Ultrafast Coulomb-Induced Intervalley Coupling in Atomically Thin WS2

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• 作者：Robert Schmidt ; Gunnar Berghäuser ; Robert Schneider ; Malte Selig ; Philipp Tonndorf ; Ermin Malić ; Andreas Knorr ; Steffen Michaelis de Vasconcellos ; Rudolf Bratschitsch
• 刊名：Nano Letters
• 出版年：2016
• 出版时间：May 11, 2016
• 年：2016
• 卷：16
• 期：5
• 页码：2945-2950
• 全文大小：420K
• 年卷期：0
• ISSN：1530-6992

文摘

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.