Spin Valley Dynamics Entangled with Optical Fields, Phonons, and Spin‐Orbit Coupling in Monolayer MoSe ₂

Abstract The ab initio nonadiabatic molecular dynamics (NAMD) approach is advanced by integrating light–matter interactions, enabling comprehensive simulations of the carrier dynamics in solid materials from photoexcitation to relaxation. Using this method, the excited electron and hole dynamics are investigated in monolayer MoSe ₂ entangled with optical field, phonons and spin‐orbit coupling (SOC), encompassing the dynamics from valley polarization to depolarization. During the initial 0.6 ps after photoexcitation, the optical field dominates, leading to rapid electron valley polarization and a high‐polarization plateau, alongside phonon‐assisted intervalley photoexcitation. Subsequently, electron‐phonon interactions and SOC starts to play a role in the electron depolarization, diminishing polarization to zero around 1.6 ps. Hole polarization is also induced by photoexcitation, and it depolarizes more slowly than electrons without an optical field but becomes dependent on the optical field when laser is present. This work provides a powerful tool for studying the coherent effects of optical fields, phonons, and SOC in photoexcitation dynamics, which is crucial for the design of next‐generation optoelectronic devices.