Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

Transition metal dichalcogenides are attracting widespread attention for their appealing optoelectronic properties. Using a combination of numerical and experimental techniques, the exciton binding energy is now determined for MoSe 2 on graphene. Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as a new platform for exploring 2D semiconductor physics 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Reduced screening in two dimensions results in markedly enhanced electron–electron interactions, which have been predicted to generate giant bandgap renormalization and excitonic effects 10 , 11 , 12 , 13 . Here we present a rigorous experimental observation of extraordinarily large exciton binding energy in a 2D semiconducting TMD. We determine the single-particle electronic bandgap of single-layer MoSe 2 by means of scanning tunnelling spectroscopy (STS), as well as the two-particle exciton transition energy using photoluminescence (PL) spectroscopy. These yield an exciton binding energy of 0.55 eV for monolayer MoSe 2 on graphene—orders of magnitude larger than what is seen in conventional 3D semiconductors and significantly higher than what we see for MoSe 2 monolayers in more highly screening environments. This finding is corroborated by our ab initio GW and Bethe–Salpeter equation calculations 14 , 15 which include electron correlation effects. The renormalized bandgap and large exciton binding observed here will have a profound impact on electronic and optoelectronic device technologies based on single-layer semiconducting TMDs.