Quantum effects in the dynamics of He probed by inelastic x-ray scattering

Abstract

Quantum effects in the teraherz dynamics of supercritical 4He have been studied as a function of both density rho and temperature T; they have been characterized through their effects on the second and third spectral moments of the dynamic structure factor S(Q, omega), measured by the inelastic x-ray scattering (IXS) technique. The IXS spectra were collected in the low-Q region below and around the position of the first diffraction peak Q(m), i.e., in a range relatively unusual in this kind of investigation. The measured spectral moments clearly show a departure from their high-T classical expected values. We observe, moreover, that the amplitude of quantum deviations increases slightly with increasing density. This experimental method allows us to extract, even in a region where the dynamics still maintains a collective character, such typical single particle properties as the mean atomic kinetic energy.

High-Frequency Acoustic Modes in Liquid Gallium at the Melting Point

“…A generalized hydrodynamic analysis allows a quantitative determination of relevant parameters such as the structural relaxation time and the generalized viscosities. More importantly, it reveals how the main features of the collective dynamics in this system are very similar to the ones reported in different elements such as Li, Na, Al [7] and noble fluids [14,15]. This is an important indication of how -beside quantitative differences-the high frequency dynamics in simple fluids exhibit universal features which go beyond system dependent details such as the electronic structure, bond nature, atomic interaction and structural properties.…”

“…Taking advantage of the results obtained in several other liquid metals (Li, Al, Na) [7,12] and fluids (noble gases) [13,14,15], we utilized a memory function composed by two relevant time-scales associated to two processes of viscous origin, plus an exponential contribution that accounts for the thermal relaxation process. For the two viscous terms we adopted a simple Debye law (exponential decay) to account for the structural relaxation and an instantaneous approximation (delta-function) for the faster, microscopic contribution.…”

The THz Spectrum of Density Fluctuations of Water: The Viscoelastic Regime

“…Here ( , ) is the generic model used for the classic part of the dynamic structure factor, while the symbol "⊗" represents the convolution operator; finally, and are -independent terms representing, respectively, an overall scaling factor and a plateau term, including spectral background and electronic noise of the detectors. A line-shape model similar to the one described above was successfully employed in several IXS experiments on samples as diverse as HB liquids [13,88], noble gases [89], liquid metals [90], diatomic liquids [91], supercooled molecular systems [92], glasses [93], and even quantum systems [94,95].…”

Revealing the Mechanism of the Viscous-to-Elastic Crossover in Liquids

“…Here, we used a simplified expression for the memory function which consistently describes the high frequency spectrum of noble gases 2,13,22 as well as other simple fluids, 23 specifically…”