Hexcitons and oxcitons in monolayer WSe$_2$

TL;DR

This paper reports the observation and interpretation of complex many-body excitonic states, called hexcitons and oxcitons, in electron-doped monolayer WSe$_2$, revealing new insights into high-density electron interactions in 2D semiconductors.

Contribution

It introduces the experimental identification of hexcitons and oxcitons in monolayer WSe$_2$, expanding understanding of many-body states at high electron densities.

Findings

Identification of spectral lines as hexcitons and oxcitons.

Observation of primary and satellite optical transitions.

Interpretation of these states as multi-body excitonic complexes.

Abstract

In the archetypal monolayer semiconductor WSe$_2$, the distinct ordering of spin-polarized valleys (low-energy pockets) in the conduction band allows for studies of not only simple neutral excitons and charged excitons (i.e., trions), but also more complex many-body states that are predicted at higher electron densities. We discuss magneto-optical measurements of electron-rich WSe$_2$ monolayers, and interpret the spectral lines that emerge at high electron doping as optical transitions of 6-body exciton states ("hexcitons") and 8-body exciton states ("oxcitons"). These many-body states emerge when a photoexcited electron-hole pair interacts simultaneously with multiple Fermi seas, each having distinguishable spin and valley quantum numbers. In addition, we identify the energies of primary and satellite optical transitions of hexcitons in the photoluminescence spectrum.