Transverse Acoustic Excitations in Liquid Ga

The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga in the $Q$ range above $9{\mathrm{nm}}^{-1}$ although liquid Ga is mostly described by a hard-sphere liquid. An ab initio molecular dynamics simulation clearly supports this finding. From the detailed analysis for the $S(Q,\omega )$ spectra with a good statistic quality, the lifetime of 0.5 ps and the propagating length of 0.4–0.5 nm can be estimated for the transverse acoustic phonon modes, which may correspond to the lifetime and size of cages formed instantaneously in liquid Ga.

Figure 1

$S(Q,\omega )/S(Q)$ at $Q=6.7–10.6{\mathrm{nm}}^{-1}$ (circles with error bars) together with the resolution function (dashed curve at the bottom). Solid curves indicate the best fits and residuals of 1DHO and 2DHO models. See the text for details.

Figure 2

Dispersion relation of transverselike (open circles) and longitudinal (solid triangles) modes obtained from the fits. The solid curve gives the peak energies of the transverse current spectra, and the dotted curve is those of the quasitransverse branch seen in the longitudinal current spectra, both obtained by an orbital-free ab initio MD simulation. See the text for details.

Figure 3

(a) The width, (b) lifetime, and (c) propagation length of the transverse (open circles) and longitudinal (closed triangles) excitations together with the previous longitudinal data (full circles) [9]. The dashed curve indicates the Ioffe-Regel criterion [21].