Coherent Dynamics of Neutral and Charged Biexcitons in Monolayer WSe2

Monolayer transition-metal dichalcogenides provide an ideal platform for investigating many-body excitonic complexes due to their strong Coulomb interactions and unique valley-contrasting optical selection rules. Here, we employ helicity-resolved transient absorption spectroscopy in an opposite-circular-polarization configuration to systematically study the coherent dynamics of both neutral and charged intervalley biexcitons in monolayer WSe2. Our measurements reveal a linear dependence of the biexciton signal strength on the pump fluence, indicative of an intrinsic coherent process. In contrast to the exciton, the biexciton resonances display steeper red shifts as the temperature increases, leading to increased binding energies correspondingly. This behavior is attributed to the extended wave function and heavier effective mass of biexcitons, which enhance sensitivity to both thermal lattice vibration and low-energy phonon scattering. Our work advances the fundamental understanding of coherent biexciton dynamics and many-body physics in 2D semiconductors, paving the way for future quantum optoelectronic devices.