Perfect Absorption and Strong Coupling in Supported MoS₂ 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 MoS₂. 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 MoS₂ multilayers supported by a glass substrate. We measure reflection spectra of mechanically exfoliated MoS₂ flakes at various angles beyond the light-line via Fourier plane imaging and spectroscopy and find that absorption in MoS₂ monolayers increases up to 74% at the C-exciton by illuminating at the critical angle. Perfect absorption is achieved for ultrathin MoS₂ 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 MoS₂ flakes, which could be useful for nanophotonic and light harvesting applications.