Self-Hybridized Exciton-Polaritons in the Blue and UV Regimes

The formation of hybrid quasiparticles known as exciton-polaritons (EPs) through the hybridization of excitons with cavity photons has been extensively studied across various semiconductor materials. Two-dimensional (2D) layered excitonic materials such as transition metal dichalcogenides (TMDs) and 2D perovskite exhibit strong coupling of excitons and photons due to their high exciton binding energy and large refractive index. Self-hybridization, hybridization of excitons and photon modes without the need for an external cavity, has been recently observed in layered 2D excitonic materials, enabling simpler design for exciton-polaritonic applications. EPs in the blue and UV regime hold great promise for fundamental science and applications such as polaritonic lasing. However, there is a lack of understanding in this regime due to the scarcity of layered 2D materials with large bandgap. Here, we report the self-hybridized EPs in the blue and UV regime from the layered material called mithrene (AgSePh, E_g ~ 2.7eV) which is one of the metal-organic chalcogenate (MOC) compounds. The simple open cavity design, where mithrene serves as the photonic cavity, enables self-hybridized EPs with large Rabi splitting (2g > 600 meV) due to its strong exciton oscillation strength and large refractive index (n ~ 2.8). The mithrene shows clear anti-crossing behavior in the reflectance spectrum with good agreement with the theoretical calculation. Furthermore, we investigate the self-hybridized EPs in the UV regime with another MOC compound called thiorene (AgSPh, E_g ~ 3.4eV) and hexagonal boron nitride (hBN, E_g ~ 5.9eV), a wide bandgap layered material. Thiorene and hBN exhibit a large refractive index around exciton resonance energy, which is favorable for self-hybridization. These properties lead to clear anti-crossing behavior in the reflectance spectrum, strongly indicating the formation of EPs. Our results extend the range of self-hybridized EPs into the UV regime in various layered materials.