报告题目：Helicity-changing Raman Spectra in Two-dimensional Materials
Department of Physics, Tohoku University, Sendai, 980-8578, Japan
报告时间：2020-4-13 9.00-11.00 腾讯会议ID: 37225659
Two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) have two valleys of electronic states around the K and K’ points in the hexagonal Brillouin zone.Optical absorption in the K or K’ valleys are special in which only one of helicity of circularly-polarized right (either left-handed or right-handed) is absorbed. This phenomenon is called as valley polarization . Further, in TMDs, there are two Raman modes whose oscillating directions are out-of-plane (A1g symmetry) and in-plane (E2g). When incident light is left-handed circularly polarized light, the scattered light has either left- or right-handed circularly polarized light for the A1g and E2g modes, respectively. Since a photon of circularly polarized light has an angular momentum, the angular momentum is given from the phonon in the helicity changing Raman scattering as shown in Fig. 1.
In this talk, starting with overview of Raman spectroscopy of two-dimensional materials ,we will focus our attention on Raman scattering with using circular polarized light. First we will discuss energy dependence of valley polarization on the helicity exchange Raman spectra.  Then we will discuss on conservation law of angular momentum of a photon in the Raman processes.  When we discuss optical properties of two-dimensional materials, the combination of the concepts of valley polarization and circular dichroism are important, which we will discuss possible phenomena that occur in two-dimensional materials.