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## Anomalous surface lattice dynamics in the low-temperature phase of Ba(Fe1−xCox)2As2

Teng, Jing; Chen, Chen; Xiong, Yimin; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In complex materials, how correlation between charge, spin, and lattice affects the emergent phenomena remains unclear. The newly discovered iron-based high-temperature superconductors and related compounds present to the community a prototype family of materials, where interplay between charge, spin, and lattice degrees of freedom can be explored. With the occurrence of structural, magnetic, and superconducting transitions in the bulk of these materials, creating a surface will change the delicate balance between these phases, resulting in new behavior. A surface lattice dynamics study on (001) Ba(Fe1−xCox)2As2, through electron energy loss spectroscopy measurements, reveals unusual temperature dependence of both the phonon frequency and line width in the low-temperature orthorhombic phase. The rate of change of phonon frequency with temperature is gigantic, two orders of magnitude larger than in the bulk. This behavior cannot be explained using conventional models of anharmonicity or electron–phonon coupling; instead, it requires that a large surface-spin-charge-lattice coupling be included. Furthermore, the higher surface-phase-transition temperature driven by surface stabilization of the low-temperature orthorhombic phase seems to turn the first-order transition (bulk) into the second-order type...

## Molecular dynamics calculation of mean square displacement in alkali metals and rare gas solids and comparison with lattice dynamics

Heiser, Gernot A.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
Português
Relevância na Pesquisa
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Molec ul ar dynamics calculations of the mean sq ua re displacement have been carried out for the alkali metals Na, K and Cs and for an fcc nearest neighbour Lennard-Jones model applicable to rare gas solids. The computations for the alkalis were done for several temperatures for temperature vol ume a swell as for the the ze r 0 pressure ze ro zero pressure volume corresponding to each temperature. In the fcc case, results were obtained for a wide range of both the temperature and density. Lattice dynamics calculations of the harmonic and the lowe s t order anharmonic (cubic and quartic) contributions to the mean square displacement were performed for the same potential models as in the molecular dynamics calculations. The Brillouin zone sums arising in the harmonic and the quartic terms were computed for very large numbers of points in q-space, and were extrapolated to obtain results ful converged with respect to the number of points in the Brillouin zone.An excellent agreement between the lattice dynamics results was observed molecular dynamics and in the case of all the alkali metals, e~ept for the zero pressure case of CSt where the difference is about 15 % near the melting temperature. It was concluded that for the alkalis...

## Clocking the anisotropic lattice dynamics of multi-walled carbon nanotubes by four-dimensional ultrafast transmission electron microscopy

Cao, Gaolong; Sun, Shuaishuai; Li, Zhongwen; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.144004%
Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walled carbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radial direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp2-hybridized bonds in the tubular sheets.

## Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?

Ebbinghaus, M.; Appert-Rolland, C.; Santen, L.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.229463%
Intracellular transport processes driven by molecular motors can be described by stochastic lattice models of self-driven particles. Here we focus on bidirectional transport models excluding the exchange of particles on the same track. We explore the possibility to have efficient transport in these systems. One possibility would be to have appropriate interactions between the various motors' species, so as to form lanes. However, we show that the lane formation mechanism based on modified attachment/detachment rates as it was proposed previously is not necessarily connected to an efficient transport state and is suppressed when the diffusivity of unbound particles is finite. We propose another interaction mechanism based on obstacle avoidance that allows to have lane formation for limited diffusion. Besides, we had shown in a separate paper that the dynamics of the lattice itself could be a key ingredient for the efficiency of bidirectional transport. Here we show that lattice dynamics and interactions can both contribute in a cooperative way to the efficiency of transport. In particular, lattice dynamics can decrease the interaction threshold beyond which lanes form. Lattice dynamics may also enhance the transport capacity of the system even when lane formation is suppressed.; Comment: 25 pages...

## Lattice dynamics and a magnetic-structural phase transition in the nickel orthoborate $Ni_{3}(BO_{3})_{2}$

Pisarev, R. V.; Prosnikov, M. A.; Davydov, V. Yu.; Smirnov, A. N.; Roginskii, E. M.; Boldyrev, K. N.; Molchanova, A. D.; Popova, M. N.; Smirnov, M. B.; Kazimirov, V. Yu.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.00521%
Nickel orthoborate $Ni_{3}(BO_{3})_{2}$ having a complex orthorhombic structure $P_{nnm}$ (#58, Z=2) of the kotoite type is known for quite a long time as an antiferromagnetic material below $T_{N}$ = 46 K, but up to now its physical properties including the lattice dynamics have not been explored. Six magnetic nickel $Ni^{2+}$ ions (S=1) in the unit cell are distributed over the 2a and 4f positions in the centers of distorted $[O_{6}]$ octahedra. The $[NiO_{6}]$ units are linked via rigid $[BO_{3}]$ groups and these structural particularities impose restrictions on the lattice dynamics and spin-phonon interactions. We performed the symmetry analysis of the phonon modes at the center of the Brillouin zone. The structural parameters and phonon modes were calculated using Dmol3 program. We report and analyze results of infrared and Raman studies of phonon spectra measured in all required polarizations. Most of the even and odd phonons predicted on the basis of the symmetry analysis and theoretical calculations were reliably identified in the measured spectra. Absorption measurements in the infrared region showed emergence of several very narrow and weak phonons at the magnetic ordering temperature $T_{N}$. This observation proves the existence of a structural phase transition not reported before which is evidently coupled intrinsically with the magnetic dynamics of $Ni_{3}(BO_{3})_{2}$. A clear evidence of spin-phonon interaction was observed for some particular phonons below $T_{N}$.; Comment: 25 pages...

## Choose interelement coupling to preserve self-adjoint dynamics in multiscale modelling and computation

Roberts, A. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.2092%
Consider the macroscale modelling of microscale spatiotemporal dynamics. Here we develop a new approach to ensure coarse scale discrete models preserve important self-adjoint properties of the fine scale dynamics. The first part explores the discretisation of microscale continuum dynamics. The second addresses how dynamics on a fine lattice are mapped to lattice a factor of two coarser (as in multigrids). Such mapping of discrete lattice dynamics may be iterated to empower us in future research to explore scale dependent emergent phenomena. The support of dynamical systems, centre manifold, theory ensures that the coarse scale modelling applies with a finite spectral gap, in a finite domain, and for all time. The accuracy of the models is limited by the asymptotic resolution of subgrid coarse scale processes, and is controlled by the level of truncation. As given examples demonstrate, the novel feature of the approach developed here is that it ensures the preservation of important conservation properties of the microscale dynamics.

## Strong Influence of the diffuse component on the lattice dynamics in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$

Stock, C.; Luo, H.; Viehland, D.; Li, J. F.; Swainson, I.; Birgeneau, R. J.; Shirane, G.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.13293%
The temperature and zone dependence of the lattice dynamics in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ is characterized using neutron inelastic scattering. A strong correlation between the diffuse and phonon scattering is measured. The lattice dynamics in Brillouin zones where the diffuse scattering is strong is observed to display qualitatively different behavior than those zones where the diffuse scattering is weak. In the (220) and (200) zones, where there is a weak diffuse component, the dynamics are well described by coupled harmonic oscillators. Compared with SrTiO$_{3}$, the coupling is weak and isotropic, resulting in only a small transfer of spectral weight from one mode to another. A comparison of the scattering in these zones to the (110) zone, where a strong diffuse component is present, reveals a strong coupling of the diffuse (or central) component to the acoustic mode. We speculate that the coupling to the central peak is the reason for several recent conflicting interpretations of the lattice dynamics based on data from zones with a strong diffuse component.; Comment: 7 pages, 7 figures

## Structure of Defective Crystals at Finite Temperatures: A Quasi-Harmonic Lattice Dynamics Approach

Yavari, Arash; Angoshtari, Arzhang
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.087954%
In this paper we extend the classical method of lattice dynamics to defective crystals with partial symmetries. We start by a nominal defect configuration and first relax it statically. Having the static equilibrium configuration, we use a quasiharmonic lattice dynamics approach to approximate the free energy. Finally, the defect structure at a finite temperature is obtained by minimizing the approximate Helmholtz free energy. For higher temperatures we take the relaxed configuration at a lower temperature as the reference configuration. This method can be used to semi-analytically study the structure of defects at low but non-zero temperatures, where molecular dynamics cannot be used. As an example, we obtain the finite temperature structure of two 180^o domain walls in a 2-D lattice of interacting dipoles. We dynamically relax both the position and polarization vectors. In particular, we show that increasing temperature the domain wall thicknesses increase.

## Lattice Fluid Dynamics from Perfect Discretizations of Continuum Flows

Katz, E.; Wiese, U. -J.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.077607%
We use renormalization group methods to derive equations of motion for large scale variables in fluid dynamics. The large scale variables are averages of the underlying continuum variables over cubic volumes, and naturally live on a lattice. The resulting lattice dynamics represents a perfect discretization of continuum physics, i.e. grid artifacts are completely eliminated. Perfect equations of motion are derived for static, slow flows of incompressible, viscous fluids. For Hagen-Poiseuille flow in a channel with square cross section the equations reduce to a perfect discretization of the Poisson equation for the velocity field with Dirichlet boundary conditions. The perfect large scale Poisson equation is used in a numerical simulation, and is shown to represent the continuum flow exactly. For non-square cross sections we use a numerical iterative procedure to derive flow equations that are approximately perfect.; Comment: 25 pages, tex., using epsfig, minor changes, refernces added

## Symmetry-mode-based classical and quantum mechanical formalism of lattice dynamics

Seman, Tsezar F.; Moon, Jichan; Ahn, K. H.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.087954%
We present classical and quantum mechanical descriptions of lattice dynamics, from the atomic to the continuum scale, using atomic scale symmetry modes and their constraint equations. This approach is demonstrated for a one-dimensional chain and a two-dimensional square lattice with a monatomic basis. For the classical description, we find that rigid modes, in addition to the distortional modes found before, are necessary to describe the kinetic energy. The long wavelength limit of the kinetic energy terms expressed in terms of atomic scale modes is shown to be consistent with the continuum theory, and the leading order corrections are obtained. For the quantum mechanical description, we find conjugate momenta for the atomic scale symmetry modes. In direct space, graphical rules for their commutation relations are obtained. Commutation relations in the reciprocal space are also calculated. As an example, phonon modes are analyzed in terms of symmetry modes. We emphasize that the approach based on atomic scale symmetry modes could be useful, for example, for the description of multiscale lattice dynamics and the dynamics near structural phase transition.

## Direct characterization of photo-induced lattice dynamics in BaFe2As2

Gerber, S.; Kim, K. W.; Zhang, Y.; Zhu, D.; Plonka, N.; Yi, M.; Dakovski, G. L.; Leuenberger, D.; Kirchmann, P. S.; Moore, R. G.; Chollet, M.; Glownia, J. M.; Feng, Y.; Lee, J. -S.; Mehta, A.; Kemper, A. F.; Wolf, T.; Chuang, Y. -D.; Hussain, Z.; Kao, C.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.11809%
Ultrafast light pulses can modify the electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins, and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved x-ray scattering to measure the lattice dynamics of photo-excited BaFe2As2. Upon optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photo-induced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can generally be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands near the Fermi level.

## Caricature of Hydrodynamics for Lattice Dynamics

Dudnikova, T. V.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.02156%
The lattice dynamics in $\mathbb{Z}^d$, $d\ge1$, is considered. The initial data are supposed to be random function. We introduce the family of initial measures $\{\mu_0^\epsilon,\epsilon>0\}$ depending on a small scaling parameter $\epsilon$. We assume that the measures $\mu_0^\epsilon$ are locally homogeneous for space translations of order much less than $\epsilon^{-1}$ and nonhomogeneous for translations of order $\epsilon^{-1}$. Moreover, the covariance of $\mu_0^\epsilon$ decreases with distance uniformly in $\epsilon$. Given $\tau\in\mathbb{R}\setminus 0$, $r\in\mathbb{R}^d$, and $\kappa>0$, we consider the distributions of random solution in the time moments $t=\tau/\epsilon^\kappa$ and at lattice points close to $[r/\epsilon]\in\mathbb{Z}^d$. The main goil is to study the asymptotics of these distributions as $\epsilon\to0$ and derive the limit hydrodynamic equations of the Euler or Navier-Stokes type. The similar results are obtained for lattice dynamics in the half-space $\mathbb{Z}^d_+$.; Comment: 43 pages

## Nonlinear Fractional Dynamics on a Lattice with Long Range Interactions

Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.13293%
A unified approach has been developed to study nonlinear dynamics of a 1D lattice of particles with long-range power-law interaction. A classical case is treated in the framework of the generalization of the well-known Frenkel-Kontorova chain model for the non-nearest interactions. Quantum dynamics is considered following Davydov's approach for molecular excitons. In the continuum limit the problem is reduced to dynamical equations with fractional derivatives resulting from the fractional power of the long-range interaction. Fractional generalizations of the sine-Gordon, nonlinear Schrodinger, and Hilbert-Schrodinger equations have been found. There exists a critical value of the power s of the long-range potential. Below the critical value (s<3) we obtain equations with fractional derivatives while for s>3 we have the well-known nonlinear dynamical equations with space derivatives of integer order. Long-range interaction impact on the quantum lattice propagator has been studied. We have shown that the quantum exciton propagator exhibits transition from the well-known Gaussian-like behavior to a power-law decay due to the long-range interaction. A link between 1D quantum lattice dynamics in the imaginary time domain and a random walk model has been discussed.; Comment: 28 pages...

## The ideal energy of classical lattice dynamics

Margolus, Norman
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.938813%
We define, as local quantities, the least energy and momentum allowed by quantum mechanics and special relativity for physical realizations of some classical lattice dynamics. These definitions depend on local rates of finite-state change. In two example dynamics, we see that these rates evolve like classical mechanical energy and momentum.; Comment: 12 pages, 4 figures, includes revised portion of arXiv:0805.3357

## Clocking the anisotropic lattice dynamics of multi-walled carbon nanotubes by four-dimensional ultrafast transmission electron microscopy

Cao, Gaolong; Sun, Shuaishuai; Li, Zhongwen; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.144004%
Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walled carbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radical direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp2-hybridized bonds in the tubular sheets.; Comment: 23pages,5figures,includes 4pages supplementary information

## Lattice dynamics of coesite

Wehinger, Björn; Bosak, Alexeï; Chumakov, Aleksandr; Mirone, Alessandro; Winkler, Björn; Dubrovinsky, Leonid; Dubrovinskaia, Natalia; Brazhkin, Vadim; Dyuzheva, Tatiana; Krisch, Michael
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.087954%
The lattice dynamics of coesite has been studied by a combination of diffuse x-ray scattering, inelastic x-ray scattering and an ab initio lattice dynamics calculation. The combined technique gives access to the full lattice dynamics in harmonic description and thus eventually provides detailed information on the elastic properties, the stability and metastability of crystalline systems. The experimentally validated calculation was used for the investigation of eigenvectors, mode character and their influence on the density of vibrational states. High symmetry sections of the reciprocal space distribution of diffuse scattering and inelastic x-ray scattering spectra as well as the density of vibrational states and the dispersion relation are reported and compared to the calculation. A critical point at the zone boundary is found to contribute strongly to the main peak of the low energy part in the density of vibrational states. Comparison with the most abundant SiO2 polymorph - alpha-quartz - reveals similarities and distinct differences in the low-energy vibrational properties.

## Local stationarity for lattice dynamics in the harmonic approximation

Dudnikova, T. V.; Spohn, H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.02156%
We consider the lattice dynamics in the harmonic approximation for We consider the lattice dynamics in the harmonic approximation for a simple hypercubic lattice with arbitrary unit cell. The initial data are random according to a probability measure which enforces slow spatial variation on the linear scale $\epsilon^{-1}$. We establish two time regimes. For times of order $\epsilon^{-\gamma}$, $0<\gamma<1$, locally the measure converges to a Gaussian measure which is space-time stationary with a covariance inherited from the initial (in general, non-Gaussian) measure. For times of order $\epsilon^{-1}$ this local space covariance changes in time and is governed by a semiclassical transport equation.

## Atomistic Coupling between Magnetization and Lattice Dynamics from First Principles

Bhattacharjee, S.; Fransson, J.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.31712%
We formulate a new scheme to study the combined magnetization and lattice dynamics in magnets, so-called magnetoelastics. The coupling between magnetization and lattice are considered through an expansion of electron-phonon coupling, while the magnetization is coupled to electrons through sd-like interaction. We show the that the time-scale of the magnetization dynamics due to coupling between magnetic degrees of freedom and electronic degrees of freedom can be transferred to lattice degrees of freedom and therefore can give rise to lattice dynamics on the same time-scale. This opens a new route to understand and treat ultrafast lattice dynamics induced by magnetization dynamics. We also show that all the parameters necessary to simulate this coupled lattice and magnetization dynamics can be obtained from first-principles.; Comment: The paper's been withdrawn due inconsistencies in the model definition. This is has been corrected in a different submission

## Data for "Lattice dynamics and electron-phonon coupling calculations using non-diagonal supercells"

Lloyd-Williams, Jonathan; Monserrat, Bartomeu
Tipo: Relatório Formato: CASTEP input files are compatible with CASTEP version 8.0 and later. For information on how to obtain a copy of CASTEP visit: http://www.castep.org -- The LTE research code was originally written by Neil Drummond and has been modified by Jonathan Lloyd-Wi
Português
Relevância na Pesquisa
66.938813%
All relevant data present in "Lattice dynamics and electron-phonon coupling calculations using non-diagonal supercells"; This record will be updated with publication details.; This work was supported by the EPSRC [grant numbers EP/J017639/1 and EP/K013564/1].

## Numerical schemes for coarse-graining of stochastic lattice dynamics

Song, Yan
Fonte: University of Delaware Publicador: University of Delaware