The valley exciton dynamics in two-dimensional transition metal dichalcogenides (TMDs) is crucial for the spin-valleytronics. However, a real-time ab initio method for the spin-resolved exciton dynamics is still missing. Here we develop an ab initio nonadiabatic molecular dynamics (NAMD) method based on GW plus real-time Bethe-Salpeter equation (GW+rtBSE-NAMD) for the spin-resolved exciton dynamics. From investigations on MoS2, we provide a comprehensive picture of spin-valley exciton dynamics where the electron-phonon (e-ph) scattering, spin-orbit interaction (SOI) and electron-hole (e-h) interactions come into play collectively. Especially, we provide a direct evidence that e-h exchange interaction plays a dominant role in the fast valley depolarization within few picoseconds in excellent agreement with experiments. Moreover, there are bright-to-dark exciton transitions induced by e-ph scattering and SOI. Our study proves that e-h many-body effects are essential to understand the spin-valley exciton dynamics in TMDs and the newly developed GW+rtBSE-NAMD method provides a powerful tool for exciton dynamics in extended systems with time, space, momentum, energy and spin resolution.

Real-time GW-BSE investigations on spin-valley exciton dynamics in monolayer transition metal dichalcogenide

ACS Fall 2021

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