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SUMMARY:Thermal transport beyond Fourier\, and beyond Boltzmann - Michele 
 Simoncelli\, Theory and Simulation of Materials (THEOS) and National Centr
 e for Computational Design and Discovery of Novel Materials (MARVEL)\, Éc
 ole Polytechnique Fédérale de Lausanne\, Switzerland
DTSTART:20200226T113000Z
DTEND:20200226T123000Z
UID:TALK139567@talks.cam.ac.uk
CONTACT:Angela Harper
DESCRIPTION:We explore the atomistic mechanisms of thermal transport in so
 lids\, elucidating how current\nformulations can be extended to enlarge th
 eir domain of applicability. First\, starting from a\ndensity-matrix forma
 lism\, we show how the phonon Boltzmann transport equation is missing\nan 
 off-diagonal tunneling term that becomes dominant in complex or glassy mat
 erials. The\nresulting formalism describes on an equal footing heat conduc
 tion in crystals\, glasses\, and\nanything in between. In particular\, it 
 predicts correctly and in agreement with experiments the\nopposite trends 
 of thermal conductivity in ordered and disordered systems\, and the mixed\
 nregime of complex thermoelectrics. Then\, we show how the Boltzmann trans
 port equation can\nbe coarse grained into a set of viscous heat equations 
 that describe both Fourier diffusion and\nheat hydrodynamics\, matching th
 e recent discovery of hydrodynamic transport/second sound\nin graphitic de
 vices.\n\nM. Simoncelli\, N. Marzari\, and F. Mauri\, Nat. Phys. 15\, 809 
 (2019).\n\nM. Simoncelli\, N. Marzari\, and A. Cepellotti\, Phys. Rev. X 1
 0\, 011019 (2020).
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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