Damping of sound waves in the terahertz range and strength of the boson peak

Abstract

By applying a new two-step line-shape analysis to inelastic neutron and x-ray scattering spectra of glassy systems, we were able to resolve the acoustic excitations from the low-frequency excess modes and to accurately estimate the damping of sound waves in the terahertz frequency range. Using this approach, we estimated the damping parameter for terahertz acoustic waves in a wide class of chemically different glasses and did a quantitative comparison of the results with prediction of theoretical models. By comparing the estimates of the mean-free path of the acoustic modes in different glasses and the corresponding boson peak strengths, we show the existence of a simple correlation between these two quantities. The relationship between attenuation of the terahertz acoustic modes, strength of the boson peak, and fragility is discussed.

Structural and dynamic origin of the boson peak in a Cu-Zr metallic glass

“…5(a), the curve of π L (q) crosses the dispersion curve well above the linear dispersion. Our finding is consistent with recent measurements on Ni-Zr metallic glass 24 and in agreement with recent work by Bove et al, 40 who pointed out that this feature holds for fragile systems, which is indeed the case for Cu-Zr alloys. 8,25 Interestingly, the Ioffe-Regel limit of TA modes coincides with the BP frequency, as seen in the left panel of Fig.…”

“…5(b) (with a linear fitting, we find a slope of 2.19 and 2.25 for L (q) and T (q), respectively, with a standard deviation of 0.3). This q 2 behavior seems to be well established experimentally 40 with L (q) = (η L /ρ)q 2 and T (q) = (η T /ρ)q 2 , η L and η T being the longitudinal and transverse viscosities, respectively, and ρ the mass density. As q increases, both line widths display a crossover towards a rather linear behavior, indicating a change of the behavior of the sound attenuation and the onset of a negative dispersion for both branches.…”

“…The coincidence of the BP frequency with the change of sound attenuation in this paper could be rather an indication that the change of sound attenuation is due to the perturbation of the propagation of acoustic modes when the wavelength of these modes approaches the scale imposed by the low-density defective structures. 40 It would be interesting to investigate the role of anharmonic effects and distribution of two-level systems 43 in connection with the BP, which is a question beyond the harmonic concept of the vibrational density of states. 15 By essence, the molecular dynamics method fully treats anharmonic effects.…”

Dynamic-to-static crossover in the acoustic attenuation of v-GeO 2

“…A possible explanation for the crossover from q 4 to q 2 regime can be found in a recently proposed elastic continuum model [49]. In this framework the crossover in the acoustic attenuation is associated to the onset of the excess in the density of states with respect to the Debye prediction [50,51].…”

Emergence of Crystal-like Atomic Dynamics in Glasses at the Nanometer Scale

“…The acoustic modes persist up to frequencies of a few terahertz [14], close to and above the frequency, BP , of the ''boson peak'' (BP), the peculiar excess of vibrational states over the gðÞ $ 2 Debye density of states [15][16][17][18][19][20]. Below BP , the linewidth, À, of the excitation, which is proportional to the sound attenuation coefficient, grows with the fourth power of the frequency: À $ 4 [21][22][23][24][25][26][27][28][29].…”