Coherent Electronic Coupling in Atomically Thin MoSe2

We report the first direct spectroscopic evidence for coherent electronic coupling between excitons and trions in atomically thin transition metal dichalcogenides, specifically monolayer MoSe2. Signatures of coupling appear as isolated cross-peaks in two-color pump-probe spectra, and the line shape of the peaks reveals that the coherent coupling originates from many- body interactions. Excellent agreement between the experiment and density matrix calculations suggests that coherent exciton-trion coupling leads to the formation of a correlated state with a remarkably large binding energy.