title: Anomalous enhancement of valley polarization in multilayer WS2at room temperature.
abstract: We probe the polarization of the "A" exciton photoluminescence from monolayer and multilayer WS2at 10 K and 295 K under near-resonant and off-resonant conditions. The monolayer WS2exhibits relatively low valley polarization, around 24% at 10 K and 8% at 295 K, while all multilayer WS2samples show very high valley polarization, which is a more or less constant value of around 80% at 10 K under near-resonant excitation. At room temperature, it is observed experimentally that valley polarization in multilayer WS2monotonously increases with shrinking of the indirect bandgap energy. The phonon-assisted intervalley scattering via the K-Γ-K(K') valleys is identified as the primary valley polarization relaxation channel, which could be gradually suppressed as the thickness increases, leading to a valley polarization of up to 70% in multilayer WS2(>3 unit layers).
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. daijf@sustc.edu.cn.
authors.forename: Huimin
authors.initials: H
authors.lastname: Su
authors.forename: Chengrong
authors.initials: C
authors.lastname: Wei
authors.forename: Aiying
authors.initials: A
authors.lastname: Deng
authors.forename: Dongmei
authors.initials: D
authors.lastname: Deng
authors.forename: Chunlei
authors.initials: C
authors.lastname: Yang
authors.forename: Jun-Feng
authors.initials: JF
authors.lastname: Dai