Phonon-like and single particle dynamics in liquid lithium

TL;DR

This study investigates the evolution of collective phonon-like excitations to single particle dynamics in liquid lithium using inelastic x-ray scattering, revealing how these modes change across different momentum transfers.

Contribution

The paper provides detailed experimental data on the dynamic structure factor of liquid lithium, illustrating the transition from collective to single particle behavior with increasing momentum transfer.

Findings

Identification of a sound mode with positive dispersion at low Q

Observation of phonon-like excitations at intermediate Q

Approach to Gaussian shape indicating single particle dynamics at high Q

Abstract

The dynamic structure factor, S(Q,E), of liquid lithium (T=475 K) has been determined by inelastic x-ray scattering (IXS) in the momentum transfer region (Q = 1.4-110 nm-1). These data allow to observe how, in a simple liquid, a phonon-like collective mode evolves towards the single particle dynamics. As a function of Q, one finds: i) at low Q's, a sound mode with a positive dispersion of the sound velocity, ii) at intermediate Q's, excitations whose energy oscillates similarly to phonons in the crystal Brillouin zones, and iii) at high Q's, the S(Q,E) approaches a Gaussian shape, indicating that the single particle dynamics has been reached.