prediction of performance and/or optimization of structures. The approach to solve the linearized phonon Boltzmann transport equations stochastically by Monte Carlo method has been demonstrated to be useful to obtain phonon transport properties in mesoscale and complex structures. In this study, we have performed the Monte Carlo simulations to investigate phonon transport properties in nanostructured thermoelectric materials. With the mode-dependent bulk phonon transport properties obtained by first-principles-based calculations, the Monte Carlo simulations are performed to investigate the influence of nanostructure length-scales on the mode-dependent lattice thermal conductivity and its sensitivity to interfacial phonon transmission. This work is partially supported by the Japan Society for the Promotion of Science and JST PRESTO.
Nonlinear phononics and structural control of strongly correlated materials
Energy Technology Data Exchange (ETDEWEB)
Mankowsky, Roman
2016-01-20
Mid-infrared light pulses can be used to resonantly excite infrared-active vibrational modes for the phase control of strongly correlated materials on subpicosecond timescales. As the energy is transferred directly into atomic motions, dissipation into the electronic system is reduced, allowing for the emergence of unusual low energy collective properties. Light-induced superconductivity, insulator-metal transitions and melting of magnetic order demonstrate the potential of this method. An understanding of the mechanism, by which these transitions are driven, is however missing. The aim of this work is to uncover this process by investigating the nonlinear lattice dynamics induced by the excitation and to elucidate their contribution to the modulation of collective properties of strongly correlated materials. The first signature of nonlinear lattice dynamics was reported in the observation of coherent phonon oscillations, resonant with the excitation of an infrared-active phonon mode in a manganite. This nonlinear phononic coupling can be described within a model, which predicts not only oscillatory coherent phonons dynamics but also directional atomic displacements along the coupled modes on average, which could cause the previously observed transitions. We verified this directional response and quantified the anharmonic coupling constant by tracing the atomic motions in a time-resolved hard X-ray diffraction experiment with sub-picometer spatial and femtosecond temporal resolution. In a subsequent study, we investigated the role of nonlinear lattice dynamics in the emergence of superconductivity far above the equilibrium transition temperature, an intriguing effect found to follow lattice excitation of YBa{sub 2}Cu{sub 3}O{sub 6+x}. By combining density functional theory (DFT) calculations of the anharmonic coupling constants with time-resolved X-ray diffraction experiments, we identified a structural rearrangement, which appears and decays with the same temporal
Phonon Sensor Dynamics for Cryogenic Dark Matter Search Experiment
Energy Technology Data Exchange (ETDEWEB)
Yen, Jeffrey [Stanford Univ., CA (United States)
2015-01-01
Understanding the quasiparticle diffusion process inside sputtered aluminum (Al thin films (~ 0.1-1 μm is critical for the Cryogenic Dark Matter Search (CDMS experiment to further optimize its detectors to directly search for dark matter. An initial study with Al films was undertaken by our group ~ 20 years ago, but some important questions were not answered at the time. This thesis can be considered a continuation of that critical study. The CDMS experiment utilizes high purity silicon and germanium crystals to simultaneously measure ionization and phonons created by particle interactions. In addition to describing some of the rich physics involved in simultaneously detecting ionization and phonons with a CDMS detector, this thesis focuses on the detailed physics of the phonon sensors themselves, which are patterned onto CDMS detector surfaces. CDMS detectors use thin sputtered Al films to collect phonon energy when it propagates to the surfaces of the detector crystals. The phonon energy breaks Cooper pairs and creates quasiparticles (qps). These qps diffuse until they get trapped in an proximitized “overlap” region where lower-Tc tungsten films connect to the Al film. These tungsten films are the transition edge sensors (W-TESs CDMS uses to readout phonon signals. We performed a wide range of experiments using several sets of test devices designed and fabricated specifically for this work. The devices were used mostly to study quasiparticle (qp transport in Al films and qp transmission through Al/W interfaces. The results of this work are being used to optimize the design of detectors for SuperCDMS SNOLAB. This thesis is intended for CDMS collaborators who are interested in knowing more about the detailed fundamentals of how our phonon sensors work so they can take full advantage of their benefits. However, this work can also be read by general readers who are interested in particle detection using TES technology. This thesis contains eight chapters. The
2017-06-12
i.e., they partially convert different phonon modes into graphene after the transmission. For instance, the longitudinal acoustic (LA) mode incident...Unclassified b. ABSTRACT Unclassified c. THIS PAGE Unclassified Kurt Eyink 19b. TELEPHONE NUMBER (Include Area Code ) (937) 656-5710...packet method. Surprisingly, we have observed phonon mode conversion behavior for all incident phonon modes from CNT, i.e., they partially convert
Yang, Zhenshan; Zhang, Xia; Wang, Minghong; Bai, Chenglin
2017-07-01
We show that an entangled traveling photon-phonon pair can be generated in a resonator-waveguide structure via optomechanical interaction. We employ the "backward Heisenberg picture" approach to write an analytic expression for the output quantum state, from which the generation efficiency and the entanglement of the photon-phonon pair are calculated. We find that the photon-phonon entanglement can be manipulated by adjusting the spectral width of the input pulse.
Wang, Lei; Cai, Wei; Zhang, Xinzheng; Xu, Jingjun
2014-01-01
The interaction between graphene plasmons and surface phonons of a semiconductor substrate is investigated, which can be efficiently controlled by the carrier injection of the substrate. The energy and lifetime of surface phonons in a substrate depend a lot on the carrier concentration, which provides a new machanism to tune plasmon-phonon coupled modes (PPCMs). More specifically, the dispersion and lifetime of PPCMs can be controlled by the carrier concentration change of the substrate. The ...
Four-phonon scattering significantly reduces intrinsic thermal conductivity of solids
Feng, Tianli; Lindsay, Lucas; Ruan, Xiulin
2017-10-01
For decades, the three-phonon scattering process has been considered to govern thermal transport in solids, while the role of higher-order four-phonon scattering has been persistently unclear and so ignored. However, recent quantitative calculations of three-phonon scattering have often shown a significant overestimation of thermal conductivity as compared to experimental values. In this Rapid Communication we show that four-phonon scattering is generally important in solids and can remedy such discrepancies. For silicon and diamond, the predicted thermal conductivity is reduced by 30% at 1000 K after including four-phonon scattering, bringing predictions in excellent agreement with measurements. For the projected ultrahigh-thermal conductivity material, zinc-blende BAs, a competitor of diamond as a heat sink material, four-phonon scattering is found to be strikingly strong as three-phonon processes have an extremely limited phase space for scattering. The four-phonon scattering reduces the predicted thermal conductivity from 2200 to 1400 W/m K at room temperature. The reduction at 1000 K is 60%. We also find that optical phonon scattering rates are largely affected, being important in applications such as phonon bottlenecks in equilibrating electronic excitations. Recognizing that four-phonon scattering is expensive to calculate, in the end we provide some guidelines on how to quickly assess the significance of four-phonon scattering, based on energy surface anharmonicity and the scattering phase space. Our work clears the decades-long fundamental question of the significance of higher-order scattering, and points out ways to improve thermoelectrics, thermal barrier coatings, nuclear materials, and radiative heat transfer.
Quantum Theory of Conditional Phonon States in a Dual-Pumped Raman Optical Frequency Comb
Mondloch, Erin
In this work, we theoretically and numerically investigate nonclassical phonon states created in the collective vibration of a Raman medium by the generation of a dual-pumped Raman optical frequency comb in an optical cavity. This frequency comb is generated by cascaded Raman scattering driven by two phase-locked pump lasers that are separated in frequency by three times the Raman phonon frequency. We characterize the variety of conditioned phonon states that are created when the number of photons in all optical frequency modes except the pump modes are measured. Almost all of these conditioned phonon states are extremely well approximated as three-phonon-squeezed states or Schrodinger-cat states, depending on the outcomes of the photon number measurements. We show how the combinations of first-, second-, and third-order Raman scattering that correspond to each set of measured photon numbers determine the fidelity of the conditioned phonon state with model three-phonon-squeezed states and Schrodinger-cat states. All of the conditioned phonon states demonstrate preferential growth of the phonon mode along three directions in phase space. That is, there are three preferred phase values that the phonon state takes on as a result of Raman scattering. We show that the combination of Raman processes that produces a given set of measured photon numbers always produces phonons in multiples of three. In the quantum number-state representation, these multiples of three are responsible for the threefold phase-space symmetry seen in the conditioned phonon states. With a semiclassical model, we show how this three-phase preference can also be understood in light of phase correlations that are known to spontaneously arise in single-pumped Raman frequency combs. Additionally, our semiclassical model predicts that the optical modes also grow preferentially along three phases, suggesting that the dual-pumped Raman optical frequency comb is partially phase-stabilized.
Bloch wave deafness and modal conversion at a phononic crystal boundary
Vincent Laude; Rayisa P. Moiseyenko; Sarah Benchabane; Nico F. Declercq
2011-01-01
International audience; We investigate modal conversion at the boundary between a homogeneous incident medium and a phononic crystal, with consideration of the impact of symmetry on the excitation of Bloch waves. We give a quantitative criterion for the appearance of deaf Bloch waves, which are antisymmetric with respect to a symmetry axis of the phononic crystal, in the frame of generalized Fresnel formulas for reflection and transmission at the phononic crystal boundary. This criterion is u...
Effect of electron-phonon interaction on the impurity binding energy in a quantum wire
Chen, Yueh-Nan; Chuu, Der-San; Lin, Yuh-Kae
2003-01-01
The effect of electron-optical phonon interaction on the hydrogenic impurity binding energy in a cylindrical quantum wire is studied. By using Landau and Pekar variational method, the hamiltonian is separated into two parts which contain phonon variable and electron variable respectively. A perturbative-variational technique is then employed to construct the trial wavefunction for the electron part. The effect of confined electron-optical phonon interaction on the binding energies of the grou...
Zone centre phonons in high Tc CaBi 2Sr 2Cu 2O 8
Gupta, H. C.
1988-10-01
The zone centre phonons have been investigated in CaBi 2Sr 2Cu 2O 8 using radial and tangential force constants. It is found that the phonons due to Bi O layers do not play an important role from the point of view of superconductivity. The calculation provides an information on the phonons which may be important for explaining the high temperature superconductivity.
Three-phonon Umklapp process in zigzag single-walled carbon nanotubes
Xiao, Y; Cao, J X; Ding, J W
2003-01-01
The rate of relaxation of zigzag single-walled carbon nanotubes is calculated by consideration of three-phonon Umklapp process. The results show that the relaxation rate increases exponentially with phonon frequency at low frequency. The linear dependence of the relaxation rate on temperature is obtained. It is shown that the value of the phonon mean free path reaches a few micrometres, which is consistent with the estimated experimental result. (letter to the editor)
Hot-phonon lifetime in AlGaN/GaN at a high lattice temperature
Matulionis, A.; Liberis, J.; Ardaravicius, L.; Eastman, L. F.; Shealy, J. R.; Vertiatchikh, A.
2004-04-01
A microwave noise technique is applied to study hot phonons in a biased two-dimensional AlGaN/GaN channel. The longitudinal optical (LO)-phonon-conversion lifetime is estimated from the measured dependence of hot-electron temperature on supplied power. At a lattice temperature of 373 K, the mean value of the effective LO-phonon lifetime (350 fs) is close to the value obtained at room temperature.
Resonant exciton-phonon coupling in ZnO nanorods at room temperature
Directory of Open Access Journals (Sweden)
Soumee Chakraborty
2011-09-01
Full Text Available Vibronic and optoelectronic properties, along with detailed studies of exciton-phonon coupling at room temperature (RT for random and aligned ZnO nanorods are reported. Excitation energy dependent Raman studies are performed for detailed analysis of multi-phonon processes in the nanorods. We report here the origin of coupling between free exciton and its associated phonon replicas, including its higher order modes, in the photoluminescence spectra at RT. Resonance of excitonic electron and resonating first order zone center LO phonon, invoked strongly by Frolich interaction, are made responsible for the observed phenomenon.
Resonant generation of nonequilibrium phonons in GaAs/AlAs quantum wells via intersubband scattering
Energy Technology Data Exchange (ETDEWEB)
Su, Z.P.; Ruf, T.; Wald, K.R.; Yu, P.Y. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States). Materials Sciences Div.; Chan, K.T. [Chinese Univ. of Hong Kong (Hong Kong)
1994-07-01
The authors have studied the resonant intersubband scattering of optical phonons or RISOP theoretically and by picosecond scattering. Experimentally, the authors have established a way to determine phonon occupancy in quantum wells. The model calculation shows that a significant amount of long wavelength LO phonons are generated by RISOP in GaAs/A1As quantum wells. However, they measured a much smaller phonon population than predicted. The discrepancy can be explained by a breakdown of in-plane wavevector conservation due to interface roughness.
Theory of phonon properties in doped and undoped CuO nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Bahoosh, S.G. [Institute of Physics, Martin-Luther-University, D-06099 Halle (Germany); Apostolov, A.T. [University of Architecture, Civil Engineering and Geodesy Faculty of Hydrotechnics, Department of Physics, 1, Hristo Smirnenski Blvd., 1046 Sofia (Bulgaria); Apostolova, I.N. [University of Forestry, Faculty of Forest Industry, 10, Kl. Ohridsky Blvd., 1756 Sofia (Bulgaria); Wesselinowa, J.M., E-mail: julia@phys.uni-sofia.bg [University of Sofia, Department of Physics, 5 J. Bouchier Blvd., 1164 Sofia (Bulgaria)
2012-07-02
We have studied the phonon properties of CuO nanoparticles and have shown the importance of the anharmonic spin–phonon interaction. The Raman peaks of CuO nanoparticles shift to lower frequency and become broader as the particle size decreases in comparison with those of bulk CuO crystals owing to size effects. By doping with different ions, in dependence of their radius compared to the host ionic radius the phonon energies ω could be reduced or enhanced. The phonon damping is always enhanced through the ion doping effects. -- Highlights: ► The phonon properties of CuO nanoparticles are studied using a miscroscopic model. ► The phonon energy decreases whereas the damping increases with decreasing of particle size. ► It is shown the importance of the anharmonic spin–phonon interaction. ► By doping with RE-ions the phonon energy is reduced, whereas with TM-ions it is enhanced. ► The phonon damping is always enhanced through the ion doping effects.
Experimental evidence of zone-center optical phonon softening by accumulating holes in thin Ge
Energy Technology Data Exchange (ETDEWEB)
Kabuyanagi, Shoichi; Nishimura, Tomonori; Yajima, Takeaki; Toriumi, Akira [Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656 (Japan)
2016-01-15
We discuss the impact of free carriers on the zone-center optical phonon frequency in germanium (Ge). By taking advantage of the Ge-on-insulator structure, we measured the Raman spectroscopy by applying back-gate bias. Phonon softening by accumulating holes in Ge film was clearly observed. This fact strongly suggests that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than the dopant atom counterpart. Furthermore, we propose that the free carrier effect on phonon softening is simply understandable from the viewpoint of covalent bonding modification by free carriers.
Effect of the Substrate on Phonon Properties of Graphene Estimated by Raman Spectroscopy
Tivanov, M. S.; Kolesov, E. A.; Korolik, O. V.; Saad, A. M.; Komissarov, I. V.
2018-01-01
Low-temperature Raman studies of supported graphene are presented. A linear temperature dependence of 2D peak linewidths was observed with the coefficients of 0.036 and 0.033 cm^{-1}/K for graphene on copper and glass substrates, respectively, while G peak linewidths remained unchanged throughout the whole temperature range. The different values observed for graphene on glass and copper substrates were explained in terms of the substrate effect on phonon-phonon and electron-phonon interaction properties of the material. The results of the present study can be used to consider substrate effects on phonon transport in graphene for nanoelectronic device engineering.
Band gaps and cavity modes in dual phononic and photonic strip waveguides
Directory of Open Access Journals (Sweden)
Y. Pennec
2011-12-01
Full Text Available We discuss theoretically the simultaneous existence of phoxonic, i.e., dual phononic and photonic, band gaps in a periodic silicon strip waveguide. The unit-cell of this one-dimensional waveguide contains a hole in the middle and two symmetric stubs on the sides. Indeed, stubs and holes are respectively favorable for creating a phononic and a photonic band gap. Appropriate geometrical parameters allow us to obtain a complete phononic gap together with a photonic gap of a given polarization and symmetry. The insertion of a cavity inside the perfect structure provides simultaneous confinement of acoustic and optical waves suitable to enhance the phonon-photon interaction.
Thermal Transport of Flexural and In-Plane Phonons Modulated by Bended Graphene Nanoribbons
Directory of Open Access Journals (Sweden)
Changning Pan
2016-01-01
Full Text Available Ballistic thermal transport properties are investigated comparatively for out-of-plane phonon modes (FPMs and in-plane phonon modes (IPMs in bended graphene nanoribbons (GNRs. Results show that the phonon modes transports can be modulated separately by the phonon dispersion mismatch between armchair and zigzag GNRs in considered system. The contribution of FPMs to total thermal conductance is larger than 50% in low temperature for perfect GNRs. But it becomes less than 20% in the bended GNRs. Furthermore, this contribution can be modulated by changing the structural parameters of the bended GNRs. The result is useful for the design of thermal or thermoelectric nanodevices in future.
Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons
Hussain, A.
2010-06-17
There have been several reports of phase-dependent noise in time-domain reflectivity studies of optical phonons excited by femtosecond laser pulses in semiconductors, semimetals, and superconductors. It was suggested that such behavior is associated with the creation of squeezed phonon states although there is no theoretical model that directly supports such a proposal. We have experimentally re-examined the studies of phonons in bismuth and gallium arsenide, and find no evidence of any phase-dependent noise signature associated with the phonons. We place an upper limit on any such noise at least 40–50 dB lower than previously reported.
National Research Council Canada - National Science Library
Margine, E R; Lambert, Henry; Giustino, Feliciano
2016-01-01
Using the ab initio anisotropic Eliashberg theory including Coulomb interactions, we investigate the electron-phonon interaction and the pairing mechanism in the recently-reported superconducting Ca...
Nonlocal electron-phonon coupling in the pentacene crystal: Beyond the Γ-point approximation
Yi, Yuanping
2012-01-01
There is currently increasing interest in understanding the impact of the nonlocal (Peierls-type) electron-phonon mechanism on charge transport in organic molecular semiconductors. Most estimates of the non-local coupling constants reported in the literature are based on the Γ-point phonon modes. Here, the influence of phonon modes spanning the entire Brillouin zone (phonon dispersion) on the nonlocal electron-phonon couplings is investigated for the pentacene crystal. The phonon modes are obtained by using a supercell approach. The results underline that the overall nonlocal couplings are substantially underestimated by calculations taking sole account of the phonons at the Γ point of the unit cell. The variance of the transfer integrals based on Γ-point normal-mode calculations at room temperature is underestimated in some cases by 40% for herringbone-type dimers and by over 80% for cofacial dimers. Our calculations show that the overall coupling is somewhat larger for holes than for electrons. The results also suggest that the interactions of charge carriers (both electrons and holes) with acoustic and optical phonons are comparable. Therefore, an adequate description of the charge-transport properties in pentacene and similar systems requires that these two electron-phonon coupling mechanisms be treated on the same footing. © 2012 American Institute of Physics.
Room temperature ferromagnetism and phonon properties of pure and doped TiO{sub 2} nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Apostolova, I.N. [University of Forestry, Faculty of Forest Industry, 10, Kl. Ohridsky Blvd., 1756 Sofia (Bulgaria); Apostolov, A.T. [University of Architecture, Civil Engineering and Geodesy, Faculty of Hydrotechnics, Department of Physics, 1, Hristo Smirnenski Blvd., 1046 Sofia (Bulgaria); Bahoosh, S.G. [Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany); Wesselinowa, J.M., E-mail: julia@phys.uni-sofia.bg [University of Sofia, Department of Physics, 5, J. Bouchier Blvd., 1164 Sofia (Bulgaria)
2014-03-15
We have considered the origin of RTFM in TiO{sub 2} nanoparticles (NPs). Further we have studied the properties of the E{sub g1} phonon mode. The phonon frequency of anatase TiO{sub 2} NPs increases whereas in the case of rutile TiO{sub 2} NPs it decreases as the particle size decreases. The phonon damping is always enhanced in the nanosized materials. The hardening of the E{sub g1} mode and the softening of the E{sub g3} mode in anatase TiO{sub 2} NPs could be explained with the different anharmonic spin–phonon interaction constants of these modes. The doping effects with different transition metal ions on the E{sub g1} phonon mode are also discussed. - Highlights: • The origin of RTFM in TiO{sub 2} nanoparticles is investigated. • With decreasing of particle size the phonon frequency of anatase and rutile TiO{sub 2} NPs increases and decreases, respectively. • This could be explained with the different anharmonic spin–phonon interaction constants of these modes. • The phonon damping is always enhanced in the nanosized materials. • The doping effects with different transition metal ions on the E{sub g1} phonon mode are also discussed.
Self-consistent calculation of phonon gyromagnetic ratios in 208Pb
Saperstein, E. E.; Kamerdzhiev, S. P.; Krewald, S.; Speth, J.; Tolokonnikov, S. V.
2014-01-01
Within the Theory of Finite Fermi Systems the gyromagnetic ratios g {/L ph } of all low-lying phonons in 208Pb are calculated. The input data, i.e., single-particle energies, single-particle wavefunctions, and the ph interaction are derived from the Energy Density Functional by Fayans et al. For the 3{1/-} phonon which is the most collective state, the g {/L ph } value is close to the prediction of the collective Bohr-Mottelson (BM) model. Gyromagnetic ratios of other phonons that are included in our calculations, two 5- states and six positive parity phonons, differ significantly from the BM model prediction.
Phonons in Solid Hydrogen and Deuterium Studied by Inelastic Coherent Neutron Scattering
DEFF Research Database (Denmark)
Nielsen, Mourits
1973-01-01
Phonon dispersion relations have been measured by coherent neutron scattering in solid para-hydrogen and ortho-deuterium. The phonon energies are found to be nearly equal in the two solids, the highest energy in each case lying close to 10 meV. The pressure and temperature dependence of the phonon...... energies have been measured in ortho-deuterium and the lattice change determined by neutron diffraction. When a pressure of 275 bar is applied, the phonon energies are increased by about 10%, and heating the crystal to near the melting point decreases them by about 7%. The densities of states, the specific...
Acoustic phonons in the hexagonal perovskite CsNiCl3 around the Gamma-point
DEFF Research Database (Denmark)
Visser, D.; Monteith, A.R.; Rønnow, H.M.
2000-01-01
The acoustic phonon dispersion curves of the hexagonal perovskite CsNiCl3 were measured at room temperature in the vicinity of the Gamma-point along the [0 0 1] and [1 1 0] directions. The derived velocity of sound values for the longitudinal and transverse acoustic phonons are compared with the ......The acoustic phonon dispersion curves of the hexagonal perovskite CsNiCl3 were measured at room temperature in the vicinity of the Gamma-point along the [0 0 1] and [1 1 0] directions. The derived velocity of sound values for the longitudinal and transverse acoustic phonons are compared...
Korkusinski, M.; Studenikin, S. A.; Aers, G.; Granger, G.; Kam, A.; Sachrajda, A. S.
2017-02-01
Manipulating qubits via electrical pulses in a piezoelectric material such as GaAs can be expected to generate incidental acoustic phonons. In this Letter we determine theoretically and experimentally the consequences of these phonons for semiconductor spin qubits using Landau-Zener-Stückelberg interferometry. Theoretical calculations predict that phonons in the presence of the spin-orbit interaction produce both phonon-Rabi fringes and accelerated evolution at the singlet-triplet anticrossing. Observed features confirm the influence of these mechanisms. Additionally, evidence is found that the pulsed gates themselves act as phonon cavities increasing the influence of phonons under specific resonant conditions.
Synthesis and characterization of thermotropic liquid crystalline ...
Indian Academy of Sciences (India)
The synthesised mesogens were characterized by different techniques including nuclear magnetic resonance and Fourier transform infrared spectroscopy. Liquid crystalline polymers (LCPs) were synthesised using pyromellitic dianhydride and 4-[(4-aminobenzylidene)amino]aniline or 4-aminophenyl-4-aminobenzoate.
Syntheses, molecular and crystalline architectures, and ...
Indian Academy of Sciences (India)
Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base. SUBHASIS ROYa, SOMNATH CHOUBEYa, SUMITAVA KHANa, KISHALAY BHARa,. PARTHA MITRAb and BARINDRA ...
Optical waveguides in hard crystalline materials
Pollnau, Markus
2005-01-01
The recent results of our research group and collaborators in the field of fabrication, characterization, and applications of optical waveguides in hard crystalline materials, specifically in sapphire and Ti:sapphire, are reviewed.
High-efficiency crystalline silicon technology development
Prince, M. B.
1984-01-01
The rationale for pursuing high efficiency crystalline silicon technology research is discussed. Photovoltaic energy systems are reviewed as to their cost effectiveness and their competitiveness with other energy systems. The parameters of energy system life are listed and briefly reviewed.
Metal Organic Framework: Crystalline Stacked Molecular Containers
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 19; Issue 12. Metal Organic Framework: Crystalline Stacked Molecular Containers. Ramanathan Vaidhyanathan. General Article Volume 19 Issue 12 December 2014 pp 1147-1157 ...
Nanoparticle-Liquid Crystalline Elastomer Composites
Yan Ji; Terentjev, Eugene M.; Marshall, Jean E.
2012-01-01
Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat and the resulting thermal actuation act by promoting entropic disorder, as does the addition of solvents. Photo-isomerization is another mechanism of actuation, reducing th...
Energy Technology Data Exchange (ETDEWEB)
Chen, Xuliang [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China); Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Yang, Zhaorong, E-mail: zryang@issp.ac.cn [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China); Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China)
2016-05-15
Frustration makes a tremendous amount of degenerate ground states which provides no energy scale of its own. Any perturbation has to be considered strong and fascinating phenomena may be emergent upon relieving of frustration. Here, we report the evolution of spin phonon coupling in the frustrated spinel system Zn{sub 1−x}Cd{sub x}Cr{sub 2}Se{sub 4} (0 ≤ x ≤ 1) from magnetization, specific heat and thermal conductivity. Our results give clear evidences that the spin-orientated structural transitions decay rapidly as x going from 0 to 0.4 while the correlations between spin and lattice degrees of freedom for 0.6 ≤ x ≤ 1 become weak and can be explained in terms of the traditional magnetostriction effect. In addition, for 0 ≤ x ≤ 0.4 thermal carriers reveal strong scattering from spin fluctuations in the vicinity of T{sub N} owing to strong frustration, in stark contrast with those for 0.6 ≤ x ≤ 1 where traditional phonon-like heat conduction behaviors are observed. Moreover, it is shown that a moderate applied magnetic field can drive readily the fluctuations-scattered thermal conductivity toward traditional phonon-like one as observed in CdCr{sub 2}Se{sub 4}, reaching about 30% for x = 0.4 at 25 K in 1 T. Such strong field-sensitive effects may introduce new promising functionalities for potential applications.
Low-pressure phase diagram of crystalline benzene from quantum Monte Carlo
Azadi, Sam
2016-01-01
We study the low-pressure (0 to 10 GPa) phase diagram of crystalline benzene using quantum Monte Carlo (QMC) and density functional theory (DFT) methods. We consider the $Pbca$, $P4_32_12$, and $P2_1/c$ structures as the best candidates for phase I and phase II. We perform diffusion quantum Monte Carlo (DMC) calculations to obtain accurate static phase diagrams as benchmarks for modern van der Waals density functionals. We use density functional perturbation theory to compute phonon contribution in the free-energy calculations. Our DFT enthalpy-pressure phase diagram indicates that the $Pbca$ and $P2_1/c$ structures are the most stable phases within the studied pressure range. The DMC Gibbs free-energy calculations predict that the room temperature $Pbca$ to $P2_1/c$ phase transition occurs at 2.1(1) GPa. This prediction is consistent with available experimental results at room temperature. Our DMC calculations show an estimate of 50.6$\\pm$0.5 kJ/mol for crystalline benzene lattice energy.
Determining volcanic eruption styles on Earth and Mars from crystallinity measurements.
Wall, Kellie T; Rowe, Michael C; Ellis, Ben S; Schmidt, Mariek E; Eccles, Jennifer D
2014-10-03
Both Earth and Mars possess different styles of explosive basaltic volcanism. Distinguishing phreatomagmatic eruptions, driven by magma-water interaction, from 'magmatic' explosive eruptions (that is, strombolian and plinian eruptions) is important for determining the presence of near-surface water or ice at the time of volcanism. Here we show that eruption styles can be broadly identified by relative variations in groundmass or bulk crystallinity determined by X-ray diffraction. Terrestrial analogue results indicate that rapidly quenched phreatomagmatic ejecta display lower groundmass crystallinity (eruptions (>40%). Numerical modelling suggests Martian plinian eruptive plumes moderate cooling, allowing 20-30% syn-eruptive crystallization, and thus reduce the distinction between eruption styles on Mars. Analysis of Mars Curiosity rover CheMin X-ray diffraction results from Gale crater indicate that the crystallinity of Martian sediment (52-54%) is similar to pyroclastic rocks from Gusev crater, Mars, and consistent with widespread distribution of basaltic strombolian or plinian volcanic ejecta.
Determining volcanic eruption styles on Earth and Mars from crystallinity measurements
Wall, Kellie T.; Rowe, Michael C.; Ellis, Ben S.; Schmidt, Mariek E.; Eccles, Jennifer D.
2014-10-01
Both Earth and Mars possess different styles of explosive basaltic volcanism. Distinguishing phreatomagmatic eruptions, driven by magma-water interaction, from ‘magmatic’ explosive eruptions (that is, strombolian and plinian eruptions) is important for determining the presence of near-surface water or ice at the time of volcanism. Here we show that eruption styles can be broadly identified by relative variations in groundmass or bulk crystallinity determined by X-ray diffraction. Terrestrial analogue results indicate that rapidly quenched phreatomagmatic ejecta display lower groundmass crystallinity (40%). Numerical modelling suggests Martian plinian eruptive plumes moderate cooling, allowing 20-30% syn-eruptive crystallization, and thus reduce the distinction between eruption styles on Mars. Analysis of Mars Curiosity rover CheMin X-ray diffraction results from Gale crater indicate that the crystallinity of Martian sediment (52-54%) is similar to pyroclastic rocks from Gusev crater, Mars, and consistent with widespread distribution of basaltic strombolian or plinian volcanic ejecta.
Coupling Nuclear Induced Phonon Propagation with Conversion Electron Moessbauer Spectroscopy
2015-06-18
electric current would be oscillated to create pole flipping in the stainless steel 85 that would induce phonons. The frequency of the...Source 168.3 22 Pre-mix He-3%CH4 1200V 44 2” SS310 Rod 241 Am Source flipped – Figure 24 (b) (A) 218.1 (B) 383.4 (C) 459.9 (D...hours, respectively. But Run34 flipped the bar around from surface 1 to surface 2 to see if there was an inhomogeneity in the material from one
Fast identification of rubrene polymorphs by lattice phonon Raman microscopy
Socci, Joseph; Salzillo, Tommaso; Della Valle, Raffaele Guido; Venuti, Elisabetta; Brillante, Aldo
2017-09-01
Confocal Raman microscopy in the lattice phonon region has been used to study the polymorphism of the organic semiconductor 5,6,11,12-tetraphenyl-tetracene (rubrene). Following literature guidelines, crystals of rubrene have been prepared using a number of solution growth and vapour deposition methods, obtaining samples of different morphologies which could be related to the various polymorphs of this compound. The technique has enabled us an easy and non invasive identification of the three known polymorphs and of their phase homogeneity with a lateral spatial resolution below 1 μm.
Multiple beam splitting in elastic phononic crystal plates.
Lee, Hyuk; Oh, Joo Hwan; Kim, Yoon Young
2015-02-01
This work presents an experimental evidence for triple beam splitting in an elastic plate with an embedded elastic phononic crystal (PC) prism and elaborates on its working mechanism. While there were reports on negative refraction and double beam splitting with PCs, no experimental evidence on the splitting of triple or more ultrasonic elastic beams through PCs has been shown yet. After the experimental results are presented in case of triple beam splitting, further analysis is carried out to explain how triple or more beams can be split depending on elastic PC prism angles. Copyright © 2014 Elsevier B.V. All rights reserved.
Negative-refraction imaging with two-dimensional phononic crystals
Ke, Manzhu; Liu, Zhengyou; Qiu, Chunyin; Wang, Wengang; Shi, Jing; Wen, Weijia; Sheng, Ping
2005-08-01
We report negative refraction imaging for acoustic waves in a two-dimensional phononic crystal. The sample consists of a triangular array of steel rods immersed in water. Both the observed negative refraction behavior and imaging effect are in excellent agreement with numerical simulations by the multiple scattering theory method. The existence of nearly circular dispersion surfaces for the phonic crystal sample means that the negative refraction is well defined for all angles of incidence, and very robust in its realization and application to focusing and imaging.
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.
Structural electronic and phonon properties of some transition metal aluminides
Fatima, Bushra; Pandit, Premlata; Sanyal, Sankar P.
2012-06-01
The structural and electronic properties of some Transition metal Aluminides (TMAl) namely ruthenium aluminide (RuAl), nickel aluminide (NiAl) and cobalt aluminide (CoAl) have been studied using plane wave pseudopotential method (PWSCF) within the local density approximation (LDA). The three TMAl's crystallizes in the CsCl-type structure (B2 phase). From the analysis of band structure and density of state, we found that these TMAl's are metallic in nature. The vibrational properties in terms of phonon dispersion curves and density of state have also been reported for RuAl using density functional perturbation theory (DFPT).
Focusing of Rayleigh waves with gradient-index phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Zhao, Jinfeng [CNRS, UMR 7588, Institut des NanoSciences de Paris, F-75005 Paris (France); School of Aerospace Engineering and Applied Mechanics, Tongji University, 100 Zhangwu Road, 200092 Shanghai (China); Bonello, Bernard, E-mail: bernard.bonello@insp.jussieu.fr; Becerra, Loïc; Boyko, Olga; Marchal, Rémi [CNRS, UMR 7588, Institut des NanoSciences de Paris, F-75005 Paris (France)
2016-05-30
We report on the subwavelength focusing of Rayleigh waves using gradient-index (GRIN) phononic crystals (PCs) made of air holes scatters in a thick silicon substrate. The subwavelength focusing is demonstrated both in the inner and in the silicon substrate behind the GRIN PCs by using a non-contact experimental technique. In both situations, the focal zone was observed at the position, which is in very good agreement with our theoretical predictions, at a frequency in the sound cone free of radiation into the substrate.
Coalescence towards exceptional contours in synthetic phononic media
DEFF Research Database (Denmark)
Christensen, Johan
2016-01-01
Parity-time symmetric media, also referred to as synthetic media, have been devised in many optical systems with the ground breaking potential to create non-reciprocal structures and one-way cloaks of invisibility. Here we demonstrate a feasible approach for the case of sound where gain and loss...... are induced via the acousto-electric effect in electrically biased piezoelectric semiconductors. We study how wave attenuation and amplification can be tuned, and when combined, can give rise to phononic synthetic media with unidirectional suppressed reflectance, a feature directly applicable to evading sonar...
Phonon-mediated versus coulombic backaction in quantum dot circuits.
Harbusch, D; Taubert, D; Tranitz, H P; Wegscheider, W; Ludwig, S
2010-05-14
Quantum point contacts (QPCs) are commonly employed to detect capacitively the charge state of coupled quantum dots (QDs). An indirect backaction of a biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure is observed. Energy is emitted by nonequilibrium charge carriers in the leads of the biased QPC. Part of this energy is absorbed by the double QD where it causes charge fluctuations that can be observed under certain conditions in its stability diagram. By investigating the spectrum of the absorbed energy, we find that both acoustic phonons and Coulomb interaction can be involved in the backaction, depending on the geometry and coupling constants.
Band structures in the nematic elastomers phononic crystals
Yang, Shuai; Liu, Ying; Liang, Tianshu
2017-02-01
As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.
Electron-phonon coupling in quasi free-standing graphene
DEFF Research Database (Denmark)
Christian Johannsen, Jens; Ulstrup, Søren; Bianchi, Marco
2013-01-01
Quasi free-standing monolayer graphene can be produced by intercalating species like oxygen or hydrogen between epitaxial graphene and the substrate crystal. If the graphene is indeed decoupled from the substrate, one would expect the observation of a similar electronic dispersion and many......-body effects, irrespective of the substrate and the material used to achieve the decoupling. Here we investigate the electron-phonon coupling in two different types of quasi free-standing monolayer graphene: decoupled from SiC via hydrogen intercalation and decoupled from Ir via oxygen intercalation. Both...
The phonon-coupling model for Skyrme forces
Lyutorovich, N.; Tselyaev, V.; Speth, J.; Krewald, S.; Reinhard, P.-G.
2016-11-01
A short review on the self-consistent RPA based on the energy-density functional of the Skyrme type is given. We also present an extension of the RPA where the coupling of phonons to the single-particle states is considered. Within this approach we present numerical results which are compared with data. The self-consistent approach is compared with the Landau-Migdal theory. Here we derive from the self-consistent ph interaction, the Landau-Migdal parameters as well as their density dependence. In the Appendix a new derivation of the reduced matrix elements of the ph interaction is presented.
The phonon-coupling model for Skyrme forces
Energy Technology Data Exchange (ETDEWEB)
Lyutorovich, N.; Tselyaev, V. [St. Petersburg State University (Russian Federation); Speth, J., E-mail: J.Speth@fz-juelich.de; Krewald, S. [Forschungszentrum Jülich, Institut für Kernphysik (Germany); Reinhard, P.-G. [Universität Erlangen-Nürnberg, Institut für Theoretische Physik II (Germany)
2016-11-15
A short review on the self-consistent RPA based on the energy-density functional of the Skyrme type is given. We also present an extension of the RPA where the coupling of phonons to the single-particle states is considered. Within this approach we present numerical results which are compared with data. The self-consistent approach is compared with the Landau–Migdal theory. Here we derive from the self-consistent ph interaction, the Landau–Migdal parameters as well as their density dependence. In the Appendix a new derivation of the reduced matrix elements of the ph interaction is presented.
Finite Element Modeling of Acoustic Shielding via Phononic Crystal structures
Lipp, Clémentine Sophie Sarah; Lozzi, Andrea
2016-01-01
Quality factor of Contour Mode Resonators (CMR) are mainly affected by energy losses due to acoustic waves leaving the resonator through the anchors. An engineering of the anchors in order to create a periodic variation in the acoustic impedance of the material, structures known as Phononic Crystals (PnCs), can help improve the Q factor by reflecting part of the acoustic waves. During this project, FEM models have been validated for both 1D and 2D PnCs. The behavior of the band diagram and qu...
Grange, T; Somaschi, N; Antón, C; De Santis, L; Coppola, G; Giesz, V; Lemaître, A; Sagnes, I; Auffèves, A; Senellart, P
2017-06-23
Solid-state emitters are excellent candidates for developing integrated sources of single photons. Yet, phonons degrade the photon indistinguishability both through pure dephasing of the zero-phonon line and through phonon-assisted emission. Here, we study theoretically and experimentally the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity as a function of temperature. We show that a large coupling to a high quality factor cavity can simultaneously reduce the effect of both phonon-induced sources of decoherence. It first limits the effect of pure dephasing on the zero-phonon line with indistinguishabilities above 97% up to 18 K. Moreover, it efficiently redirects the phonon sidebands into the zero-phonon line and brings the indistinguishability of the full emission spectrum from 87% (24%) without cavity effect to more than 99% (76%) at 0K (20K). We provide guidelines for optimal cavity designs that further minimize the phonon-induced decoherence.
Energy Technology Data Exchange (ETDEWEB)
Kang, Hyung-sun; Koh, Young Ha; Jin, Jae Sik [Chosun College of Science and Technology, Gwangju (Korea, Republic of)
2017-06-15
The aim of this study is to understand the phonon transfer characteristics of a silicon thin film transistor. For this purpose, the Joule heating mechanism was considered through the electron-phonon interaction model whose validation has been done. The phonon transport characteristics were investigated in terms of phonon mean free path for the variations in the device power and silicon layer thickness from 41 nm to 177 nm. The results may be used for developing the thermal design strategy for achieving reliability and efficiency of the silicon-on-insulator (SOI) transistor, further, they will increase the understanding of heat conduction in SOI systems, which are very important in the semiconductor industry and the nano-fabrication technology.
Strong moderate deviation theorems
Inglot, Tadeusz; Kallenberg, W.C.M.; Ledwina, Teresa
1992-01-01
Strong moderate deviation theorems are concerned with relative errors in the tails caused by replacing the exact distribution function by its limiting distribution function. A new approach for deriving such theorems is presented using strong approximation inequalities. In this way a strong moderate
Moderation for Professional Learning
Earle, Sarah
2017-01-01
Moderation is put forward as they key strategy for improving the reliability of teacher assessment. However, for many teachers the word "moderation" conjures up ideas of uncomfortable situations in which marking is being checked by others and there are prolonged arguments about tiny features of individual work. In this article, the…
Depth-dependent Detection Mechanisms of Coherent Phonons in n-type GaAs
Directory of Open Access Journals (Sweden)
Petek Hrvoje
2013-03-01
Full Text Available Transient reflectivity measurements at different probing wavelengths reveal detection mechanisms of coherent phonon and phonon-plasmon coupled modes of n-doped GaAs to be strongly depth-dependent due to the carrier depletion at the surface.
Electron-phonon scattering from Green’s function transport combined with molecular dynamics
DEFF Research Database (Denmark)
Markussen, Troels; Palsgaard, Mattias Lau Nøhr; Stradi, Daniele
2017-01-01
We present a conceptually simple method for treating electron-phonon scattering and phonon limited mobilities. By combining Green’s function based transport calculations and molecular dynamics, we obtain a temperature dependent transmission from which we evaluate the mobility. We validate our...
Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo
2015-01-01
We study the relaxation of the Holstein model after a sudden switch-on of the interaction by means of the nonequilibrium dynamical mean field theory, with the self-consistent Migdal approximation as an impurity solver. We show that there exists a qualitative change in the thermalization dynamics as the interaction is varied in the weak-coupling regime. On the weaker interaction side of this crossover, the phonon oscillations are damped more rapidly than the electron thermalization time scale, as determined from the relaxation of the electron momentum distribution function. On the stronger interaction side, the relaxation of the electrons becomes faster than the phonon damping. In this regime, despite long-lived phonon oscillations, a thermalized momentum distribution is realized temporarily. The origin of the "thermalization crossover" found here is traced back to different behaviors of the electron and phonon self-energies as a function of the electron-phonon coupling. In addition, the importance of the phonon dynamics is demonstrated by comparing the self-consistent Migdal results with those obtained with a simpler Hartree-Fock impurity solver that neglects the phonon self-energy. The latter scheme does not properly describe the evolution and thermalization of isolated electron-phonon systems.
Jacobi, N.; Zmuidzinas, J. S.
1974-01-01
A formalism was developed for temperature-dependent, self-consistent phonons in quantum solids with defects. Lattice vacancies and interstitials in solid helium and metallic hydrogen, as well as electronic excitations in solid helium, were treated as defects that modify properties of these systems. The information to be gained from the modified phonon spectrum is discussed.
Study of optical phonon modes of CdS nanoparticles using Raman ...
Indian Academy of Sciences (India)
In the case of nanostructured materials, confinement of optical phonons can produce noticeable changes in their vibrational spectra compared to those of bulk crystals. In this paper we report the study of optical phonon modes of nanoparticles of CdS using Raman spectroscopy. Nanoparticle sample for the present study ...
Unified phonon-based approach to the thermodynamics of solid, liquid and gas states
Bolmatov, Dima; Zav'yalov, Dmitry; Zhernenkov, Mikhail; Musaev, Edvard T.; Cai, Yong Q.
2015-12-01
We introduce a unified approach to states of matter (solid, liquid and gas) and describe the thermodynamics of the pressure-temperature phase diagram in terms of phonon excitations. We derive the effective Hamiltonian with low-energy cutoff in two transverse phonon polarizations (phononic band gaps) by breaking the symmetry in phonon interactions. Further, we construct the statistical mechanics of states of aggregation employing the Debye approximation. The introduced formalism covers the Debye theory of solids, the phonon theory of liquids, and thermodynamic limits such as the Dulong-Petit thermodynamic limit (cV = 3kB), the ideal gas limit (cV =3/2 kB) and the new thermodynamic limit (cV = 2kB), dubbed here the Frenkel line thermodynamic limit. We discuss the phonon propagation and localization effects in liquids above and below the Frenkel line, and explain the "fast sound" phenomenon. As a test for our theory we calculate velocity-velocity autocorrelation and pair distribution functions within the Green-Kubo formalism. We show the consistency between dynamics of phonons and pair correlations in the framework of the unified approach. New directions towards advancements in phononic band gaps engineering, hypersound manipulation technologies and exploration of exotic behaviour of fluids relevant to geo- and planetary sciences are discussed. The presented results are equally important both for practical implications and for fundamental research.
The temperature dependence of Cr3+ : YAG zero-phonon lines
Marceddu, Marco; Manca, Marianna; Ricci, Pier Carlo; Anedda, Alberto
2012-01-01
This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr3+ ions in an yttrium aluminium garnet (YAG) matrix. Experimental data were analysed in the framework of electron-phonon coupling in the quadratic approximation and it was found that Cr3+ ions in the YAG
DEFF Research Database (Denmark)
Nielsen, Per Kær; Nielsen, Torben Roland; Lodahl, P.
2012-01-01
We investigate the influence of the electron-phonon interaction on the decay dynamics of a quantum dot coupled to an optical microcavity. We show that the electron-phonon interaction has important consequences on the dynamics, especially when the quantum dot and cavity are tuned out of resonance,...
Electron and phonon transport in silicon nanowires: Atomistic approach to thermoelectric properties
DEFF Research Database (Denmark)
Markussen, Troels; Jauho, Antti-Pekka; Brandbyge, Mads
2009-01-01
We compute both electron and phonon transmissions in thin disordered silicon nanowires (SiNWs). Our atomistic approach is based on tight-binding and empirical potential descriptions of the electronic and phononic systems, respectively. Surface disorder is modeled by introducing surface silicon va...
DEFF Research Database (Denmark)
Ulstrup, Søren; Bianchi, Marco; Guan, Dandan
2012-01-01
The temperature-dependent electronic structure and electron-phonon coupling of weakly doped supported graphene is studied by angle-resolved photoemission spectroscopy and ab initio molecular dynamics simulations. The electron-phonon coupling is found to be extremely weak, reaching the lowest valu...
Theoretical study of the transverse acoustic phonons of GaSb at ...
Indian Academy of Sciences (India)
The transverse acoustic phonons as a function of pressure have been compared with the recently measured inelastic neutron scattering data which show a strong softening near the zone boundaries. The calculated one-phonon density of states show pronounced shift in the peak positions with the increase in pressure.
Effects of vdW and Electrostatic Interactions on Phonon Velocity and Thermal Transport in Polymers
Rashidi, Vahid; Coyle, Eleanor; Kieffer, John; Pipe, Kevin
Bulk amorphous polymers typically have a low thermal conductivity ( 0.2 W/mK). This low thermal conductivity is believed to be due to weak inter-chain interactions, e.g., van der Waals and electrostatic. Heat transfer along polymer chains, however, is considered very robust due to strong covalent bonds between the atoms. In this work we show that this explanation does not give a clear picture of precisely what contributes to heat transfer in various polymers with different structures. Here we show that the abundance of vdW and electrostatic interactions can greatly impact heat transfer in polymers at room temperature. Through molecular dynamics calculations, we show that the propagation velocities of acoustic phonons at moderate frequencies ( 1THz), which contribute significantly to heat transfer at room temperature, are much higher when non-bonding interactions are present in the system versus when they are excluded. This relationship has important implications for designing amorphous polymers with high thermal conductivity.
Phonons and thermal transport in graphene and graphene-based materials
Nika, Denis L.; Balandin, Alexander A.
2017-03-01
A discovery of the unusual thermal properties of graphene stimulated experimental, theoretical and computational research directed at understanding phonon transport and thermal conduction in two-dimensional material systems. We provide a critical review of recent results in the graphene thermal field focusing on phonon dispersion, specific heat, thermal conductivity, and comparison of different models and computational approaches. The correlation between the phonon spectrum in graphene-based materials and the heat conduction properties is analyzed in details. The effects of the atomic plane rotations in bilayer graphene, isotope engineering, and relative contributions of different phonon dispersion branches are discussed. For readers’ convenience, the summaries of main experimental and theoretical results on thermal conductivity as well as phonon mode contributions to thermal transport are provided in the form of comprehensive annotated tables.
Two-phonon giant resonances in {sup 136}Xe, {sup 208}Pb, and {sup 238}U
Energy Technology Data Exchange (ETDEWEB)
Boretzky, K.; Gruenschloss, A.; Ilievski, S.; Adrich, P.; Aumann, T.; Bertulani, C.A.; Cub, J.; Dostal, W.; Eberlein, B.; Elze, T.W.; Emling, H.; Fallot, M.; Holeczek, J.; Holzmann, R.; Kozhuharov, C.; Kratz, J.V.; Kulessa, R.; Leifels, Y.; Leistenschneider, A.; Lubkiewicz, E.; Mordechai, S.; Ohtsuki, T.; Reiter, P.; Simon, H.; Stelzer, K.; Stroth, J.; Suemmerer, K.; Surowiec, A.; Wajda, E.; Walus, W.
2003-07-01
The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nuclei impinging on targets of high nuclear charge with energies of 500-700 MeV/nucleon. New experimental data are presented for {sup 136}Xe and {sup 238}U together with further analysis of earlier data on {sup 208}Pb. Differential cross sections d{sigma}/dE{sup *} and d{sigma}/d{theta} for electromagnetic excitations were deduced. Depending on the isotope, cross sections appear to be enhanced in comparison to those expected from a purely harmonic nuclear dipole response. The cumulative effect of excitations of two-phonon states composed of one dipole and one quadrupole phonon, of predicted anharmoniticies in the double-phonon dipole response, and of damping of the dipole resonance during the collision may account for the discrepancy. In addition, decay properties of two-phonon resonances were studied and compared to that of a statistical decay. (orig.)
Ab initio study of mechanical and thermal properties of GaN nanotubes by phonon calculations
Directory of Open Access Journals (Sweden)
H Tashakori
2015-01-01
Full Text Available In this work, we calculated the phonon dispersion of GaNNTs (4,0 and (4,4 by quantum ESPRESSO package using Density Functional Theory (DFT, pseudo potentials, and plane wave self-consistent field (PWscf method. For the purpose of lattice-dynamical calculation and phononic properties, we used PWscf and Phonon codes. The former produces the self-consistent electronic and all related computations (forces, stresses, structural optimization. The latter solves the DFPT equations and calculates dynamical matrices for a single wave-vector or for a uniform grid of wave-vectors. The stability of these nanotubes was studied by phonon curves. According to the calculations, the breathing mode was distinguished for both nanotubes. The mechanical properties of these nanotubes were characterized by the results obtained for phonon dispersion curves. Finally, a quantitative comparison was made between the values of stiffness of GaNNTs (4,0 and (4,4.
Quantum kinetic exciton-LO-phonon interaction in CdSe
DEFF Research Database (Denmark)
Woggon, Ulrike; Gindele, Frank; Langbein, Wolfgang
2000-01-01
Oscillations with a period of similar to 150 fs are observed in the four-wave mixing (FWM) signal of bulk CdSe and interpreted in terms of non-Markovian exciton-LO-phonon scattering. The experiments show evidence of phonon quantum kinetics in semiconductors of strong polar coupling strength and h...... and high exciton binding energy. By comparison of the spectral and temporal response of the FWM signal in bulk CdSe and CdSe quantum dots, we demonstrate the influence of continuum states on the interference of electron-hole pair polarizations coupled via an LO phonon.......Oscillations with a period of similar to 150 fs are observed in the four-wave mixing (FWM) signal of bulk CdSe and interpreted in terms of non-Markovian exciton-LO-phonon scattering. The experiments show evidence of phonon quantum kinetics in semiconductors of strong polar coupling strength...
Measurement of phonon dispersion relation in negative thermal expansion compound ZrW2O8
Mittal, R.; Chaplot, S. L.; Pintschovius, L.; Achary, S. N.; Kowach, G. R.
2007-12-01
Isotropic negative thermal expansion (NTE) is found in cubic AX2O8(A = Zr, Hf: X=W, Mo) up to high temperatures (1050 K). Anharmonicity of low energy phonon modes plays an important role in leading to the NTE behaviour. Earlier we verified our predictions of large phonon softening for low energy phonons (below 8 meV) through high-pressure inelastic neutron scattering measurements on powder samples at ILL, France. Now we have measured the phonon dispersion relation from a single crystal of ZrW2O8. The measurements are useful to verify our prediction of highly anharmonic nature of specific phonon branches, in particular the transverse acoustic branch, and other branches up to 10 meV. These modes below 10 meV mainly contribute to the NTE in ZrW2O8.
Phonon-interference resonance effects by nanoparticles embedded in a matrix
Feng, Lei; Shiga, Takuma; Han, Haoxue; Ju, Shenghong; Kosevich, Yuriy A.; Shiomi, Junichiro
2017-12-01
We report an unambiguous phonon resonance effect originating from germanium nanoparticles embedded in silicon matrix. Our approach features the combination of the phonon wave-packet method with atomistic dynamics and the finite element method rooted in continuum theory. We find that multimodal phonon resonance, caused by destructive interference of coherent lattice waves propagating through and around the nanoparticle, gives rise to sharp and significant transmittance dips, blocking the lower-end frequency range of phonon transport that is hardly diminished by other nanostructures. The resonance is sensitive to the phonon coherent length, where the finiteness of the wave-packet width weakens the transmittance dip even when coherent length is longer than the particle diameter. Further strengthening of transmittance dips is possible by arraying multiple nanoparticles, which gives rise to the collective vibrational mode. Finally, it is demonstrated that these resonance effects can significantly reduce thermal conductance in the lower-end frequency range.
Kim, Chang-Il; Kang, Chol-Jin; Yun, Chol-Song; Choe, Myong-Il; Ahn, Jong-Kwan
2017-11-01
We investigate the quantum phase transition in triple quantum dot system with triangular geometry, in which one of the dots is connected to metallic leads and electrons in the dot interact with a local phonon mode. The influence of electron-phonon interaction on the quantum phase transition between local moment phase and Kondo screened strong coupling phase at the particle-hole symmetric point is studied based on the analytical arguments and the numerical renormalization group method. The results show that the critical value of tunnel-coupling between side dots decreases with the increase of electron-phonon coupling in "spin Kondo" regime. Furthermore, at a certain critical value of electron-phonon coupling, there appears only strong coupling phase, irrespective of tunnel-coupling between dots. The study of the influence of electron-phonon interaction on the quantum phase transition in triple quantum dot has the great importance for clarifying the mechanism of Kondo screening in the system.
Wang, Zi-Wu; Li, Wei-Ping; Xiao, Yao; Li, Run-Ze; Li, Zhi-Qing
2017-06-01
We theoretically investigate the correction of exciton binding energy arising from the exciton-optical phonon coupling in monolayer transition metal dichalcogenides (TMDs) using the linear operator and Lee-Low-Pines unitary transformation methods. We take into account not only the exciton coupling with intrinsic longitudinal optical phonon modes but also the surface optical phonon modes induced by polar substrates supporting monolayer TMDs. We find that the exciton binding energies are corrected on a large scale due to these exciton-optical phonon couplings. We discuss the dependences of exciton binding energy on the cut-off wave vector of optical phonon modes, the polarization strength of substrate materials, and the distance between polar substrates and TMDs. These results provide potential explanations for the divergence of the exciton binding energy between the experiment and theory in TMDs.
Infrared-active optical phonons in LiFePO4 single crystals
Stanislavchuk, T. N.; Middlemiss, D. S.; Syzdek, J. S.; Janssen, Y.; Basistyy, R.; Sirenko, A. A.; Khalifah, P. G.; Grey, C. P.; Kostecki, R.
2017-07-01
Infrared-active optical phonons were studied in olivine LiFePO4 oriented single crystals by means of both rotating analyzer and rotating compensator spectroscopic ellipsometry in the spectral range between 50 and 1400 cm-1. The eigenfrequencies, oscillator strengths, and broadenings of the phonon modes were determined from fits of the anisotropic harmonic oscillator model to the data. Optical phonons in a heterosite FePO4 crystal were measured from the delithiated ab-surface of the LiFePO4 crystal and compared with the phonon modes of the latter. Good agreement was found between experimental data and the results of solid-state hybrid density functional theory calculations for the phonon modes in both LiFePO4 and FePO4.
Energy Technology Data Exchange (ETDEWEB)
Khurgin, Jacob B., E-mail: jakek@jhu.edu [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Bajaj, Sanyam; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)
2015-12-28
Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results.
A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale
Energy Technology Data Exchange (ETDEWEB)
Bong, Victor N-S; Wong, Basil T. [Swinburne Sarawak Research Centre for Sustainable Technologies, Faculty of Engineering, Computing & Science, Swinburne University of Technology Sarawak Campus, 93350 Kuching, Sarawak (Malaysia)
2015-08-28
Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering.
Spin dynamics of low-dimensional excitons due to acoustic phonons
Energy Technology Data Exchange (ETDEWEB)
Thilagam, A; Lohe, M A [Department of Physics, University of Adelaide, Adelaide 5005 (Australia)
2006-03-29
We investigate the spin dynamics of excitons interacting with acoustic phonons in quantum wells, quantum wires and quantum discs by employing a multiband model based on the 4 x 4 Luttinger Hamiltonian. We also use the Bir-Pikus Hamiltonian to model the coupling of excitons to both longitudinal acoustic phonons and transverse acoustic phonons, thereby providing us with a realistic framework in which to determine details of the spin dynamics of excitons. We use a fractional dimensional formulation to model the excitonic wavefunctions and we demonstrate explicitly the decrease of spin relaxation time with dimensionality. Our numerical results are consistent with experimental results of spin relaxation times for various configurations of the GaAs/Al{sub 0.3}Ga{sub 0.7}As material system. We find that longitudinal and transverse acoustic phonons are equally significant in processes of exciton spin relaxations involving acoustic phonons.
Spin dynamics of low-dimensional excitons due to acoustic phonons
Thilagam, A.; Lohe, M. A.
2006-03-01
We investigate the spin dynamics of excitons interacting with acoustic phonons in quantum wells, quantum wires and quantum discs by employing a multiband model based on the 4 × 4 Luttinger Hamiltonian. We also use the Bir-Pikus Hamiltonian to model the coupling of excitons to both longitudinal acoustic phonons and transverse acoustic phonons, thereby providing us with a realistic framework in which to determine details of the spin dynamics of excitons. We use a fractional dimensional formulation to model the excitonic wavefunctions and we demonstrate explicitly the decrease of spin relaxation time with dimensionality. Our numerical results are consistent with experimental results of spin relaxation times for various configurations of the GaAs/Al0.3Ga0.7As material system. We find that longitudinal and transverse acoustic phonons are equally significant in processes of exciton spin relaxations involving acoustic phonons.
Designing Nanostructures for Phonon Transport via Bayesian Optimization
Ju, Shenghong; Shiga, Takuma; Feng, Lei; Hou, Zhufeng; Tsuda, Koji; Shiomi, Junichiro
2017-04-01
We demonstrate optimization of thermal conductance across nanostructures by developing a method combining atomistic Green's function and Bayesian optimization. With an aim to minimize and maximize the interfacial thermal conductance (ITC) across Si-Si and Si-Ge interfaces by means of the Si /Ge composite interfacial structure, the method identifies the optimal structures from calculations of only a few percent of the entire candidates (over 60 000 structures). The obtained optimal interfacial structures are nonintuitive and impacting: the minimum ITC structure is an aperiodic superlattice that realizes 50% reduction from the best periodic superlattice. The physical mechanism of the minimum ITC can be understood in terms of the crossover of the two effects on phonon transport: as the layer thickness in the superlattice increases, the impact of Fabry-Pérot interference increases, and the rate of reflection at the layer interfaces decreases. An aperiodic superlattice with spatial variation in the layer thickness has a degree of freedom to realize optimal balance between the above two competing mechanisms. Furthermore, the spatial variation enables weakening the impact of constructive phonon interference relative to that of destructive interference. The present work shows the effectiveness and advantage of material informatics in designing nanostructures to control heat conduction, which can be extended to other nanostructures and properties.
Lattice phonons of coronene single crystal polymorphs: a theoretical approach
Bannister, Nicola; da Como, Enrico; Crampin, Simon
Coronene, a polyaromatic carbon based molecule of disk shape, exhibits a range of peculiar physical properties from room temperature phosphorescence to superconductivity. The fundamental interest in this molecule is linked to its diamagnetism, originating from the delocalized pi electrons. Recently, we reported the discovery of a new crystal structure of coronene, the beta phase, apparently favoured by the presence of an external magnetic field during crystal growth. Ab-initio density functional theory (DFT) calculations of the lattice energy for the two coronene polymorphs, the known gamma and the new beta phase, indicate that the latter has a lower energy minimum and thus should be favoured. Instead experimentally we find that the gamma phase is stable at room temperature and converts into beta at 150K. This observation calls for a more complete description of the relative energetic stability of the polymorphs including the role of phonons. We present our efforts in describing the lattice phonons of the two structures by performing DFT simulations and comparing them with data from low frequency Raman spectroscopy.
Electron-Phonon coupling in magnetized semiconductor quantum plasmas
Ghosh, S.; Muley, Apurva
2017-05-01
Present paper deals with electron-phonon coupling in piezoelectric n-type magnetized semiconductor plasma under quantum regime. A quantum modified dispersion relation is derived for the evolution of desired electron-phonon coupling in semiconductor plasma using quantum hydrodynamic (QHD) model. The main ingredients of this study are the role of non-dimensional quantum parameter-H and externally applied magneto-static field. The presence of quantum parameter-H includes the contributions of Fermi degenerate pressure and quantum diffraction. It represents the ratio of plasmon energy to Fermi energy of the system, hence is a function of doping concentration n0. An expression for gain coefficient of acoustic wave is obtained in terms of quantum parameter-H and magnetic field under the collision dominated limit. We present the effects of doping in medium and orientation of magnetic field on gain profile of acoustic wave. The results show that the presence of magnetic field and quantum effects through quantum parameter-H effectively modifies the gain per unit length of acoustic wave.
Prediction of phonon-mediated superconductivity in borophene
Gao, Miao; Li, Qi-Zhi; Yan, Xun-Wang; Wang, Jun
2017-01-01
Superconductivity in two-dimensional compounds is widely studied, not only because of its application in constructing nano-superconducting devices, but also for general scientific interest. Very recently, borophene (a two-dimensional boron sheet) has been successfully grown on the Ag(111) surface, through direct evaporation of a pure boron source. The experiment unveiled two types of borophene structures, namely β12 and χ3. Herein, we employed density-functional first-principles calculations to investigate the electron-phonon coupling and superconductivity in both structures of borophene. The band structures of β12 and χ3 borophenes exhibit inherent metallicity. We found that electron-phonon coupling constants in the two compounds are larger than that in MgB2. The superconducting transition temperatures were determined to be 18.7 K and 24.7 K through the McMillian-Allen-Dynes formula. These temperatures are much higher than the theoretically predicted 8.1 K and experimentally observed 7.4 K superconductivity in graphene. Our findings will enrich nano-superconducting device applications and boron-related materials science.
Goldstone-like phonon modes in a (111)-strained perovskite
Marthinsen, A.; Griffin, S. M.; Moreau, M.; Grande, T.; Tybell, T.; Selbach, S. M.
2018-01-01
Goldstone modes are massless particles resulting from spontaneous symmetry breaking. Although such modes are found in elementary particle physics as well as in condensed-matter systems like superfluid helium, superconductors, and magnons, structural Goldstone modes are rare. Epitaxial strain in thin films can induce structures and properties not accessible in bulk and has been intensively studied for (001)-oriented perovskite oxides. Here we predict Goldstone-like phonon modes in (111)-strained SrMn O3 by first-principles calculations. Under compressive strain the coupling between two in-plane rotational instabilities gives rise to a Mexican hat-shaped energy surface characteristic of a Goldstone mode. Conversely, large tensile strain induces in-plane polar instabilities with no directional preference, giving rise to a continuous polar ground state. Such phonon modes with U (1) symmetry could emulate structural condensed-matter Higgs modes. The mass of this Higgs boson, given by the shape of the Mexican hat energy surface, can be tuned by strain through proper choice of substrate.
Topological Design of Cellular Phononic Band Gap Crystals.
Li, Yang Fan; Huang, Xiaodong; Zhou, Shiwei
2016-03-10
This paper systematically investigated the topological design of cellular phononic crystals with a maximized gap size between two adjacent bands. Considering that the obtained structures may sustain a certain amount of static loadings, it is desirable to ensure the optimized designs to have a relatively high stiffness. To tackle this issue, we conducted a multiple objective optimization to maximize band gap size and bulk or shear modulus simultaneously with a prescribed volume fraction of solid material so that the resulting structures can be lightweight, as well. In particular, we first conducted the finite element analysis of the phononic band gap crystals and then adapted a very efficient optimization procedure to resolve this problem based on bi-directional evolutionary structure optimization (BESO) algorithm in conjunction with the homogenization method. A number of optimization results for maximizing band gaps with bulk and shear modulus constraints are presented for out-of-plane and in-plane modes. Numerical results showed that the optimized structures are similar to those obtained for composite case, except that additional slim connections are added in the cellular case to support the propagation of shear wave modes and meanwhile to satisfy the prescribed bulk or shear modulus constraints.
Topological Design of Cellular Phononic Band Gap Crystals
Directory of Open Access Journals (Sweden)
Yang Fan Li
2016-03-01
Full Text Available This paper systematically investigated the topological design of cellular phononic crystals with a maximized gap size between two adjacent bands. Considering that the obtained structures may sustain a certain amount of static loadings, it is desirable to ensure the optimized designs to have a relatively high stiffness. To tackle this issue, we conducted a multiple objective optimization to maximize band gap size and bulk or shear modulus simultaneously with a prescribed volume fraction of solid material so that the resulting structures can be lightweight, as well. In particular, we first conducted the finite element analysis of the phononic band gap crystals and then adapted a very efficient optimization procedure to resolve this problem based on bi-directional evolutionary structure optimization (BESO algorithm in conjunction with the homogenization method. A number of optimization results for maximizing band gaps with bulk and shear modulus constraints are presented for out-of-plane and in-plane modes. Numerical results showed that the optimized structures are similar to those obtained for composite case, except that additional slim connections are added in the cellular case to support the propagation of shear wave modes and meanwhile to satisfy the prescribed bulk or shear modulus constraints.
U(6)-Phonon model of nuclear collective motion
Ganev, H. G.
2015-05-01
The U(6)-phonon model of nuclear collective motion with the semi-direct product structure [HW(21)]U(6) is obtained as a hydrodynamic (macroscopic) limit of the fully microscopic proton-neutron symplectic model (PNSM) with Sp(12, R) dynamical group. The phonon structure of the [HW(21)]U(6) model enables it to simultaneously include the giant monopole and quadrupole, as well as dipole resonances and their coupling to the low-lying collective states. The U(6) intrinsic structure of the [HW(21)]U(6) model, from the other side, gives a framework for the simultaneous shell-model interpretation of the ground state band and the other excited low-lying collective bands. It follows then that the states of the whole nuclear Hilbert space which can be put into one-to-one correspondence with those of a 21-dimensional oscillator with an intrinsic (base) U(6) structure. The latter can be determined in such a way that it is compatible with the proton-neutron structure of the nucleus. The macroscopic limit of the Sp(12, R) algebra, therefore, provides a rigorous mechanism for implementing the unified model ideas of coupling the valence particles to the core collective degrees of freedom within a fully microscopic framework without introducing redundant variables or violating the Pauli principle.
Technology towards a SAW based phononic crystal sensor
Schmidt, Marc-Peter; Oseev, Aleksandr; Lucklum, Ralf; Hirsch, Soeren
2015-05-01
Phononic crystals (PnC) with a specifically designed defect have been recently introduced as novel sensor platform. Those sensors feature a band gap covering the typical input span of the measurand as well as a narrow transmission peak within the band gap where the frequency of maximum transmission is governed by the measurand. This innovative approach has been applied for determination of compounds in liquids [1]. Improvement of sensitivity requires higher probing frequencies around 100 MHz and above. In this range surface acoustic wave devices (SAW) provide a promising basis for PnC based microsensors [2]. The respective feature size of the PnC SAW sensor has dimensions in the range of 100 μm and below. Whereas those dimensions are state of the art for common MEMS materials, etching of holes and cavities in piezoelectric materials having an aspect ratio diameter/depth is challenging. In this contribution we describe an improved technological process to manufacture considerably deep and uniform phononic crystal structures inside of SAW substrates.
Performance of heterojunction p+ microcrystalline silicon n crystalline silicon solar cells
van Cleef, M. W. M.; Rath, J. K.; Rubinelli, F. A.; van der Werf, C. H. M.; Schropp, R. E. I.; van der Weg, W. F.
1997-12-01
We have studied by Raman spectroscopy and electro-optical characterization the properties of thin boron doped microcrystalline silicon layers deposited by plasma enhanced chemical vapor deposition (PECVD) on crystalline silicon wafers and on amorphous silicon buffer layers. Thin 20-30 nm p+ μc-Si:H layers with a considerably large crystalline volume fraction (˜22%) and good window properties were deposited on crystalline silicon under moderate PECVD conditions. The performance of heterojunction solar cells incorporating such window layers were critically dependent on the interface quality and the type of buffer layer used. A large improvement of open circuit voltage is observed in these solar cells when a thin 2-3 nm wide band-gap buffer layer of intrinsic a-Si:H deposited at low temperature (˜100 °C) is inserted between the microcrystalline and crystalline silicon [complete solar cell configuration: Al/(n)c-Si/buffer/p+μc-Si:H/ITO/Ag)]. Detailed modeling studies showed that the wide band-gap a-Si:H buffer layer is able to prevent electron backdiffusion into the p+ μc-Si:H layer due to the discontinuity in the conduction band at the amorphous-crystalline silicon interface, thereby reducing the high recombination losses in the microcrystalline layer. At the same time, the discontinuity in the valence band is not limiting the hole exit to the front contact and does not deteriorate the solar cell performance. The defect density inside the crystalline silicon close to the amorphous-crystalline interface has a strong effect on the operation of the cell. An extra atomic hydrogen passivation treatment prior to buffer layer deposition, in order to reduce the number of these defects, did further enhance the values of Voc and fill factor, resulting in an efficiency of 12.2% for a cell without a back surface field and texturization.
First-principles study of crystalline and amorphous AlMgB{sub 14}-based materials
Energy Technology Data Exchange (ETDEWEB)
Ivashchenko, V. I.; Shevchenko, V. I., E-mail: shev@materials.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky Str. 3, 03142 Kyiv (Ukraine); Turchi, P. E. A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, California 94551 (United States); Veprek, S. [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Leszczynski, Jerzy [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Gorb, Leonid [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Badger Technical Services, LLC, Vicksburg, Mississippi 39180 (United States); Hill, Frances [U.S. Army ERDC, Vicksburg, Mississippi 39180 (United States)
2016-05-28
We report first-principles investigations of crystalline and amorphous boron and M1{sub x}M2{sub y}X{sub z}B{sub 14−z} (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm{sup −1}, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm{sup −1}. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B{sub 12} units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.
Radiation-Induced Amorphization of Crystalline Ice
Fama, M.; Loeffler, M. J.; Raut, U.; Baragiola, R. A.
2009-01-01
We study radiation-induced amorphization of crystalline ice, ana lyzing the resu lts of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the temperature dependence of amorphization in terms of the 'thermal spike' model. We then discuss the common use of the 1.65 micrometer infrared absorption band of water as a measure of degree of crystallinity, an increasingly common procedure to analyze remote sensing data of astronomical icy bodies. The discussion is based on new, high quality near-infrared refl ectance absorption spectra measured between 1.4 and 2.2 micrometers for amorphous and crystalline ices irradiated with 225 keV protons at 80 K. We found that, after irradiation with 10(exp 15) protons per square centimeter, crystalline ice films thinner than the ion range become fully amorphous, and that the infrared absorption spectra show no significant changes upon further irradiation. The complete amorphization suggests that crystalline ice observed in the outer Solar System, including trans-neptunian objects, may results from heat from internal sources or from the impact of icy meteorites or comets.
Glass-clad single crystalline fiber lasers
Lai, C. C.; Hsu, K. Y.; Huang, C. W.; Jheng, D. Y.; Wang, S. C.; Lin, S. L.; Yang, M. H.; Lee, Y. W.; Huang, D. W.; Huang, S. L.
2012-06-01
Yttrium aluminium garnet (YAG) has been widely used as a solid-state laser host because of its superior optical, thermal, mechanical properties, as well as its plurality in hosting active ions with a wide range of ionic radii. Drawing YAG into single crystalline fiber has the potential to further scale up the attainable power level with high mode quality. The recent advancement on the codrawing laser-heated pedestal growth (CDLHPG) technique can produce glass-clad YAG crystalline fibers for laser applications. The drawing speed can reach 10 cm/min for mass production. The CDLHPG technique has shown advantages on transition-metal ion doped YAG and short-fluorescent-lifetime ion doped YAG host. Compared to silica fiber lasers, the crystalline core offers high emission cross section for transition metal ions because of the unique local matrix. The challenges on the development of glass-clad YAG fibers, including core crystallinity, diameter uniformity, dopant segregation, residual strain, post-growth thermal treatment, and the thermal expansion coefficient mismatch between the crystalline core and glass clad are discussed. Chromium, ytterbium, and neodymium ions doped YAG fiber lasers have been successfully achieved with high efficiency and low threshold power. Power scaling with a clad-pump/side-coupling scheme using single clad or double clad YAG fibers is also discussed.
First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene
Gu, Xiaokun; Yang, Ronggui
2015-01-01
There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ˜10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides.
First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene
Energy Technology Data Exchange (ETDEWEB)
Gu, Xiaokun; Yang, Ronggui, E-mail: Ronggui.Yang@Colorado.Edu [Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309 (United States)
2015-01-14
There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ∼10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides.
Topological crystalline insulators in transition metal oxides.
Kargarian, Mehdi; Fiete, Gregory A
2013-04-12
Topological crystalline insulators possess electronic states protected by crystal symmetries, rather than time-reversal symmetry. We show that the transition metal oxides with heavy transition metals are able to support nontrivial band topology resulting from mirror symmetry of the lattice. As an example, we consider pyrochlore oxides of the form A2M2O7. As a function of spin-orbit coupling strength, we find two Z2 topological insulator phases can be distinguished from each other by their mirror Chern numbers, indicating a different topological crystalline insulators. We also derive an effective k·p Hamiltonian, similar to the model introduced for Pb(1-x)Sn(x)Te, and discuss the effect of an on-site Hubbard interaction on the topological crystalline insulator phase using slave-rotor mean-field theory, which predicts new classes of topological quantum spin liquids.
Structural changes in bunched crystalline ion beams
Bussmann, M; Schätz, T; Habs, D
2003-01-01
Measurements of the spatial distribution of bunched crystalline ion beams in the radio frequency quadrupole storage ring PALLAS are presented for different ratios of the longitudinal and the transverse confinement strengths. The length of highly elongated crystalline ion bunches and its dependence on the bunching voltage is compared to predictions for a one-dimensional ion string and three-dimensional space-charge-dominated beams. The length is found to be considerably shorter than that predicted by the models. Furthermore, the scaling of the length with the bunching voltage is shown to differ from the expected inverse cube root scaling. These differences can partially be attributed to the formation of a mixed crystalline structure. Additionally, a concise mapping of the structural transition from a string to a zig-zag configuration as a function of the ratio of the confinement strengths is presented, which in a similar way deviates from the predictions.
Cooling and heating of crystalline ion beams
Schramm, U; Bussmann, M; Habs, D
2003-01-01
The crystallization of ion beams has recently been established in the rf quadrupole storage ring PALLAS (PAul Laser CooLing Acceleration System) for laser-cooled sup 2 sup 4 Mg sup + ion beams at an energy of about 1 eV. Yet, unexpectedly sharp constraints had to be met concerning the confinement strength and the longitudinal laser cooling rate. In this paper, related and up to now unseen heating mechanisms are pinpointed for crystalline beams. The weak but inevitable diffusive transverse heating associated with the laser cooling process itself is investigated, possibly allowing the future measurement of the latent heat of the ion crystal. As a function of the beam velocity, the influence of bending shear on the attainability of larger crystalline structures is presented. Finally, rf heating of crystalline beams of different structure is studied for discontinuous cooling.
Search for the 3-phonon state of {sup 40}Ca; Recherche de l'etat a trois phonons dans le {sup 40}Ca
Energy Technology Data Exchange (ETDEWEB)
Fallot, M
2002-09-01
We study collective vibrational states of the nucleus: giant resonances and multiphonon states. It has been shown that multiphonon states, which are built with several superimposed giant resonances, can be excited in inelastic heavy ion scattering near the grazing angle. No three photon states have been observed until now. An experiment has been performed at GANIL, aiming at the observation of the 3-phonon state built with the giant quadrupole resonance (GQR) in {sup 40}Ca, with the reaction {sup 40}Ca + {sup 40}Ca at 50 A.Me.V. The ejectile was identified in the SPEG spectrometer. Light charged particles were detected in 240 CsI scintillators of the INDRA 4{pi} array. The analysis confirms the previous results about the GQR and the 2-phonon state in {sup 40}Ca. For the first time, we have measured an important direct decay branch of the GQR by alpha particles. Applying the so-called 'missing energy method' to events containing three protons measured in coincidence with the ejectile, we observe a direct decay branch revealing the presence of a 3-phonon state in the excitation energy region expected for the triple GQR. Dynamical processes are also studied in the inelastic channel, emphasizing a recently discovered mechanism named towing-mode. We observe for the first time the towing-mode of alpha particles. The energies of multiphonon states in {sup 40}Ca and {sup 208}Pb have been computed microscopically including some anharmonicities via boson mapping methods. The basis of the calculation has been extended to the 3-phonon states. Our results show large anharmonicities (several MeV), due to the coupling of 3-phonon states to 2-phonon states. The extension of the basis to 4-phonon states has been performed for the first time. The inclusion of the 4 phonon states in the calculation did not affect the previous observations concerning the 2-phonon states. Preliminary results on the anharmonicities of the 3-phonon states are presented. (author)
Electronic processes in non-crystalline materials
Mott, Nevill Francis
2012-01-01
Since the first edition of this highly successful book the field saw many great developments both in experimental and theoretical studies of electrical properties of non-crystalline solids. It became necessary to rewrite nearly the whole book, while the aims of the second edition remained the same: to set out the theoretical concepts, to test them by comparison with experiment for a wide variety of phenomena, and to apply them to non-crystalline materials. Sir Nevill Mott shared the1977 Nobel Prize for Physics, awarded for his research work in this field. The reissue of this book as part of th
Used fuel disposition in crystalline rocks
Energy Technology Data Exchange (ETDEWEB)
Wang, Y. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Hadgu, Teklu [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kalinina, Elena Arkadievna [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jerden, James L. [Argonne National Lab. (ANL), Argonne, IL (United States); Copple, Jacqueline M. [Argonne National Lab. (ANL), Argonne, IL (United States); Cruse, T. [Argonne National Lab. (ANL), Argonne, IL (United States); Ebert, W. [Argonne National Lab. (ANL), Argonne, IL (United States); Buck, E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Eittman, R. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Tinnacher, R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Tournassat, Christophe. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Davis, J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Viswanathan, H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dittrich, T. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, F. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Karra, S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Makedonska, N. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, P. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Zavarin, Mavrik [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Joseph, C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-09-01
The U.S. Department of Energy Office of Nuclear Energy, Office of Fuel Cycle Technology established the Used Fuel Disposition Campaign (UFDC) in fiscal year 2010 (FY10) to conduct the research and development (R&D) activities related to storage, transportation and disposal of used nuclear fuel and high level nuclear waste. The objective of the Crystalline Disposal R&D Work Package is to advance our understanding of long-term disposal of used fuel in crystalline rocks and to develop necessary experimental and computational capabilities to evaluate various disposal concepts in such media.
Design of materials configurations for enhanced phononic and electronic properties
Daraio, Chiara
The discovery of novel nonlinear dynamic and electronic phenomena is presented for the specific cases of granular materials and carbon nanotubes. This research was conducted for designing and constructing optimized macro-, micro- and nano-scale structural configurations of materials, and for studying their phononic and electronic behavior. Variation of composite arrangements of granular elements with different elastic properties in a linear chain-of-sphere, Y-junction or 3-D configurations led to a variety of novel phononic phenomena and interesting physical properties, which can be potentially useful for security, communications, mechanical and biomedical engineering applications. Mechanical and electronic properties of carbon nanotubes with different atomic arrangements and microstructures were also investigated. Electronic properties of Y-junction configured carbon nanotubes exhibit an exciting transistor switch behavior which is not seen in linear configuration nanotubes. Strongly nonlinear materials were designed and fabricated using novel and innovative concepts. Due to their unique strongly nonlinear and anisotropic nature, novel wave phenomena have been discovered. Specifically, violations of Snell's law were detected and a new mechanism of wave interaction with interfaces between NTPCs (Nonlinear Tunable Phononic Crystals) was established. Polymer-based systems were tested for the first time, and the tunability of the solitary waves speed was demonstrated. New materials with transformed signal propagation speed in the manageable range of 10-100 m/s and signal amplitude typical for audible speech have been developed. The enhancing of the mitigation of solitary and shock waves in 1-D chains were demonstrated and a new protective medium was designed for practical applications. 1-D, 2-D and 3-D strongly nonlinear system have been investigated providing a broad impact on the whole area of strongly nonlinear wave dynamics and creating experimental basis for new
Evolution of the phonon density of states of LaCoO3 over the spin state transition
Energy Technology Data Exchange (ETDEWEB)
Golosova, N. O. [Joint Institute for Nuclear Research, Dubna, Russia; Kozlenko, D. P. [Joint Institute for Nuclear Research, Dubna, Russia; Kolesnikov, Alexander I [ORNL; Kazimirov, V. Yu. [Joint Institute for Nuclear Research, Dubna, Russia; Smirnov, M. B. [St. Petersburg State University, St. Petersburg, Russia; Jirak, Z. [Institute of Physics, Czech Republic; Savenko, B. N. [Joint Institute for Nuclear Research, Dubna, Russia
2011-01-01
The phonon spectra of LaCoO3 were studied by inelastic neutron scattering in the temperature range of 4 120 K. The DFT calculations of the lattice dynamics have been made for interpretation of the experimental data. The observed and calculated phonon frequencies were found to be in a reasonable agreement. The evolution of the phonon density of states over the spin state transition was analyzed. In the low-temperature range (T < 50 K), an increase in the energy of resolved breathing, stretching, and bending phonon modes was found, followed by their softening and broadening at higher temperatures due to the spin state transition and relevant orbital-phonon coupling.
Temperature effects on the phonon spectrum in YBa2Cu3O7 single crystal and thin films
Feile, Rudolf; Leiderer, Paul; Kowalewski, Jerzy; Assmus, Wolf; Schubert, J.; Poppe, Ulrich
1988-01-01
We have performed detailed investigations on the temperature dependence of the 335 cm 1 phonon in single crystals and thin films of the YBa2Cu3O7 superconductor. The frequency of this phonon exhibits a downshift of about 5 cm 1 on passing the superconducting transition from above. The shift of the phonon in thin epitaxial films on MgO or SrTiO3 substrates is only about 2.5 cm 1. The width of the asymmetric phonon line displays a slight increase below Tc due to the electron-phonon interaction ...
Interface defect-assisted phonon scattering of hot carriers in graphene
Menabde, Sergey G.; Cho, Hyunwoo; Park, Namkyoo
2017-08-01
The broadband and ultrafast photoresponse of graphene has been extensively studied in recent years, although the photoexcited carrier dynamics is still far from being completely understood. Different experimental approaches imply either one of two fundamentally different scattering mechanisms for hot electrons. One is high-energy optical phonons, while the other is disorder-driven supercollisions with acoustic phonons. However, the concurrent relaxation via both optical and acoustic phonons has not been considered so far, hindering the interpretation of different experiments within a unified framework. Here we expand the optical phonon-mediated cooling model, to include electron scattering with the acoustic phonons. By assuming the enhancement of electron-acoustic phonon supercollisions from the localized defect at the photothermoelectric current-generating interface, we provide a broader perspective to the ultrafast photoresponse of graphene, highlighting the previously overlooked effect of the interface for cooling dynamics. We show that the transient photothermoelectric response, which has been attributed exclusively to supercollisions, can be successfully explained without rejecting the established optical phonon relaxation pathway, demonstrating that the two cooling mechanisms are not mutually exclusive but complement each other.
Reigue, Antoine; Iles-Smith, Jake; Lux, Fabian; Monniello, Léonard; Bernard, Mathieu; Margaillan, Florent; Lemaitre, Aristide; Martinez, Anthony; McCutcheon, Dara P S; Mørk, Jesper; Hostein, Richard; Voliotis, Valia
2017-06-09
We investigate the temperature dependence of photon coherence properties through two-photon interference (TPI) measurements from a single quantum dot (QD) under resonant excitation. We show that the loss of indistinguishability is related only to the electron-phonon coupling and is not affected by spectral diffusion. Through these measurements and a complementary microscopic theory, we identify two independent separate decoherence processes, both of which are associated with phonons. Below 10 K, we find that the relaxation of the vibrational lattice is the dominant contribution to the loss of TPI visibility. This process is non-Markovian in nature and corresponds to real phonon transitions resulting in a broad phonon sideband in the QD emission spectra. Above 10 K, virtual phonon transitions to higher lying excited states in the QD become the dominant dephasing mechanism, this leads to a broadening of the zero phonon line, and a corresponding rapid decay in the visibility. The microscopic theory we develop provides analytic expressions for the dephasing rates for both virtual phonon scattering and non-Markovian lattice relaxation.
Isotopic phonon effects in β-rhombohedral boron--non-statistical isotope distribution.
Werheit, H; Filipov, V; Kuhlmann, U; Schwarz, U; Armbrüster, M; Antadze, M
2012-05-02
On the basis of the spectra of IR- and Raman-active phonons, the isotopic phonon effects in β-rhombohedral boron are analysed for polycrystalline (10)B- and (11)B-enriched samples of different origin and high-purity (nat)B single crystals. Intra- and inter-icosahedral B-B vibrations are harmonic, hence meeting the virtual crystal approximation (VCA) requirements. Deviations from the phonon shift expected according to the VCA are attributed to the anharmonic share of the lattice vibrations. In the case of icosahedral vibrations, the agreement with calculations on α-rhombohedral boron by Shirai and Katayama-Yoshida is quite satisfactory. Phonon shifts due to isotopic disorder in (nat)B are separated and determined. Some phonon frequencies are sensitive to impurities. The isotopic phonon effects yield valuable specific information on the nature of the different phonon modes. The occupation of regular boron sites by isotopes deviates significantly from the random distribution. © 2012 IOP Publishing Ltd
Electronic and phononic modulation of MoS2 under biaxial strain
Moghadasi, A.; Roknabadi, M. R.; Ghorbani, S. R.; Modarresi, M.
2017-12-01
Dichalcogenides of transition metals are attractive material due to its unique properties. In this work, it has been investigated the electronic band structure, phonon spectrum and heat capacity of MoS2 under the applied tensile and compressive biaxial strain using the density functional theory. The Molybdenum disulfide under compressive (tensile) strain up to 6% (10%) has stable atomic structure without any negative frequency in the phonon dispersion curves. The tensile biaxial strain reduces the energy gap in the electronic band structure and the optical-acoustic gap in phonon dispersion curves. The tensile biaxial strain also increases the specific heat capacity. On the other hand, the compressive biaxial strain in this material increases phonon gap and reduces the heat capacity and the electronic band gap. The phonon softening/hardening is reported for tensile/compressive biaxial strain in MoS2. We report phonon hardening for out of plane ZA mode in the presence of both tensile and compressive strains. Results show that the linear variation of specific heat with strain (CV ∝ε) and square dependency of specific heat with the temperature (CV ∝T2) for low temperature regime. The results demonstrate that the applied biaxial strain tunes the electronic energy gap and modifies the phonon spectrum of MoS2.
Phonon interactions with methyl radicals in single crystals
Directory of Open Access Journals (Sweden)
James W. Wells
2017-04-01
Full Text Available The high temperature ESR spectra’s anomalous appearance at very low temperatures for the methyl radical created in single crystals is explained by magnetic dipole interactions with neighboring protons. These protons acting via phonon vibrations induce resonant oscillations with the methyl group to establish a very temperature sensitive ‘‘relaxation’’ mode that allows the higher energy ‘‘E’’ state electrons with spin 12 to ‘‘decay’’ into ‘‘A’’ spin 12 states. Because of the amplitude amplification with temperature, the ‘‘E’’ state population is depleted and the ‘‘A’’ state population augmented to produce the high temperature ESR spectrum. This phenomenon is found to be valid for all but the very highest barriers to methyl group tunneling. In support, a time dependent spin population study shows this temperature evolution in the state populations under this perturbation.
Demonstration of acoustic waveguiding and tight bending in phononic crystals
Ghasemi Baboly, M.; Raza, A.; Brady, J.; Reinke, C. M.; Leseman, Z. C.; El-Kady, I.
2016-10-01
The systematic design, fabrication, and characterization of an isolated, single-mode, 90° bend phononic crystal (PnC) waveguide are presented. A PnC consisting of a 2D square array of circular air holes in an aluminum substrate is used, and waveguides are created by introducing a line defect in the PnC lattice. A high transmission coefficient is observed (-1 dB) for the straight sections of the waveguide, and an overall 2.3 dB transmission loss is observed (a transmission coefficient of 76%) for the 90° bend. Further optimization of the structure may yield higher transmission efficiencies. This manuscript shows the complete design process for an engineered 90° bend PnC waveguide from inception to experimental demonstration.
Phonon-mediated path-interference in electronic energy transfer.
Hossein-Nejad, Hoda; Olaya-Castro, Alexandra; Scholes, Gregory D
2012-01-14
We present a formalism to quantify the contribution of path-interference in phonon-mediated electronic energy transfer. The transfer rate between two molecules is computed by considering the quantum mechanical amplitudes associated with pathways connecting the initial and final sites. This includes contributions from classical pathways, but also terms arising from interference of different pathways. We treat the vibrational modes coupled to the molecules as a non-Markovian harmonic oscillator bath, and investigate the correction to transfer rates due to the lowest-order interference contribution. We show that depending on the structure of the harmonic bath, the correction due to path-interference may have a dominant vibrational or electronic character, and can make a notable contribution to the transfer rate in the steady state.
Quantum State Transfer via Noisy Photonic and Phononic Waveguides.
Vermersch, B; Guimond, P-O; Pichler, H; Zoller, P
2017-03-31
We describe a quantum state transfer protocol, where a quantum state of photons stored in a first cavity can be faithfully transferred to a second distant cavity via an infinite 1D waveguide, while being immune to arbitrary noise (e.g., thermal noise) injected into the waveguide. We extend the model and protocol to a cavity QED setup, where atomic ensembles, or single atoms representing quantum memory, are coupled to a cavity mode. We present a detailed study of sensitivity to imperfections, and apply a quantum error correction protocol to account for random losses (or additions) of photons in the waveguide. Our numerical analysis is enabled by matrix product state techniques to simulate the complete quantum circuit, which we generalize to include thermal input fields. Our discussion applies both to photonic and phononic quantum networks.
Sound-Particles and Phonons with Spin 1
Directory of Open Access Journals (Sweden)
Minasyan V.
2011-01-01
Full Text Available We present a new model for solids which is based on the stimulated vibration of inde- pendent neutral Fermi-atoms, representing independent harmonic oscillators with natu- ral 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 fi- nite 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.
Experimental progress toward single phonon creation in a mechanical resonator
O'Connell, Aaron; Ansmann, M.; Bialczak, R. C.; Hofheinz, M.; Lucero, E.; Neeley, M.; Sank, D.; Wang, H.; Wenner, J.; Martinis, J. M.; Cleland, A. N.
2009-03-01
Coupling a high frequency (˜6 GHz) mechanical resonator to a Josephson phase qubit may enable the creation and manipulation of single phonons. Previously, we have shown the creation of arbitrary photon states in a superconducting coplanar waveguide (CPW) resonator coupled to a phase qubit (Max Hofheinz et al., Nature 454, 310-314, 2008). That experiment illustrated the capability of the phase qubit to controllably create and measure quantum states in a capacitively coupled resonator. By replacing the CPW resonator with a film bulk acoustic resonator (FBAR) we can potentially transfer the quantum state of the phase qubit to a vibrational mode of the FBAR. This talk will focus on our experimental progress to date in realizing this aim.
Infrared ellipsometry on semiconductor layer structures phonons, plasmons, and polaritons
Schubert, Mathias
2004-01-01
The study of semiconductor-layer structures using infrared ellipsometry is a rapidly growing field within optical spectroscopy. This book offers basic insights into the concepts of phonons, plasmons and polaritons, and the infrared dielectric function of semiconductors in layered structures. It describes how strain, composition, and the state of the atomic order within complex layer structures of multinary alloys can be determined from an infrared ellipsometry examination. Special emphasis is given to free-charge-carrier properties, and magneto-optical effects. A broad range of experimental examples are described, including multinary alloys of zincblende and wurtzite structure semiconductor materials, and future applications such as organic layer structures and highly correlated electron systems are proposed.
Quantum State Transfer via Noisy Photonic and Phononic Waveguides
Vermersch, B.; Guimond, P.-O.; Pichler, H.; Zoller, P.
2017-03-01
We describe a quantum state transfer protocol, where a quantum state of photons stored in a first cavity can be faithfully transferred to a second distant cavity via an infinite 1D waveguide, while being immune to arbitrary noise (e.g., thermal noise) injected into the waveguide. We extend the model and protocol to a cavity QED setup, where atomic ensembles, or single atoms representing quantum memory, are coupled to a cavity mode. We present a detailed study of sensitivity to imperfections, and apply a quantum error correction protocol to account for random losses (or additions) of photons in the waveguide. Our numerical analysis is enabled by matrix product state techniques to simulate the complete quantum circuit, which we generalize to include thermal input fields. Our discussion applies both to photonic and phononic quantum networks.
Seismic isolation of buildings on two dimensional phononic crystal foundation
Han, Lin; Li, Xiao-mei; Zhang, Yan
2017-11-01
In order to realize the seismic isolation of buildings, we establish the two dimensional phononic crystal (PC) foundation which has the cell with the size close to the regular concrete test specimens, and is composed of the concrete base, rubber coating and lead cylindrical core. We study the in-plane band gap (BG) characteristics in it, through the analysis of the frequency dispersion relation and frequency response result. To lower the start BG frequency to the seismic frequency range, we also study the influences of material parameters (the elastic modulus of coating and density of cylindrical core) and geometry parameters (the thickness of coating, radius of cylindrical core and lattice constant) on BG ranges. The study could help to design the PC foundation for seismic isolation of building.
Accidental degeneracy of double Dirac cones in a phononic crystal
Chen, Ze-Guo
2014-04-09
Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect.
Acoustic cloaking by a near-zero-index phononic crystal
Zheng, Li-Yang
2014-04-21
Zero-refractive-index materials may lead to promising applications in various fields. Here, we design and fabricate a near Zero-Refractive-Index (ZRI) material using a phononic crystal (PC) composed of a square array of densely packed square iron rods in air. The dispersion relation exhibits a nearly flat band across the Brillouin zone at the reduced frequency f = 0.5443c/a, which is due to Fabry-Perot (FP) resonance. By using a retrieval method, we find that both the effective mass density and the reciprocal of the effective bulk modulus are close to zero at frequencies near the flat band. We also propose an equivalent tube network model to explain the mechanisms of the near ZRI effect. This FP-resonance-induced near ZRI material offers intriguing wave manipulation properties. We demonstrate both numerically and experimentally its ability to shield a scattering obstacle and guide acoustic waves through a bent structure.
Localized surface phonon polariton resonances in polar gallium nitride
Energy Technology Data Exchange (ETDEWEB)
Feng, Kaijun, E-mail: kfeng@nd.edu; Islam, S. M.; Verma, Jai; Hoffman, Anthony J. [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Streyer, William; Wasserman, Daniel [Department of Electrical and Computer Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 (United States); Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14850 (United States)
2015-08-24
We demonstrate the excitation of localized surface phonon polaritons in an array of sub-diffraction pucks fabricated in an epitaxial layer of gallium nitride (GaN) on a silicon carbide (SiC) substrate. The array is characterized via polarization- and angle-dependent reflection spectroscopy in the mid-infrared, and coupling to several localized modes is observed in the GaN Reststrahlen band (13.4–18.0 μm). The same structure is simulated using finite element methods and the charge density of the modes are studied; transverse dipole modes are identified for the transverse electric and magnetic polarizations and a quadrupole mode is identified for the transverse magnetic polarization. The measured mid-infrared spectrum agrees well with numerically simulated spectra. This work could enable optoelectronic structures and devices that support surface modes at mid- and far-infrared wavelengths.
Acoustic frequency filter based on anisotropic topological phononic crystals
Chen, Zeguo
2017-11-02
We present a design of acoustic frequency filter based on a two-dimensional anisotropic phononic crystal. The anisotropic band structure exhibits either a directional or a combined (global + directional) bandgap at certain frequency regions, depending on the geometry. When the time-reversal symmetry is broken, it may introduce a topologically nontrivial bandgap. The induced nontrivial bandgap and the original directional bandgap result in various interesting wave propagation behaviors, such as frequency filter. We develop a tight-binding model to characterize the effective Hamiltonian of the system, from which the contribution of anisotropy is explicitly shown. Different from the isotropic cases, the Zeeman-type splitting is not linear and the anisotropic bandgap makes it possible to achieve anisotropic propagation characteristics along different directions and at different frequencies.
Spinon phonon interaction and ultrasonic attenuation in quantum spin liquids.
Zhou, Yi; Lee, Patrick A
2011-02-04
Several experimental candidates for quantum spin liquids have been discovered in the past few years which appear to support gapless fermionic S=1/2 excitations called spinons. The spinons may form a Fermi sea coupled to a U(1) gauge field, and may undergo a pairing instability. We show that despite being charge neutral, the spinons couple to phonons in exactly the same way that electrons do in the long wavelength limit. Therefore, we can use sound attenuation to measure the spinon mass and lifetime. Furthermore, transverse ultrasonic attenuation is a direct probe of the onset of pairing because the Meissner effect of the gauge field causes a "rapid fall" of the attenuation at T(c) in addition to the reduction due to the opening of the energy gap. This phenomenon, well known in clean superconductors, may reveal the existence of the U(1) gauge field.
Phonon mediated spin relaxation in a moving quantum dot
Zhao, Xinyu; Huang, Peihao; Hu, Xuedong
2015-03-01
We study decoherence of an electron spin qubit that is being transported in a moving quantum dot. Our focus is on spin relaxation due to phonon noise through the spin-orbit interaction. We find that the effective magnetic field caused by the motion of the electron can either enhance or suppress spin relaxation depending on the angle between the moving direction and the external magnetic field. At low external magnetic field (BAlt 0 . 5 T), the suppression effect can be significant, which indicates that a moving quantum dot can maintain spin coherence better than a static dot. We also find that the spin relaxation rate is not a monotonically increasing function of the applied magnetic field when the motion of the electron is taken into account. We thank financial support by US ARO and NSF PIF.
Observation of the Phononic Lamb Shift with a Synthetic Vacuum
Directory of Open Access Journals (Sweden)
T. Rentrop
2016-11-01
Full Text Available In contrast to classical empty space, the quantum vacuum fundamentally alters the properties of embedded particles. This paradigm shift allows one to explain the discovery of the celebrated Lamb shift in the spectrum of the hydrogen atom. Here, we engineer a synthetic vacuum, building on the unique properties of ultracold atomic gas mixtures, offering the ability to switch between empty space and quantum vacuum. Using high-precision spectroscopy, we observe the phononic Lamb shift, an intriguing many-body effect originally conjectured in the context of solid-state physics. We find good agreement with theoretical predictions based on the Fröhlich model. Our observations establish this experimental platform as a new tool for precision benchmarking of open theoretical challenges, especially in the regime of strong coupling between the particles and the quantum vacuum.
Directory of Open Access Journals (Sweden)
Leena Aggarwal
2016-06-01
Full Text Available We report direct observation of local ferroelectric ordering above room temperature in rocksalt SnTe, which is a topological crystalline insulator and a good thermoelectric material. Although SnTe is known to stabilize in a ferroelectric ground state (rhombohedral phase below ∼100 K, at high temperatures it was not expected to show any ferroelectric ordering forbidden by its globally centro-symmetric crystal structure (Fm-3m. Here, we show that SnTe exhibits local ferroelectric ordering that is robust above room temperature through direct imaging of ferroelectric domains by piezoresponse force microscopy and measurement of local polarization switching using switching spectroscopy. Using first-principles theoretical analysis, we show how the local ferroelectricity arises from soft bonding and competing phonon instabilities at intermediate wavelengths, which induce local Sn-off centering in the otherwise cetrosymmetric SnTe crystal structure. The results make SnTe an important member of the family of new multi-functional materials namely the ferroelectric-thermoelectrics.
Phonon dispersion models for MgB{sub 2} with application of pressure
Energy Technology Data Exchange (ETDEWEB)
Alarco, Jose A., E-mail: jose.alarco@qut.edu.au; Talbot, Peter C., E-mail: p.talbot@qut.edu.au; Mackinnon, Ian D.R., E-mail: ian.mackinnon@qut.edu.au
2017-05-15
Highlights: • Ab initio DFT MgB{sub 2} phonon dispersion for pressures up to 20 GPa are presented. • Extent of E{sub 2g} phonon anomaly and thermal energy, T{sub δ,} are pressure dependent. • Phonon anomaly thermal energy equivalent to experimental T{sub c} values for MgB{sub 2}. • Computational method to measure T{sub δ} is an effective predictor of T{sub c}. - Abstract: We evaluate, via the Local Density and the Generalised Gradient Approximations to the Density Functional Theory (DFT), the change in form and extent of the E{sub 2g} phonon anomaly of MgB{sub 2} with increase in applied pressure up to 20 GPa. Ab initio DFT calculations on the phonon dispersion (PD) for MgB{sub 2} show a phonon anomaly symmetrically displaced around Γ, the reciprocal lattice origin. This anomaly is related to nesting between diametrically opposite sides of tubular elements of Fermi surfaces, which correspond to sigma bonding and run approximately parallel to the Γ–A reciprocal space direction. The anomaly is parallel to Γ–A and along Γ–M and Γ–K. The extent of the E{sub 2g} phonon anomaly, δ, along Γ–M and Γ–K is a measure of the thermal energy, T{sub δ}, that matches within error the experimental onset superconducting transition temperature, T{sub c}. Ab initio DFT calculations with pressure for −5 GPa < P < 20 GPa show a linear reduction in T{sub δ} that closely matches experimental T{sub c} values for MgB{sub 2}. For phonon-mediated superconductors with AlB{sub 2}–type structures, the thermal energy of the phonon anomaly, T{sub δ}, is a reliable predictor of T{sub c}.
Carrier-phonon interaction in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Seebeck, Jan
2009-03-10
In recent years semiconductor quantum dots have been studied extensively due to their wide range of possible applications, predominantly for light sources. For successful applications, efficient carrier scattering processes as well as a detailed understanding of the optical properties are of central importance. The aims of this thesis are theoretical investigations of carrier scattering processes in InGaAs/GaAs quantum dots on a quantum-kinetic basis. A consistent treatment of quasi-particle renormalizations and carrier kinetics for non-equilibrium conditions is presented, using the framework of non-equilibrium Green's functions. The focus of our investigations is the interaction of carriers with LO phonons. Important for the understanding of the scattering mechanism are the corresponding quasi-particle properties. Starting from a detailed study of quantum-dot polarons, scattering and dephasing processes are discussed for different temperature regimes. The inclusion of polaron and memory effects turns out to be essential for the description of the carrier kinetics in quantum-dot systems. They give rise to efficient scattering channels and the obtained results are in agreement with recent experiments. Furthermore, a consistent treatment of the carrier-LO-phonon and the carrier-carrier interaction is presented for the optical response of semiconductor quantum dots, both giving rise to equally important contributions to the dephasing. Beside the conventional GaAs material system, currently GaN based light sources are of high topical interest due to their wide range of possible emission frequencies. In this material additionally intrinsic properties like piezoelectric fields and strong band-mixing effects have to be considered. For the description of the optical properties of InN/GaN quantum dots a procedure is presented, where the material properties obtained from an atomistic tight-binding approach are combined with a many-body theory for non
Topological crystalline insulator SnTe nanoribbons
Dahal, Bishnu R.; Dulal, Rajendra P.; Pegg, Ian L.; Philip, John
2017-03-01
Topological crystalline insulators are systems in which a band inversion that is protected by crystalline mirror symmetry gives rise to nontrivial topological surface states. SnTe is a topological crystalline insulator. It exhibits p-type conductivity due to Sn vacancies and Te antisites, which leads to high carrier density in the bulk. Thus growth of high quality SnTe is a prerequisite for understanding the topological crystalline insulating behavior. We have grown SnTe nanoribbons using a solution method. The width of the SnTe ribbons varies from 500 nm to 2 μm. They exhibit rock salt crystal structure with a lattice parameter of 6.32 Å. The solution method that we have adapted uses low temperature, so the Sn vacancies can be controlled. The solution grown SnTe nanoribbons exhibit strong semiconducting behavior with an activation energy of 240 meV. This activation energy matches with the calculated band gap for SnTe with a lattice parameter of 6.32 Å, which is higher than that reported for bulk SnTe. The higher activation energy makes the thermal excitation of bulk charges very difficult on the surface. As a result, the topological surfaces will be free from the disturbance caused by the thermal excitations
Crystalline Fullerenes. Round Pegs in Square Holes
Fleming, R.M.; Hessen, B.; Siegrist, T.; Kortan, A.R.; Marsh, P.; Tycko, R.; Dabbagh, G.; Haddon, R.C.
1992-01-01
The fullerenes C60 and C70 act as spherical building blocks in crystalline solids to form a variety of crystal structures. In many cases, the icosahedral molecular symmetry of C60 appears to play little role in determining the crystal structure. In this chapter we discuss our results on the
Quasi-crystalline geometry for architectural structures
DEFF Research Database (Denmark)
Wester, Ture; Weinzieri, Barbara
The quasi-crystal (QC) type of material was discovered in 1983 by Dan Schechtman from Technion, Haifa. This new crystalline structure of material broke totally with the traditional conception of crystals and geometry introducing non-periodic close packing of cells with fivefold symmetry in 3D space...
Donor-hydrogen complexes in crystalline silicon
Liang, Z.N.; Niesen, L; Haas, C; Denteneer, P.J.H.
1996-01-01
Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing Sb-119 --> Sn-119 source Mossbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the Mossbauer intensity associated with
Crystalline amino acids and nitrogen emission
Verstegen, M.W.A.; Jongbloed, A.W.
2003-01-01
Reductions in dietary protein level and supplementation with certain crystalline amino acids is a well-established method of formulating diets to achieve a more ideal amino acid pattern and to reduce nitrogen excretion. Up to 35% reduction in nitrogen excretion may be achieved by supplementing pig
Gamma crystallins of the human eye lens.
Vendra, Venkata Pulla Rao; Khan, Ismail; Chandani, Sushil; Muniyandi, Anbukkarasi; Balasubramanian, Dorairajan
2016-01-01
Protein crystallins co me in three types (α, β and γ) and are found predominantly in the eye, and particularly in the lens, where they are packed into a compact, plastic, elastic, and transparent globule of proper refractive power range that aids in focusing incoming light on to the retina. Of these, the γ-crystallins are found largely in the nuclear region of the lens at very high concentrations (>400 mg/ml). The connection between their structure and inter-molecular interactions and lens transparency is an issue of particular interest. We review the origin and phylogeny of the gamma crystallins, their special structure involving the use of Greek key supersecondary structural motif, and how they aid in offering the appropriate refractive index gradient, intermolecular short range attractive interactions (aiding in packing them into a transparent ball), the role that several of the constituent amino acid residues play in this process, the thermodynamic and kinetic stability and how even single point mutations can upset this delicate balance and lead to intermolecular aggregation, forming light-scattering particles which compromise transparency. We cite several examples of this, and illustrate this by cloning, expressing, isolating and comparing the properties of the mutant protein S39C of human γS-crystallin (associated with congenital cataract-microcornea), with those of the wild type molecule. In addition, we note that human γ-crystallins are also present in other parts of the eye (e.g., retina), where their functions are yet to be understood. There are several 'crucial' residues in and around the Greek key motifs which are essential to maintain the compact architecture of the crystallin molecules. We find that a mutation that replaces even one of these residues can lead to reduction in solubility, formation of light-scattering particles and loss of transparency in the molecular assembly. Such a molecular understanding of the process helps us construct the
Effect of crystalline electric field on heat capacity of LnBaCuFeO5 (Ln = Gd, Ho, Yb)
Lal, Surender; Mukherjee, K.; Yadav, C. S.
2018-02-01
Structural, magnetic and thermodynamic properties of layered perovskite compounds LnBaCuFeO5 (Ln = Ho, Gd, Yb) have been investigated. Unlike the iso-structural compound YBaCuFeO5, which shows commensurate antiferromagnetic to incommensurate antiferromagnetic ordering below ∼200 K, the studied compounds do not show any magnetic transition in measured temperature range of 2-350 K. The high temperature heat capacity of the compounds is understood by employing contributions from both optical and acoustic phonons. At low temperature, the observed upturn in the heat capacity is attributed to the Schottky anomaly. The magnetic field dependent heat capacity shows the variation in position of the anomaly with temperature, which appears due to the removal of ground state degeneracy of the rare earth ions, by the crystalline electric field.
Dri, Fernando L.; Shang, ShunLi; Hector, Louis G., Jr.; Saxe, Paul; Liu, Zi-Kui; Moon, Robert J.; Zavattieri, Pablo D.
2014-12-01
Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose Iβ were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500 K) of the monoclinic cellulose Iβ lattice parameters, constant pressure heat capacity, Cp, entropy, S, enthalpy, H, the linear thermal expansion components, ξi, and components of the isentropic and isothermal (single crystal) elastic stiffness matrices, CijS (T) and CijT (T) , respectively. Thermodynamic quantities from phonon calculations computed with DFT and the supercell method provided necessary inputs to compute the temperature dependence of cellulose Iβ properties via the quasi-harmonic approach. The notable exceptions were the thermal conductivity components, λi (the prediction of which has proven to be problematic for insulators using DFT) for which the reverse, non-equilibrium molecular dynamics approach with a force field was applied. The extent to which anisotropy of Young's modulus and Poisson's ratio is temperature-dependent was explored in terms of the variations of each with respect to crystallographic directions and preferred planes containing specific bonding characteristics (as revealed quantitatively from phonon force constants for each atomic pair, and qualitatively from charge density difference contours). Comparisons of the predicted quantities with available experimental data revealed reasonable agreement up to 500 K. Computed properties were interpreted in terms of the cellulose Iβ structure and bonding interactions.
First-principles electron transport with phonon coupling: Large scale at low cost
DEFF Research Database (Denmark)
Gunst, Tue; Markussen, Troels; Palsgaard, Mattias L. N.
2017-01-01
Phonon-assisted tunneling plays a crucial role for electronic device performance and even more so with future size down-scaling. We show how one can include this effect in large-scale first-principles calculations using a single "special thermal displacement" (STD) of the atomic coordinates......-to-band and source-to-drain tunneling. In a diode the phonons lead to a rectification ratio suppression in good agreement with experiments, while in an ultrathin body transistor the phonons increase off currents by four orders of magnitude, and the subthreshold swing by a factor of 4, in agreement with perturbation...
Prediction of phonon-mediated superconductivity in hole-doped black phosphorus.
Feng, Yanqing; Sun, Hongyi; Sun, Junhui; Lu, Zhibin; You, Yong
2018-01-10
We study the conventional electron-phonon mediated superconducting properties of hole-doped black phosphorus by density functional calculations and get quite a large electron-phonon coupling (EPC) constant λ ~ 1.0 with transition temperature T C ~ 10 K, which is comparable to MgB 2 when holes are doped into the degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency [Formula: see text] optical mode and its phonon displacement, which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC. These factors are favorable for BCS superconductivity.
Measuring the effective phonon density of states of a quantum dot in cavity quantum electrodynamics
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Nielsen, Per Kær; Kreiner-Møller, Asger
2013-01-01
We employ detuning-dependent decay-rate measurements of a quantum dot in a photonic-crystal cavity to study the influence of phonon dephasing in a solid-state quantum-electrodynamics experiment. The experimental data agree with a microscopic non-Markovian model accounting for dephasing from...... longitudinal acoustic phonons, and the analysis explains the difference between nonresonant cavity feeding in different nanocavities. From the comparison between experiment and theory we extract the effective phonon density of states experienced by the quantum dot in the nanocavity. This quantity determines...
Evidence of a Love wave bandgap in a quartz substrate coated with a phononic thin layer
Energy Technology Data Exchange (ETDEWEB)
Liu, Ting-Wei; Wu, Tsung-Tsong, E-mail: wutt@ntu.edu.tw [Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan (China); Lin, Yu-Ching; Tsai, Yao-Chuan [WPI-AIMR, Tohoku University, Sendai (Japan); Ono, Takahito; Tanaka, Shuji [Department of Mechanical Engineering, Tohoku University, Sendai (Japan)
2014-05-05
This paper presents a numerical and experimental study of Love wave propagation in a micro-fabricated phononic crystal (PC) structure consisting of a 2D, periodically etched silica film deposited on a quartz substrate. The dispersion characteristics of Love waves in such a phononic structure were analyzed with various geometric parameters by using complex band structure calculations. For the experiment, we adopted reactive-ion etching with electron-beam lithography to fabricate a submicrometer phononic structure. The measured results exhibited consistency with the numerical prediction. The results of this study may serve as a basis for developing PC-based Love wave devices.
DEFF Research Database (Denmark)
Willatzen, Morten; Duggen, Lars
2017-01-01
-growth direction, and will be jointly excited by electrical stimulus. We demonstrate this for an electrically excited freestanding slab for two cases of high-symmetry crystal-growth directions and finally show the impact of the Drude model for permittivity on the phonon dispersion. In particular, it is verified...... that the piezoelectric effect leads to a drastically enhanced coupling of acoustic and optical phonon modes and increase in the local phonon density of states near the plasma frequency where the permittivity approaches zero....
A Strategy to Suppress Phonon Transport in Molecular Junctions Using pi-Stacked Systems
DEFF Research Database (Denmark)
Li, Qian; Strange, Mikkel; Duchemin, Ivan
2017-01-01
Molecular junctions are promising candidates for thermoelectric devices due to the potential to tune the electronic and thermal transport properties. However, a high figure of merit is hard to achieve, without reducing the phononic contribution to thermal conductance. Here, we propose a strategy...... to suppress phonon transport in graphene-based molecular junctions preserving high electronic power factor, using nonbonded pi-stackal systems. Using first-principles calculations, we find that the thermal conductance of pi-stacked systems can be reduced by about 95%, compared with that of a covalently bonded...... of the very low phononic thermal conductance, leaving tom for further optimization of the electronic properties....
Laser structuring for control of coupling between THz light and phonon modes
Wang, X W; Balcytis, A; Kasalynas, I; Jakstas, V; Janonis, V; Venckevicius, R; Buividas, R; Appadoo, D; Valusis, G; Juodkazis, S
2016-01-01
Modification of surface and volume of sapphire is shown to affect reflected and transmitted light at THz spectral range. Structural modifications were made using ultra-short 230 fs laser pulses at 1030 nm and 257.5 nm wavelengths forming surface ripples of ~250 nm and 60 nm period, respectively. Softening of the transverse optical phonon TO1 mode due to disorder was the most pronounced in reflection from laser ablated surface. It is shown that sub-surface periodic patterns of laser damage sites have also modified reflection spectrum due to coupling of THz radiation with phonons. Application potential of laser structuring and disordering for phononic engineering is discussed.
Resonant Scattering of Acoustic Phonons by Randomly Distributed Two-Level Systems
Kayanuma, Yosuke; Yamada, Hiroshi; Tanaka, Satoshi
1985-07-01
A Green function formalism is developed for the resonant scattering of acoustic phonons by randomly distributed two-level systems. The randomness is treated by the coherent potential approximation. The theory reproduces the Jacobsen-Stevens dispersion law in the dense limit of the concentration of the two-level system and the results obtained so far by the average t-matrix approximation in the dilute limit. The gradual change of the character of the resonantly scattered phonons as the concentration is varied is investigated through the calculation of various quantities such as the phonon density of states, the neutron scattering cross sections and the sound velocity.
DEFF Research Database (Denmark)
Hansen, Flemming Yssing; Alldredge, G. P.; McMurry, H. L.
1983-01-01
The phonon density of states for trigonal selenium has been calculated on the basis of a short range force model giving good overall agreement with experimental room temperature phonon dispersion data. A qualitative comparison with an experimental determination of the phonon density of states shows...... similarities in the gross features, but the experimental data lacks many of the finer details shown by the theoretical results due to resolution effects. The lattice dynamical contribution to the heat capacity CV is calculated and is found to be in good agreement with experimental determinations of Cp after...... transforming Cp to CV. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....
Features of electron-phonon interactions in nanotubes with chiral symmetry in magnetic field
Kibis, O V
2001-01-01
Interaction of the electrons with acoustic phonons in the nanotube with chiral symmetry by availability of the magnetic field, parallel to the nanotube axis, is considered. It is shown that the electron energy spectrum is asymmetric relative to the electron wave vector inversion and for that reason the electron-phonon interaction appears to be different for similar phonons with mutually contrary directions of the wave vector. This phenomenon leads to origination of the electromotive force by the spatially uniform electron gas heating and to appearance of the quadrupole component in the nanotube volt-ampere characteristics
Spin decoherence of a confined exciton due to one- and two-phonon assisted transitions
Roszak, K.; Machnikowski, P.; Axt, V. M.; Kuhn, T.
2010-01-01
Exciton spin decay in a self-assembled InAs/GaAs quantum dot is studied. The spin relaxation results from an interplay of two factors: the Bir-Pikus Hamiltonian and the short-range exchange interaction, leading to one- and two-phonon assisted transitions. We establish a hierarchy between the resulting transition rates; the one-phonon assisted transition to dark states is the fastest process. We also show the dominating role of transverse phonons for all of the transitions.
Directory of Open Access Journals (Sweden)
Subodh K. Gautam
2015-12-01
Full Text Available The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1 mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.
Directory of Open Access Journals (Sweden)
Andrei TOMA
2011-01-01
Full Text Available The present paper formulates a consensus moderation system based on the negotiation of the actors involved. There are a series of steps in the moderation process, the first of which is constructing a front of Pareto optimal solutions. Since this in itself will likely not lead to consensus in a real life scenario, Kaldor-Hicks compromises are then detected. Compromises are recommended at every iteration of the negotiation process which can lead to a lengthy negotiation time, which is addressed by using a recommendation engine based on the previous behavior of the actor.
Phonons in two-dimensional colloidal crystals with bond-strength disorder
Gratale, Matthew D.; Yunker, Peter J.; Chen, Ke; Still, Tim; Aptowicz, Kevin B.; Yodh, A. G.
2013-05-01
We study phonon modes in two-dimensional colloidal crystals composed of soft microgel particles with hard polystyrene particle dopants distributed randomly on the triangular lattice. This experimental approach produces close-packed lattices of spheres with random bond strength disorder, i.e., the effective springs coupling nearest neighbors are very stiff, very soft, or of intermediate stiffness. Particle tracking video microscopy and covariance matrix techniques are then employed to derive the phonon modes of the corresponding “shadow” crystals with bond strength disorder as a function of increasing dopant concentration. At low frequencies, hard and soft particles participate equally in the phonon modes, and the samples exhibit Debye-like density of states behavior characteristic of crystals. For mid- and high-frequency phonons, the relative participation of hard versus soft particles in each mode is found to vary systematically with dopant concentration. Additionally, a few localized modes, primarily associated with hard particle motions, are found at the highest frequencies.
Phonon thermal properties of graphene on h-BN from molecular dynamics simulations
Zou, Ji-Hang; Cao, Bing-Yang
2017-03-01
Phonon thermal properties of graphene on hexagonal boron nitride are investigated by the molecular dynamics simulations combined with lattice dynamics theory. It is found that the dispersion curves have minor changes for supported graphene because the interlayer coupling is too weak to shift the harmonic phonon properties. The ZA and ZO phonon lifetimes are significantly reduced in supported graphene due to the breakdown of the symmetry-based selection rule. The dominant mean free path (MFP) of graphene is reduced from 90-800 nm to 60-500 nm at 300 K. The mode thermal conductivities of free and supported graphene are 3517 W/ (m.K) and 2200 W/ (m.K) at 300 K, respectively. The thermal conductivity of supported graphene decreases by about 37.4% due to the large reduction of flexural phonon lifetimes, and the relative contribution of flexural modes decreases from 35.0% to 16.7%.
Microscopic modeling of the effect of phonons on the optical properties of solid-state emitters
Norambuena, Ariel; Reyes, Sebastián A.; Mejía-Lopéz, José; Gali, Adam; Maze, Jerónimo R.
2016-10-01
Understanding the effect of vibrations in optically active nanosystems is crucial for successfully implementing applications in molecular-based electro-optical devices, quantum information communications, single photon sources, and fluorescent markers for biological measurements. Here, we present a first-principles microscopic description of the role of phonons on the isotopic shift presented in the optical emission spectrum associated to the negatively charged silicon-vacancy color center in diamond. We use the spin-boson model and estimate the electron-phonon interactions using a symmetrized molecular description of the electronic states and a force-constant model to describe molecular vibrations. Group theoretical arguments and dynamical symmetry breaking are presented in order to explain the optical properties of the zero-phonon line and the isotopic shift of the phonon sideband.
Wang, Lei; Cai, Wei; Niu, Linyu; Luo, Weiwei; Ma, Zenghong; Du, Chenglin; Xue, Shuqing; Zhang, Xinzheng; Xu, Jingjun
2015-11-16
The coupled modes between graphene plasmons and surface phonons of a semiconductor substrate are investigated, which can be efficiently controlled by carrier injection of the substrate. A new physical mechanism on tuning plasmon-phonon coupled modes (PPCMs) is proposed due to the fact that the energy and lifetime of substrate surface phonons depend a lot on the carrier concentration. Specifically, the change of dispersion and lifetime of PPCMs can be controlled by the carrier concentration of the substrate. The energy of PPCMs for a given momentum increases as the carrier concentration of the substrate increases. On the other hand, the momentum of PPCMs for a given energy decreases when the carrier concentration of the substrate increases. The lifetime of PPCMs is always larger than the intrinsic lifetime of graphene plasmons without plasmon-phonon coupling.
A Neutron Study for Phonon Dispersion Relations in HgTe
DEFF Research Database (Denmark)
Kepa, H.; Gebicki, W.; Giebultowicz, T.
1980-01-01
Dispersion relations for acoustic phonons in mercury telluride in three high symmetry directions [111], [110] and [001] are presented. The eleven-parameter rigid-ion model is fitted to the experimental data....
Evolution of phonon anharmonicity in Se-doped S b2T e3 thermoelectrics
Das, Diptasikha; Das, Subarna; Singha, P.; Malik, K.; Deb, A. K.; Bhattacharyya, A.; Kulbachinskii, V. A.; Basu, Raktima; Dhara, Sandip; Bandyopadhyay, S.; Banerjee, Aritra
2017-08-01
The phonon anharmonicity in Se-doped S b2T e3 system is probed both macroscopically and microscopically using temperature-dependent synchrotron powder diffraction, Raman spectroscopic studies, and heat-capacity measurements. Gruneisen parameter (γG) is calculated to explain anharmonicity in the polycrystalline S b2T e3 -xS ex samples. The thermal variation of structural parameters, structural anisotropy, Debye temperature, velocity of sound, and isothermal compressibility of S b2T e3 -xS ex at room temperature are estimated. Analysis revealed that structural anisotropy and phonon anharmonicity are correlated. Further, lattice thermal conductivities (κL), evaluated in the Umklapp scattering limit in terms of γG, indicate that the phonon anharmonicity increasing with Se(x ) content reduces κL. A plausible explanation is provided on the basis of Se-doped softening of transverse optical phonon mode.
Renormalization effects and phonon density of states in high temperature superconductors
Directory of Open Access Journals (Sweden)
Vinod Ashokan
2013-02-01
Full Text Available Using the versatile double time thermodynamic Green's function approach based on many body theory the renormalized frequencies, phonon energy line widths, shifts and phonon density of states (PDOS are investigated via a newly formulated Hamiltonian (does not include BCS type Hamiltonian that includes the effects of electron-phonon, anharmonicities and that of isotopic impurities. The automatic appearance of pairons, temperature, impurity and electron-phonon coupling of renormalized frequencies, widths, shifts and PDOS emerges as a characteristic feature of present theory. The numerical investigations on PDOS for the YBa2Cu3O7 − δ crystal predicts several new feature of high temperature superconductors (HTS and agreements with experimental observations.
Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model
Energy Technology Data Exchange (ETDEWEB)
Aprea, G. [INFM-CNR SMC Center, and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , piazzale Aldo Moro 5, I-00185 Rome (Italy); Di Castro, C. [INFM-CNR SMC Center, and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , piazzale Aldo Moro 5, I-00185 Rome (Italy); Grilli, M. [INFM-CNR SMC Center, and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , piazzale Aldo Moro 5, I-00185 Rome (Italy)]. E-mail marco.grilli@roma1.infn.it; Lorenzana, J. [INFM-CNR SMC Center, and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , piazzale Aldo Moro 5, I-00185 Rome (Italy)
2006-06-12
We investigate the interplay between the electron-electron and the electron-phonon interaction in the Hubbard-Holstein model. We implement the flow-equation method to investigate within this model the effect of correlation on the electron-phonon effective coupling and, conversely, the effect of phonons in the effective electron-electron interaction. Using this technique we obtain analytical momentum-dependent expressions for the effective couplings and we study their behavior for different physical regimes. In agreement with other works on this subject, we find that the electron-electron attraction mediated by phonons in the presence of Hubbard repulsion is peaked at low transferred momenta. The role of the characteristic energies involved is also analyzed.
Bloch wave deafness and modal conversion at a phononic crystal boundary
Directory of Open Access Journals (Sweden)
Vincent Laude
2011-12-01
Full Text Available We investigate modal conversion at the boundary between a homogeneous incident medium and a phononic crystal, with consideration of the impact of symmetry on the excitation of Bloch waves. We give a quantitative criterion for the appearance of deaf Bloch waves, which are antisymmetric with respect to a symmetry axis of the phononic crystal, in the frame of generalized Fresnel formulas for reflection and transmission at the phononic crystal boundary. This criterion is used to index Bloch waves in the complex band structure of the phononic crystal, for directions of incidence along a symmetry axis. We argue that within deaf frequency ranges transmission is multi-exponential, as it is within frequency band gaps.
National Research Council Canada - National Science Library
Mohammadi, Saeed; Adibi, Ali
2011-01-01
In this paper, we report the evidence for the possibility of achieving complex signal processing functionalities such as multiplexing/demultiplexing at high frequencies using phononic crystal (PnC) slabs...
Steele, A
2000-01-01
this thesis data from phonon experiments are used to directly determine values for the parameters of an STJ such as the quasiparticle loss and tunnel rates in its electrodes. It is also shown how the input energy, in the form of phonons capable of breaking Cooper pairs, and the corresponding charge output from the device can be determined. These values are then compared with those obtained from x-ray absorption data. This thesis is concerned with the use of nanosecond phonon pulses to study quasiparticle behaviour in the electrodes of high-quality niobium superconducting tunnel junctions (STJs). This work is part of a collaboration with the Astrophysics Research and Development Division of the European Space Agency (ESA) at ESTEC. STJs are being widely investigated as photon detectors over a broad range of the electromagnetic spectrum. They potentially offer excellent energy resolution, time response and photon counting capabilities. The primary aim of this research was to use phonon pulses to investigate qua...
3D continuum phonon model for group-IV 2D materials
Willatzen, Morten
2017-06-30
A general three-dimensional continuum model of phonons in two-dimensional materials is developed. Our first-principles derivation includes full consideration of the lattice anisotropy and flexural modes perpendicular to the layers and can thus be applied to any two-dimensional material. In this paper, we use the model to not only compare the phonon spectra among the group-IV materials but also to study whether these phonons differ from those of a compound material such as molybdenum disulfide. The origin of quadratic modes is clarified. Mode coupling for both graphene and silicene is obtained, contrary to previous works. Our model allows us to predict the existence of confined optical phonon modes for the group-IV materials but not for molybdenum disulfide. A comparison of the long-wavelength modes to density-functional results is included.
Electron-Phonon Coupling and Photoluminescence in monolayer MoS2
Nayyar, Neha; Turkowski, Volodymyr; Le, Duy; Rahman, Talat
2014-03-01
We have carried out first principles calculations of the photoluminescent properties of monolayer MoS2 using density functional theory. In particular, we have analyzed the role of electron-phonon interactions in the photoluminescence process. Phonon dispersion curves calculated using density functional perturbation theory served as the basis for the evaluation of the system electron-phonon coupling, which in turn was used to calculate electron self-energy and the electron spectral function within the Eliashberg approach. We find that the resulting photoemission spectrum is in good agreement with experimental data. We pay special attention to the ultrafast relaxation of the electron system as manifested by the electron-phonon coupling and evaluate the ultrafast photoluminescence of the excited system by using the two-temperature model. It is shown that similar to graphene, MoS2 may demonstrate significant ultrafast photoluminescence. Work supported by DOE Grant No. DE-FG02-07ER46354.
Impact of confined LO-phonons on the Hall effect in doped semiconductor superlattices
Directory of Open Access Journals (Sweden)
Nguyen Quang Bau
2016-06-01
Full Text Available Based on the quantum kinetic equation method, the Hall effect in doped semiconductor superlattices (DSSL has been theoretically studied under the influence of confined LO-phonons and the laser radiation. The analytical expression of the Hall conductivity tensor, the magnetoresistance and the Hall coefficient of a GaAs:Si/GaAs:Be DSSL is obtained in terms of the external fields, lattice period and doping concentration. The quantum numbers N, n, m were varied in order to characterize the effect of electron and LO-phonon confinement. Numerical evaluations showed that LO-phonon confinement enhanced the probability of electron scattering, thus increasing the number of resonance peaks in the Hall conductivity tensor and decreasing the magnitude of the magnetoresistance as well as the Hall coefficient when compared to the case of bulk phonons. The nearly linear increase of the magnetoresistance with temperature was found to be in good agreement with experiment.
Control of coherent information via on chip photonic-phononic emitter-receivers
Shin, Heedeuk; Jarecki, Robert; Starbuck, Andrew; Wang, Zheng; Rakich, Peter T
2014-01-01
Rapid progress in silicon photonics has fostered numerous chip-scale sensing, computing, and signal processing technologies. However, many crucial filtering and signal delay operations are difficult to perform with all-optical devices. Unlike photons propagating at luminal speeds, GHz-acoustic phonons with slow velocity allow information to be stored, filtered, and delayed over comparatively smaller length-scales with remarkable fidelity. Hence, controllable and efficient coupling between coherent photons and phonons enables new signal processing technologies that greatly enhance the performance and potential impact of silicon photonics. Here, we demonstrate a novel mechanism for coherent information processing based on traveling-wave photon-phonon transduction, which achieves a phonon emit-and-receive process between distinct nanophotonic waveguides. Using this device physics-which can support 1-20GHz frequencies-we create wavelength-insensitive radio-frequency photonic filters with an unrivaled combination ...
Local symmetry breaking and spin–phonon coupling in SmCrO{sub 3} orthochromite
Energy Technology Data Exchange (ETDEWEB)
El Amrani, M. [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Zaghrioui, M., E-mail: zaghrioui@univ-tours.fr [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Ta Phuoc, V.; Gervais, F. [GREMAN CNRS UMR 7347, Université F. Rabelais, IUT de Blois, 15 rue de la Chocolatrie 41029 Blois cedex (France); Massa, Néstor E. [Laboratorio Nacional de Investigacion y Servicios en Espectroscopia Optica-Centro CEQUINOR, Universidad Nacional de La Plata, C. C. 962, 1900 La Plata (Argentina)
2014-06-01
Raman scattering and infrared reflectivity performed on polycrystalline SmCrO{sub 3} support strong influence of the antiferromagnetic order on phonon modes. Both measurements show softening of some modes below T{sub N}. Such a behavior is explained by spin–phonon coupling in this compound. Furthermore, temperature dependence of the infrared spectra has demonstrated important changes compared to the Raman spectra, suggesting strong structural modifications due to the cation displacements rather to those of the oxygen ions. Our results reveal that polar distortions originating in local symmetry breaking, i.e. local non-centrosymmetry, resulting in Cr off-centring. - Highlights: • We investigated Raman and infrared phonon modes of SmCrO{sub 3} versus temperature. • Results reveal strong influence of the antiferromagnetic order on phonon modes. • Temperature dependence of the infrared spectra shows strong structural modifications suggesting local symmetry breaking.
Electron-phonon scattering rates in complex polar crystals from ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Prange, Micah P.; Campbell, Luke W.; Kerisit, Sebastien N.
2017-09-17
The thermalization of fast electrons by phonons is studied in CsI, NaI, SrI2, and YAP. This numerical study uses an improvement to a recently developed ab initio method based on a density functional perturbation theoretical description of the phonon modes that provides a way to go beyond widely used phonon models based on binary crystals. Improvements to this method are described, and scattering rates are presented and discussed. The results here treat polar and nonpolar scattering on equal footing and allow an assessment of the relative importance of the two types of scattering. The relative activity of the numerous phonon modes in materials with complicated structures is discussed, and a simple criterion for finding the modes that scatter strongly is presented.
Acoustic phonon dynamics in strained cubic and hexagonal GaN/Al2O3 superlattices
Sesion, P. D., Jr.; Albuquerque, E. L.; Vasconcelos, M. S.; Mauriz, P. W.; Freire, V. N.
2006-06-01
We study the acoustic-phonon spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from III V nitride materials (GaN) intercalated by sapphire (Al2O3). Due to the misalignments between the sapphire and the GaN layers that can lead to threading dislocation densities as high as 108-1010 cm-1, and a significant lattice mismatch (~14%), the phonon dynamics is described beyond the continuum elastic model using coupled elastic and electromagnetic equations, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon dispersion relation. Furthermore, a quantitative analysis of the localization and magnitude of the allowed band widths in the phonon's spectra, as well as their scale law and the parametric spectrum of singularities f(α), are presented and discussed.
Dynamically induced robust phonon transport and chiral cooling in an optomechanical system
Kim, Seunghwi; Taylor, Jacob M; Bahl, Gaurav
2016-01-01
The transport of sound and heat, in the form of phonons, has a fundamental material limit: disorder-induced scattering. In electronic and optical settings, introduction of chiral transport - in which carrier propagation exhibits broken parity symmetry - provides robustness against such disorder by preventing elastic backscattering. Here we experimentally demonstrate a path for achieving robust phonon transport even in the presence of material disorder, by dynamically inducing chirality through traveling-wave optomechanical coupling. Using this approach, we demonstrate dramatic optically-induced chiral transport for clockwise and counterclockwise phonons in a symmetric resonator. This induced chirality also enhances isolation from the thermal bath and leads to gain-free reduction of the intrinsic damping of the phonons. Surprisingly, this passive mechanism is also accompanied by a chiral reduction in heat load leading to a novel optical cooling of the mechanics. This technique has the potential to improve upon...
First-principles electron transport with phonon coupling: Large scale at low cost
Gunst, Tue; Markussen, Troels; Palsgaard, Mattias L. N.; Stokbro, Kurt; Brandbyge, Mads
2017-10-01
Phonon-assisted tunneling plays a crucial role for electronic device performance and even more so with future size down-scaling. We show how one can include this effect in large-scale first-principles calculations using a single "special thermal displacement" (STD) of the atomic coordinates at almost the same cost as elastic transport calculations, by extending the recent method of Zacharias et al. [Phys. Rev. B 94, 075125 (2016), 10.1103/PhysRevB.94.075125] to the important case of Landauer conductance. We apply the method to ultrascaled silicon devices and demonstrate the importance of phonon-assisted band-to-band and source-to-drain tunneling. In a diode the phonons lead to a rectification ratio suppression in good agreement with experiments, while in an ultrathin body transistor the phonons increase off currents by four orders of magnitude, and the subthreshold swing by a factor of 4, in agreement with perturbation theory.
Phononic and magnonic dispersions of surface waves on a permalloy/BARC nanostructured array
Pan, Huihui; Zhang, Vanessa Li; Di, Kai; Kuok, Meng Hau; Lim, Hock Siah; Ng, Ser Choon; Singh, Navab; Adeyeye, Adekunle Olusola
2013-03-01
Phononic and magnonic dispersions of a linear array of periodic alternating Ni80Fe20 and bottom anti-reflective coating nanostripes on a Si substrate have been measured using Brillouin light scattering. The observed phononic gaps are considerably larger than those of laterally patterned multi-component crystals previously reported, mainly a consequence of the high elastic and density contrasts between the stripe materials. Additionally, the phonon hybridization bandgap has an unusual origin in the hybridization and avoided crossing of the zone-folded Rayleigh and pseudo-Sezawa waves. The magnonic band structure features near-dispersionless branches, with unusual vortex-like dynamic magnetization profiles, some of which lie below the highly-dispersive fundamental mode branch. Finite element calculations of the phononic and magnonic dispersions of the magphonic crystal accord well with experimental data.
Phononic and magnonic dispersions of surface waves on a permalloy/BARC nanostructured array
National Research Council Canada - National Science Library
Pan, Huihui; Zhang, Vanessa Li; Di, Kai; Kuok, Meng Hau; Lim, Hock Siah; Ng, Ser Choon; Singh, Navab; Adeyeye, Adekunle Olusola
2013-01-01
Phononic and magnonic dispersions of a linear array of periodic alternating Ni80Fe20 and bottom anti-reflective coating nanostripes on a Si substrate have been measured using Brillouin light scattering...
Feng, Tianli
The prediction of spectral phonon relaxation time, mean-free-path, and thermal conductivity can provide significant insights into the thermal conductivity of bulk and nanomaterials, which are important for thermal management and thermoelectric applications. We perform frequency-domain normal mode analysis (NMA) on pure bulk argon and pure bulk germanium. Spectral phonon properties, including the phonon dispersion, relaxation time, mean free path, and thermal conductivity of argon and germanium at different temperatures have been calculated. We find the dependence of phonon relaxation time tau on frequency o and temperature T vary from ~o-1.3 to ~o -1.8 and ~T-0.8 to ~T-1.8 for argon, and from ~o-0.6 to ~o-2.8 and ~T -0.4 to ~T-2.5 for germanium. The predicted thermal conductivities are in reasonable agreement with those obtained from the Green-Kubo method. We show, using both analytical derivations and numerical simulations, that the eigenvectors are necessary in time-domain NMA but unnecessary in frequency-domain NMA. The function of eigenvectors in frequency-domain NMA is to distinguish each phonon branch. Furthermore, it is found in solids not only the phonon frequency but also the phonon eigenvector can shift from harmonic lattice profile at finite temperature, due to thermal expansion and anharmonicity of interatomic potential. The anharmonicity of phonon eigenvector, different with that of frequency, only exists in the materials which contain at least two types of atoms and two different interatomic forces. Introducing anharmonic eigenvectors makes it easier to distinguish phonon branches in frequency-domain NMA although does not influence the results. For time-domain NMA, anharmonic eigenvectors make the results more accurate than harmonic eigenvectors. In addition, the phonon spectral relaxation time of defective silicon is calculated from frequency-domain NMA based on molecular dynamics. We show that the thermal conductivity k predicted from this approach
DEFF Research Database (Denmark)
Traulsen, Janine Morgall; Almarsdóttir, Anna Birna; Björnsdóttir, Ingunn
2004-01-01
There has been an upsurge of academic interest in using focus groups (FGs) as a main or stand-alone qualitative method. In this article, the authors introduce a recently developed ancillary method to FGs called interviewing the moderator. The method is employed immediately after an FG and consists...
DEFF Research Database (Denmark)
Larsen, Bøje
"normale" industrivirksomheder, men den er absolut set begrænset. Årsagerne til denne kun "moderate revolution" af organisationsformerne diskuteres: Er det fordi klassisk organisation og social nærkontakt er nødvendig i den nye økonomi, eller er det manglende fantasi og tryghedsbehov? Begge muligheder...
Cheaito, Ramez; Gaskins, John T.; Caplan, Matthew E.; Donovan, Brian F.; Foley, Brian M.; Giri, Ashutosh; Duda, John C.; Szwejkowski, Chester J.; Constantin, Costel; Brown-Shaklee, Harlan J.; Ihlefeld, Jon F.; Hopkins, Patrick E.
2015-01-01
The advances in phonon spectroscopy in homogeneous solids have unveiled extremely useful physics regarding the contribution of phonon energies and mean-free paths to the thermal transport in solids. However, as material systems decrease to length scales less than the phonon mean-free paths, thermal transport can become much more impacted by scattering and transmission across interfaces between two materials than the intrinsic relaxation in the homogeneous solid. To elucidate the fundamental interactions driving this thermally limiting interfacial phonon scattering process, we analytically derive and experimentally measure a thermal boundary conductance accumulation function. We develop a semiclassical theory to calculate the thermal boundary conductance accumulation function across interfaces using the diffuse mismatch model, and validate this derivation by measuring the interface conductance between eight different metals on native oxide/silicon substrates and four different metals on sapphire substrates. Measurements were performed at room temperature using time-domain thermoreflectance and represent the first-reported values for interface conductance across several metal/native oxide/silicon and metal/sapphire interfaces. The various metal films provide a variable bandwidth of phonons incident on the metal/substrate interface. This method of varying phonons' cutoff frequency in the film while keeping the same substrate allows us to mimic the accumulation of thermal boundary conductance and thus provides a direct method to experimentally validate our theory. We show that the accumulation function can be written as the product of a weighted average of the interfacial phonon transmission function and the accumulation of the temperature derivative of the phonon flux incident on the interface; this provides the framework to extract an average, spectrally dependent phonon transmissivity from a series of thermal boundary conductance measurements. Our approach provides
Thermotropic liquid crystalline polyesters derived from 2-chloro ...
Indian Academy of Sciences (India)
Home; Journals; Journal of Chemical Sciences; Volume 129; Issue 9. Thermotropic liquid crystalline polyesters derived from 2-chloro ... These polyesters exhibited thermotropic liquid crystalline behavior and showed nematic texture except decamethylene spacer. Decamethylene spacer based polyester showed marble ...
Stable liquid crystalline phases of colloidally dispersed exfoliated layered niobates.
Nakato, Teruyuki; Miyamoto, Nobuyoshi; Harada, Akiko
2004-01-07
Colloidally dispersed niobium oxide nanosheets obtained by exfoliation of layered niobates HNb(3)O(8) and HTiNbO(5) formed stable liquid crystalline phases; their liquid crystallinity was dependent on the niobate species exfoliated.
Phonon-limited carrier mobility and resistivity from carbon nanotubes to graphene
Li, Jing; Pereira Coutada Miranda, Henrique; Niquet, Yann-Michel; Genovese, Luigi; Duchemin, Ivan; Wirtz, Ludger; Delerue, Christophe
2015-01-01
Under which conditions do the electrical transport properties of one-dimensional (1D) carbon nanotubes (CNTs) and 2D graphene become equivalent? We have performed atomistic calculations of the phonon-limited electrical mobility in graphene and in a wide range of CNTs of different types to address this issue. The theoretical study is based on a tight-binding method and a force-constant model from which all possible electron-phonon couplings are computed. The electrical resistivity of graphene ...
Electron-phonon energy transfer in hot-carrier solar cells
Luque López, Antonio; Martí Vega, Antonio
2010-01-01
Hot-carrier solar cells may yield very high efficiency if the heat transfer from electrons to phonons is low enough. In this paper we calculate this heat transfer for the two inelastic mechanisms known to limit the electric conductivity: the multi-valley scattering in non-polar semiconductors and the coupling of electrons to longitudinal optical phonons in polar semiconductors. Heat transfer is ruled by matrix elements deduced from electric conductivity measurements. The cell power extracted ...
Interatomic forces, phonons, the Foreman-Lomer Theorem and the Blackman Sum Rule
Stewart, A. M.
2011-01-01
Foreman and Lomer proposed in 1957 a method of estimating the harmonic forces between parallel planes of atoms of primitive cubic crystals by Fourier transforming the squared frequencies of phonons propagating along principal directions. A generalized form of this theorem is derived in this paper and it is shown that it is more appropriate to apply the method to certain combinations of the phonon dispersion relations rather than to individual dispersion relations themselves. Further, it is al...
First-Principles Prediction of Phononic Thermal Conductivity of Silicene: a Comparison with Graphene
Gu, Xiaokun; Yang, Ronggui
2014-01-01
There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scatte...
One and Two Phonon Assisted Transitions between Exciton Spin States in a Quantum Dot
Roszak, K.; Machnikowski, P.; Axt, V. M.; Kuhn, T.
2008-11-01
Exciton spin decay is studied in a self-assembled InAs/GaAs quantum dot. The spin relaxation results from an interplay of two factors: the Bir-Pikus Hamiltonian and the short-range exchange interaction, leading to one and two phonon assisted transitions. We establish a hierarchy between the resulting transition rates and show the dominating role of transverse phonons for all the transitions.
Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins.
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Ekta Tiwary
Full Text Available Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA-crystallin (αA N101D and αA N123D displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET, both αA-deamidated mutants (αA N101D and αA N123D exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively compared to WT αA-crystallin (18±4%. Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE, N-terminal domain (NTD, and core domain (CD of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin
Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation
Directory of Open Access Journals (Sweden)
Lutz Waldecker
2016-04-01
Full Text Available The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.
Electromagnetic Processes in strong Crystalline Fields
2007-01-01
We propose a number of new investigations on aspects of radiation from high energy electron and positron beams (10-300 GeV) in single crystals and amorphous targets. The common heading is radiation emission by electrons and positrons in strong electromagnetic fields, but as the setup is quite versatile, other related phenomena in radiation emission can be studied as well. The intent is to clarify the role of a number of important aspects of radiation in strong fields as e.g. observed in crystals. We propose to measure trident 'Klein-like' production in strong crystalline fields, 'crystalline undulator' radiation, 'sandwich' target phenomena, LPM suppression of pair production as well as axial and planar effects in contributions of spin to the radiation.
Basic research challenges in crystalline silicon photovoltaics
Energy Technology Data Exchange (ETDEWEB)
Werner, J.H. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)
1995-08-01
Silicon is abundant, non-toxic and has an ideal band gap for photovoltaic energy conversion. Experimental world record cells of 24 % conversion efficiency with around 300 {mu}m thickness are only 4 % (absolute) efficiency points below the theoretical Auger recombination-limit of around 28 %. Compared with other photovoltaic materials, crystalline silicon has only very few disadvantages. The handicap of weak light absorbance may be mastered by clever optical designs. Single crystalline cells of only 48 {mu}m thickness showed 17.3 % efficiency even without backside reflectors. A technology of solar cells from polycrystalline Si films on foreign substrates arises at the horizon. However, the disadvantageous, strong activity of grain boundaries in Si could be an insurmountable hurdle for a cost-effective, terrestrial photovoltaics based on polycrystalline Si on foreign substrates. This talk discusses some basic research challenges related to a Si based photovoltaics.
Thermally switched PDLC liquid-crystalline composites
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Krzysztof Sułkowski
2016-03-01
Full Text Available The thermooptical properties of conventional polymer-dispersed nematic liquid crystals (PDLC composites in visual and near IR ranges have been studied. It has been confirmed that the composite film can be switched from the scattering milky state to the transparent state just by reaching a threshold temperature range, namely liquid crystal clearing phase transition to the isotropic one with satisfactory contrast ratio. The optical contrast and switching temperature range can be adjusted by the proper choice of the components of liquid crystalline mixture. This effect could be adopted for a construction of panes with “intelligent” heat transmission.[b]Keywords[/b]: materials engineering, liquid-crystalline composites, thermooptical effect
Liquid Crystalline Semiconductors Materials, properties and applications
Kelly, Stephen; O'Neill, Mary
2013-01-01
This is an exciting stage in the development of organic electronics. It is no longer an area of purely academic interest as increasingly real applications are being developed, some of which are beginning to come on-stream. Areas that have already been commercially developed or which are under intensive development include organic light emitting diodes (for flat panel displays and solid state lighting), organic photovoltaic cells, organic thin film transistors (for smart tags and flat panel displays) and sensors. Within the family of organic electronic materials, liquid crystals are relative newcomers. The first electronically conducting liquid crystals were reported in 1988 but already a substantial literature has developed. The advantage of liquid crystalline semiconductors is that they have the easy processability of amorphous and polymeric semiconductors but they usually have higher charge carrier mobilities. Their mobilities do not reach the levels seen in crystalline organics but they circumvent all of t...
Yoshino, S; Oohata, G; Mizoguchi, K
2015-10-09
We report on dynamical interference between short-lived Rabi oscillations and long-lived coherent phonons in CuCl semiconductor microcavities resulting from the coupling between the two oscillations. The Fourier-transformed spectra of the time-domain signals obtained from semiconductor microcavities by using a pump-probe technique show that the intensity of the coherent longitudinal optical phonon of CuCl is enhanced by increasing that of the Rabi oscillation, which indicates that the coherent phonon is driven by the Rabi oscillation through the Fröhlich interaction. Moreover, as the Rabi oscillation frequency decreases upon crossing the phonon frequency, the spectral profile of the coherent phonon changes from a peak to a dip with an asymmetric structure. The continuous wavelet transformation reveals that these peak and dip structures originate from constructive and destructive interference between Rabi oscillations and coherent phonons, respectively. We demonstrate that the asymmetric spectral structures in relation to the frequency detuning are well reproduced by using a classical coupled oscillator model on the basis of dynamical Fano-like interference.
Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry
Lüker, S.; Kuhn, T.; Reiter, D. E.
2017-12-01
Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches, the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach, we show that, indeed, lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatiotemporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot, the phonon emission is strongly concentrated along the direction of the smallest axis of the dot, which is important for the use of phonons for the communication between different dots.
Analytical Modeling of Acoustic Phonon-Limited Mobility in Strained Graphene Nanoribbons
Yousefvand, Ali; Ahmadi, Mohammad T.; Meshginqalam, Bahar
2017-11-01
Recent advances in graphene nanoribbon-based electronic devices encourage researchers to develop modeling and simulation methods to explore device physics. On the other hand, increasing the operating speed of nanoelectronic devices has recently attracted significant attention, and the modification of acoustic phonon interactions because of their important effect on carrier mobility can be considered as a method for carrier mobility optimization which subsequently enhances the device speed. Moreover, strain has an important influence on the electronic properties of the nanoelectronic devices. In this paper, the acoustic phonons mobility of armchair graphene nanoribbons ( n-AGNRs) under uniaxial strain is modeled analytically. In addition, strain, width and temperature effects on the acoustic phonon mobility of strained n-AGNRs are investigated. An increment in the strained AGNR acoustic phonon mobility by increasing the ribbon width is reported. Additionally, two different behaviors for the acoustic phonon mobility are verified by increasing the applied strain in 3 m, 3 m + 2 and 3 m + 1 AGNRs. Finally, the temperature effect on the modeled AGNR phonon mobility is explored, and mobility reduction by raising the temperature is reported.
Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces
Giri, Ashutosh; Gaskins, John T.; Donovan, Brian F.; Szwejkowski, Chester; Warzoha, Ronald J.; Rodriguez, Mark A.; Ihlefeld, Jon; Hopkins, Patrick E.
2015-03-01
We study the electron and phonon thermal coupling mechanisms at interfaces between gold films with and without Ti adhesion layers on various substrates via pump-probe time-domain thermoreflectance. The coupling between the electronic and the vibrational states is increased by more than a factor of five with the inclusion of an ˜3 nm Ti adhesion layer between the Au film and the non-metal substrate. Furthermore, we show an increase in the rate of relaxation of the electron system with increasing electron and lattice temperatures induced by the laser power and attribute this to enhanced electron-electron scattering, a transport channel that becomes more pronounced with increased electron temperatures. The inclusion of the Ti layer also results in a linear dependence of the electron-phonon relaxation rate with temperature, which we attribute to the coupling of electrons at and near the Ti/substrate interface. This enhanced electron-phonon coupling due to electron-interface scattering is shown to have negligible influence on the Kapitza conductances between the Au/Ti and the substrates at longer time scales when the electrons and phonons in the metal have equilibrated. These results suggest that only during highly nonequilibrium conditions between the electrons and phonons (Te ≫ Tp) does electron-phonon scattering at an interface contribute to thermal boundary conductance.
Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces
Energy Technology Data Exchange (ETDEWEB)
Giri, Ashutosh; Gaskins, John T.; Donovan, Brian F.; Szwejkowski, Chester; Hopkins, Patrick E., E-mail: phopkins@virginia.edu [Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Warzoha, Ronald J. [Department of Mechanical Engineering, United States Naval Academy, Annapolis, Maryland 21401 (United States); Rodriguez, Mark A.; Ihlefeld, Jon [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)
2015-03-14
We study the electron and phonon thermal coupling mechanisms at interfaces between gold films with and without Ti adhesion layers on various substrates via pump-probe time-domain thermoreflectance. The coupling between the electronic and the vibrational states is increased by more than a factor of five with the inclusion of an ∼3 nm Ti adhesion layer between the Au film and the non-metal substrate. Furthermore, we show an increase in the rate of relaxation of the electron system with increasing electron and lattice temperatures induced by the laser power and attribute this to enhanced electron-electron scattering, a transport channel that becomes more pronounced with increased electron temperatures. The inclusion of the Ti layer also results in a linear dependence of the electron-phonon relaxation rate with temperature, which we attribute to the coupling of electrons at and near the Ti/substrate interface. This enhanced electron-phonon coupling due to electron-interface scattering is shown to have negligible influence on the Kapitza conductances between the Au/Ti and the substrates at longer time scales when the electrons and phonons in the metal have equilibrated. These results suggest that only during highly nonequilibrium conditions between the electrons and phonons (T{sub e} ≫ T{sub p}) does electron-phonon scattering at an interface contribute to thermal boundary conductance.