Miguel M. Ugeda1*†, Aaron J. Bradley1†, Su-Fei Shi1†, Felipe H. da Jornada1,2, Yi Zhang3,4,

Diana Y. Qiu1,2,Wei Ruan1,5, Sung-Kwan Mo3, Zahid Hussain3, Zhi-Xun Shen4,6, FengWang1,2,7,

Steven G. Louie1,2 and Michael F. Crommie1,2,7*

 

Two-dimensional (2D) transition metal dichalcogenides

(TMDs) are emerging as a new platform for exploring

2D semiconductor physics1–9. Reduced screening in two

dimensions results in markedly enhanced electron–electron

interactions, which have been predicted to generate giant

bandgap renormalization and excitonic eects10–13. 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 MoSe2 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

MoSe2 on graphene—orders of magnitude larger than what

is seen in conventional 3D semiconductors and significantly

higher than what we see for MoSe2 monolayers in more highly

screening environments. This finding is corroborated by our

ab initio GW and Bethe–Salpeter equation calculations14,15

which include electron correlation eects. 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.