报告题目： Valley Polarization of Trions and Magnetoresistance in MoS2/YIG Heterostructures
彭波，电子科技大学，教授、博士生导师。研究领域：（1）磁性二维材料异质结界面电子自旋调控及输运特性的研究；（2）面向激光相控阵雷达系统的智能超表面。近几年，在ACS Nano、Nano lett、Adv Mater等国际知名学术期刊上发表论文40余篇，ISI他引1000余次。
Manipulation of spin degree of freedom (DOF) of electrons is the fundamental to spintronic and valleytronic devices. Two-dimensional transition metal dichalcogenides (2-D TMDCs) exhibit an emerging valley pseudospin, in which spin up (down) electrons are distributed in +K (-K) valley. This valley polarization gives a new DOF for spintronic and valleytronic devices. Recently, magnetic exchange interactions between graphene and magnetic insulator Yttrium Iron Garnet (YIG) have been exploited. However, the physics of 2-D TMDCs with YIG have not been shown before. Here we demonstrate strong many-body effects in a heterostructure geometry comprising MoS2 monolayer and YIG. High-order trions are directly identified by mapping absorption and photoluminescence at 12 K. The electron doping density is up to ~1013 cm-2, resulting in a large splitting of ~40 meV between trion and exciton. The trions exhibit a high circular polarization of ~80% under optical pumping by circularly polarized light at ~1.96 eV. It is confirmed experimentally that both phonon scattering and electron-hole interaction to contribute to the valley depolarization; and the interfacial spin accumulation from YIG determines the magnetoresistance behavior of MoS2 monolayer, thus imparting them significant possibility toward spin manipulation at elevated temperature.