Imaging the effect of high photoexcited densities on valley polarization and coherence in MoS2 monolayers

• Main Authors: Cadiz, F. (Author), Gerl, S. (Author), Taniguchi, T. (Author), Watanabe, K. (Author)
• Format: Article
• Language: English
• Published: Nature Research 2022
• Subjects: Energy relaxation; Excitation power; Exciton-exciton scattering; Excitons; Landforms; Laser excitation; Laser induced; Layered semiconductors; Local heating; Molybdenum compounds; Momentum scattering; Monolayers; Non-monotonic dependence; Polarization; Power densities; Scattering rates; Spatial positions; Sulfur compounds
• Online Access: View Fulltext in Publisher

 We have investigated the laser-induced valley polarization and coherence of encapsulated MoS2 monolayer as a function of temperature, power density, and spatial position. Besides a non-monotonic dependence on temperature, recently attributed to a dependence of the valley relaxation time on the momentum scattering rate, we observe a two-fold increase of the valley polarization when increasing the laser excitation power. We attribute this effect to a local heating induced by the energy relaxation of photoexcited excitons and to an increase of the exciton-exciton scattering rate. In contrast, only a moderate enhancement of valley coherence is observed, which exhibits a dramatic drop after further increasing the excitation power. We attribute this behaviour to the detrimental role of exciton-exciton interactions on the pure dephasing rate responsible for the loss of coherence between the valleys. This manifests itself by a strong dip in the spatial profile of the valley coherence at high photoexcited densities. © 2022, The Author(s).