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SUMMARY:New understanding of liquid thermodynamics\, viscosity and its low
 er bounds - Kostya Trachenko ( Queen Mary\, University of London)
DTSTART:20211111T140000Z
DTEND:20211111T150000Z
UID:TALK161917@talks.cam.ac.uk
CONTACT:Edgar Engel
DESCRIPTION:Understanding most basic thermodynamic properties of the liqui
 d state \nsuch as energy and heat capacity turned out to be a long-standin
 g \nproblem in physics [1]. Landau&Lifshitz textbook states that no genera
 l \nformulas can be derived for liquid thermodynamic functions because the
  \ninteractions are both strong and system-specific. Phrased differently\,
  \nliquids have no small parameter. Recent experimental and theoretical \n
 results open a new way to understand liquid thermodynamics on the basis \n
 of collective modes (phonons) as is done in the solid state theory. \nTher
 e are important differences between phonons in solids and  liquids\, \nand
  we have recently started to understand and quantify this difference. \nI 
 will review collective modes in liquids including high-frequency \nsolid-l
 ike transverse modes and will discuss how a gap in the reciprocal \nspace 
 emerges and develops in their spectrum [2\,3]. This reduces the \nnumber o
 f phonons with temperature\, consistent with the experimental \ndecrease o
 f constant-volume specific heat with temperature [1].  I will \ndiscuss th
 e implication of the above theory for fundamental \nunderstanding of liqui
 ds. I will also mention how this picture can be \nextended above the criti
 cal point where the recently proposed Frenkel \nline on the phase diagram 
 separates liquid-like and gas-like states of \nsupercritical dynamics [1\,
 4]. I will subsequently describe how this \nleads to the theory of minimal
  quantum viscosity in terms of fundamental \nphysical constants and will c
 ompare this minimum to the holographic \nbound [5]. The minimum of thermal
  diffusivity can be equally written as \nthe same combination of fundament
 al constants\, in agreement with \nexperiments. I also mention an upper bo
 und on the speed of sound in \nterms of fundamental constants following fr
 om a similar approach [6]. \nFinally\, I will note that the kinematic visc
 osity of the quark-gluon \nplasma is surprisingly close to the kinematic v
 iscosity of liquids at \ntheir minimum [7].\n\n1. K Trachenko and V Brazhk
 in\, Collective modes and thermodynamics of \nthe liquid state\, Reports o
 n Progress in Physics 79\, 016502 (2016)\n2. C Yang\, M T Dove\, V Brazhki
 n and K Trachenko\, Physical Review Letters \n118\, 215502 (2017)\n3. M Ba
 ggioli\, M Vasin\, V Brazhkin and K Trachenko\, Physics Reports 865\, \n1 
 (2020)\n4. C Cockrell\, V Brazhkin and K Trachenko\, arXiv:2104.10619\n5. 
 K Trachenko and V Brazhkin\, Minimal quantum viscosity from \nfundamental 
 physical constants\, Science Adv. 6\, eaba3747 (2020)\n6. K Trachenko\, B 
 Monserrat\, C Pickard and V Brazhkin\, Science Adv. 6\, \neabc8662 (2020)\
 n7. K Trachenko\, V Brazhkin and M Baggioli\, Similarity between the \nkin
 ematic viscosity of quark-gluon plasma and liquids at the viscosity \nmini
 mum\, SciPost Phys 10\, 118 (2021)
LOCATION:Details of video conferencing will be distributed nearer the time
 .
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