“Optical investigation of strong light-matter interactions in 2D materials”
题? 目：Optical investigation of strong light-matter interactions in 2D materials
报告人：Prof. Ting YU (Nanyang Technological University)
地? 点：工程实验大楼240、244 多媒体报告厅
时? 间：2019年6月21日（周五）下午 2:30-3:30
Ting YU received his PhD in Department of Physics, National University of Singapore in 2003 and is currently a Professor in Division of Physics and Applied Physics, Nanyang Technological University, Singapore. Dr. YU has received many prestigious awards including Nanyang Excellence Award for Research and Innovation (2008), National Young Scientist Award, National Research Foundation Fellowship Award (2009), Outstanding Young Scientist for the 3rd Inter Academy Panel/World Economic Forum (Summer Davos Forum) ((IAP/WEF, Representative of Singapore, 2010) and Institute of Physics Singapore, Nanotechnology award (2011). His research interests cover fabrication of low dimensional, especially 2D materials and investigation of their optical, optoelectrical and eletrochemical properties for developing novel electronics, optoelectronics and energy conversion/storage. Dr Yu has published more than 260 SCI papers and received over 10,000 nonself-citations. His H-index is 75.
Two-dimensional (2D) materials, such as graphene and monolayer transitional-metal-dichalcogenides (TMDs), have aroused great attention due to the underlying fundamental physics and the promising atomically-thin optoelectronic applications. Optical properties of these 2D materials are fundamentally interesting such as collective charge-density-wave (CDW) states of TMDs and strong excitonic emission in monolayer WS2. Meanwhile, development of practical optoelectronics based on 2D materials is very promising, which opens many opportunities for the next-generation light-emitting applications such as valley light-emitting diodes and on-chip vertical-cavity surface-emitting lasers (VCSELs). Here, we report observations of CDW phase transitions of 1T-phase TiSe2 and 2H-NbSe2 layers, wealthy excitonic emission states of monolayer WS2, and 2D semiconductor lasing from monolayer WS2 embedded VCSELs. Variable temperature-dependent Raman spectroscopic measurements were carried out to estimate the CDW phase transition temperatures of 1T-TiSe2 and 2H-NbSe2 layers, indicative of high crystal quality. By electrostatic and optical doping, tunable excitonic emission has been achieved due to interplay of various excitonic states. Meanwhile, the doping dependences of excitons, trions, biexcitons and diverse bound excitons associated with impurities and structural defects have been discussed. Furthermore, we realize room-temperature low-threshold lasing from monolayer WS2 activated VCSELs under continuous-wave optical pumping, which are intrinsically compatible with the prevailing monolithic integration technology. Overall, our studies provide many new understandings on fundamental light-matter interactions in atomically thin materials and pave ways to develop industrially attractive light-emitting applications based on 2D semiconductors.