报告题目：Emerging Phenomena in 2D Semiconductors

报 告 人：Yilei Li,Stanford University

报告时间：2015年9月2日9：30

报告地点：理科楼三楼报告厅（C302）

报告摘要：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.