Optical spectroscopy of excited Rydberg excitons to 65 tesla in monolayer semiconductors

Monolayer transition-metal dichalcogenide (TMD) semiconductors, such as MoS₂, host very tightly-bound excitons due to reduced dielectric screening and relatively heavy electron / hole masses. Advances in the encapsulation of monolayer TMDs in atomically-flat hexagonal boron nitride (hBN) result in narrow neutral exciton resonances, as well as spectral features associated with excited Rydberg states. Optical spectroscopy in high magnetic fields was recently demonstrated to be a powerful way to uniquely identify these states in WSe₂ and to determine fundamental properties such as the exciton size, mass and binding energy [1]. Here, we report 65 T magneto-absorption spectroscopy of excited Rydberg excitons in hBN-encapsulated WS₂, MoS₂ and MoSe₂ monolayers. The distinct diamagnetic shifts of these excited states (2s, 3s, …, ns) permits their unambiguous identification, and provide a direct measure of the reduced exciton masses. We compare our experimental results with numerical simulations of the non-hydrogenic Rytova-Keldysh potential for strictly 2D semiconductors, and more general models describing Coulomb interactions in thin-film semiconductors. [1]Stier et al., PRL 120, 057405 (2018).