简介: |
Ten years since graphene, there have been remarkable advances in the synthesis and understanding of atomically thin 2D systems based on layered van der Waals crystals. Of particular interest is the family of semiconducting transition metal dichalcogenides (TMDCs). In this talk, I will present two recent developments on the emerging new phenomena in these 2D semiconductors. First, I will discuss the distinct symmetry properties of the monolayers that are probed by nonlinear optical spectroscopy. The prominent optical second-harmonic response reveals broken inversion symmetry in the monolayers and provides a convenient optical probe to determine their crystallographic orientation. The observed broken inversion symmetry has profound impact on the physical properties of monolayer TMDCs. In the second part of my talk, I will present experimental evidences for the valley contrast magnetic moments, which are allowed only in the absence of inversion symmetry. The valley contrast magnetic moments open up new mechanisms to control the valley degree of freedom. I will illustrate how to lift the valley degeneracy and how to create a valley polarization using magnetic field. At the end of my talk, future directions and emerging frontiers of the field will be discussed.
个人简介：Dr. Yilei Li received his PhD degree in physics from Columbia University in 2014, and his BEng degree (with distinction) in Electrical Engineering from Hong Kong university of Science and Technology in 2010. He is currently a postdoc in Prof. Tony Heinz’s group at Stanford University. His current research interest is focused on novel electronic and optical properties of 2D materials.
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