Crossover of collective modes and positive sound dispersion in supercritical stateстатья
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Дата последнего поиска статьи во внешних источниках: 18 февраля 2017 г.
Аннотация:Supercritical state has been viewed as an intermediate state between gases and liquids with
largely unknown physical properties. Here, we address the important ability of supercritical
fluids to sustain collective excitations. We directly study propagating modes on the basis
of correlation functions calculated in molecular dynamics simulations and find that the
supercritical system sustains propagating solid-like transverse modes below the Frenkel
line but not above where there is one longitudinal mode only. Important thermodynamic
implications of this finding are discussed. We directly detect positive sound dispersion (PSD)
below the Frenkel line where transverse modes are operative and quantitatively explain its
magnitude on the basis of transverse and longitudinal velocities. PSD disappears above the
Frenkel line which therefore demarcates the supercritical phase diagram into two areas where
PSD does and does not operate.