Re-evaluation of bottleneck effect in coupled monolayer WS2/photonic crystal heterostructure

Exciton-polariton condensates, as one type of Bose Einstein condensates (BEC), is a fascinating phenomenon in condensed matter physics. For exciton-cavity system, the fundamental requirement of realizing exciton-polariton condensates is that the exciton-polaritons must relax effectively and rapidly to the energy minima located in polariton energy bands. The cooling dynamics of the high-energy exciton-polaritons usually is blocked due to bottleneck effect which occurs around the anticrossing regions of polariton dispersion. Although the exciton-polariton bottleneck effect has been extensively observed in various polariton system, but there is no a unified views of physical origin. In this work, we constructed the coupling system of exciton-trion-photon in monolayer (ML) WS ₂ /photonic crystal (PhC) slab heterostructure. Momentum-resolved photoluminescence (PL) spectroscopy exhibits clearly the anticrossing polariton dispersions for the exciton resonance, while there is no characteristic anticrossing for trion resonance at low temperature of ~12 K. Rabi splittings of ~57 meV and ~5 meV are obtained for exciton and trion resonances, respectively. More significantly, the emergence of the trion resonance gives rise to an abnormally intensive polariton emission at momentum k _// =±0.10 of trion-polariton crossing. The momentum position of this enhanced polariton emission is pinned by trion resonance in polariton dispersion with elevating temperature. Meanwhile, there is only a normal polariton emission around anticrossing regimes. We attributes this exotic phenomenon to bottleneck effect. These results reveal that the bottleneck effect strongly depends on the coupling strength and the smaller Rabi splitting is the unified origin of bottleneck effect in polariton system.