Observation of collective excitations in heavy water in the 108 cm−1 momentum range

Bosi, P.; Dupré, Florence; Menzingee, F.; Sacchetti, F.; Spinelli, M.

doi:10.1007/bf02763195

Cited by 47 publications

(52 citation statements)

References 11 publications

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“…The procedure has already been discussed in the previous section. These dispersion curves compare well with the experimental results [28] In figure 5 we show the FWHM as a function of frequency. It is clear that there is strong evidence of mode and k-dependence.…”

Section: B the Ni88cr12 Alloysupporting

confidence: 85%

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Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in thekrepresentation

Alam

Mookerjee

2004

Phys. Rev. B

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We present here an augmented space recursive technique in the k-representation which include diagonal, off-diagonal and the environmental disorder explicitly : an analytic , translationally invariant , multiple scattering theory for phonons in random binary alloys. We propose the augmented space recursion (ASR) as a computationally fast and accurate technique which will incorporate configuration fluctuations over a large local environment. We apply the formalism to N i55P d45 , N i88Cr12 and N i50P t50 alloys which is not a random choice. Numerical results on spectral functions, coherent structure factors, dispersion curves and disordered induced FWHM's are presented. Finally the results are compared with the recent itinerant coherent potential approximation (ICPA) and also with experiments.

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Section: B the Ni88cr12 Alloysupporting

confidence: 85%

“…We shall choose this alloy as being the nearest to that studied experimentally by Bosi et.al [28]. Determination of the force constant matrices for this alloy becomes difficult, because pure Cr is body centered cubic, but alloyed with Ni, up to 30% Cr it forms face centered cubic alloys.…”

Section: B the Ni88cr12 Alloymentioning

confidence: 99%

Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in thekrepresentation

Alam

Mookerjee

2004

Phys. Rev. B

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“…This second excitation has a (almost) Q-independent energy, and becomes visible only at Q larger than ≈4 nm −1 . This second feature, observed in the S(Q, ω) of ambient condition liquid water by INS [6,8,9,10] and IXS [12,13,16], has been attributed to transverse-like dynamics on the basis of a MD study [18] where the comparison between longitudinal and transverse current spectra was performed. The existence of the second feature and its transverse origin can be explained within the same viscoelastic framework which has been successfully used to describe the longitudinal dynamics.…”

Section: Introductionmentioning

confidence: 96%

“…The key quantity in most of these studies is the so-called dynamical structure factor S(Q, ω) ( Q and ω = E denote the momentum and energy transfer, respectively), which is the time and space Fourier transform of the atomic density-density pair correlation function [5]. Starting from the pioneering work by Bosi et al [6] and by Texeira et al [7], several neutron experiments [8,9,10] and x-ray studies [11,12,13,14,15,16,17] have been devoted to the study of the THz-frequency dynamics in liquid water.…”

Section: Introductionmentioning

confidence: 99%

High-frequency longitudinal and transverse dynamics in water

et al. 2005

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High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor S(Q, ω) of liquid water have been performed for wave vectors Q between 4 and 30 nm −1 in distinctly different thermodynamic conditions (T= 263 -420 K ; at, or close to, ambient pressure and at P = 2 kbar). In agreement with previous inelastic x-ray and neutron studies, the presence of two inelastic contributions (one dispersing with Q and the other almost non-dispersive) is confirmed.The study of their temperature-and Q-dependence provides strong support for a dynamics of liquid water controlled by the structural relaxation process. A viscoelastic analysis of the Q-dispersing mode, associated with the longitudinal dynamics, reveals that the sound velocity undergoes the complete transition from the adiabatic sound velocity (c 0 ) (viscous limit) to the infinite frequency sound velocity (c ∞ ) (elastic limit). On decreasing Q, as the transition regime is approached from the elastic side, we observe a decrease of the intensity of the second, weakly dispersing feature, which completely disappears when the viscous regime is reached. These findings unambiguously identify the second excitation to be a signature of the transverse dynamics with a longitudinal symmetry component, which becomes visible in the S(Q, ω) as soon as the purely viscous regime is left.

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“…Two experimental determinations of the coherent dynamic structure factor of liquid D 2 O were in fact performed using neutron spectroscopy respectively in 1978 and in 1985. The first experiment was executed by P. Bosi and collaborators [2] using a triple axis spectrometer on the TRIGA reactor (Enea-Casaccia, Rome, I). The kinematics region explored in this experiment, however, did not permit to cover the q − ω region where the excitations branch associated with the fast sound was expected.…”

Section: Introductionmentioning

confidence: 99%

The history of the "fast sound" in liquid water

Ruocco¹,

Sette²

2008

Condens. Matter Phys.

111

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This paper aims to discuss the present understanding of the high frequency dynamics in liquid water, with particular attention to a specific phenomenon -the so-called fast sound -since its first appearance in the literature up to its most recent explanation. A particular role in this history is played by the inelastic x-ray scattering (IXS) technique, which -with its introduction in the middle '90-allowed to face a large class of problems related to the high frequency dynamics in disordered materials, such as glass and liquids. The results concerning the fast sound in water obtained using the IXS technique are here compared with the inelastic neutron scattering (INS) and molecular dynamics simulation works. The IXS work has allowed us to demonstrate experimentally the existence of two branches of collective modes in liquid water: one linearly dispersing with the momentum (apparent sound velocity of ≈3200 m/s, the "fast sound") and the other at almost constant energy (5÷7 meV). It has been possible to show that the dispersing branch originates from the viscoelastic bend up of the ordinary sound branch. The study of this sound velocity dispersion, marking a transition from the ordinary sound, co to the "fast sound", c∞, as a function of temperature, has made it possible to relate the origin of this phenomenon to a structural relaxation process, which presents many analogies to those observed in glass-forming systems. The possibility to estimate from the IXS data the value of the relaxation time, τ , as a function of temperature leads to relating the relaxation process to the structural re-arrangements induced by the making and breaking of hydrogen bonds. In this framework, it is then possible to recognize an hydrodynamical "normal" regime, i. e. when one considers density fluctuations whose period of oscillation is on a timescale long with respect to τ , and a solid-like regime in the opposite limit. In the latter regime, the density fluctuations feel the liquid as frozen and the sound velocity is much higher: this is "fast sound" whose value is equivalent to the sound velocity found in crystalline ice.

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Observation of collective excitations in heavy water in the 108 cm−1 momentum range

Cited by 47 publications

References 11 publications

Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in thekrepresentation

Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in thekrepresentation

High-frequency longitudinal and transverse dynamics in water

The history of the "fast sound" in liquid water

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