Strong light-matter coupling in MoS$_2$

TL;DR

This study demonstrates strong light-matter coupling in MoS$_2$, showing it as a promising material for polariton devices due to its high coupling strength exceeding exciton losses.

Contribution

The paper provides experimental evidence of very strong light-matter coupling in MoS$_2$, with detailed dispersion measurements using near-field optical microscopy.

Findings

Coupling strength of 40-100 meV exceeds exciton losses.

In-plane excitons are in the strong coupling regime.

Coupling is comparable to exciton binding energy.

Abstract

Polariton-based devices require materials where light-matter coupling under ambient conditions exceeds losses, but our current selection of such materials is limited. Here we measured the dispersion of polaritons formed by the $A$ and $B$ excitons in thin MoS$_2$ slabs by imaging their optical near fields. We combined fully tunable laser excitation in the visible with a scattering near-field optical microscope to excite polaritons and image their optical near fields. We obtained the properties of bulk MoS$_2$ from fits to the slab dispersion. The in-plane excitons are in the strong regime of light-matter coupling with a coupling strength ($40-100\,$meV) that exceeds their losses by at least a factor of two. The coupling becomes comparable to the exciton binding energy, which is known as very strong coupling. MoS$_2$ and other transition metal dichalcogenides are excellent materials for future polariton devices.