This study investigates the excitonic dark states in single-layer tungsten disulfide (WS₂) using two-photon excitation spectroscopy. The researchers found that the optical response of WS₂ is dominated by excitonic effects, with a quasiparticle band gap of 2.7 eV, significantly larger than previously reported. The excitons in WS₂ are Wannier-like and exhibit an exceptionally large binding energy of about 0.7 eV, which is an order of magnitude larger than that of conventional semiconductors. These strongly bound exciton states are stable even at room temperature and show robustness against environmental perturbations. The findings suggest that the strong light-matter interaction in WS₂ is primarily due to many-electron effects, which could have significant implications for the development of optoelectronic devices and heterostructures based on WS₂ and other transition metal dichalcogenides (TMDCs). The study also highlights the importance of considering excitonic effects in the design of TMDC-based devices and heterostructures.This study investigates the excitonic dark states in single-layer tungsten disulfide (WS₂) using two-photon excitation spectroscopy. The researchers found that the optical response of WS₂ is dominated by excitonic effects, with a quasiparticle band gap of 2.7 eV, significantly larger than previously reported. The excitons in WS₂ are Wannier-like and exhibit an exceptionally large binding energy of about 0.7 eV, which is an order of magnitude larger than that of conventional semiconductors. These strongly bound exciton states are stable even at room temperature and show robustness against environmental perturbations. The findings suggest that the strong light-matter interaction in WS₂ is primarily due to many-electron effects, which could have significant implications for the development of optoelectronic devices and heterostructures based on WS₂ and other transition metal dichalcogenides (TMDCs). The study also highlights the importance of considering excitonic effects in the design of TMDC-based devices and heterostructures.