Monolayer transition metal dichalcogenides, MX2 (M = Mo, W and X = S, Se), are direct-gap semiconductors with some interesting properties. First, the low-dimensional hexagonal structure leads to two inequivalent K-points, K and K’, in the brillioun zone. Second, this valley index and spin are intrinsically coupled, and spin-dependent selection rules enable one to independently populate and interrogate a unique K valley with circularly polarized light. Here we probe the degree of circular polarization of the emitted photoluminescence as function of the photo-excitation energy and temperature to elucidate spin-dependent inter- and intra-valley relaxation mechanisms. Monolayer flakes of MoS2 and MoSe2 show a strong depolarization as the excitation energy is increased. However, WS2 maintains significant polarization for high excitation energies, even at room temperature when properly prepared. We discuss the behavior of the polarization in terms of various phonon assisted intervalley scattering processes. This work was supported by NRL and the NRL Nanoscience Institute
Aubrey Hanbicki, Marc Currie, George Kioseoglou, C. Stephen Hellberg, Kathleen M. McCreary, Adam L. Friedman, and Berend T. Jonker, "Spin relaxation and intervalley scattering in 2D semiconductors (Presentation Recording)," Proc. SPIE 9551, Spintronics VIII, 95510Z (Presented at SPIE Nanoscience + Engineering: August 10, 2015; Published: 5 October 2015); https://doi.org/10.1117/12.2190196.4519370534001.
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