title: Ultrafast Coulomb-Induced Intervalley Coupling in Atomically Thin WS2.
abstract: 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.
authors.affiliation: Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Schmidt
authors.affiliation: Department for Applied Physics, Chalmers University of Technology , SE-41296, Gothenburg, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Berghäuser
authors.affiliation: Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Schneider
authors.affiliation: Department for Theoretical Physics, Technical University Berlin , 10623 Berlin, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Selig
authors.affiliation: Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Tonndorf
authors.affiliation: Department for Applied Physics, Chalmers University of Technology , SE-41296, Gothenburg, Sweden.
authors.forename: Ermin
authors.initials: E
authors.lastname: Malić
authors.affiliation: Department for Theoretical Physics, Technical University Berlin , 10623 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Knorr
authors.affiliation: Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Michaelis de Vasconcellos
authors.affiliation: Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Bratschitsch
keywords: 2D materials; screened Coulomb matrix elements; transition metal dichalcogenides; ultrafast valley dynamics