Transient Superdiffusion of Energetic Carriers in Transition Metal Dichalcogenides Visualized by Ultrafast Pump-Probe Microscopy  

作　　者：Yun-Ke Zhou Xiao-Ze Li Qian-Ni Zhou Ren-Hao Xing Yan Zhang Benfeng Bai Hong-Hua Fang Hong-Bo Sun 

机构地区：[1]State Key Laboratory of Precision Measurement Technology and Instruments,Department of Precision Instrument,Tsinghua University,Beijing 100084,P.R.China

出　　处：《Ultrafast Science》2022年第6期9-18,共10页超快科学（英文）

基　　金：financially supported by the National Natural Science Foundation of China(no.62075115);Tsinghua University Initiative Scientific Research Program.

摘　　要：Because of the strong Coulomb interaction and quantum confinement effect,2-dimensional transitionmetal dichalcogenides possess a stable excitonic population.To realize excitonic device applications,such as excitonic circuits,switches,and transistors,it is of paramount importance for understanding the optical properties of transition metal dichalcogenides.Furthermore,the strong quantum confinement in 2-dimensional space introduces exotic properties,such as enhanced phonon bottlenecking effect,many-body interaction of excitons,and ultrafast nonequilibrium exciton-exciton annihilation.Exciton diffusion is the primary energy dissipation process and a working horse in excitonic devices.In this work,we investigated time-resolved exciton propagation in monolayer semiconductors of wSe_(2),MowSe_(2),and MoSe_(2),with a home-built femtosecond pump-probe microscope.We observed ultrafast exciton expansion behavior with an equivalent diffusivity of up to 502 cm^(2)s^(-1)at the initial delay time,followed by a slow linear dffusive regime(20.9 cm^(2)s^(-1))in the monolayer WSe_(2).The fast expansion behavior is attributed to energetic carrier-dominated superdiffusive behavior.We found that in the monolayers MowSe_(2)and MoSe_(2),the energetic carrier-induced exciton expansion is much more effective,with diffusivity up to 668 and 2295 cm^(2)s^(-1),respectively.However,the"cold"exciton transport is trap limited in MowSe_(2)and MoSe_(2),leading to negative diffusion behavior at later time.Our findings are helpful to better understand the ultrafast nonlinear diffusive behavior in strongly quantum-confined systems.It may be harnessed to break the limit of conventional slow diffusion of excitons for advancing more efficient and ultrafast optoelectronicdevices.

关 键 词：diffusion EXPANSION quantum 

分 类 号：TH742[机械工程—光学工程]