Coupled relaxation channels of excitons in monolayer MoSe2

摘要

Using ultrafast degenerate pump-probe spectroscopy, we have investigated the ultrafast exciton dynamics of monolayer MoSe2 at different pump fluences. The exciton-exciton annihilation, typically occurring tens of picoseconds after pump excitation, has been found to have a substantial correlation with the initial relaxation process dominated by the defect trapping of excitons. A new exciton-exciton annihilation model has been proposed by introducing a coupling term that accounts for the initial relaxation contribution. This coupling term can be tuned by varying the pump excitation intensity and at a high intensity it vanishes due to the full occupation of the defect states. At the same time, the final electronhole recombination is found to be affected by the heat accumulation effect originating from the high intensity pump pulses.