A. Giugni | Searcharxiv

arXiv2004

Sound attenuation in an unexplored frequency region: Brillouin Ultraviolet Light Scattering measurements in v-SiO2

We report Ultraviolet Brillouin light scattering experimental data on v-SiO2 in an unexplored frequency region, performed with a newly available spectrometer up to exchanged wavevector q values of 0.075 nm^{-1}, as a function of temperature. The measured attenuation scales on visible data following a q^2 behavior and is temperature-dependent. Such temperature dependence is found in a good agreement with that measured at lower q, suggesting that its origin is mainly due to a dynamic attenuation mechanism. The comparison between the present data with those obtained by Inelastic X-ray Scattering suggests the existence of a cross-over to a different attenuation regimes.

cond-mat.dis-nn↗

arXiv2004

Collective dynamics in molten potassium: an Inelastic X-ray Scattering study

The high frequency collective dynamics of molten potassium has been investigated by inelastic x-ray scattering, disclosing an energy/momentum transfer region unreachable by previous neutron scattering experiments (INS). We find that a two-step relaxation scenario, similar to that found in other liquid metals, applies to liquid potassium. In particular, we show how the sound velocity determined by INS experiments, exceeding the hydrodynamic value by $\approx 30 %$, is the higher limit of a speed up, located in the momentum region $1<Q<3$ nm$^{-1}$, which marks the departure from the isothermal value. We point out how this phenomenology is the consequence of a microscopic relaxation process that, in turn, can be traced back to the presence of ''instantaneous'' disorder, rather than to the crossover from a liquid to solid-like response.

cond-mat.dis-nn↗