Disentangling Many-Body Effects in the Coherent Optical Response of 2D Semiconductors

In single-layer (1L) transition metal dichalcogenides, the reduced Coulomb screening results in strongly bound excitons which dominate the linear and the nonlinear optical response. Despite the large number of studies, a clear understanding on how many-body and Coulomb correlation effects affect the excitonic resonances on a femtosecond time scale is still lacking. Here, we use ultrashort laser pulses to measure the transient optical response of 1L-WS2. In order to disentangle many-body effects, we perform exciton line-shape analysis, and we study its temporal dynamics as a function of the excitation photon energy and fluence. We find that resonant photoexcitation produces a blue shift of the A exciton, while for above resonance photoexcitation the transient response at the optical bandgap is largely determined by a reduction of the exciton oscillator strength. Microscopic calculations based on excitonic Heisenberg equations of motion quantitatively reproduce the nonlinear absorption of the material and its dependence on excitation conditions.

Automated summary

In this study, transient optical response of single-layer WS2 was measured using ultrashort laser pulses, and the effects of many-body interactions and Coulomb correlations on excitonic resonances were analyzed. It was found that resonant photoexcitation caused a blue shift of the A exciton, while above resonance photoexcitation resulted in a reduction of the exciton oscillator strength dominating the transient response at the optical bandgap.