Excess of low-energy excitations in glasses

Acoustic properties of borate glasses

“…It results, however, that the loss peaks are unexplainable in terms of a single relaxation time, as provided by the well known Debye equation, a ¼ D x 2 s 1þx 2 s 2 , where the relaxation strength D is related to the number of relaxing particles, x is the acoustic angular frequency and s the relaxation time. Therefore their accurate description can be obtained by considering a distribution of relaxation times arising from the inherent structural randomness of glasses [1]. No attempt was made to fit the attenuation peaks by a distribution function, because the limited temperature range prevents the accurate evaluation of a temperature independent, but frequency dependent background loss [12].…”

“…They cause anomalies in the thermal, acoustic, optical and dielectric properties of glasses at low temperatures [1,2]. The attenuation and the velocity of ultrasounds, in particular, show behaviors which are usually well accounted for by thermally activated motions at high temperatures (T > 10 K) and by tunneling motions at low temperatures (T < 10 K) of localized structural defects, i.e.…”

Physical aging effect on the boson peak and heterogeneous nanostructure of a silicate glass

“…It was deduced, from the comparison of the VDOS with the Raman intensity, that C ab (x) shows no maximum. It is in general found from experiment that in the spectral range of the boson peak C ab (x) has a quasi-linear frequency dependence [12][13][14][15][16]. In consequence, the Raman boson peak is directly related to the VDOS excess, and therefore to the maximum of g(x)/x 2 .…”

Low-frequency Raman scattering in model disordered solids: percolators above threshold

“…The investigation of the frequency dependence of C(ω) for model disordered solids is becoming more and more attractive also in view of the recent demonstration, by Fontana and coworkers [20,21], that a combination of Raman and specific heat experiments allows for the determination of the density of vibrational states with an accuracy comparable to neutron scattering experiments, and therefore provides the functional form of C(ω).…”