The connection between enhanced phonon-exciton interaction next to localization centers and photoluminescence of few-body complexes in tungsten-based transition metal dichalcogenide monolayers.

Photoluminescence (PL) experiments in WSe2 show that the neutral-exciton peak X0 in the charge-neutral regime is often accompanied by additional lower-energy peak. The spectral position of the peak is below X0 by one phonon energy. Recently, several groups reported on trion-exciton complexes in encapsulated WSe2 [1,2,3,4,5], where once again, their PL spectra reveal that the peak attributed to the five-particle complex is one phonon energy below that of the biexciton. We show that these PL peaks stem from phonon-assisted recombination of excitons or biexcitons next to localized electrons (i.e., these are not real trions or trion-exciton complexes that can diffuse in the monolayer). We explain why the proposed PL mechanism is prevalent in these monolayers while being absent in absorption-type experiments [6], showing that it supports the observed PL dependences on temperature and background charge density.
[1] S. Y. Chen et. al., Nat. Comm. 9, 3717 (2018).
[2] Z. Ye et. al., Nat. Comm. 9, 3718 (2018).
[3] Z. Li et. al., Nat. Comm. 9, 3719 (2018).
[4] C. E. Stevens et. al., Nat. Comm. 9, 3720 (2018).
[5] M. Barbone et. al., Nat. Comm. 9, 3721 (2018).
[6] Dinh Van Tuan et. al., arXiv:1805.08722