DMSE Doctoral Thesis Defense - Zhiwei Ding
Wednesday, May 05, 2021 at 2:00pm to 3:00pmVirtual Event
DMSE Doctoral Thesis Defense
Phonon hydrodynamic transport at elevated temperature
Wednesday, May 5, 2021
2:00 – 3:00 PM EST
Contact firstname.lastname@example.org for Zoom link.
For over half a century, phonon hydrodynamic transport was deemed exotic and mattered only at extremely low temperatures. In this work, by combining the theoretical and experimental approach, we successfully predict and confirm the existence of phonon hydrodynamic transport in graphite above 200 K. More specifically, we introduce a direction-dependent definition of normal and Umklapp scattering, which gives an improved description of mode-specific phonon dynamics. By extending the classical Fuchs-Sondheimer solution, we developed a first-principles framework to study phonon hydrodynamics under the size effect with mode-by-mode phonon scattering details. We unambiguously revealed the Poiseuille heat flow by studying the variation of heat flow as the graphite ribbon width and identified for the first time the existence of phonon Knudsen minimum – an unusual phenomenon unique to hydrodynamic regime – which can be observed up to 90 K. Using a sub-picosecond transient grating technique, we directly observed second sound in graphite at record-high temperatures of 200 K. With the enlarged grating-period window, we firstly reported the dispersion of thermal wave, whose velocity increases with decreasing grating period. Our experimental findings are well explained with the interplay among “three fluids”: ballistic, diffusive, and hydrodynamic phonons. We believe our study may stimulate further work into discovering more material systems possessing significant phonon hydrodynamic features, as well as new research into understanding and manipulating the phonon transport in the hydrodynamic scheme.
Keith A. Nelson, Haslam and Dewey Professor, Chemistry, Massachusetts Institute of Technology
Ju Li, Battelle Energy Alliance Professor, Nuclear Science and Engineering, Materials Science and Engineering, Massachusetts Institute of Technology
Jeffrey C. Grossman, Morton and Claire Goulder and Family Professor, Materials Science and Engineering, Massachusetts Institute of Technology
Elsa Olivetti, Esther and Harold E. Edgerton Associate Professor, Materials Science and Engineering, Massachusetts Institute of Technology