Perfect Absorption and Strong Coupling in Supported MoS Multilayers.

Perfect absorption and strong coupling are two highly sought-after regimes of light-matter interactions. Both regimes have been studied as separate phenomena in excitonic 2D materials, particularly in MoS. However, the structures used to reach these regimes often require intricate nanofabrication. Here, we demonstrate the occurrence of perfect absorption and strong coupling in thin MoS multilayers supported by a glass substrate. We measure reflection spectra of mechanically exfoliated MoS flakes at various angles beyond the light-line via Fourier plane imaging and spectroscopy and find that absorption in MoS monolayers increases up to 74% at the C-exciton by illuminating at the critical angle. Perfect absorption is achieved for ultrathin MoS flakes (4-8 layers) with a notable angle and frequency sensitivity to the exact number of layers. By calculating zeros and poles of the scattering matrix in the complex frequency plane, we identify perfect absorption (zeros) and strong coupling (poles) conditions for thin (<10 layers) and thick (>10 layers) limits. Our findings reveal rich physics of light-matter interactions in bare MoS flakes, which could be useful for nanophotonic and light harvesting applications.