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Miller, Bastian; Lindlau, Jessica; Bommert, Max; Neumann, Andre; Yamaguchi, Hisato; Holleitner, Alexander; Hoegele, Alexander; Wurstbauer, Ursula (2019): Tuning the Fröhlich exciton-phonon scattering in monolayer MoS2. In: Nature Communications, Vol. 10, 807
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Abstract

Charge carriers in semiconducting transition metal dichalcogenides possess a valley degree of freedom that allows for optoelectronic applications based on the momentum of excitons. At elevated temperatures, scattering by phonons limits valley polarization, making a detailed knowledge about strength and nature of the interaction of excitons with phonons essential. In this work, we directly access exciton-phonon coupling in charge tunable single layer MoS2 devices by polarization resolved Raman spectroscopy. We observe a strong defect mediated coupling between the long-range oscillating electric field induced by the longitudinal optical phonon in the dipolar medium and the exciton. This so-called Frohlich exciton phonon interaction is suppressed by doping. The suppression correlates with a distinct increase of the degree of valley polarization up to 20% even at elevated temperatures of 220 K. Our result demonstrates a promising strategy to increase the degree of valley polarization towards room temperature valleytronic applications.