We demonstrate the exfoliation of large-area monolayer flakes prepared from bulk MoS2 crystals. The flakes are first characterized using Raman and photoluminescence measurements. We then utilize time-resolved Kerr rotation (TRKR) measurements to probe the valley dynamics in the monolayer flakes at low temperatures. This technique allows resonant excitation of the excitonic transitions and yields sub-picosecond resolution. We find valley lifetimes of about 40 ps at a temperature of 4 K in monolayer MoS2 for resonant excitation. With increasing temperatures, we observe a dramatic decrease of the valley lifetimes, indicating that valley dephasing is mediated by phonon-related scattering processes.
Gerd Plechinger, Philipp Nagler, Christian Schüller, and Tobias Korn, "Time-resolved spectroscopy of coupled spin-valley-dynamics in monolayer transition metal dichalcogenides at low temperatures," Proc. SPIE 9551, Spintronics VIII, 95510V (Presented at SPIE Nanoscience + Engineering: August 10, 2015; Published: 8 September 2015); https://doi.org/10.1117/12.2186402.
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