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Strong Coulomb interaction in monolayers (1L) of transition metal dichalcogenides (TMDCs) gives rise to exciton many-body effects. Exciton-exciton annihilation (EEA) is a known phenomenon [1,2] where one exciton non-radiatively recombines and provides its energy to another one, which forms free ‘hot’ electron-hole pair. In this regard, trion-trion annihilation (TTA) is nontrivial because of their like charges and has not been hitherto observed in these 1L-TMDCs.

In this work, we demonstrate TTA in a gated WS₂ sample by using a pulsed excitation at low temperature (5 K). In particular, we observe that (1) the negative trion and biexciton exhibit an ‘anti-crossing’ like behavior with increasing ; (2) the trion PL intensity reduces gradually (while the biexciton intensity increases) in the spectral overlap region between trion and biexciton; and (3) the TRPL FWHM in the same region also indicates a faster trion decay. These three experimental observations indicate towards spectrally tunable Auger interaction between a bright and dark trion. We model the phenomenon using the Auger rate equation, which suggests a strong enhancement of the Auger rate when the spectral overlap between the trion and the charged biexciton is large.

References:

1. Daniel Erkensten et al, PRB, 103(4):045426, 2021.

2. Darwin F Cordovilla Leon et al, PRB, 100(24):241401, 2019.