Ultrafast phonon dynamics under extreme conditions: from 2D thermoelectrics to Earth materials
Wen-Pin Hsieh1*
1Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan
* Presenter:Wen-Pin Hsieh, email:wphsieh@earth.sinica.edu.tw
One of the fundamental challenges in condensed matter physics is to decipher the dynamics of carriers transporting in novel materials as well as complex interactions among them. Understanding of the ultrafast dynamics of phonons and electrons at nanometer length scale could offer critical insights to many fundamental physics as well as to design and engineer novel devices with energy applications. In this talk, I will present our recent exciting results about using ultrafast optical pump-probe method to explore heat transfer through several single- and few-layered 2D materials (graphene, transition-metal-dichalcogenides, etc.). We find that the presence of these 2D materials substantially suppresses heat transfer in the devices and shows promising thermoelectric performance. In addition, high pressure offers a unique route to systematically tune the physical properties of materials and to induce remarkable phase transitions that show many interesting physics. Combined with the ultrafast laser techniques, recently we also study phonon transport dynamics and thermal conductivity of iron-doped materials at high pressures. We find that their thermal conductivities change drastically upon a pressure-induced spin state transition. These results not only provide direct data for modeling the thermal structure of deep Earth, but also open up a new window to further study ultrafast dynamics of condensed matter systems under extreme conditions.

Keywords: ultrafast laser, 2D materials, phonon dynamics, high pressure