2D monolayer semiconductors have emerged as an important class of materials for fundamental physics and many applications. Due to strong Coulomb interaction, they provide an important platform for studying many-body complexes or quasi-particles such as excitons, trions, bi-excitons, and other possible new species. This talk will focus on our recent results of spectroscopic studies of the monolayer MoTe2, especially the existence of possible new species involving three and four electrons and holes. We will show that the common concept of a trion needs to be re-examined and there is a spectral splitting between a charged exciton and a genuei trion. In the case of four fermions, our combined theoretical and experimental results will be presented to show strong evidence for the existence of a new four-particle entity, a genuei four-body bound state called quadruplon which does not involve excitons and is different from the bi exciton.

Dr. Ning is a Chaired Professor and a College Dean at Shenzhen Tech University. He obtained his PhD at University of Stuttgart and was a winner of Humbold Research Award. He has been a Professor at Tsinghua University, the founding Director of Tsinghua International Center for Nano-Optoelectronics, and Professor at Arizona State University. He is widely recognized for his research on semiconductor lasers and nanolasers, nanophotonic materials, physics, and devices. Among many of his research accomplishments, his team demonstrated the first plasmonic nanolasers and the first monolithic white lasers. Dr. Ning is a Fellow of the Optica (OSA), IEEE, and the Electromagnetic Academy, and a member of US National Academy of Invention.