Exciton dynamics in atomically thin MoS2: inter-excitonic interaction and broadening kinetics

We report ultrafast pump-probe spectroscopy examining exciton dynamics in atomically thin MoS2. Spectrally- and temporally-resolved measurements are performed to investigate the interaction dynamics of two important direct-gap excitons (A and B) and their associated broadening kinetics. The two excitons show strongly correlated inter-excitonic dynamic, in which the transient blue-shifted excitonic absorption originates from the internal A-B excitonic interaction. The observed complex spectral response is determined by the exciton collision-induced linewidth broadening; the broadening of the B exciton linewidth in turn lowers the peak spectral amplitude of the A exciton. Resonant excitation at the B exciton energy reveals that inter-excitonic scattering plays a more important role in determining the broadening kinetics than free-carrier scattering.