Selectively Strong Coupling of MoS2 Excitons to a Metamaterial at Room Temperature

Abstract

Light emitters in the vicinity of a hyperbolic metamaterial (HMM) show a range of quantum optical phenomena from spontaneous decay-rate enhancement to strong coupling. In this study, we integrate a monolayer molybdenum disulfide (${\mathrm{Mo}\mathrm{S}}_{2}$) emitter in the near-field region of the HMM. The ${\mathrm{Mo}\mathrm{S}}_{2}$ monolayer has $A$ and $B$ excitons, which emit in the red region of the visible spectrum. We find that the $B$ excitons couple to the HMM differently compared to $A$ excitons. The fabricated HMM transforms to a hyperbolic dispersive medium at 2.14 eV, from an elliptical dispersive medium. The selective coupling of $B$ excitons to the HMM modes is attributed to the inbuilt field gradient of the transition. The $B$ exciton energy lies close to the transition point of the HMM, relative to the $A$ exciton. So, the HMM modes couple more to the $B$ excitons and the metamaterial functions as a selective coupler. The coupling strength calculations show that coupling is 2.5 times stronger for $B$ excitons relative to $A$ excitons. High near field of HMM, large magnitude, and the in-plane transition dipole moment of ${\mathrm{Mo}\mathrm{S}}_{2}$ excitons, result in strong coupling of $B$ excitons and formation of hybrid light-matter states. The measured differential reflection and photoluminescence spectra indicate the presence of hybrid light-matter states, i.e., exciton polaritons. Rabi splitting of $143.5\phantom{\rule{0.2em}{0ex}}\mathrm{meV}\ifmmode\pm\else\textpm\fi{}14.4$ meV at room temperature is observed. The low-temperature photoluminescence measurement shows mode anticrossing, which is a characteristic feature of hybrid states. Our results show that the HMM works as an energy-selective coupler for multiexcitonic systems as ${\mathrm{Mo}\mathrm{S}}_{2}$.