Boltzmann in materials - tales of heat and electricity, the death of phonons, and the birth of relaxons
Event details
| Date | 30.05.2016 |
| Hour | 10:30 |
| Speaker | Prof. N. Marzari & A. Cepellotti, National Centre for Competence in Research NCCR MARVEL, EPFL |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
Quantum-mechanical simulations are driving a revolution in our capabilities to understand, predict, and design the properties and performance of novel materials and devices, and I'll try and illustrate this paradigm, both with an introduction to the field, and then focusing on electrical and thermal transport, showing how density-functional theory and density-functional perturbation theory can provide us with accurate thermomechanical properties, many-body perturbation theory with electronic spectra, and how phonon lifetimes and electron scattering rates can endow with predictive accuracy the Boltzmann transport equation for electrons and phonons in crystalline materials.
In the process, I will highlight how in two-dimensional materials normal heat-flux conserving processes dominate over Umklapp scattering. As a result, the phonon gas behaves as an ideal fluid and novel regimes emerge, with collective excitations carrying heat over macroscopic system sizes and Poiseuille and Ziman hydrodynamics, hitherto confined to cryogenic temperatures, characterizing transport at ordinary conditions. In several cases wave-like heat transfer appears in addition to ballistic or diffusive propagation, where second sound may be present at room temperature. Most importantly, this analysis will underline why we cannot consider phonons as the heat carriers in crystals, and how we can construct a kinetic theory of heat transport through novel excitations - termed here relaxons.
In the process, I will highlight how in two-dimensional materials normal heat-flux conserving processes dominate over Umklapp scattering. As a result, the phonon gas behaves as an ideal fluid and novel regimes emerge, with collective excitations carrying heat over macroscopic system sizes and Poiseuille and Ziman hydrodynamics, hitherto confined to cryogenic temperatures, characterizing transport at ordinary conditions. In several cases wave-like heat transfer appears in addition to ballistic or diffusive propagation, where second sound may be present at room temperature. Most importantly, this analysis will underline why we cannot consider phonons as the heat carriers in crystals, and how we can construct a kinetic theory of heat transport through novel excitations - termed here relaxons.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci
Contact
- Prof. P. Ricci