Crossover of collective modes and positive sound dispersion in supercritical state

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...

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Bibliographic Details
Published in:Journal of physics. Condensed matter 2016-11, Vol.28 (43), p.43LT01-43LT01
Main Authors: Fomin, Yu D, Ryzhov, V N, Tsiok, E N, Brazhkin, V V, Trachenko, K
Format: Article
Language:English
Subjects:
Frenkel line
liquids
phonons
positive sound dispersion
supercritical state
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Summary: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.
ISSN:0953-8984
1361-648X
DOI:10.1088/0953-8984/28/43/43LT01