Dissecting intervalley coupling mechanisms in monolayer transition metal dichalcogenides
Oleg Dogadov, Henry Mittenzwey, Micol Bertolotti, Nicholas Olsen, Thomas Deckert, Chiara Trovatello, Xiaoyang Zhu, Daniele Brida, Giulio Cerullo, Andreas Knorr, Stefano Dal Conte
Published: 2025/7/22
Abstract
Monolayer (1L) transition metal dichalcogenides (TMDs) provide a unique opportunity to control the valley degree of freedom of optically excited charge carriers due to the spin-valley locking effect. Despite extensive studies of the valley-contrasting physics, stimulated by perspective valleytronic applications, a unified picture of competing intervalley coupling processes in 1L-TMDs is lacking. Here, we apply broadband helicity-resolved transient absorption to explore exciton valley polarization dynamics in 1L-WSe${}_2$. By combining experimental results with microscopic simulations, we dissect individual intervalley coupling mechanisms and reveal the crucial role of phonon-assisted scattering in the fast decay of the A exciton circular dichroism and the formation of the dichroism of opposite polarity for the B exciton. We further provide a consistent description of the valley depolarization driven by the combined action of Coulomb scattering processes and indicate the presence of efficient single spin-flip mechanisms. Our study brings us closer to a complete understanding of exciton dynamics in TMDs.