Polariton condensate far-detuned from exciton resonance in WS2 bound states in the continuum

Abstract

While most approaches to polariton research focus on achieving strong coupling between excitons in monolayer transition metal dichalcogenides (TMDCs) and external microcavities, bulk TMDCs have been largely overlooked due to their reduced exciton oscillator strength and indirect bandgap nature. Here, we report the observation of polariton condensation within the indirect-transition range, enabled by a condensation mechanism in 50-nm-thick WS₂-based bound state in the continuum (BIC) cavities. Our photonic-like BIC polaritons exhibit a significant Rabi splitting energy ( ~ 294 meV) and clear evidence of condensation driven by a mechanism involving indirect excitons that directly inject photons into BIC polaritons. Remarkably, the interaction-induced confinement of polariton condensates can be optically tuned by adjusting the pump laser size, despite a minimal exciton fraction of 6%, distinguishing this system from purely photonic counterparts. These findings open new avenues for exploring polariton physics with indirect excitons in TMDCs and other emerging materials.