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Ultrafast Coulomb-Induced Intervalley Coupling in Atomically Thin WS2

R. Schmidt ; Gunnar Berghäuser (Institutionen för fysik, Kondenserade materiens teori (Chalmers)) ; R. Schneider ; M. Selig ; P. Tonndorf ; Ermin Malic (Institutionen för fysik, Kondenserade materiens teori (Chalmers)) ; A. Knorr ; S. M. de Vasconcellos ; R. Bratschitsch
Nano letters (1530-6984). Vol. 16 (2016), 5, p. 2945-2950.
[Artikel, refereegranskad vetenskaplig]

Monolayers of semiconducting transition metal dichalcogenides hold the promise for a new paradigm in electronics by exploiting the valley degree of freedom in addition to charge and spin. For MoS2, WS2, and WSe2, valley polarization can be conveniently initialized and read out by circularly polarized light. However, the underlying microscopic processes governing valley polarization in these atomically thin equivalents of graphene are still not fully understood. Here, we present a joint experiment theory study on the ultrafast time resolved intervalley dynamics in monolayer WS2. Based on a microscopic theory, we reveal the many-particle mechanisms behind the observed spectral features. We show that Coulomb-induced intervalley coupling explains the immediate and prominent pump probe signal in the unpumped valley and the seemingly low valley polarization degrees typically observed in pump probe measurements compared to photoluminescence studies. The gained insights are also applicable to other light-emitting monolayer transition metal dichalcogenides, such as MoS2 and WSe2, where the Coulomb-induced intervalley coupling also determines the initial carrier dynamics.

Nyckelord: 2D materials, transition metal dichalcogenides, ultrafast valley dynamics, screened Coulomb matrix elements

Denna post skapades 2016-06-17.
CPL Pubid: 237853


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Denna publikation är ett resultat av följande projekt:

Graphene-Based Revolutions in ICT And Beyond (GRAPHENE) (EC/FP7/604391)