Ultrafast investigation of room temperature valley polarization in “optical bilayer” WS2

• Published in: Science China. Technological sciences 2024, Vol.67 (1), p.91-97
• Main Authors: Zhao, LeYi, Wang, Hai, Liu, TianYu, Li, FangFei, Zhou, Qiang, Wang, HaiYu
• Format: Article
• Language: English
• Subjects: Bilayers; Depolarization; Engineering; Interlayers; Monolayers; Optical properties; Photoluminescence; Polarization; Room temperature; Transition metal compounds; Tungsten disulfide
• ISSN: 1674-7321; 1869-1900
• DOI: 10.1007/s11431-022-2414-5

Monolayer transition metal dichalcogenides (TMDCs) have become a promising platform in valleytronics due to possessing the regulatable valley degrees of freedom. While, as a result of the rapid intervalley scattering, it is difficult to measure the PL valley polarization of monolayer TMDCs at room temperature, which limits their application in valleytronics devices. Here, we report a room temperature photoluminescence (PL) valley polarization up to 3.73% in an “optical bilayer” WS 2 formed by transferring monolayer WS 2 onto flat Ag film. Furthermore, in the transient absorption (TA) measurements, a remarkably long valley depolarization lifetime is found. Thus, we demonstrate the valley properties of such “optical bilayer” WS 2 resemble actual bilayer WS 2 , in which the robust valley polarization can be attributed to the phonons depletion effect and the blocked interlayer hopping processes. These peculiar valley features in “optical bilayer” WS 2 provide a particularly simple method to enhance valley control at room temperature.