Скачать или смотреть 2019/07/24 I²CNER Seminar Series : Prof. Xiulin Ruan

[Title] Higher-order, non-equilibrium, and nonlinear phonon transport in emerging materials: Predictions guiding experiments
[Speaker] Prof. Xiulin Ruan
Professor,
School of Mechanical Engineering, and
Birck Nanotechnology Center
Purdue University, USA
[Date & Time] Monday, June 10, 2019
[Place]I²CNER hall, I²CNER Bldg.1, Ito Campus, Kyushu University

[Abstract] Phonon thermal transport is crucial to many important energy applications. This talk will cover several unusual theoretical findings, including higher-order, non-equilibrium, and nonlinear phonon transport, and will show how these theories have inspired and guided experimental confirmations. The first part of the talk will establish four-phonon scattering as an important advance of the quantum theory of phonon scattering. For decades, four-phonon scattering had been persistently unclear and hence ignored. However, we have developed a rigorous perturbation method to predict four-phonon scattering rates, and found its significance on thermal conductive and radiative properties for nearly all materials at high temperature. Strikingly, it is significant even at room temperature for many materials including boron arsenide, graphene, PbTe, and GaAs. The second part of the talk will discuss local non-equilibrium phonon transport in graphene and across interfaces. We show that electrons and different phonon modes in graphene are driven out of thermal equilibrium when irradiated with laser. Hence, the apparent thermal conductivity obtained from Raman spectroscopy needs careful interpretation. We also show that phonons are out of local thermal equilibrium across interfaces. We have developed non-equilibrium Landauer approach and multi-temperature models to account for such effects. The third part of the talk will cover nonlinear thermal transport in graphene. We have predicted that asymmetric graphene nanoribbons function as thermal diodes, which has been experi- mentally confirmed recently.