Ultrafast Coulomb-Induced Intervalley Coupling in Atomically Thin WS2
Artikel i vetenskaplig tidskrift, 2016

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.

2D materials

transition metal dichalcogenides

screened Coulomb matrix elements

ultrafast valley dynamics


R. Schmidt

Universität Münster

Gunnar Berghäuser

Chalmers, Fysik, Kondenserade materiens teori

R. Schneider

Universität Münster

M. Selig

Technische Universität Berlin

P. Tonndorf

Universität Münster

Ermin Malic

Chalmers, Fysik, Kondenserade materiens teori

A. Knorr

Technische Universität Berlin

S. M. de Vasconcellos

Universität Münster

R. Bratschitsch

Universität Münster

Nano Letters

1530-6984 (ISSN) 1530-6992 (eISSN)

Vol. 16 2945-2950

Graphene-Based Revolutions in ICT And Beyond (Graphene Flagship)

Europeiska kommissionen (FP7), 2013-10-01 -- 2016-03-31.