Journal Article

Magnetic brightening and control of dark excitons in monolayer WSe2

Lin, Yu-Chuan, Louie, Steven G., Heinz, Tony F., Wang, Ying, Li, Zhiqiang, Smirnov, Dmitry, Lu, Zhengguang, Hone, James C., Cao, Ting, Robinson, Joshua A., Zhang, Xiao-Xiao, Zhang, Fan

2017

Overview

Monolayer transition metal dichalcogenide crystals, as direct-gap materials with strong light–matter interactions, have attracted much recent attention. Because of their spin-polarized valence bands and a predicted spin splitting at the conduction band edges, the lowest-lying excitons in WX 2 (X = S, Se) are expected to be spin-forbidden and optically dark. To date, however, there has been no direct experimental probe of these dark excitons. Here, we show how an in-plane magnetic field can brighten the dark excitons in monolayer WSe 2 and permit their properties to be observed experimentally. Precise energy levels for both the neutral and charged dark excitons are obtained and compared with ab initio calculations using the GW-BSE approach. As a result of their spin configuration, the brightened dark excitons exhibit much-increased emission and valley lifetimes. These studies directly probe the excitonic spin manifold and reveal the fine spin-splitting at the conduction band edges. Magnetic brightening enables direct observation of spin-forbidden dark excitons in a monolayer WSe 2 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 119/118 / 140/125 / 639/624/400/1101 / 639/925/357/1018 / Brightening / Conduction / Conduction bands / Crystals / Emission analysis / Energy levels / Excitation / Excitons / Magnetic fields / MATERIALS SCIENCE / Nanotechnology / Nanotechnology and Microengineering / Splitting