Spin and valley dynamics of excitons in transition metal dichalcogenides monolayers

Abstract

Monolayers of transition metal dichalcogenides, namely, molybdenum and tungsten disulfides and diselenides demonstrate unusual optical properties related to the spin-valley locking effect. Particularly, excitation of monolayers by circularly polarized light selectively creates electron-hole pairs or excitons in non-equivalent valleys in momentum space, depending on the light helicity. This allows studying the inter-valley dynamics of charge carriers and Coulomb complexes by means of optical spectroscopy. Here we present a concise review of the neutral exciton fine structure and its spin and valley dynamics in monolayers of transition metal dichalcogenides. It is demonstrated that the long-range exchange interaction between an electron and a hole in the exciton is an efficient mechanism for rapid mixing between bright excitons made of electron-hole pairs in different valleys. We discuss the physical origin of the long-range exchange interaction and outline its derivation in both the electrodynamical and $\mathbf{k}\cdot \mathbf{p}$ approaches. We further present a model of bright exciton spin dynamics driven by an interplay between the long-range exchange interaction and scattering. Finally, we discuss the application of the model to describe recent experimental data obtained by time-resolved photoluminescence and Kerr rotation techniques.

15 pages, 12+1 figures, Feature article submitted to pss b as contribution of IWEPNM 2015

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• Atomically inspired $k\cdot p$ approach and valley Zeeman effect in transition metal dichalcogenide monolayers
• Novel valley depolarization dynamics and valley Hall effect of exciton in mono- and bilayer MoS${}_2$
• Valley polarized relaxation and upconversion luminescence from Tamm-Plasmon Trion-Polaritons with a MoSe2 monolayer
• Resonance profiles of valley polarization in single-layer MoS${}_2$ and MoSe${}_2$
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• Wannier-Function-Based Approach to Coupled Exciton-Phonon-Photon Dynamics in Two-Dimensional Semiconductors
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• Trapping the carrier in the spin-locked MoS2 atomic valley by absorption of chiral L-cysteine
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• Intersubband electric dipole spin resonance in transition metal dichalcogenide heterobilayers
• Valley pseudospin relaxation of charged excitons in monolayer MoTe${}_2$
• Stability of vortices in exciton-polariton condensates with spin-orbital-angular-momentum coupling