Abstract
Abstract
Intervalley scattering mechanisms strongly affect the dynamics of excitonic complexes in transition metal dichalcogenide monolayers. Here, we investigate the excitation energy dependence of the valley polarization of excitons in a WSe2 monolayer. We observe that the valley polarization drastically decreases when the excitation is resonant with the B
1
s
resonance. This behavior can be explained by a Dexter-like coupling in the momentum space between exciton states residing in opposite valleys but with the same spin configuration. This induces a net transfer of the exciton population from the optically driven valley towards the opposite, undriven valley. We observe the long-term fingerprints of this population transfer as a vanishing valley polarization for the neutral exciton, and a negative valley polarization for biexcitonic complexes, in qualitative agreement with theoretical predictions based on a fully microscopic many-particle approach. This, together with a decrease of the PL energy when the excitation is resonant with the B
1
s
state, points to the prominent role of the Dexter-like coupling in the exciton dynamics of atomically thin semiconductors.
Funder
Narodowe Centrum Nauki
Japan Society for the Promotion of Science
Agence Nationale de la Recherche
Deutsche Forschungsgemeinschaft
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics,General Materials Science,General Chemistry