Many-body exciton and inter-valley correlations in heavily electron-doped WSe$_2$ monolayers

TL;DR

This study reveals the many-body and inter-valley correlation nature of the $X^{-\prime}$ excitonic state in heavily electron-doped WSe$_2$ monolayers through high magnetic field polarized absorption spectroscopy.

Contribution

It provides new insights into the origin of the $X^{-\prime}$ resonance, demonstrating its many-body and inter-valley correlated nature beyond single-particle explanations.

Findings

Quenching of Landau level absorption with magnetic field

Absorption changes in higher Landau levels in both valleys

Evidence of many-body and inter-valley correlations in $X^{-\prime}$

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 ($X^\pm$) is well documented. However, in WSe$_2$ monolayers, an additional absorption resonance, often called $X^{-\prime}$, emerges at high electron density. Its origin is not understood. Here we investigate the $X^{-\prime}$ state via polarized absorption spectroscopy of electrostatically-gated WSe$_2$ 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 $X^{-\prime}$ quasiparticle state.