Spin Valley dynamics of phonons entangled with circularly polarized light in WSe2

Abstract

Monolayer transition metal dichalcogenides (TMDs) have generated considerable interest in optoelectronics and valence-band electronics due to their unique electronic structures. In this paper, we incorporate the spin-orbit coupling effects and use the lefthanded circularly polarized excitation of K-valley electrons as an example to investigate the excited-state dynamics of the coupling between the optical field and phonons in WSe2. We reveal that left-handed light selectively excites K-valley electrons, while right-handed light selectively excites K'-valley electrons, inducing periodic Rabi oscillations. As the temperature increases from 100K to 300K, enhanced phonon interactions alter the primary electron relaxation pathways. At 100K, postdepolarisation equilibrium sees over 70% of electrons distributed across and CB@K'↑, with approximately 20% residing in the CB@K↑ state. At 300K, enhanced spin-orbit coupling induces frequent spin flips between the CB@K↓ and CB@K'↑ states following depolarisation equilibrium. By defining the initial electron on the K-valley VB@K↑ and employing left-handed circularly polarised excitation, a comprehensive simulated process can be achieved: under the combined action of the light field and phonons, the electron transitions from the ground state to the excited state, then relaxes from the excited state to the equilibrium state. This combined action of light field and phonons activates the inter-valley scattering pathway (CB@K↑→CB@K'↑).