Ye Jialiang, Li Ying, Yan Tengfei, Zhai Guihao, Zhang Xinhui
State Key Laboratory of Superlattices and Microstructures , Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083 , P.R. China.
Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China.
J Phys Chem Lett. 2019 Jun 6;10(11):2963-2970. doi: 10.1021/acs.jpclett.9b01068. Epub 2019 May 22.
We investigated the build-up and relaxation processes of spin-polarized A- and B-exciton dynamics in monolayer, bilayer, and bulk WSe using helicity-resolved two-color pump-probe spectroscopy. Substantial spin polarization was confirmed in bulk crystals, though the spin polarization degree of A excitons decreased from monolayer to bulk. However, the spin polarization of A excitons almost vanished in all different layered-flakes when resonantly pumping the B-exciton transition, owing to the dominant role of interexciton transfer. When resonantly pumping the A-exciton transition, the spin polarization of the up-converted B excitons was inverted in all layers because of the efficient Dexter-like coupling and phonon-assisted scattering. The same short spin relaxation time (1.8 ± 0.2 ps) of A excitons was found for all studied flakes in the subsequent spin depolarization processes, which was ascribed to the active electron-phonon scattering resulting from the intrinsic small conduction-band spin-orbit coupling splitting in layered WSe.
我们使用螺旋度分辨双色泵浦-探测光谱，研究了单层、双层和体相WSe₂中自旋极化的A激子和B激子动力学的积累和弛豫过程。尽管从单层到体相，A激子的自旋极化程度降低，但在体相晶体中证实了显著的自旋极化。然而，当共振泵浦B激子跃迁时，由于激子间转移的主导作用，A激子的自旋极化在所有不同层状薄片中几乎消失。当共振泵浦A激子跃迁时，由于有效的类德克斯特耦合和声子辅助散射，上转换B激子的自旋极化在所有层中都发生了反转。在随后的自旋去极化过程中，所有研究的薄片中都发现A激子具有相同的短自旋弛豫时间（1.8±0.2皮秒），这归因于层状WSe₂中固有的小导带自旋-轨道耦合分裂导致的活跃电子-声子散射。
