一、报告题目

Large valley splitting and emission anisotropy of magnetic brightened dark excitons and biexcitons in monolayer WS2

二、报告人

Prof. Fanyao Qu (屈凡尧教授)

Institute of Physics, University of Brasilia (巴西利亚大学物理系)

三、报告时间

2018年12月20日 (周四) 下午16:00

四、报告地点

知新楼量子报告厅C702

五、邀请人

解士杰教授

六、摘要

Exploiting the “valley” degree of freedom to store and manipulate information is an emerging direction of condensed matter physics, and provides a novel paradigm for future electronics. Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. For either application, a long valley polarization lifetime and controllabel valley degree of freedom are crucial. We theoretically investigate the valley dynamics and steady state emissions of multiexcitons, including bright and dark excitons as well as biexcitons formed by either one-bright and one dark excitons (XXd) or two bright excitons (XX) in monolayer WS2 subjected to a tilted magnetic field. We demonstrate that both brightened dark excitons and biexcitons exhibit large valley splittings; nevertheless, the former is twice as large as the latter. Besides, their magneto-photoluminecence (PL) display very strong valley anisotropy. Aside from magnitude of magnetic field, both the valley splitting and anisotropy of the multiexciton emissions can also be tuned by magnetic field geometric configuration. Remarkably, both magneto-PL intensity and the valley anisotropy of XX is strongly enhanced as the temperature rises. Therefore the long lifetime and large valley splitting of the dark exciton and XXd biexciton in monolayer WS2 make them promising for long-distance transport and macroscopic quantum state generations.

七、报告人简介

屈凡尧现任巴西利亚大学物理系教授，曾先后在曲阜师范大学物理系、南加州大学伯克利分校物理系、加拿大科学院、巴西乌伯兰迪亚联邦大学、意大利国际理论物理研究中心和德克萨斯大学奥斯汀分校任职或访学。研究兴趣包括：二维材料和范德瓦尔斯异质结的电子结构、光热、量子输运及拓扑性质，范德瓦尔斯异质结的自旋和多激子的谷动力学，量子信息和纳米器件模拟，等。先后在Phys. Rev. Lett.、Phys. Rev. B和Appl. Phys. Lett等主流物理期刊发表论文近百篇，参与Quantum-dot Based Light-emitting Diodes等4部专著的编纂，在国际大会作邀请报告19次，并组织国际会议2次。