Many-body exciton and inter-valley correlations in heavily electron-doped WSe2 monolayers
Abstract
In monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when photoexcited electron-hole pairs (excitons) are introduced into a 2D Fermi sea of mobile carriers. At low carrier densities, the formation of positively and negatively charged excitons (X) is well documented. However, in WSe2 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 electrostatically-gated WSe2 monolayers in high magnetic fields to 60~T. 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, however, these quenchings are accompanied by absorption changes to higher-lying 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 inter-valley correlations of the X- quasiparticle state.