k-Resolved Ultrafast Light-Induced Band Renormalization in Monolayer WS₂ on Graphene

Understanding and controlling the electronic properties of two-dimensional materials are crucial for their potential applications in nano- and optoelectronics. Monolayer transition metal dichalcogenides have garnered significant interest due to their strong light-matter interaction and extreme sensitivity of the band structure to the presence of photogenerated electron-hole pairs. In this study, we investigate the transient electronic structure of monolayer WS₂ on a graphene substrate after resonant excitation of the A-exciton using time- and angle-resolved photoemission spectroscopy. We observe a pronounced band structure renormalization, including a substantial reduction of the transient band gap in good quantitative agreement with our ab initio theory, revealing the importance of both intrinsic WS₂ and extrinsic substrate contributions. Our findings deepen the fundamental understanding of band structure dynamics in two-dimensional materials and offer valuable insights for the development of novel electronic and optoelectronic devices based on monolayer TMDs and their heterostructures with graphene.