Many-Body Exciton and Intervalley Correlations in Heavily Electron-Doped WSe 2 Monolayers.

In monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when electron-hole pairs (excitons) are photoexcited into a 2D Fermi sea of mobile carriers. At low carrier densities, the formation of charged excitons ( X ± ) is well documented. However, in WSe 2 monolayers, an additional absorption resonance, often called X - ', emerges at high electron density. Its origin is not understood. Here, we investigate the X - ' state via polarized absorption spectroscopy of gated WSe 2 monolayers in magnetic fields to 60T. Field-induced filling and emptying of the lowest optically active Landau level in the K ' valley causes repeated quenching of the corresponding optical absorption. Surprisingly, these quenchings are accompanied by absorption changes to higher Landau levels in both K ' and K valleys, which are unoccupied. These results cannot be reconciled within a single-particle picture, and demonstrate the many-body nature and intervalley correlations of the X - ' quasiparticle state.