Trion-trion annihilation in monolayer WS$_2$

TL;DR

This paper reports the first experimental observation of trion-trion annihilation in monolayer WS$_2$, revealing non-radiative Auger processes and tunable Auger coefficients influenced by gate voltage, advancing understanding of many-body effects in 2D semiconductors.

Contribution

It demonstrates the direct observation of trion-trion annihilation in monolayer WS$_2$ and shows how the process can be controlled via gate voltage, which was previously unexplored.

Findings

Suppression of trion emission correlates with increased gate voltage.

Tunable Auger coefficient by a factor of ten through spectral overlap control.

Evidence of non-radiative Auger recombination leading to dark trion and charged biexciton states.

Abstract

Strong Coulomb interaction in monolayer transition metal dichalcogenides can facilitate nontrivial many-body effects among excitonic complexes. Many-body effects like exciton-exciton annihilation (EEA) have been widely explored in this material system. However, a similar effect for charged excitons (or trions), that is, trion-trion annihilation (TTA), is expected to be relatively suppressed due to repulsive like-charges, and has not been hitherto observed in such layered semiconductors. By a gate-dependent tuning of the spectral overlap between the trion and the charged biexciton through an "anti-crossing"-like behaviour in monolayer WS$_2$, here we present an experimental observation of an anomalous suppression of the trion emission intensity with an increase in gate voltage. The results strongly correlate with time-resolved measurements, and are inferred as a direct evidence of a nontrivial TTA resulting from non-radiative Auger recombination of a bright trion, and the corresponding energy resonantly promoting a dark trion to a charged biexciton state. The extracted Auger coefficient for the process is found to be tunable ten-fold through a gate-dependent tuning of the spectral overlap.