过渡金属硫化物非线性吸收的激子暗态调制效应研究

Transition-metal dichalcogenide (TMDC) layered nanomaterials have been emerging as one of significant candidates in developing ultrafast on-chip all-optical components and devices due to large optical nonlinearity in nanoscale, ultrafast response, flexibility and low cost. It has gained much attention in the field of layered semiconductor photonics. Different from the tremendous progress in the parametric process of TMDC, one of the bottleneck for the photonics device application is the scarcity of its fundamental knowledge about non-parametric process, especially the mechanism of nonlinear optical absorption, its variation along with the bright and dark exciton state, the reason why dark exciton states generate. In this project, we choose WS2 and WSe2 as preferential TMDC materials in the research since the energy gap between A and B exciton is relatively large. Combining with the theoretical model of G. D. Houser & E. Garmire, the nonlinear optical absorption spectroscopy method will be utilized to study the nonlinear absorption properties which are accompanied by bright and dark exciton state. The third-order nonlinear optical susceptibility (absolute value), influence of electron spin distinction of W and Mo series, dark exciton energy level, electronic band gap (not optical one) will be determined experimentally. The results are expected to provide theory and technique support for practical application of TMDC in micro-plane ultrafast photonic devices in future.

过渡金属硫化物层状纳米材料因具有“纳米尺度强光学非线性、超快响应、柔性、成本低”等特点成为芯片级全光调制器件开发的重要备选材料之一。然而与其光学参量过程研究形成巨大反差的是，过渡金属硫化物非参量过程尤其是非线性吸收机制、与激子亮、暗态关系、激子暗态形成原因等方面机理性问题仍然存在，是制约其器件化的主要瓶颈。本项目拟首选A、B激子能级间距较大的WS2和WSe2，利用非线性吸收光谱的方法结合G. D. Houser & E. Garmire理论模型研究暗激子态对非线性吸收的调制规律；研究W系Mo系电子自旋差异带来的影响和非线性吸收系数、三阶非线性极化率、暗激子能级位置和电子带隙的变化规律，为未来基于过渡金属硫化物的微平面光调制器件开发提供良好的物理支撑。

具有优异非线性光学特性的低维半导体材料是构筑未来高性能光电、全光信息系统的关键之一。作为最早开展二维材料非线性光学工作的研究课题组之一，我们在国际上率先揭示了石墨烯、过渡金属硫化物和黑磷等重要二维材料的非线性光学特性。经过本研究的执行，负责人及团队开展了以PtSe2，MoS2为代表的二维半导体、半金属等材料超快非线性光学性质的研究工作，在层状过渡金属化合物的非线性特性、超快载流子弛豫、低频声子振动谱等方面取得多项原创研究成果，发表SCI论文9篇，其中第一作者1篇，通讯作者5篇，合作作者3篇。