Intrinsic multi-particle bound-state luminescence emission from high-quality monolayer tungsten diselenide

Monolayer WSe₂ is an interesting semiconductor that hosts versatile light emitting manybody states. While the bright exciton photoluminescence (PL) is ubiquitous, PL at higher energies are challenging to observe due to Kasha’s rule, and PL at lower energies are often plagued by extrinsic peaks from trapped excitons. In this talk, I’ll show that with our high-quality samples, excited Rydberg exciton PL up to the 4s exciton become visible, and in the lower energy window PL due to four-particle biexcitons and five-particle exciton-trions are resolved. In magnetic fields up to 31 Tesla, the Rydberg exciton energy displays increasing curvature against magnetic field strength from 1s to 4s, reflecting their increasingly larger diameter. The biexciton and the exciton-trion are found to be intervalley complexes composed of a dark exciton in one valley and a bright exciton / trion in the other valley. This spin-valley configuration gives rise to counter-intuitive inverted PL valley polarization as compared to the two-particle bright and dark excitons.
[1] S.-Y. Chen et al. Nature Commun. 9, 3717 (2018).
[2] S.-Y. Chen et al. Phys. Rev. Lett. 120, 046402 (2018).