2025/11/10(Mon) 14:30 -16:00 一樓演講廳 1F, Auditorium
Title
Ultrafast carrier dynamics and optical nonlinearity of van der Waals materials
Speaker
林宮玄研究技師 (中央研究院物理研究所) Dr. Kung-Hsuan Lin (Institute of Physics, Academia Sinica)Abstract
In this talk, I will share our recent studies of a few van der Waals materials by using ultrafast lasers. The first part is ultrafast carrier and exciton dynamics of InSe. We utilized ultrafast optical spectroscopy to investigate In-plane (IP) and out-of-plane (OP) optical features of InSe. From polarization-resolved absorption spectra, we measure the energy difference between excitons with IP and OP dipole responses in InSe to be 0.4 meV. Under photoexcitation with femtosecond pulses, the photocarriers screen the excitons and can increase the energy difference between IP and OP optical responses to as much as 8 meV. This energy difference results from the varying screening lengths along the IP and OP directions. In addition, we observed the dependence of thickness on carrier lifetimes in InSe. The recombination process is dominated by surface recombination when the thickness is thinner than a few tens of nanometers. The second part of this talk is optical nonlinearity of Group IV monochalcogenides (such as GeSe, GeS, SnSe, SnS), which have been predicted to be multiferroic materials with in-plane ferroelectricity and ferroelasticity in its monolayer form. I will report the giant second-order nonlinearity of SnS and SnSe with ferroelectric stacking. From theoretical and experimental results, the susceptibility of second harmonic generation (SHG) from SnS and SnSe with ferroelectric stacking is two to three orders of magnitude higher than the values of traditional nonlinear crystals such as BBO and KTP. We also demonstrated ferroelastic transformation of SnSe by using mechanical forces. Finally, I will briefly mention our ongoing work and future plans.
Poster
Language
演講語言 (Language): in English