Excitonic complexes in $n$-doped WS$_2$ monolayer

TL;DR

This study explores the origins of emission lines in low-temperature photoluminescence spectra of n-doped WS2 monolayers, identifying various excitonic complexes and their magnetic properties through experiments and calculations.

Contribution

It provides a detailed identification of multiple excitonic complexes, including bright and dark trions and biexcitons, using combined experimental and theoretical approaches.

Findings

Identification of emission lines as negatively charged excitons.

Distinction between bright, dark, and phonon replica emissions.

Determination of g-factors for exciton complexes and band subbands.

Abstract

We investigate the origin of emission lines apparent in the low-temperature photoluminescence spectra of $n$-doped WS$_2$ monolayer embedded in hexagonal BN layers using external magnetic fields and first-principles calculations. Apart from the neutral A exciton line, all observed emission lines are related to the negatively charged excitons. Consequently, we identify emissions due to both the bright (singlet and triplet) and dark (spin- and momentum-forbidden) negative trions as well as the phonon replicas of the latter optically-inactive complexes. The semi-dark trions and negative biexcitons are distinguished. Based on their experimentally extracted and theoretically calculated $g$-factors, we identify three distinct families of emissions due to exciton complexes in WS$_2$: bright, intravalley and intervalley dark. The $g$-factors of the spin-split subbands in both the conduction and valence bands are also determined.