Probing charged biexciton through controlled many-body interaction

The light-matter interaction of monolayer transition metal dichalcogenides is dominated by excitons and the high binding energy of these makes TMDC monolayers an ideal platform for the exploration of many-body exciton complexes [1-2].
In this work, using hBN-capped monolayer WS₂ placed on a metallic back reflector, we demonstrate the manipulation of the charged biexciton kinetics through systematic gate voltage and temperature-dependent variation of the relationship between the exciton and charged biexciton PL peak intensities. The results are supported by a detailed three-particle rate equation. We show that the binding energy of the charged biexciton must be less than the separation between the emission peaks of the neutral exciton and the charged biexciton. We also propose that there is a stark difference between the recombination mechanisms of the neutral exciton and the charged biexciton. In the former case, the momentum-direct radiative recombination is restricted within the light cone due to the small photon momentum but the presence of near-parallel bands of excited and final states indicate that recombination is not restricted by the light cone in the latter case.
References:
1. Ziliang Ye et al, Nat Commun. 9, 3718 (2018)
2. Mak K. et al, Nature Mater. 12, 207–211 (2013)