Many-Body Exciton and Intervalley Correlations in Heavily Electron-Doped WSe₂ Monolayers.

Abstract

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 (<i>X</i>^±) is well documented. However, in WSe₂ monolayers, an additional absorption resonance, often called <i>X</i>^-', emerges at high electron density. Its origin is not understood. Here, we investigate the <i>X</i>^-' state via polarized absorption spectroscopy of gated WSe₂ monolayers in magnetic fields to 60T. Field-induced filling and emptying of the lowest optically active Landau level in the <i>K</i>' valley causes repeated quenching of the corresponding optical absorption. Surprisingly, these quenchings are accompanied by absorption changes to higher Landau levels in both <i>K</i>' and <i>K</i> 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 <i>X</i>^-' quasiparticle state.