AlbaNova and Nordita Colloquium
Taras Bryk (Institute of Condensed Matter Systems, Ukraine Academy of Sciences, L'viv, Ukraine)
FR4 Oskar Kleins Auditorium
Tuesday 18 June
15:00 - 16:00
The idea of the sensitivity of dynamic properties of fluids on the liquid-like or gas-like state of the system proposed in  was a breakthrough in understanding the dynamic dissimilarities of supercritical fluids. For fluids a purely dynamic quantity that was suggested to discriminate between the liquid-like and solid-like states is the so-called positive dispersion of collective excitations and inealstic X-ray scattering (IXS) experiments proved this assumption . The experiments revealed that the positive sound dispersion vanished at the thermodynamic point that could be treated as a continuation of the Widom line (maximum of the specific heat Cp(p) dependence) into the supercritical region. Later on a theory of positive dispersion in supercritical fluids  was constructed based on an analytical approach of Generalized Collective Modes (GCM) [4,5]. This theory revealed the leading role of non-hydrodynamic structural relaxation in positive sound dispersion.
In this talk recent results from simulations and theory of collective dynamics in supercritical Argon  and soft-sphere fluids will be discussed and a comparison will be made with a recently proposed “rigid”-”non-rigid” fluid dynamic crossover .
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